| Author | Message | ||
     Mark Unregistered guest Posted From: 81.156.143.20 |
Hi, I have just spent a couple of hours tinkering with B72DA. I was just making sure it started for tomorrow. I am going to take my car to work as they have a ramp as I intend changing the car to negative earth, (thanks Ashley and Laurie for all your help off forum). Could I ask for a little more help from you all please? I left the engine running at slightly fast tickover, then after several minutes once the water was hot, a steady stream of water leaked out of the radiator cap. When I let the engine idle normally this does not happen. The seal on the cap looks a bit perished (can you get these??). My main concern was if I seal this cap so its watertight where will the pressure go? On modern vehicles there is a pressure release valve with a drain off pipe back into the header tank. I am not sure what the Bentley has can anyone tell me and also what will happen if the engine boils over. I am also worried about bursting a hose or worse a radiator. I am going to steam clean the radiator and engine block with a hot pressure washer. I was a little worried about what antifreeze to put in. I was going to use green or blue ethylene glycol (not sure spelling) mainly because its free at work!! I have seen a few conflicting reports on this type of anti-freeze. Can someone please give me some advice. Air filter, I removed the large "drum" as I am cleaning the engine compartment and wanted to get into all the nooks and crannies. When I removed the air filter the engine revs shot up and it sounds sweet as a nut. I dropped the tickover down on the idle screws and the engine revs much better now. My air filter is missing the mesh at the end so I had intended to remove it anyway. I looked at the air filter inlet manifold (where the large rubber pipe goes and wondered if a K&N racing filter would work? I am not too bothered about looks, in fact it would better as you can get to the engine easily and would make maintenance simpler. Has anybody done a conversion to their filter and could you see any problems I may have. Thanking you all in advance Mark Anson (Message approved by david_gore) | ||
| Martin Cutler New User Username: martin Post Number: 4 Registered: 10-2004 |
Hi Mark, How much did the revs rise when you removed the filter from the end of the drum? Is it the original filter, ie, expanded steel mesh? Is the filter clean? | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 450 Registered: 4-2003 |
Your pressure relief valve is on the right hand side of the header tank (viewed from the driver's seat, ie opposite side from the radiator filler cap), and has a copper drain tube going down the front of the radiator. R-R fooled around with these so there were originally several types. At one stage, the valve plunger was removed, another the return spring was removed. The final solution was to have a hollow valve plunger with a very weak spring. The system should be unpressurised, but the dummy valve stops the coolant from splashing out. Rumour has it that the head gaskets did not behave at all well when the systems were pressurised, hence the experimentation by the factory. New cap seals are freely available and should never leak. As for antifreeze, I go for a non-phosphate inhibited ethylene glycol. You can't go wrong as long as it's at least 40% glycol. Measuring with a hydrometer is OK. Air filter: I have never understood a need to change from the original. The cars have never suffered in over 50 years, so why change now ? Any change to the type of air filter requires a different set of carburettor needles eg SC with the factory mesh filter or SF with the superior factory oil bath air filter. Try another type and you open a can of worms. To be quite candid, I feel the same about converting the battery polarity. | ||
| John Dare Unregistered guest Posted From: 144.138.194.139 |
Hello Mark, I have the number recorded (somewhere) for a "Valiant" paper filter element which fits readily onto the end of the standard "drum", in place of the "wire" original, which someone once noted, only kept birds out. Another member may have that (or another alternative) part no. to hand, thereby providing you with some options which may still present a stock appearance. (Message approved by david_gore) | ||
| Martin Cutler Experienced User Username: martin Post Number: 7 Registered: 10-2004 |
Hi John, My filter keeps birds and small children out. Would be interested in the reference number for a paper element. Would be a small one! | ||
| Bill Coburn Grand Master Username: bill_coburn Post Number: 279 Registered: 4-2003 |
Your exchange about filters got my bile flowing. Some months ago our esteemed bi-monthly publication produced one of those slightly unctious reports on a restoration of a Mark VI as I recall and mentioned in passing that he/she had found a paper filter that fitted etc. These accounts reduce me to a rage sometimes since they turn out to be (probably not intended I hasten to add) an account of how clever/wealthy/capable I am to have got this vehicle to this standard. But seldom if ever do we have an account of how some difficult process was performed or who did it or what materials were used!!! Bah - humbug as Dickens would say. Anyway now I feel better. The filter mentioned in the story was not identified. If I had one of these chicken wire units I would want to use a paper one but I would need to be able to check mixtures etc after fitting since the comparative properties would surely not be the same. I had a Cloud III some time back with the wrong filter in it which really gummed the engine through effectively choking the car due to presumably its different density - it was quite clean! | ||
| Martin Cutler Experienced User Username: martin Post Number: 9 Registered: 10-2004 |
Hi Bill, I don't operate the car in dusty conditions, so running the original filter is probably doing enough to keep grit out of the engine. My 1930 Austin 7 and 1925 Dodge have been running filterless since they where constructed, albiet the mileage is fairly low these days. I run my Mk VI slightly rich to try and keep temperatures down. Most circular paper filters have a fairly large circumference, I have not seen one that would fit the diameter of the drum, but it would be an interesting experiment that would only cost a couple of dollars. | ||
| John Dare Unregistered guest Posted From: 144.138.194.128 |
Thank you Martin. I now recall the ref.no.is in a book at the holiday home which I will visit this coming week end. I will post details soon thereafter. Regards (Message approved by david_gore) | ||
| Bill Vatter Experienced User Username: bill_vatter Post Number: 9 Registered: 9-2004 |
Marty, The factory filter actually does much better than to keep out small birds and large bugs when it is installed correctly. Its appearance is deceiving in that regard. The filter should be thouroughly oiled, left to drain, and then put in place. It works on the principle that when the air changes course passing through the mesh, fine particles are flung to the side, and they stick to the oily surfaces. Really very effective. If you install a paper element, that might improve filtration (maybe not), but it will increase the pressure drop across the filter element, which will cause an overly rich mixture. In the US, a manufacturer has developed a "new technology" filter, based on the principles of the original wire mesh filter, but using a very fine fiberous filter media. These filters have much less pressure drop than a paper filter, are highly efficient in removing particulate (better than paper), and they can be cleaned and reused many times. They are pricy at around $35 USD. http://knfilters.com/ These filters appear at first glance to be similar to the paper filters but they are really quite different. Like the original factory mesh, they need to be oiled for effectiveness, but you use a special oil. (For the factory mesh, any engine oil works well.) K&N part # E2520 for the twin carburetor cars, and E-4583 for the single carburetor. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 454 Registered: 4-2003 |
It's quite hilarious really. If you look at the US site, they are hellbent on replacing Spirit paper air filters with KN mesh filters (why ? so you can reuse it, but at what price), and here we are talking of replacing mesh filters by paper elements. Don't forget, unless a car is fuel injected, the filter behavious is critical to mixture dynamically.. | ||
| Mark Anson Yet to post message Username: bentleybloke Post Number: 1 Registered: 11-2004 |
Hi "Fellow members" and guests....I can say that now as I have been officially accepted as a RROC member by they who shall be obeyed!  Do I get a badge now? Anyway, sorry for not responding to your posts sooner and thanks for your replies. With regards the filter I am going to go with the K&N racing filter. My main reasons are for ease of cleaning and easy maintenance. I think I have mentioned this before, the car is going to be used for weddings and needs to be reliable. I have also found that removing the large drum filter has given me lots of easy access to the engine, this is something I hope I will never need on a wedding trip but would make tinkering with carbs and water pipes etc a lot less trouble. To answer Martins question, the revs increased slightly and the engine ticked over more smoothly. The air filter had no mesh in it at all so dirt and dust was being sucked inside the engine. I also hear the dawn chorus each morning under my bonnet due to the flock of birds nesting in there after being sucked in  . My mixture is running quite rich, removing the filter weakened it slightly causing the revs to pick up. I have ordered carb restoration kits from Burlen Fuel Systems so will set the mixture after this and filter installation. I think Richard mentioned my recent polarity change (which went very very well by the way). The main reasons for doing this is I have insurance conditions. They have asked for a Thatcham approved car alarm as the vehicle is parked on the driveway at home. Unfortunately Thatcham positive earth alarms don't exist. Not only was the alarm going to cause problems but the CD player, Holley fuel pump and electronic ignition system would not function either. I do not intend making this car concours so I am not to bothered about things being original...As long as it works and works well thats all that matters. Cheers Mark | ||
| Martin Cutler Experienced User Username: martin Post Number: 10 Registered: 10-2004 |
Hi Mark, My understanding is (others may correct me) that the large drum acts as a still air box, allowing for smoother running.It also quietens the induction noise. I would try and retain the drum. If you are missing the filter off the end, then a new K & N filter might work fine. The filter fits on the end of the drum, held by a wing nut. If there was no filter, I'm not sure why the revs rose when you took the drum off. The drum shouldn't do anything to restrict the air flow. What you need to determine is if the car is running rich at idle, or all through the rev range. When SU's wear, they run rich at idle, but generally run OK through the rev range. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 456 Registered: 4-2003 |
The drum is simply a tuned silencer, as described in the workshop manual. It is not there for fun. Take it off if you want induction roar and poor intake air flow. I suggest you inform yourself by example: remove the drum and filter, and go for a drive. At anything above 1/3 throttle, the motor will cough and backfire through the inlet manifold. Even on low throttle, the noise will drive you nuts. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 457 Registered: 4-2003 |
Martin, you are correct about rich at idle and OK elsewhere as the needles and jets usually only wear at the idle points. Wear occurs usually because the needles have not been properly centred during maintenance. However, the result is that you will always tune the carbs to be correct at idle to have a smooth tickover. The trouble is that it will then run lean elsewhere. New needles, and probably new jets as well, are the only proper way to go. In any case, any change in filter or induction geometry would require a completely different needle. Just the difference between the original export oil bath cleaner and the UK market mesh type requires a change in grade by three levels. Even the two different mesh type filters (the very early Bentley type and the later AC type)require different needles. You can get it all sorted out with, for example, a Sun analyser and a dynamometer, plus a range of SU needle grades to try out. It wouldn't be cheap and would take quite a few iterations. Would that really be worthwhile when the original setup is so well sorted out ? Hmmn. | ||
| Martin Cutler Frequent User Username: martin Post Number: 11 Registered: 10-2004 |
Hi Richard, You are correct. I had a hell of a time tuning the SU's on the MG Magnette, after I changed the engine to MGA block, MGB head, bigger exhaust, different cam, etc. I changed the oil bath filter to a unifilter insert, still inside the oil bath housing, so it all looks original. I turned to a friend called Bob Winley, been tuning race cars out at Amaroo for many years. The MG has great torque in the mid range now, can hold 70mph up the hill on the freeway leaving Hornsby, no mean feat! I think I will leave the idea of changing the air filter alone. As you say, why upset it when it is driving perfectly well. Marty | ||
| John Dare Unregistered guest Posted From: 144.138.194.53 |
Hello Martin Cutler; On 23/11, I said that I would locate and supply a local part no. for a paper type air filter element as presently fitted to my "R" type and known to suit Chrysler "Valiant". Regrettably, my records simply show the hurried endorsement, "Valiant", so unless another member has a part no. you might like to approach Repco and view what they have (for "Valiant") should you ever decide to change from the original type. John Vawser originally rebuilt my engine and Robert Chapman now tunes and maintains it. I think he experimented with needles in the "new" S.Us (ex Midel) and I have to say the performance (speed/torque etc.) of the car is rather amazing. Of course being a manual, one does have the opportunity to extend the revolutions (when on the highway etc), much to the consternation of drivers of modern cars!. Unable therefore to anticipate any real need to fit that 1959 4.9L/"SI" engine lurking at the rear of the shed. Tempting though. (Message approved by david_gore) | ||
| Martin Cutler Frequent User Username: martin Post Number: 15 Registered: 10-2004 |
Hi John, Since reading this post, I took my air cleaner out, cleaned it with compressed air, and re-oiled it. My friend who runs a workshop around the corner, has a cupboard full of air filters, carrying around 40 different types in stock. None where even close to being the correct diameter for the Mk VI, but he didn't have any valiant ones in his stock. My 4.5 litre motor is also attached to a manual gearbox, but I resist the temptation to wind it out. 60mph is my self imposed limit. My friend's R Type has seen 90mph, (not with me at the wheel!), with no detrimental results, but another R Type I know of which has recently been sold to Ron McCann in Queensland had a piston crack after seeing a 90mph run. This motor took 2 months of constant tension to release the head from the block! I leave my high speed runs to the bike. The Laverda triple recently saw 7000 rpm in top gear, which equates to 238km/h, not bad for something originally built in 1974! | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 466 Registered: 4-2003 |
Hell, Martin, those are very conservative figures. An R-Type which only reaches 90mph is a pretty sick one. Foot on the floor, or held in 3, an R-Type automatic with 11:41 rear axle should not shift to fourth before 65mph, and kick down close to 60. Mine certainly does. On the flat, an indicated 110mph is not too difficult but the last 10 take a while. I admit that I do have a few motor tweaks. Also, down a hill I can wind the needle off the clock, indication a surely over-optimistic 115+. I have not done this for years given the punative penalties these days, but the car is still capable of it for sure. With a decent radar detector, the Hume Highway was just grand for that before radar use and sophistication skyrocketed. If the motor is in good condition, this is not exactly stressing it given its extremely robust nature. Possibly one with manual transmission accelerates a bit harder, but the huge expense of rebuilding those beautiful but a little fragile transmissions has always deterred me from temptation. | ||
| Mark Anson Frequent User Username: bentleybloke Post Number: 11 Registered: 11-2004 |
Hi All, Thought I would update you with the air filter saga. As I said in previous post I have removed the drum air filter. A Friend had a Honda Civic racing type K&N filter for sale. this came with a long curved chrome pipe. The pipe is the same diameter as the rubber hose that links the drum to the manifold. This made fitting the racing filter easy.I had to cable tie it to the engine whilst I carried out my tests. I first did a run with no filter attached. Just the bare manifold. This seemed OK (I don't thrash the car anyway) There was slight induction noise, but this was a "deep" tone, not the normal hiss or high pitch raw you would get with twin carbs with no air filter manifold. I then fixed the racing filter on and straight away the induction noise disappeared. I took the car for a run and guess what.....no difference in the running!!! I have not checked the mixture yet but I am more than happy with the results. I am going to make proper brackets and fit the new filter. It was said about drum causing still air...why would you want still air? Surely the more air the engine can get, the better the combustion. Why is it DC40s and some SUs on racing cars have coned trumpets with no filter? Perhaps its so the maximum air can get into the carbs. (IMHO) Cheers Mark | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 131 Registered: 9-2004 |
To speed up the air,more volume. Richard Treacy is your man on this. | ||
| Martin Cutler Frequent User Username: martin Post Number: 16 Registered: 10-2004 |
Hi Mark, A still air box is a technique developed by Japanese motorcycle manufacturers, (nothing new under the sun though) for multi cylinder carburettor setups. The theory is, (as I understand it) is you need to have (at higher speeds) an amount of air ready to fill the cylinders. This is on constant velocity carbs that need vacuum to operate. This overcomes the reduction in flow caused by the air filter. On my friends race bike, the volumetic capacity of the air box is 16 litres, he has calculated the flow rate of the filter, versus the amount of air needed, and this is the correct size. Doesn't really apply to 50 year old Bentleys, but interesting never the less. | ||
| John Dare Unregistered guest Posted From: 144.138.194.89 |
Yes Mark, I recall indeed the old "grey" Holden motor with triple "SU"s as fitted with the coned trumpets (sans air cleaners) said trumpets being subject to much experimentation with length, in order to maximise performance. R.T may have alluded to this some time ago. (Message approved by david_gore) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 468 Registered: 4-2003 |
Way off subject I know, but as a parting comment, we called the trumpets air rams. Repco sold them in various tuned lengths. Fiddled around with them on my first car at 16: one-owner '58 Holden wagon (my dad bought it new from Commonwealth Motors, Canberra Avenue, Kingston in in Canberra when I was 3) : 132.5 cu-in + wear grey motor. Chasing no-gain, perhaps 2 horsepower and lots of noise, and despite the noise my mum could still drive me to school in it. I never got the tripple SUs right, and eventually transplanted the motor to double the horsepower so my mum could not drive it anymore. On subject: why the hell remove the silencer / still air box from a 6-cylinder Bentley ? Call me a petrol head if you like, but this makes no sense even to me. The gentle beast is over 50 years old. Leave its noble parts alone. | ||
| Ashley James Unregistered guest Posted From: 80.229.46.15 |
Long or tuned inlet tracts are necessary where racing or semi racing type valve timing is used. Because the inlet and exhaust valves are both open simultaneously on this type of engine, there is a tendency for fuel to be blown out of the carburettor below the power band. If the inlet tracts are a suitable length the fuel will be sucked back in before it leaves the tract. The breathing of these types of engines is a bit like a tuned circuit, once the engine enters the power band, the extraction effect of a suitably tuned exhaust draws fuel into the engine and the inlets tracks lengths matter less. Air boxes on modern engines provide still air in sufficient volume for the engine to function correctly and reduce noise. Modern engines are quite highly tuned but need to be tractable which explains why they have more complex inlet and exhaust arrangements than our Bentleys. Anybody who is familier with the characteristics of race tuned engines will know that they will often run at low revs, splutter in the mid band and then take of like a banshee when they hit the power band. Modern car and bike engines are bit like racing engines with the mid band problems resolved. (Message approved by david_gore) |
