Lotus Elan

rear seal and oil presure

PostPost by: wolfchen » Sun Apr 15, 2018 11:56 am

I am a new Elan owner and my series 2 was rebuilt to SE specs by previous owner. He told me that he installed a high output oil pump and that for street use should go back to "regular output" pump as the 80 lbs when at full revs would blow out rear seal. Spoke to a race engine builder who works on these Twin Cams and he told be that rear seal isn't affected by oil pressure from pump and not to change it out. I believe car has original type
of rear seal. Seems odd to me that rear seal isn't pressurized. Anyone else have this experience?

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PostPost by: nigelrbfurness » Mon Apr 16, 2018 1:00 pm

There isn't any oil pressure at the rear seal. Using a high pressure relief valve doesn't usually cause leakage problems in Twin Cams in my experience, though contemporary engines like the Austin A-series ran higher oil pressures than Fords and were very prone to leaks so there may be some correlation. However, 80lbs at high revs when hot in a TC is higher than I would expect to see. Around 60lbs is usually the max and the standard pump relief valve can be tweaked to give 45lbs at 1500-2000rpm when hot which is a comfort to some. However, it has been said many times that it is flow rate, rather than oil pressure that is beneficial to an engine. A TC will happily run its full life with a hot pressure of 35-40lbs/sq in at 1500 rpm and above, often with the gauge dropping almost to zero at idle. At around 90K miles (assuming no intermediate rebuilds) the main bearings will be sufficiently worn to start to influence the maximum oil pressure you can achieve. I used to change the mains at 40K miles in order to extend the engine's life but then other factors start to affect performance such as bore wear and valve guide wear.
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PostPost by: gjz30075 » Tue Apr 17, 2018 9:23 am

Correct. No oil pressure at the seal. However high crankcase pressure will cause the seal to leak, along with
other places.
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PostPost by: wolfchen » Tue Apr 17, 2018 12:11 pm

gjz30075 wrote:Correct. No oil pressure at the seal. However high crankcase pressure will cause the seal to leak, along with
other places.

so how is the crankcase pressure regulated if it's not part of the oil pump path ?

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PostPost by: Foxie » Tue Apr 17, 2018 12:33 pm

wolfchen wrote:
gjz30075 wrote:Correct. No oil pressure at the seal. However high crankcase pressure will cause the seal to leak, along with
other places.

so how is the crankcase pressure regulated if it's not part of the oil pump path ?

Jeffrey


I think wolfchen is talking about excessive crankcase gas pressure caused by leakage past the rings and a restricted breather :)
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PostPost by: gjz30075 » Tue Apr 17, 2018 1:11 pm

Yes, the breathers, head to block and head to airbox should not be restricted.
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PostPost by: prezoom » Tue Apr 17, 2018 3:40 pm

My S2 has a road draft tube rather than routing the breather from the head to the air box, which has no provision for attaching the breather. The addition of breather at the front of the cam cover can assist in reducing the pressure buildup in the crankcase. If the road draft tube has a ducks bill style restrictor at the end of the tube, it could be clogged up or too tight to easily allow the crankcase pressure to escape.
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