Lotus Elan

Tests for excessive blow by (update)

PostPost by: jono » Tue Feb 06, 2018 3:13 pm

How do you obtain the 'correct' crush height for the front cover gasket?

Does the front cover assembly need to be slightly below the deck face or should you rely solely on centring the cover plate on the crank and leave the cork gasket to sort itself out?

Would it be wise to make a centring bush/ring to locate the front cover perfectly on the crank nose?
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PostPost by: jono » Tue Feb 06, 2018 3:31 pm

some photos of my engine with the curiously swollen oil drain tube and mysterious disappearing gasket!

has anyone had this happen with an oil drain tube (narrow one is an original old tube, swollen one is 15k miles old and, I think, from QED). 20/50 Classic Mineral oil used in engine.

My thinking is that the constricted tube will not have helped the engine to breath
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PostPost by: nmauduit » Tue Feb 06, 2018 4:18 pm

jono wrote:Many thanks Rohan, that's very interesting and makes perfect sense when I think about it!

I've done a compression test with the engine hot after a run out, all plugs out, throttle wide open, no oil down bores and spinning for 10 seconds in each case. This produced the following results:

cyl 1 - 192 psi
cyl 2 - 192 psi
cyl 3 - 195 psi
cyl 4 - 190 psi

I'm reasonably encouraged by this, what do you think - is this sufficient to rule out excessive blow by?



Did you do a leak-down test prior to dismantling ? in case chamber pressure somehow found its way to some places it should not (not necessarily past the piston rings)...
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PostPost by: jono » Tue Feb 06, 2018 4:42 pm

I didn't do a leak down test based upon satisfactory compression test results.

everything looks good on strip down - bores (hone marks still visible), head gasket good and no evidence of escape from combustion chambers

Also the engine feels very strong and 'happy'. The only reasons I have pulled it is to cure the oils leaks and given what i've seen in terms of the timing case gasket I think I've found the main problem.

the constricted oil drain tube will, I expect, also be limiting the ability of the crackcase to vent and, as I do drive enthusiastically, I feel quite confident now that I have discovered the source of the leaks. Interestingly I found no evidence of leakage from the crank pulley area (or sump gaskets) so I must have done at least soemthing right when I built it up 15k miles ago.

My aim now is to rebuild the engine oil tight!
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PostPost by: nmauduit » Tue Feb 06, 2018 5:03 pm

jono wrote:I didn't do a leak down test based upon satisfactory compression test results.

everything looks good on strip down - bores (hone marks still visible), head gasket good and no evidence of escape from combustion chambers


ok, but I don't consider compression and leak down testing the same things exactly (e.g. perfect compression and leak down yet with constant pressure developing a slight passage between one chamber and say, the water system).

Hope you'll manage to reach your goal, now that you have made the effort to pull the engine...
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PostPost by: Orsom Weels » Tue Feb 06, 2018 6:45 pm

jono wrote:the constricted oil drain tube will, I expect, also be limiting the ability of the crackcase to vent and, as I do drive enthusiastically, I feel quite confident now that I have discovered the source of the leaks.


I would say you are on the right track. The breather has been modified on my Elan to vent via a pipe into a catch bottle in the nose, rather than into the air box as std. Prior to my ownership, the PO managed to put a small kink in the pipe whilst fixing an air horn issue, resulting in a slightly reduced diameter of the pipe. He never drove the car hard at all, in fact very gently, but in not many miles it had caused countless oil leaks, & finally pushed the cork gasket out between head & timing cover before the cause was discovered. Prior to this, the engine had been relatively oil tight. We stripped it down, replaced all gaskets & seals, made sure the breather pipe was clear & a good diameter throughout it's length, & all has been well since, even with a bit more 'spirited' driving from yours truly :)

Regards, Tim
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PostPost by: richardcox_lotus » Tue Feb 06, 2018 7:56 pm

Tim I think he?s referring to the head to block drain tube rather than the breather to air box.

But good to check both !

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PostPost by: jono » Tue Feb 06, 2018 8:24 pm

Yes, I am however I think the same drain tube is the direct vent from the crankcase to the breather tube via the head casting so each is as important as the other are they not?
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PostPost by: seniorchristo » Tue Feb 06, 2018 11:05 pm

I have similar oil leaking concerns about my next rebuild.

Question: The breather hole towards the back of the head behind #4 intake runner. Is this hole vented to the top of the head (below cam cover)? Instead of venting from the cam cover I plan to use this vent hole in the head and tee into a vent from the fuel pump cover (picture below) and run into a catch can. Would this vent both the upper and lower areas sufficiently?
I also remember reading somewhere that new front timing covers should be machined to properly index with the top of the block. Whether this is level with the block or somewhat below would depend on the crush of the gaskets I guess.
Thanks,
Chris :)
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PostPost by: Orsom Weels » Wed Feb 07, 2018 8:14 am

richardcox_lotus wrote:Tim I think he?s referring to the head to block drain tube rather than the breather to air box.

But good to check both !

Regards
Richard


Yes, I'm aware jono is referring to the head to block tube, but that in turn vents from the head, usually into the air box. The point I was trying to make is that even a small restriction in the ability to vent crankcase pressure caused countless weeping gaskets & seals on my twincam in a relatively short time. I'm pretty sure jono's swollen drain tube is a significant contributing factor to his oil leaks & head to timing cover gasket being pushed out.

Regards, Tim
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PostPost by: jono » Wed Feb 07, 2018 9:18 am

Seniorchristo,

I had the same idea, however Rohan was of the view that there is a hell of a lot of oil sloshing about next to the fuel pump aperture and so it's not an ideal location for a second breather.

The wisdom on this seem to be to fit a second breather in the front of the cam cover (a 'Hart' breather) - I may yet do that but will see how I get on with a new head drain tube and better gasket installation practice first.

I'm still curious as to whether anyone else has had the same experience with the head drain tube swelling up like a banana?
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PostPost by: rgh0 » Wed Feb 07, 2018 9:33 am

jono wrote:How do you obtain the 'correct' crush height for the front cover gasket?

Does the front cover assembly need to be slightly below the deck face or should you rely solely on centring the cover plate on the crank and leave the cork gasket to sort itself out?

Would it be wise to make a centring bush/ring to locate the front cover perfectly on the crank nose?


Yes use a centering bush or measure carefully to centre the front cover seal on the crank, then ensure it does not move when bolting the head down.

When centered the top of the front cover may be above equal with or below the block depending on tolerances and previous machining done on the various components..

Depending on where it is you can do more machining or select a suitable thickness cork gasket. Cork gaskets like to have around 30% compression of original thickness to seal well and not squeeze out. the original style head gasket and more modern composite fibre head gaskets also compress about 30% from the original thickness when torqued down. MLS head gaskets compress less and how much depends on how many layers

based on all the above select a suitable thickness if you can find one

cheers
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PostPost by: jono » Wed Feb 07, 2018 9:51 am

Brilliant explanation, many thanks Rohan!

Jon
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