Lotus Elan

Twincam Rebuild Saga

PostPost by: type26owner » Tue Dec 21, 2004 2:50 pm

Rohan,
The orginal style seal stil leaks a little but less than the CR seal.

I'm assuming you're refering to the red ones. Are those silicone seals? The 1-7/16" ID seal at 6500 rpms is scooting along at ~2500 surface feet per minute. Hey, that's close to the boundary were most of the common elastomers stop working cause they burn up from friction.

IIRC, somewhere I got ahold of one PTFE pulley seal which one of the Lotus Parts vendors supplied me. Just I can't remember which vendor is was now. I didn't pay that much attention to it when it got installed because there where many oil leaks all over the engine at that time so monitoring it for a leak was hopeless. PTFE (teflon) appears to be the ticket for high rpms applications. It had a PTFE lipseal and the steel frame which was neoprene covered that had concentric raised nibs on the outer diameter. I thought it looked wimpy by the fact it lacked a spring to load the lip but after exploring seal technology I've realized that's the way all the low friction teflon seals are configured. The superior pulley seal might be available but has gone unnoticed at least by me. These seals don't tolerate much runout though and may leak because the crankshaft snout is rattling around. Here again a viscous dampener might calm down the vibes appreciably.

The last item on my engine which only lasts 50k miles before they need replacing are the main and conrod bearings . From what I've read other engine's bearings can wear out quickly if the harmonic balancer is not functioning correctly. Wondering if the benefits to the twincam would offset the fuss and bother. They are available for the Cossies.
-Keith
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PostPost by: type26owner » Wed Dec 22, 2004 5:32 pm

Rohan,
Since the crankshaft does not suffer from fatigue due to torsional vibrations then perhaps the simplist solution is to coax the snout into vibrating at a lower frequency with less amplitude. Perhaps the present seals would work better and not be so prone to leakage under those conditions. I'm thinking of just adding a few pounds onto the pulley to increase the rotating mass. This approach is one heck of a lot easier than trying to apply any sort of dampener. Have you tried this already?
-Keith
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PostPost by: type26owner » Thu Dec 23, 2004 7:08 pm

Has anyone tried using the front crankshaft pulley seal from the BDA Cosworth before? Been advised they'll fit and they're possibly teflon.
-Keith
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PostPost by: rgh0 » Fri Dec 24, 2004 6:11 am

Keith

I have never tried teflon seals. The red ones are silicone I believe. Never seen any evidence of burning or even signficant wear on the seals I have replaced.

The vibration around the nose of the engine is caused by the out of balance couple inherent in any straight 4 cylinder motor driving the vibration. What problems occur depend when the resonance frequency of components matches the exitation frequency which varies with engine speed.

At 8000 rpm their is a resonance in the oil pump that causes cracks, if you leave off the gasket and use loctite only it stiffens up the mount moves the resonance above 8000 rpm and the crackng stops if you are using a 8000 rpm limit. At lower rpm you get resonances in the standard Lucas alternator which cause cracks in the brackets and alloy front case where the top brack mounts, similar mods can stifen this up to miniise the problem.

Adding mass to the nose of the crankshaft via a heavier pulley will lower the resonance frequency for the end of the shaft but could increase the deflection at resonance due to the increased mass what precisely will happen depends on how the crackshaft is being exited to vibrate. I have gone to a lighter smaller 3 inch pulley and this will have moved the resonance up and reduced deflection at resonance I hope. I get little leakage at normal road driving but more when racing which suggests most of the resonance vibation problem is in the higher rev range say from 5000 to 8000 rpm with my lighter pulley. Putting the lightest possible pulley made out of aluminium alloy would potentially put the resonance up above the engine speed you are using and reduce the leakage.

No simple answer, like I said, you really need to do a complete and complex vibration analysis to determine what to do. Perhaps trial and error is easiest and you build 2 pulleys one twice the weight and one as light as poisble and see which one works best.

Rohan
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PostPost by: type26owner » Tue Dec 28, 2004 12:36 am

Romac Performance Products makes a harmonic balancer for the Kent engines. :D
-Keith
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PostPost by: type26owner » Sat Jan 08, 2005 3:40 pm

Can't find the source for the PTFE crankshaft pulley seal I once obtained. The BDA one turned out to be another red silicone lipseal just a bit longer at .48". In combination with any vibrational attenuation of the harmonic dampener perhaps a silicone seal will perform well.

Had a nice conversation with a vendor about the seals leaking. He claimed he'd installed dozens of these seals and they NEVER leaked. As we talked it became clear his definition of 'not leaking' and mine greatly differed. His was the leak rate of the oil level in the oilpan dropping but as long as it was very slow that was a non-leaker but it was normal for the outside surfaces of the engine to covered with it. Mine is NO oil at all on any outside surfaces of the engine period. Perhaps this is a pipedream.

Could always add a vacuum pump to evacuate the crankcase to reduce the pressure load on the seals. BTW, it's quite amusing the claims of horsepower gains from installing such a unit.

The other theory I've heard from multiple sources is that the dry-sump oil pumps used on racecars actually do evacuate the crankcase somewhat. Personally I've never seen any appreciable amount of airflow from the oil reservoir breather on our car. Pretty sure that's another myth too. I'm trying to stop the leaks on my Elan just so I can apply the solution later on to the BRM.

Raining here today so it's indoors play stuff. Off to build the bits for an oil to water intercooler for the Elan. :D
-Keith
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PostPost by: type26owner » Mon Jan 17, 2005 5:27 am

Helps a bunch if the 2-1/16" diameter hole in the timing chain cover which accepts the pulley seal is actually centered with respect to the crankshaft. Found today mine is shifted off by .027" in the 4-o'clock direction. The lipseal barely touches the sealing surface on that side and has obviously been like this from the factory. Pulled the head and oilpan off and removed the timing cover for repairs. Going to rebore the hole out so it's true to the crankshaft centerline and then press-in a loctited shouldered aluminum repair sleeve with a 2-1/16" ID to fit the original type seals. Along with that going to make a delrin alignment spacer which just fits over the snout of the crank and centers the 2-1/16 hole of the timing chain cover accurately while the cover is being installed. Glad to have finally identified this problem and have the chance of getting the engine totally oil-tight for the first time.

This is just an educated guess but the fact that the hole is placed wrong for my cover means that there is a good possibility that all the timing covers machined on the tooling fixture are wrong. Chances are with the low volume numbers that the twincam was produced, only one set of fixture existed back then. Suggest you check for this problem on your engine if the seal leaks too.

The timing cover surfaces which are tricky to machine and need to aligne well to adjacient features are for the pan gasket and the square cross-sectioned cork gasket which seals up the surrounding perimeter boss for pulley seal to the oilpan. Those surfaces are left as cast so are undoubtably were used as the datums to locate all the machined in features in the cover like the clearance holes for the fasteners and so forth. Typical stack tolerance error stuff from poor design but it's cheap. :angry:
-Keith
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PostPost by: rgh0 » Mon Jan 17, 2005 9:37 am

Keith

Centering the seal on the shaft is critical as you observe. I use a machined aluminium alignment tool to hold on centre the front cover before tightening the back plate in place and fixing the front cover.

There is normally enough clearance in the bolt holes to get the front cover centred OK without machining and resleeveing the seal mount. You may end up with the front covers and back plate not aligned with the block at top and bottom perfectly but this misalignment can easily be accomodated by the cork gaskets.

However even after you have done all this you will probably still have a small amount of leakage. I still have one or two drops on the garage floor after a run all from the front seal.

Rohan
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PostPost by: type26owner » Mon Jan 17, 2005 3:02 pm

Hi Rohan,
In my case the clearance holes in the front cover for the fixed fasteners would have to be enlarged in diameter a lot to get the seal centered to the crankshaft. Potentially by as much as .054" to be exact. The secondary datum that mates and mandates the alignment of both cover locations is the pattern array of threaded holes in the block. Therefore since this is a projected tolerance zone situation and the front cover is deep the resulting virtual condition boundary requires very tight positional tolerances be held given the fact the clearance holes are not much bigger in diameter then the fastener. They clearly muffed the machining location between the through clearance holes for the fasteners and the crankshaft seal. Expensive design. My front cover should have failed the inspection in Quality Control. Of course, I'm assuming there is not a tolerance problem with the engine block itself. I could be ragging on the lapse of Lotus quality control when this could be the fault of Ford.

BTW, the front pulley seal for the later 6-bolt crankshaft is a black nitrile elastomer compound instead of the red silicone. Same size too. They obviously made the change later on for a reason. Have you run one of the nitrile type before?
-Keith
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PostPost by: rgh0 » Tue Jan 18, 2005 12:24 pm

Keith

Yes I have tried the black nitrile seals also, found they leaked more than the red silicone ones. They dont appear to be as flexible to accomodate misalignment and vibration. But they are cheaper !!


The crank seal alignment problems is a stacking of tolerances issue and faulty ones are probably an issue of block tolerances at the Ford extreme and Cover tolerances at Lotus extremes. I have built engines with 4 or 5 different covers and about 8 different blocks and only found 1 combination that I could not get good alignment on the seal without working on the cover.

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PostPost by: type26owner » Tue Jan 18, 2005 4:45 pm

Yeah, I've found the nitrile is not very heat tolerant and will degrade until they are like rock-hard after awhile. Not a very good quality for an oil seal. The silicone on the otherhand saturates and swells up some with oil exposure somewhat but remains pliable in spite of the heating. For whatever reason it does not seal all that well though.

Have realized that this very type of plus/minus tolerance error issue from this time period is the classic reason why the best practice system of Geometric Dimensioning & Tolerancing has been enacted world-wide. Have to back off and state that Lotus and Ford are not at fault in this case. It's just the dimensioning system used back then was not robust enough to prevent this type of interference problem without requiring very tight and very expensive tolerances.
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PostPost by: type26owner » Wed Jan 19, 2005 2:47 pm

Have devised a way to ensure the rubber oil breather pipe between the head and the engine block does not swell up and prevent the oil from draining back into the engine. Worse yet to have the crankcase trap the blowby behind the breather restriction and have the resulting increase of pressure force the oil past the oil seals. Decided to just cutoff the bottom portion that sticks into the block. That's the problem area that would swell nearly closed. Made an aluminum fitting that inserts into the block instead and is sealed with a radially compressed o-ring. A thin protruding flange keeps the fitting from falling all the way through the hole. Topside there is a 5/8" OD pipe barb that's about 3/4" long that pushes into the rubber pipe and is sealed oil-tight with some safety wire tightened as a clamp. The inside hole through the aluminum fitting is 7/16" which should be plenty big enough to prevent the crankcase from ever pressurizing. The reason I did this was to keep the best attribute of the rubber pipe which is the large vertical compliance. Also when the pipe swells up and starts to crack a couple of years down the road I can replace it in situ.

The zero degree timing mark on the Romac harmonic balancer lined up perfectly with the TDC marker on the timing chain front cover at TDC. It fits with no interference issues and the fanbelt groove is in perfect alignment. Been quizzing the few professional mechanics I know about the possible benefits of running a harmonic balancer and all are in agreement that it's strange not to have one even on a four banger.
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