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Rich Cwik
Posted on Friday, 04 April, 2003 - 09:55:   Edit PostDelete PostView Post/Check IP

Does anyone know the main and connecting rod housing bore diameters for a 4.25 and 4.5 liter r-type bentley (one is a 1948,the other a 1953) engine?
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Bill Vatter
Posted on Saturday, 05 April, 2003 - 01:31:   Edit PostDelete PostView Post/Check IP

Mains are 2.9175 and big ends are 2.1415.

What are you trying to do? If you are looking to put modern bearings in there, I wouldn't.

First, the best you can do is a bearing that has the location of the tangs reversed, and this means you will need to machine new recesses in the rods/block/caps to fit the new bearings.

Second, what is the composition of the new bearings? RR bearings are lead-indium overlayed on a copper base. RR developed this material because they were having some difficulty with white metal bearings used pre-war. Some pre-war Bentleys driven agressively at high speed on the continent suffered main bearing failures.

Modern bearings will most likely be babbit, essentially the same as white metal. However, I do not know how you are going to find that out. Certainly your parts counter man is not going to know, and they look the same to me. Babbit has a lower load carying capacity than most other bearing metals, but I have not seen data on lead-indium. I would assume it is high load capicity, as needed to address the problems of the pre-war cars. I do know that lead-indium is harder than babbit, and requires a hardened crankshaft, which babbit does not require. Before assuming the tractor bearings recommended in Flying Lady Mar/April 1999 will be OK, you should consider the early post-war RR six is a very long stroke engine compared to modern engines and the long stroke engine has significantly higher bearing loads than a modern engine, other factors being the same.

The engineering books I have state that babbit requires a smaller clearance than other bearing metals, but again I have no data for lead indium. The clearances specified by RR are generally larger than you would expect to see for those size journals in a modern engine.

I am not a bearing engineer, and it is possible everything will be fine. I really only know that there is a difference in bearings that does not immediately meet the eye. Adrian West put the tractor bearings in his R-type Bentley, as reported in Flying Lady, and he has driven the car 15,000 miles without a problem. My Silver Wraith ran over 130,000 miles with the original bearings, and much of that was with comparatively poor quality oil. Maybe modern oil will help. Also you can increase the load carying capacity with heavier oil. RR recommended 20-20W but most people today are using 10W-40 or 20W-50. Also, the oil recommended for diesel engines, for example Shell Rotella and Chevron Delo, is very good for our cars for reasons beyone the scope of this discussion, so maybe oil will compensate for the weakness of an incorrect bearing.

So it boils down to do you want to take a chance? probably you have checked the price of bearings at your friendly Rolls-Royce dealer. I will agree that price is outrageous. However there are after-market suppliers in the UK that can supply bearings intended for the RR six at a price that while still expensive, is not unreasonable when you consider the low-volume production of these parts. Is it the same as the part sold by the dealer? Cant say. Maybe someone else knows. However, RR is not making their own bearings. They are out-sourced like most of the parts they sell for these cars, and they could well be exactly the same and come from the same manufacturer as what the after-market supplier is selling.

Well I have certainly run off on a tangent to what you originally asked. Sorry if I have been over bearing. (Ha-ha. Did not see that pun until I re-read my post. Laughing at your own jokes is great fun.) Let us know what you are doing/intending with that engine.

Regards, Bill V.
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Richard Treacy
Posted on Saturday, 05 April, 2003 - 02:39:   Edit PostDelete PostView Post/Check IP

Bill's measurements are correct. Many years ago when at 14 I first overhauled our R-Type motor in 1971, I needed these figures too to check the crankcase tunnel alignment. It was fine. If not, it would have needed the caps shaved down and then be tunnel bored to spec. To do this check, I borrowed a mandrel from York Motors. Who has it now I wonder: a steel cylinder about 2 ft by 2.9174 inch which you bolt into the caps to check.

I reiterate Bill's warning: the correct shells are freely available and not too expensive. I have heard of them being remetalled in an emegency, but that costs more. A friends F series Silver Dawn 4 1/2 had to have its mains and bigends bored last year, but the garage botched it up. Moral, only resort to tunnel boring if absolutely necessary ! Also botched were the liners (full length is mandatory to allow rings to last more than 5,000 miles) and pistons. Incidentally, I fitted new camshaft bearings on the next overhaul of my R-Type in 1984. They of course needed line boring too as they are supplied in a very undersize dimension and always require line boring.

RT.
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Richard Treacy
Posted on Saturday, 05 April, 2003 - 02:54:   Edit PostDelete PostView Post/Check IP

By the way, my machine shop who ground the crankshaft in Canberra was insisting that we tunnel bore the crankcase or he wouldn't do the job. He refused to take a chance with his reputation if the job failed. The only way we could persuade him not to was to find the mandrel. Shaving the caps only is sometimes OK, but if you machine the crancase side also the cranshaft runs higher in the block and so the whole piston and timing gear geometry changes, and that can't be good. Also, reboring the bigends shortens the conrod lenght. These two actions together fix the piston problem, but what a nightmare ! Then you must relap the timing gears. If possible, leave the tunnels alone.

RT.
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Bill Vatter
Posted on Saturday, 05 April, 2003 - 03:11:   Edit PostDelete PostView Post/Check IP

Adding to what Richard said, there is a very close tolerance in the gearcase cover for the oil seal (really just a screw thread) against the front pully. If you shift the crankshaft up, it isn't going to be right.
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Richard Treacy
Posted on Saturday, 05 April, 2003 - 05:24:   Edit PostDelete PostView Post/Check IP

And what about the gearbox alignment ? Phew. Best leave it alone. .... ..... ...... .... .... ... ... .. ..
.................(due to short post)


RT.
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Rich Cwik
Posted on Saturday, 05 April, 2003 - 11:46:   Edit PostDelete PostView Post/Check IP

Its just that(A)- I have both motors apart to rebuild,and (B)The 4.5 got really,really hot (so hot that even with the lifters out the cam turns like you are fighting the valve springs, and I thought it would be a good idea to check the main bearing alignment while its apart. I really only want to rebuild it once in my lifetime,and here in the states,its really a pretty standard check while the engine is at the machine shop being cleaned and checked. Thanks for the information-Rich
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Bill Vatter
Posted on Saturday, 05 April, 2003 - 17:21:   Edit PostDelete PostView Post/Check IP

Rich,

If your engine got very hot, you should check for cracks in the block, on the deck between the exhaust valve and the adjacent cylinder. Get it magna-fluxed in this area, and look very hard at the exhaust valve seats. The camshaft no doubt is no longer straight, but that may be unrelated to the overheating. Bowed camshafts are not uncomon. Anyway, you can get it straightened, if the cam lobes are in spec. Which camshaft(s) do you have? There will be a part number stamped on the rear end. RE XXXX or RE XXXXX.

The crankshaft may also be bowed.

You can check the alignment of the main bearing bores and the crankshaft itself with a dial indicator and the crankshaft turning on two main bearing halves in main bearing position 1 and 7.

First, before you remove the crankshaft, it should turn very freely with two fingers on the flywheel studs while the main bearing caps are still on. If so everything is probably OK. Remove all main bearing shells except #1 and #7 top halves, and with the crank resting in these (block upside down), spin the crankshaft while measuring run-out on #4 main bearing with your dial indicator. If the crankshaft is within .005 of perfectly straight and it spins freely with all main bearing caps torqued down, stop worrying about the main bearing alignment, it is OK.

If the main bearing bores are out of alignment, I believe you should start looking for a new block. Where are you located?

Regards, Bill V.
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Carl Heydon
Unregistered guest
Posted From: 203.166.96.234
Posted on Tuesday, 22 July, 2003 - 04:45:   Edit PostDelete PostView Post/Check IP

Having started on the rebuild of the 4.25 from B188AK the machine shop has asked for the finished size of the crank and cam shafts at 10 and 20 th undersize.
Would any kind person be able to supply this information for us please.
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Bill Vatter
Unregistered guest
Posted From: 66.20.177.14
Posted on Tuesday, 22 July, 2003 - 06:53:   Edit PostDelete PostView Post/Check IP

On the crank, the big ends are 1.999 -1/2 (std); 1.899 -1/2 (10 under) 1.799 (20 under), etc. The mains are 2.750 -1/2 std with undersizes at .010 intervals (2.740, 2.730, etc) as with the big ends. Better make sure you can get bearings before he starts grinding. I have not seen anything more than .030 undersize offered by the after market suppliers. Bearings from RR are very pricy.

Camshaft bearings are not available undersize. If the journals are defective, e.g. scored or oval, you will be looking for a new camshaft. More likely you will find worn lobes, which also requires a new camshaft. I have heard some had success regrinding the cams, but I have no personal knowledge. If the camshaft is bowed (likely) you can get it straightened. Your machine shop should be able to do that.

The above dimensional data is in the factory service instructions, which you apparently do not have. I think you should have the book for what you are doing. There are parts of the engine you will probably not get right without the instructions to guide you. This project is costing you some significant $. You should do it right, so you don't have to do it again. I have seen some engines that had been "overhauled" by unenlightened mechanics, and the results were not happy.

The book is available from RROC (US) Club Stores if you are a member there. Probably other clubs sell it also.
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Bill Vatter
Unregistered guest
Posted From: 67.35.56.90
Posted on Wednesday, 23 July, 2003 - 11:42:   Edit PostDelete PostView Post/Check IP

OOPS! That should have been 1.999, 1.989, 1.979 for big end undersizes. Hope I did not confuse anyone. Very sorry for my mistake.

Bill V.
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Jim Bettison
Unregistered guest
Posted From: 203.166.57.12
Posted on Wednesday, 23 July, 2003 - 21:10:   Edit PostDelete PostView Post/Check IP

Carl,
I am just nearing the end of a major rebuild of a MkVI engine (Chassis B20JO). I agree with Bill's comments, but I would add an observation aabout the camshaft. RR had about 9 (yes, 9!) different camshafts during the life of that engine series. There is some room for a regrind; but rather than go into this in detail, you might like to advise the part number as stamped into the rear end of your camshaft. I expect that it will commence RE and be followed by 4 or 5 digits. There is usually about 0.015" available for regrinding. However, there is one model which is regarded as a real dog - but more about this when you find the number.
There are some other comments about items such as the harmonic damper, and the cooling system, and valve guides, etc. that might interest you, unless you already have these covered.
Good luck. Jim Bettison.
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Richard Treacy
Prolific User
Username: richard_treacy

Post Number: 37
Registered: 4-2003
Posted on Wednesday, 23 July, 2003 - 21:58:   Edit PostDelete PostView Post/Check IP

I bought a secondhand camshaft for my R-Type camshaft reground by Waggots in Sydney. The profiles (ie overlap and shapes) were the same as those of a pushrod Jaguar and a '60s Buick, one for the inlet and one for the exhaust. They have the pattern wheels for these camshafts. They did a perfect job at a very reasonable price. I have the exact data in Canberra, and live abroad, but I am sure Waggots could easily handle it based on your existing camshaft and the specified lobe hights.
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Richard Treacy
Prolific User
Username: richard_treacy

Post Number: 38
Registered: 4-2003
Posted on Wednesday, 23 July, 2003 - 22:03:   Edit PostDelete PostView Post/Check IP

I bought a secondhand camshaft for my R-Type and had it successfully reground by Waggots in Sydney. I have kept the original which is in excellent shape. The profiles (ie overlap and shapes) were the same as those of a pushrod Jaguar and a '60s Buick, one for the inlet and one for the exhaust. They have the pattern wheels for these camshafts. They did a perfect job at a very reasonable price. At the same time, it is essential that they grind the tappet faces to match the camshaft. This applies to the tappets of new, reground or secondhand camshafts.

I have the exact data in Canberra, but live abroad, but I am sure Waggots could easily handle it based on your existing camshaft and the specified lobe heights. I'll take note of the details when next in canberra.
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Richard Treacy
Prolific User
Username: richard_treacy

Post Number: 39
Registered: 4-2003
Posted on Wednesday, 23 July, 2003 - 22:17:   Edit PostDelete PostView Post/Check IP

By the way, new camshaft bearings are indeed available quite freely. For example,Healey Bros quote camshaft bearings at 45 each, part numbers UE5985 (front) and UE5986 (rear).

It is highly advisable to replace them as they are usually leached or destroyed in the cleaning tank. They require line boring. Naturally this will ensure that the camshaft is properly aligned.