ralphw

Set the tension to the spec in the service manual regardless of new or used. The tension on the belt is specified to ensure there is always load on the belt. When the tension drops too much, then the belt sees load reversals which causes most of the damage. Personally if the belt is off, I would always put a new one on Cheers Ralph

Looking at the broken ends of the belt, did the break go straight across the belt or was it at 45 deg. If its straight across its been crimped and the cords have been damaged, if its at 45 deg then it has seen a lot of load. An 18 month old belt should be OK for normal running so I would advise that you look for a mechanical problem before putting another belt on. If the crank pulley (drives the belt) is in good condition then the increase can only come through the pulleys driven by the belt eg oil pump pulley or the cam pulleys. I have seen a lot of belt failures, but rarely seen one break without it being extremely old and work hardened or a mechanical fault. I have even run belts on dyno engines and the teeth have sheared off because the belt has been aged so much, but they have continued to run quite happily. Strange sight to watch. Cheers Ralph

See you at the Dog, Norton. May be a bit late depending on traffic out of London Dont know about the rest of you but I will be eating and yes the Dog burger is tempting Cheers Ralph

There is no reason why you cant use the frequecy method on the trap belts but they will have a different frequency to the round belts. I worked it out some time ago and posted it but I dont have time at present to go looking. The frequency method is the most accurate but it must always be done in the same place with the engine position eg 30deg otherwise you will get errors. It may not show up so much on the mechanical setting tools but mainly because of their degree of accuracy. As for the twist method, my experience is it is less accurate than the mechanical setting tools unless you get lucky or one of the few with a calibrated finger. Cheers Ralph

SHould be OK for the 19th but cant make Larling, Cambridge, Ancient Shepards is good, where were you thinking in Suffolk, the Dog at Norton? can just about make that one. Cheers Ralph

Arte Another thing to check. I come across some engines the other day (not Lotus) where the block machining was incorrect. To be specific, the threads in the block for the head bolts didnt finish deep enough, consequently the bolts were cutting the last 2 threads so the torques seemed ok / a fraction high but the head gasket blew because the clampload was insufficient. You have said that the bolts have probably been reused and may have stretched, the head has been skimmed, etc. Check that there is enough thread engagement to cope with these changes (or the bolts are close to bottoming out) before you screw it back together. Cheers Ralph

Black Bull thurs 5th OK with me. Are we just going to turn up or will a booking be needed. Next prob, I cant book at present, dont get home to Thursday morning. Cheers Ralph

Yes the issue is cooling around the exhaust valves in number 3. I remember doing some work on this years ago and due to core shift in this level of casting, it is possible that the flow around the guide on the exhaust valve can be poor, especially on the exhaust manifold side. My Sunbeam has done exactly the same thing, same valve. Cheers Ralph

I used to be involved in the testing of Brake fluids and Castrol always come out on top. Never used anything but Castrol since then Cheers Ralph

Cant do the 4th but otherwise OK Cheers Ralph

Im in, but the last week of Apr, first week of May be a bit difficult. Will check work stuff and come back. Cheers Ralph

Artie I will assume for the minute the head is OK and you will have the nip checked. Do you have any pictures of the offending headgaskets. Where have they failed, is it the same place each time, what is the failure mode. You mention head bolts, have you checked the stretch against a new bolt. I havent checked if these are torque to yield, if they are and have been reused several times the clamp load may be inadequate. Are you using the correct fasteners to hold the head down. I have found cases on other engines where the under head profiles are different to spec and consequently give a different torque reading. This could result in the torques appearing to be to spec, but with insufficient stretch to give the required clamp loads. Also check the condition of the faces on the head where the bolt heads mate as that could also contribute to torque and hence clamp load issues. Also another thought, if you are running at this higher boost and the clamp loads are incorrect, that would be enough to give the headgasket issues. Other owners running lower boosts may have the same clamp loads but the lower cylinder pressures and temps they have may be insufficient to give the same issues. By the way, the gear to measure the nip isnt too expensive and a useful addition to the toolbox as once you have it you will find other uses for it. Hope this gives you ideas to think about Regards Ralph

Thanks for letting the blue Focus pull in front of you. I was Already late for an appointment Ragards Ralph

Gavin The trapezoidal profile doesnt lend itself to that very well. The logical thing to do is to upgrade to the later pullies and belt. I have the same issue on my Sunbeam Lotus and will convert that in due course. I will never the less give your suggestion some thought, but at this time the modifications I would have to do to the belt with such a shallow tooth profile would increase the risk of belt jump and I really dont want to go down that route. Cheers Ralph

Darren Email me and we can discuss off-line ralph.wilton@virgin.net Cheers Ralph

At work, I realeased the cambelts and tensioners (plus hardware) as a kit for the simple reason that I signed the belt and tensioner off together for a set time period eg 150K miles. If the belt was changed and not the tensioner (some garages do this to alledgedly save money) I could not say that the tensioner would do another 150K miles reliably. Solution sell them as a kit so both are changed. Simples Cheers Ralph

Bibs Try the following. I have seen them used in the past with good results http://www.supertrapp.com/product_sections/auto/index.asp It then becomes up to you how much noise you want to make. Cheers Ralph

[Thanks. Not sure what the essential knowledge is behind the calculation though? What is the key logic? Dennis ] Dennis The equation has been used to tune belt tension using Clavis gauges for 22 years and has given excellent results. If you want to know a bit more about the subject, try the following site. http://www.clavis.co.uk Cheers Ralph

Thanks Richard Unfortunately while I could get some bits to SA, I also need to accompany them for some set up work and measurement work and I dont have enough free hols at present Cheers Ralph

Thanks Steve, was just looking for that. Cheers Ralph

Last year on this forum we had these discussions and I calculated the frequency for the Trap belt (square tooth) at 114.55Hz. For reference the HTD is 110Hz Cheers Ralph

Chris Yes I have a concept for an autotensioner, but needed to finish the belt first to ensure the loadings are correct. That is nearly done but I now need an engine to play with to get the Autotensioner in the right place. I dont really want to remove the engine from the Esprit for that purpose, but my Sunbeam is already out and in bits. Problem is that the Esprit get jealous then keeps looking for attention stopping me from getting on with the Sunbeam, but it is moving up the to do list quite fast.. With regard to cam timing error, this will depend on the engine the layout and the belt used. When we set our timing we set it statically. Unfortunately when the engine is running the system becomes dynamic. In our engines, there are torsion inputs coming from the crank, eg after the spark plug fires, pressure builds and subsides in the cylinder causing different rates of angular acceleration during each engine revolution. we also see positive and negative torsional effects from the camshafts as they open and close the valves plus the oil pump is also a source of variation as the oil pressure in each part of the rotors rises and falls as part of the process. When you put all this together at the same time like it or not, each cam will see a plus or minus variation (cam ref crank) from the nominal position it was originally set as the engine cycles. I have seen variations of several degrees on some engines if a system resonance is encountered making it very important to ensure the cam timing is accurate. I have seen on engine that was set up using the correct timing tools which had seen better days (a bit worn) and the valves hit the pistons. There is sometimes as little as 5° or 6° allowable before terminal damage can become reality. Note that once the belt tension drops the potential for dynamic error increases as the magnitude of cam movement can increase. The transition from slack to tight also accelerates the damage to the belt which is why autotensioner work so well, as they limit this. With regard to the adjustable pullies, they are a good way to set the cam timing to be accurate. The cam, pullies etc are all made to a tolerance so in theory there is a lot of potential variation on the timing in addition to the above. If you set the timing to be accurate using adjustable pullies then some of the variables are reduced Regards Ralph

Good info. The HNBR belt drives that go to 150K miles tend to have auto tensioners. It gives much better control of the tension on the belt and reduces the damage to the belt caused by over or under tension. The HNBR has been around now for some time. I used it ten years ago to develop the first 150K mile production belt drive and have since refined it further to allow it to run in oil. This has also been successfully in production for the last 3.5 years in a mass produced engine and many other mainstream car companies are working hard to include this technology on new models as it has should significant benefits over some chain drives, again it is signed of for 150K miles. I actually run engines for twice that distance and it was the engine that finally expired not the belt. With regard to long life belts, I have already had some 133 tooth belts produced for me not only using HBNR, but I have also been playing with the fabrics and coatings to not only get the wear reduction, but also to lower friction. I also developed this some time ago (13 years ago). A couple of these are on test, unfortunately in cars rather than on Dynos, but the extensive testing I have already done to develop this technology into powertrains means that I am confident that doubling of the service life should not be an issue. On some of the more recent ideas I have worked on, 250K miles + could be achieved. Unfortunately this would mean a massive tearup to the front of the Esprit engines so is probably not viable. I am also trying to finalise an autotensioner design that could be retro fitted so I can extend the limit further. As a matter of interest, when I have used the technology I have made the belts from, on mileage accumulation fleets, I have seen the belt life go from 30K miles in some cases, to in excess of 150K miles and still with plenty of life left (Autotensioners also fitted) Hopefully this will be available soon, currently wrestling with the commercial issues. Price will be cheaper than the $200 you quote. Regards Ralph

I haven't the time to go looking but I did calculate the frequencies for the Trap belt elsewhere on this forum. A bit of digging should find it. Regards Ralph

Well said Andy. Good to see you again. Cheers Ralph