| Author | Message | ||
     Bill Vatter (67.35.48.21) |
While returning home from the RROC national meet in Hot Springs VA, the engine in “Morgan,” our Silver Wraith WGC 66, experienced what appears to be a piston failure. After stopping at a motel for the night, we were out searching for a restaurant. While traveling about 30 mph suddenly the engine started knocking very loudly. This knock was a very sharp sound, distinctly unlike a lower end bearing that typically has a deeper and more dull sound, but not as light as a valve train noise, and it was very loud, louder than any valve train problem I have heard. Also the knock did not fade in as does a bearing knock, but was instant—one revolution silent and the next very loud and pronounced. It had just begun to rain very hard, and there was nothing to do but to keep going back to the motel, about 3 or 4 miles. The oil pressure was normal (about 10 psi at idle and 25 psi at 30 mph). Also the temperature was where it had been all day when in slow traffic with the A/C operating, about 88-90 degrees, but now with the rain it was dropping towards 80. Initially the knock was clearly every engine revolution and the same intensity at all times, but by the time we reached the motel, it had changed to loud and every revolution on overrun, but every other revolution and not as loud on acceleration. Also it became less loud at idle than was initially the case. My initial thought was that a small piece of the top ring land had broken off on one piston and was lodged between the piston and the cylinder head, hitting when the piston was at top center. However, as the broken piece became hammered into the piston or cylinder head, the pressure on top of the piston in compression and power strokes when accelerating was holding the piston away somewhat, reducing the knock. I have seen several engines that failed in this manner, and this is typically the end result of broken piston rings from overheating problems, cylinder bore wear, and cylinder liner shrinkage that is characteristic of the F-head six with cuff liners. Also, the engine was due for it. It has run 130,000 miles without overhaul. We parked the car and considered our options. After consulting with a couple of friends having extensive experience with these engines, and also after arranging for a flat bed trailer to be in standby with a friend at home, we elected to try and continue driving towards home, about 250 more miles. We selected a different route than originally planned, one where we could travel 40 mph without fear of being run down from the rear, and also within phone cells in case we failed to proceed. In the morning the engine was silent when started for the run home. This made sense as the aluminum piston would not stand as high in the bore by a couple of thousandths or so when cold. It was still silent when the coolant reached 80 degrees and the thermostat opened, but soon afterwards the knock faded in as the oil and connecting rod warmed up. As we drove I noted the engine seemed to be running quite well except for the noise. It idled smoothly without a miss, had it’s usual amount of pep, and was not smoking. Also as we drove the noise gradually faded away. By the time we had covered 50 miles the knock was gone, and it did not return, while the engine continued to run as if nothing had happened. We arrived home without further incident. No doubt whatever foreign bit that was in there has been hammered flat or imbedded into the piston or cylinder head to the point that it isn’t hitting anymore. After a good night’s sleep for all of us including the car, I went to look at the engine. The plugs all look fine, a light tan. #1 plug is very slightly darker than the others, and this only just discernible, the same as it has always been, and certainly not indicative of oil burning to any extent. A compression test showed the following: #1: 117 psi #2: 115 psi #3: 121 psi #4: 119 psi #5: 117 psi #6: 117 psi Altogether a very acceptable set of readings, and about as good as I’ve seen it with this car. So what’s wrong? Could the piston have broken off a piece and still not be passing oil and have reduced compression? Maybe it ingested something? Also I will find a borescope to peek inside at the piston tops. Any additional thoughts would be greatly appreciated. Also, if the borescope confirms the worst— the edge of a piston is beginning to break off above a broken top compression ring—how much longer is it likely to go before more comes off? There is one more meet that I really need to attend yet this year. We are the hosts and it would not be good to show up without a proper motorcar. After that the engine can come out for an overhaul. Any thoughts on this situation would be greatly appreciated. | ||
| Jim Bettison (203.166.57.11) |
Bill, Two subjects. One, relating to the camshaft, I will address in the other thread on that subject. Sufficient to say that the camshaft question arose because we were chasing an engine knock, which is the next subject. Two; Bill, it sounds as if your "Morgan" has become "Morgan le Fay" ... Seriously, your knock appears to be amazingly similar to the problem we're chasing with the Dawn that's the source of the camshaft query. In our case, the knock (producing a sound just like that which you describe) only develops as the engine gets hot, and then - as in your case - disappears as it cools down. However, our noise appears at rather lower engine temperatures than yours, including under idling conditions on a cool (15degC) day and is exacerbated in road work if the air conditioner (fitted at the time of the engine rebuild) is operating. Quite apart from cooling problems, this engine behaviour is regarded by the owner (who is one of a very small local group of RR&B people who engage the services of a particular, thorough technical man) as being unacceptable: he doesn't like to come to a Club meet in his beautifully restored Dawn, and start by apologising for the engine noise ... In the case in point the engine has done probably less than 2,000 miles in the nine months since a rebuild. Like yours, it also has cuff liners; it idles well, doesn't smoke, pulls well, has good compressions - and knocks! We have now got the engine out and stripped. Nothing was glaringly obvious at first. There is, however, evidence of scuffing at the bottom of pistons #5 and #6. Otherwise, the pistons, rings, and bearings looked just as one would expect (or hope for). The previous mechanic had used a fairly heavy oil as running-in lubricant; we would have preferred to use a couple of grades lower. The oil drained very black, but not sludgy; it looked as though there had been a heavy wash-down of carbon from the top of the bores. (I am used to seeing first charge oil come out very clear.) There was a much heavier deposition of soft carbon on the head and block than I felt was appropriate. (This gets into the subject of presently available fuels in Oz, and the effects that many of us feel are related to them. If Richard Treacy reads this - I owe a reply to him on the subject of fuel in Oz.) We convinced ourselves that there was no problem with camshaft or cam followers. There is a wear problem with the aluminium timing gear, which looks as though it had been fed with sand (or abrasive particles not cleared thoroughly from an oilway before assembly in the previous rebuild???), which might be possible since the gear isn't fed filtered oil. And it measures as just over the recommended backlash.) We need a new Al timing gear, RE9346. (Rumour has it that there are Oz gear manufacturers who can supply - any suggestions, anyone?) Examination of the block after very stringent cleaning indicates that in two or three cylinders there is an oil seepage at the lower end of the cuffs (source not identified). At this point we had Norman Geeson's excellent article to hand (I think you also have a copy, Bill). Working from Norman's reasoning, we have put up a proposition as an Aunt Sally; we think it might also fit your case: When the engine gets excessively hot the cylinder bore distorts/shrinks, to the point where piston clearance is negative, and the piston binds. It is from this binding that the knock emanates, directly or consequently. When the engine cools, clearance is restored and the knock disappears. Why should it happen now and not previously in the engine's life? Perhaps because there is local heating caused by gradual build-up of impediment to coolant flow. Perhaps because the outside temperatures, plus work loads, are just enough to encourage binding - we know that the binding/non-binding conditions can be very close. We suspect that R-R may have run very close in this regard; our MkVI tech info tells us that pistons should be fitted with .003" clearance at top of bore, and .002" interference at bottom of the bore. We are going to have the Dawn bored and re-sleeved (full length sleeves), in which process we have a machine shop not only willing but eager to follow Norman's commentaries about how things should be done, including a stress relief period. (They say it will make a pleasant relief from the stream of Holden and Ford blocks for the local hotting-up brigade.) When it comes to honing, we will hone oversize, allowing clearance at bore bottom. We reckon that this will allow for dimensional changes with temperature. Bore oversizing shouldn't cause a problem; clearances will take up when the engine is hot, and not be a problem when cold (as all RR$B owners know to let engines warm up, don't they?). When we have finished the Dawn, my MkVI is next candidate; the borescope shows clear problems at cuff liner bottoms, and I have an annoying higher-pitched noise - nearly a squeak. I'll check the above and add-on later any corrections, etc. In the meantime, comments please. And good luck, Bill. We here reckon that you'll probably be OK if you keep everything cool (or cooler) and perhaps do a bit of cleaning in coolant areas, until you have more time. And, following Norman's expose of cooling fans, which fan and pulley combination do you have? Regards, Jim. | ||
| Richard Treacy (195.232.90.66) |
Interesting problem ! When I fitted full length liners to my R-Type in 1981, I first used Peter Hepworth Components (PHC) split-skirt pistons. The oil rings were a bit perculiar, and didn't work well at all. Of course, I broke one fitting it and had to wait months for a new one from the UK. I also failed to allow sufficient gap between the small end bushes and the piston bosses. To much gap and the gudgeon pin flexes, causing early wear, but too little and Bang ! One piston failed catastrophically on the Motoway at speed, but fortunately the block and rod were OK. The insufficient clearance meant that the small end was expanding the piston into the bore, so it was overheating and eventually split in two after 20,000 miles. No warning. Next I honed the bores to +.002 thou and had custome pistons with solid skirts and Holden rings made by Repco in Melbourne. My father ran it for me very gently in Canberra fo a month and 500 miles before I started the trip back to Sydney. I gave it a squirt up to 70 mph near Collector, and WHAT: knock-nock-nock. The piston picked up on the bore and became distorted. Reason ? These motors run very cool, so they need larger than normal piston clearances, especially with solid skirt pistons. The pistons need also to be tin plated to facilitate running in. Repco very kindly made me a replacement set of tin plated pistons free of charge !! They have been excellent for 50,000 miles, the oil is always clear and it burns absolutely no oil at all. How about that ? My messages: maybe one of your new pistons has picked up ? And: I have had that sickening feeling from an engine knock many times too. On Bill's car, I suppose only a sump-off, head-off and pistons out will tell. | ||
| Richard Treacy (195.232.90.66) |
Interesting problem ! When I fitted full length liners to my R-Type in 1981, I first used Peter Hepworth Components (PHC) split-skirt pistons. The oil rings were a bit perculiar, and didn't work well at all. Of course, I broke one fitting it and had to wait months for a new one from the UK. I also failed to allow sufficient gap between the small end bushes and the piston bosses. To much gap and the gudgeon pin flexes, causing early wear, but too little and Bang ! One piston failed catastrophically on the Motoway at speed, but fortunately the block and rod were OK. The insufficient clearance meant that the small end was expanding the piston into the bore, so it was overheating and eventually split in two after 20,000 miles. No warning. Next I honed the bores to +.002 thou and had custome pistons with solid skirts and Holden rings made by Repco in Melbourne. My father ran it for me very gently in Canberra fo a month and 500 miles before I started the trip back to Sydney. I gave it a squirt up to 70 mph near Collector, and WHAT: knock-nock-nock. The piston picked up on the bore and became distorted. Reason ? These motors run very cool, so they need larger than normal piston clearances, especially with solid skirt pistons. The pistons need also to be tin plated to facilitate running in. Repco very kindly made me a replacement set of tin plated pistons free of charge !! They have been excellent for 50,000 miles, the oil is always clear and it burns absolutely no oil at all. How about that ? My messages: maybe one of your new pistons has picked up ? And: I have had that sickening feeling from an engine knock many times too. On Bill's car, I suppose only a sump-off, head-off and pistons out will tell. | ||
| Bill Vatter (67.35.48.21) |
Jim brings up several interesting points and questions. Scuffing on the piston skirts indicates they have partially seized against the cylinder bores. This could have occurred from being fitted too closely (the factory recommends zero clearance on the thrust diameter). Most piston/engine manufacturers recommend a small positive clearance, but this is dependent on the design of the piston (shape of skirt, webs inside, and configuration of slot, if any, and of course material). I suppose that RR pistons expand less than the cylinder bores as the engine heats up. Any negative clearance at any temperature is clearly going to be a problem, and would result in friction, heating, more piston expansion, more interference, and eventually the piston skirt gives way a bit. This condition is referred to in some circles as a collapsed piston, and it knocks. This seems to be your problem. (Cyls 5 & 6) Now I think any non-original piston is likely to be a little different from original, probably shape and configuration, and almost certainly alloy composition. So what is the correct clearance for the replacement piston? The piston manufacturer should tell you, but I think there is no guarantee he will be right. After all, where is his test data for running pistons with different clearances in test engine? I am quite sure RR did that as a basis for zero clearance on thrust diameter. I think it is interesting that the engine was rebuilt without removing the cuff liners. I think it is well known that they need to come out at overhaul. It sounds like this mechanic isn't very knowledgable of this particular engine's needs. Regarding block expansion, I believe the bore gets larger when hot, not smaller. If the metal expands uniformly, the hole (bore) should expand as well. Regarding timing gear, I think what you described should be made right by the person who rebuilt the engine. If he refuses, I would look for a used gear. I have one that I could be talked out of, but I have no idea what is a fair price. Do you not have a RR breaker in the sunburnt country? It seems to me that timing gears should not be scarce, since I think engines fail from broken blocks and other fatal happenings more often that they fail from worn out timing gears. Fitting a new gear to an old pinion could result in a whine when it is all back together. I know that this was a problem with PIIIs. Replace fiber gear with aluminum and a big whine results. Fitting pistons with a .002 interference fit at the bottom sounds very strange to me. I don't think I would want to do that. Another reason pistons can colapse is lugging the engine. This causes extreme piston heat. The car could also be run too hard or too fast too soon after overhaul, which seems to be what happened to Richard with his first set of Repco pistons. Maybe the clearances were also a little tight the first time, and I think the tin plating would help reduce friction as Richard suggests. To address my own problem, which I think is different from those described by Jim and Richard, I have taken my spare engine apart to examine the pistons in it. All have the top ring broken, and three pistons have the top ring groove worn out double thickness or more in a few spots where apparently a broken piece of ring was tying up against the cylinder wall and beating the top and botom of the top ring groove to death. With two pistons, the super wide spot of the top ring groove had worn through to the top of the piston, probably releasing some metal to the combustion chamber. This is what I think has happened to the engine in my car. This is my plan: I am going to remove the head, pan and pistons from the engine in my car. Hopefully at least three pistons can be reused, since three is all I have got. I am expecting to find the bores standard, as is my spare engine. I also expect to find many broken top rings, which I will replace with some from the second rings from the spare engine. I also expect to find at least one piston with pieces broken out of the top above the top ring. If the bores are not standard, I have a set of +.010 used pistons, and if that is the size I need I will also be OK. I will hone the bores lightly to remove the glaze so that the rings can re-seat. Hopefully this band-aid repair will keep me going until I can get my spare engine rebuilt. Any comments? | ||
| Norman Geeson (80.225.191.194) |
Bill I am sorry to hear of your suspected piston failure, not exactly unexpected if the engine has cuff liners. First of all if you will excuse me, a comment to Jim. You both appear to be experiencing similar problems in any case. The RE 9346 timing gears appear to be about as rare as three humped Camels. I search for eight years for one and came up with a batch which I purchased, I now have three left and know of another three.I am aware this is not a commercial site but if anyone is in trouble with RE 9346 gears they can contact me by e-mail at CC6@lineone.net. They are about 66% of the cost of the repro gears which have just gone into production in the U.K recently. I note Jim mentioned the gear wear/ appearance which is typical of a previous piston or camshaft bush breakup leaving debris on the gear. Your own problem now but I am sure you realise I am no more expert than anyone else at long range diagnostics. I may be going down a dead end here but I think you have the following problem reading from your detailed description of the failure. In particular the knock going away when cold. Jims or his friends Dawn has a similar problem and the evidence is there for both. In short both engines have loose cuff liners when the engine is hot.I don't need to tell you what this will do to the pistons and ring packs, but I will enlarge later. Jims evidence is the oil leakage from the lower end of the cuffs.Your evidence is that the engine is running too hot anyway, you stop a short while at the motel, switch off, walk away and the engine boils locally at the top end. The cuff liner already has had enough and starts to distort even more severly.You fire up again go a short distance and the liner starts telling you its loose. Come back, let it cool off and the block grips the liner again, no noise. Engine gets hot, liner comes loose again. I think by now you are on my wave length. If this has happened it will quickly bring about piston / ring failure. Not only is the top cuff liner distorting but the bottom end of the bore, you will no doubt find the split in the skirt of one piston has probably closed up.This is made worse, if the pistons are zero bottom skirt tolerance as the skirt gets an extra kick as the piston emerges 0.750 inch from the bore at the bottom of each stroke.In addition you may or may not realise that the piston travels FURTHER therefore faster in the first half of the crankshaft rotation than in the second half. The piston acceleration is about maximum at the cuff liner joint.This does not help, particularly when the cuff liner has just tilted as the piston goes over T.D.C Next let me really make your day.When the pistons are tight tolerance (e.g Original R-R spec, long since disgarded)the bore distortion very often causes the piston to travel up/ down at an angle, it has say no skirt clearance, particulary on a 4.5 ltr you will find the big end part of the rod starting to rap the side of the crankshaft.This problem is exaggerated because not only does the crankshaft flex violently between the center main bearing and no 6 big end, but it does it more so if the car is manual transmission. In short it was only in mid 1954 that R-R found out how badly the inbalance of the clutch centre plates were affecting the rear of the crankshafts. If the pistons are close tolerance and the crankshaft flexs, no5/no6 piston skirts have no where to go.Note here Jims comment about the skirts on these bores! I will add to your bad day. Not only does the shaft flex, but it also concertinas, that is it lengthens and shortens. This fact again was not known by R-R until 1954.I will now ask the question which I know you can answer, considering the cuff liners, the step to the parent bore, liner distortion, the crankshaft flex and the concertina, is there any wonder that you need piston skirt clearance and that the pistons give up? I have covered the cranks, albeit it briefly before discussing pistons, I think you will realise why, but two further points on the crankshafts.Most of these shafts are bowed, in fact R-R gave them an allowance of 0.010 inch bow allowance in service. Some are bowed much more and need checking EVERY time an engine is overhauled and straightening BEFORE the shaft is reground.A good shaft will only bow between 0.0025 and 0.004 inch at the center main when supported in the block on no2 and no5 main bearings.I have had to straightened two cranks in the last year, one with 0.016 inch and one with 0.025 bow.Even at the R-R service allowance maximum a crankshaft grinder will not be able to centre the shaft in a grinder.Many will attempt to recentre the shaft on the machine, now think what is going to happen to the alloy timing gear, it wears the teeth in one spot! If a timing gear is found with wear in one location, the crank is bowed, the crank has been recentred or the camriders have stuck in no5 cyliner. Incidently when the cam riders have stuck do not expect to find heavy scoring of the tappet or tappet bore.Sticking cam riders can be harder to detect when the engine is stripped than may first be believed. They will also cause an almost identical problem to yours and in fact are responsible for most noises which come and go on these engines. In R-R's own words, sticking cam riders sound like slack pistons! Clonk,Clonk. Don't refit any four window cam riders if you can avoid it and never to the rear three cylinders. I take Richard Treacy's point about tinning, but clearance comes first. Only from memory, but I can reseach my notes if necessary, you need 0.003 clearance on the skirts. 0.009 at the skirt top and 0.028 at the piston head.I know the JP pistons fit into this category. Correctly lined and honed from experience when fitted with these pistons an engine will do about 1300 miles per pint of oil, I like them to use a little oil. The last crankshaft point I was going to make is to study very closely the method of crankshaft grinding a R-R six cylinder. This is not usually the approach/ technique a crankshaft grinder will take. If the guy tries to center the shaft and grind from the centre outwards I can assure you the shaft main bearings will not be in line. You need to absolutely ensure the guy will grind to the R-R instructions, many will not head the advice. Just for the record R-R started with solid skirt pistons with tight / negative skirt clearances and were still committing to that recommendation in 1954 with split skirts. The piston manuafactures recommendations for the clearnaces at the time were different to R-R's. Time has proven the piston manufacturers correct. The main crankshaft problems were only realised when the S series was due to go into production and R-R did not have an Avery crankshaft balancer until about July 1954, before that ( some) crankshafts were balanced on their own machine which had limitations. The manuals I am afraid are only of limited value on the piston issue, the data was superseded long ago. To summarise, you need more piston clearances, crankshaft problems as well as liners cause piston problems/ small end failure/ knocks and timing gear wear.Don't let sticking cam riders fool you, ensure were possible you have two window cam riders, four window types crack across the window slots and you need EXTRA clearance on the two window cam riders compared to the original four window type.Don't aim for tight crankshaft end float clearances, flexing and whip cause problems if the end float is tight. Lastly your camshaft 23000? numbered is the current replacement for S/D,S/W and R type etc, 4.25/ 4.5 later engines. If I have not covered most points please advise, there are a lot of points and too many to answer fully in one session. Best Regards | ||
| Richard Treacy (195.232.90.66) |
My two bob's worth: follow Norman's advice on pistons, clearances and cam follers.. With solid skirt pistons, I used 0,004" clearance at the skirt base and 0,008" at the top after consulting with the piston manufacturer for the present set. My pistons intentionally have a 1cm shorter skirt and are better for it. Despite the zero oil consumption, helped by modern rings, neoprene valve guide seals, and that the piston skirts do not enter the crankcase so deeply, the wear rate is much less than with the original antique piston design. The rings are also not as high, so the reciprocal forces are lower. This, plus the absence of liner ridges, means that the rings are most unlikely to break. With the split skirt pistons the clearance recommended was 0,0 | ||
| Bill Vatter (67.35.48.21) |
Well, the cylinder head is off (no small task, that) and I see #5 piston has a small piece of its edge adjacent to the exhaust valve broken away. Imbedded into the cylinder head all over that flat surface that partially covers the piston at TDC, there are tiny bits (less than 1/16 in.) of piston ring embedded, somewhat reminiscent of small shot that had been blasted into it. The piston top, in the area closely covered by the cylinder head is covered with poc marks from hitting the debris on the head. You can even make out the outline of the recessed combustion chamber from the poc-marked portion of the piston. It is now quite evident that the sudden onset of knock was a piece of piston ring comming out, which was hammered against the cylinder head. This seems to be a different failure mode from that described by Jim and Richard, However, it is the same as at least 4 other engines I have seen, all of which had run high milages with Rolls-Royce pistons. I am going down to take the pistons out. More later. | ||
| Bill Vatter (67.35.48.21) |
Ok, pistons are all out. Remarkably, all are in fine shape including no broken rings, excepting of course #5 which failed. Apparently the failure was first a broken ring. Then the broken piece began to hammer at the top and second ring land, widening the ring groove considerably (about three times the width as original), and eventually it broke free to the top of the piston. Out came the bits, and bang, bang, bang. I would be pleased to share some electronic photos of the failed piston. As you probably know I am not a member of the Australia RROC, and I am not familiar with the capability of your web site. Is there a place to post pictures? Short of that I could send to interested individuals by email. The pistons in my engine are standard size, so I will select the best from the three apparently good ones that I took from that other engine that prompted the discussion "What is this 4 1/4 litre engine." I already have a new head joint comming from the UK so I should be back on the road by the end of next week. I also will take some measurements to quantify the amount of bump at the bottom of the cuff liners, and also to determine the amount of clearance at the piston skirts. I think it is noteworthy that there is no discernable ridge at the top of the bores. RR objective with the cuff liners was to stop cylinder bore wear at the top, and they suceeded quite well. Also they wanted engines to do 100,000 miles before overhaul, and with 130,000 on my clock, they made that objective as well. Of course a significant portion of that milage was with modern anti-corrosive oils, but still, I don't think 130,000 and 50 years is poor performance. Regarding water jackets, there appears to be a small amount of mud in the bottem of the water jacket, maybe 1/4 inch, but I don't think more than that. I probed the jackets with a long screwdriver, and it goes all the way to the bottom where it hits hard metal (clunk). This engine has the small water pump and fan pulley for high speed. (At least something good about this engine.) Now a couple of points to which I would like to hear some comments: 1. I am going to lightly hone #5 bore with 280 grit stones to break the glaze so that the new-old piston rings can reseat. The factory recommends finish honing with 320 stones, but I am thinking that the rougher cut will help the oil film hold on the cuff liner better. What recommendation can you offer on honing the other bores as well? 2. Does anyone know the side clearance that should exist between the ring and the groove? This may be the decision point in selecting my used piston from the three I have at hand. 3. The factory specifies .014 end gap for the rings. If heat causes the rings to break, maybe this is a little too tight. Probably I will find the rings have worn, and the gap is a bit more than .014 already, but I am thinking maybe it should be more, and maybe I should put in more clearance with a file. 3. Before I made the trip to the nationals I changed out the paper air filter element back to the wire mesh that is authentic for the car. (US RROC judging criteria strongly emphasize authenticity in all areas.) After making that change I noted a significant improvement in fuel milage, and on occasion the car seemed to be running a bit lean. For example, it would sometimes hesitate on acceleration, and I made a mental note to move the accelerator pump to the more rich position. (SU Carburettors have no such piece.) When I checked the plugs, I noted they were light tan, not black and sooty as they had been. All of this is good, but on looking inside the engine I see the exhaust valves for cyls 4-6 are WHITE! Cyls 1-3 are a light tan. Before the front cylinder spark plugs usually had more soot on them. I am curious if the rear cylinders are running too hot for the health of the exhust valves. Maybe I should put the paper air filter element back in. Any comments would be appreciated, and if you want to call ma a hack mechanic for putting in used parts, that is OK too. However, please keep in mind my objective is to have this car on the road in September, and I could not engine-out and complete overhaul by then. | ||
| Jim Bettison (203.166.57.11) |
Bill, I assume that the things you are proposing to do are to your "What is this 4-1/4 litre engine", but I'm not sure. We here have talked about your three points (and some others) and have these comments: 1. The stone you choose for honing should relate to the piston ring material. If you're using cast iron rings, then 280 grit would be our choice. If you're using a hard ring, then go to 320 grit. The primary objective is not, in our opinion, to retain oil but to facilitate the bedding of the rings - which will effectively occur in the first 1 to 5 minutes of running. Oil filling the hone marks will promote glazing. The surface left by honing, particularly when new, has an abrasive action, which will configure the ring surfaces, thereby bedding the rings. Of course, the rings will also act to configure the bore surface. In this regard it's useful to note the procedure of at least one engine manufacturer here in Oz. They assemble the rings to the pistons, and the pistons into the cylinders, using a liberal quantity of CRC on the rings and a smear of oil around the skirts. The engine (with its fill of oil in sump, but not with more or other lubrication on the pistons) is then run on no load. During this run the oil system "comes to life" and normal lubrication is supplied to the pistons and cylinders. This results in well-bedded pistons and bores, which all happens in the first couple of minutes of running, and an extremely good in-service life. We can tell you, by the way, that the cuff liners, when it comes to honing them, will use honing stones like you never imagined. The one thing that we were told by the guy who did the first assembly of the Dawn (that we're now cleaning-up) that we believe is that he used two or three stones on each cuff liner. We don't know what the grit of the stones was, however. 2. We would set up your pistons with ring side clearance in the groove of as close as possible to 1 thou (0.001") and certainly not more than 3 thou. I assume you have a local manufacturer/supplier of piston rings. The practice here is to chuck the pistons in a 4-jaw chuck, with a tail rest if possible, and clean up the grooves (both sides) with a parting-off tool, avoiding deepening the groove. Then fit the rings; you may need to lose some ring thickness by dressing on a sheet of wet-and-dry on a flat plate, or even taking a skim with a grinder. (If lucky, you can get the grooves cleaned up to the ring thickness - I prefer to try to get lucky!) One thing is certain: if you don't keep this ring-in-groove clearance small, you're heading to a re-run of your broken ring episode! 3. The workshop manual we have (for Bentley) specifies ring gap as .014". We think that you could safely go to .016". (It's a little surprising that you don't have these figures in your workshop manual - the Bentley has them all.) 4. (Your second 3.) If it were mine, I would graciously retire the paper filter and replace it with another new paper filter, or a cloth filter. What you describe is classical Clogged Filter Syndrome. How long has it been in service? Even an apparently clean - but old - filter can be really clogged. Also, don't rely on the gauze filter to do more than screen out insects ... We here have modified an after-market cloth filter; you could probably do the same and get it in behind the gauze filter. The second symptom you describe (colour difference on plugs) sounds to me as if you have an air leak into the rear end of the intake manifold. Go looking with an oil can, and squirt oil over the gaskets around the rear end of the intake manifold. Finally, I've got to say that I admire your pluck. However, I think there's a great danger that you will set up a second engine that goes sick much more quickly than your original one. I think there's a very strong case to go to a re-bore and set-up with new pistons and rings, at least. Please take this comment as being intended to be constructive. If you do go ahead as you first indicated, I suggest that you get your pistons/con-rods/gudgeons balanced as assemblies. As I'm sure you realise, there is scope for some substantial out-of-balance forces with an un-matched set of reciprocating components. Good luck, and please keep us informed. Jim. | ||
| Bill Vatter (66.20.178.55) |
Jim, Thanks for your response. Let me clarify what engines I have. Over in the corner on a stand is the partially disassembled engine from Silver Wraith WFC10, a deceased car. This engine has no engine number, only a casting number RE9421 FF. This was the subject of the thread, "what is this 4 1/4 litre engine?" Eventually, I will rebuild this engine to replace the one now in my car, but that is a long-term project. In my car is a more immediate problem. This engine had the knock comming back from the Nationals, and I want it to run a little longer so that I might properly host our fall driving tour. For this purpose, I am approaching it with the pluck you noticed. This engine has five "good" pistons (meaning they havent failed yet) with unbroken rings, and one piston that broke the top ring and a piece of this broken ring escaped to the combustion chamber where it caused the knock as the piston hammered it into the cylinder head. I have taken a piston from the "what is it" engine to use in my car as a temporary fix. All of those "what is it" pistons had broken top rings. 3 of the pistons had also experienced failures like I had in my car recently, and 2 of these were broken through to the top in 2 places. The owner of that car must have had all together 5 separate piston knock events, and yet he kept driving. Now that is what I call pluck. Now back to the car I need to get back on the road soon. I appreciate your comments regarding honing. I will hone all six cylinders because the piston rings will all need to reseat. What is the material you refer to as CRC? My five good pistons have varying side clearance between the rings and groove walls. All five have between .008 and .010 side clearance on the top ring. The second rings are all between .002 and .004 side clearance. The replacement piston (used piston from "what is it") has about .004 side clearance on the second ring, which I transferred from the piston that failed in my car because the second ring from "what is it" piston was horribly worn. (It had about .075 end gap.) The second ring that I saved from the piston that failed me had about .020 end gap, worn, but not impossibly so. Now having no usable top piston ring for my replacement piston, I ordered one from the RR dealer who stocks spares for the early post-war cars (Albers RR). It is costing me $32 US, and I expect it to arrive tomorrow or the next day. It will be interesting to see what the side clearance measures for this ring when I get it on the replacement piston. However I am not so very sure the measurements will be pleasing. Remember this piston already broke it's top ring whan it was in "what is it." The ring groove measures between .098 and .103 at various points around the circumference, which is not encouraging in that it is not uniform. I did not possess a hone, so I ordered a "glaze breaker" hone from a machine tool supplier. This is a different tool than the type hone used for finish sizing cylinders after boring. The typical engine cylinder hone is adjustable and it is tightened to drag a bit and then operated until it runs free, and then retightened. (I'm sure you know all this.) The glazebreaker, however runs only with spring pressure against the cylinder walls, a much less sophisticated tool, and it is not intended to be a tool for finish sizing of cylinders. Anyway, it comes with 280 stones, which my machine shop buddy says should do the job. Of course he knows nothing about brichrome cuff liners. The cylinder bores in my engine have a little bump at the bottom of the liners, but within the .005 my manual says is acceptable for ovality, the only acceptance dimension quoted. It is interesting to me that the greatest wear is at the front and rear of the cylinders (adjacent to the gudgeon pin ends), not at the thrust side and its opposite which I thought would wear the most. Well anyway, it's going to be damn the torpedoes and ahead full for this engine, and we will see how it works out. I think that at the worst I will shortly be back where I was when returning from the national meet, having invested less than $200 US on a head joint, a piston ring, and a glazebreaker hone. I guess I also invested time, but it was interesting, and it's fun in a perverted sense working on the old cars. I will run it until it fails again or "what is it" gets a complete overhaul, and I am sitting here with nothing to do in the middle of winter and decide to change out an engine for the fun of it. I appreciate your comment on ring side clearance, and I acknowledge that I have too much. I called a couple of machine shops and asked for ring shims, and they laughed at me saying nobody has used those since the 1960s. So to fix this side clearance problem, I would need to be finding some replacement pistons, or some kind of other piston rings. (I think that fellow up north put piston rings for a John Deer tractor (or similarly strange source) in his Bentley.) Anyway, If you fix everything you find wrong when you take one of these apart, it is called complete overhaul, and it costs real money and takes a long time. I see that the stock market is up today so maybe I actually have some money, but as for time, I have none. As you observed, plucky is how you get when you need to do something, but you don't have the best options available. | ||
| Bill Vatter (66.20.178.55) |
Second thoughts--- I am going to investigate the possibility of machining the top grooves slightly wider to fit piston rings for a Detroit whatever. That should remove the concern over rings too loose. Thoughts on this approach? | ||
| Jim Bettison (203.166.57.11) |
Bill, We'll develop an answer to your long reply to my commentary in the next couple of days. In the meantime: The correct rings to use are firstly made of acceptable material (in this case, for you, probably cast iron); and secondly of the right size for your ring grooves, as machined. Doesn't matter what or who they were made for. You may need to adjust thickness, etc, and gap, as I suggested - but that's OK. CRC is a dewatering/degreasing/lubricating fluid commonly used to repel water in auto electrics and release frozen threads. Here in Oz it commonly comes in a pressure pack and you spray it on a wet distributor or a frozen thread and, hey presto ... You should find it in any auto aftermarket shop. Let me know if I am helping ... Regards, Jim. | ||
| Jim Bettison (203.166.57.11) |
Bill, We have found a local catalogue for pistons, rings, etc which has a good summary about fitting pistons, rings, etc. If you send me your fax number (probably best to my e-mail, jbettison@internode.on.net I'll get a copy of these instructions to you. (Just at the moment my scanner is playing silly b*gg*rs.) I should have said that the juice sold as CRC also goes by other names; RP-7 and WD40 are two of them. Also, the local fraternity reckons that the best cloth air filters are K&N - an US product. I'll send you a contact address/phone number if you wish. You should find something in their range that would fit in the boom box behind the present filters, even if a bit of basic sheet metal work was necessary, Regards, Jim. | ||
| Bill Vatter (66.20.179.36) |
WGC 66, AKA "Morgan," is back together and running with one new-used piston and new top piston rings on all pistons. My new-used piston came from the spare engine which conveniently had the same size pistons. They all measure 3.5005 on the thrust diameter at the skirt (the spec of a new RR piston) which I think is quite remarkable after 130,000 miles, on mine, and who knows what on the new-used. Perfect Circle part number TF10036 ring, which is for 3 1/2 standard bore and has cross section of 0.124 in. high and 0.150 in. deep was used. These cross section specs compare with 0.092 and 0.125 respectively for the RR piston ring, which of course I could not use because the grooves had worn over-wide by quite a bit. Pistons were machined to provide .002 side clearance and .005 depth clearance. Original middle and oil rings were used. (Moved the ones from the failed piston to the new-used piston because the new-used ones were worn much more.) I honed the cylinders a good bit on the bricrome, and just a little on down about 5-6 inches or so which is about all of the surface that the rings will see. There is now about .004 dip on the fore-aft diameter and about .002-.003 on the thrust diameter just below the bricrome after honing. The hone did not touch these places. The hone took the bricrome out from 3.5005 where it had not worn to 3.5010. There are some low places that the hone did not touch but these are only in spots and at the worst measure 3.5010+. That bricrome is hard stuff, did not wear hardly at all, and took a good while to be cut the small amount that I did to it. Really all I was looking for was to rough up the surface enough to seat the new rings and re-seat the old ones. The weight of the new-used piston was only 1 dram heavier than the failed piston, so I think it has not upset the balance very much. (It seems like I scraped at least that much carbon off the piston tops anyway.) The car is runing fine. I have driven it about 80 miles after a 30 minute free running period at about 1200 rpm. It smoked quite a bit at first but this seems to have about stopped. The car seems to have maybe a bit more pep than before, maybe because I took a big bunch of carbon out of the combustion chambers. Much of it was that rock-hard carbon you get from running leaded fuel. While the carbon might have raised the compression, I am sure it adversely affected gas flow in the combustion chambers. Time will be the judge of the viability of this repair, but it has got me back on the road fast and for small expense, which is what I wanted. Jim: I would really like to see the catalog you mentioned. Assuming the repair I just did continues to work, I am thinking that a very good set of used .010 oversize RR pistons that I have on the shelf with a machine shop re-grooving job and new rings is what I might use in my spare engine, which I will re-sleeve with full-length cast iron sleeves. For this engine I am thinking to try replacement middle and oil rings also, and I want to study it out in a parts book like you describe. |
