Lotus Elan

Tests for excessive blow by (update)

PostPost by: jono » Fri Jul 21, 2017 6:35 am

My TC is becoming more like the Exon Valdez by the week.

I'm beginning to think there must be a crank pressure issue, though there is zero smoke or other evidence of oil being consumed other that by loss though various places on the engine.

Despite this, the engine does go very well and feels healthy. It was subejct to a full rebuild 10k miles ago, including re bore, new pistons, head job including new guides properly reamed etc.

I am think that perhaps I glazed the bores as I did have it running on idle for some time after first starting it up

I am determined to sort this so intend to pull the engine shortly and go though it all and fit a close ratio box at the same time.

Before I do this, what are some basic tests I can carry out to detmerine whether this is the source of the problem? I was careful to use all of the recommended sealants when I put the engine together but perhaps I have simply not been careful enough or otherwise I have a blow by issue!

I have a compression tester and know this is not the ideal tool for the job but can it tell me anything useful in relation to the possibility of, say, excessive ring gaps?

Any other practical tests/ I could probably borrow a leak down tester I guess?

Cheers

Jon
Last edited by jono on Mon Feb 05, 2018 11:00 am, edited 1 time in total.
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PostPost by: rgh0 » Fri Jul 21, 2017 9:27 am

Hi Jon

The steps I would follow If I was worried about crank case pressurizing due to excessive blow by:

1. compression and leak down tests both before and after injecting some oil into the cylinder

2. I would check the engine breather is clear and not blocked. There is a mesh filter at the head end of the breather pipe ( or should be) that can block.

3. I would then hook a temporary plastic pipe to the breather and run it so it can be observed while driving and see how much the blow by increases when accelerating under full throttle.

cheers
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PostPost by: jono » Fri Jul 21, 2017 11:40 am

Thanks as ever for your wise counsel Rohan,

I omitted to mention that I have removed the crank breather from the air box and just have it dangling below the car.

How significant is engine vacuum on the original set up as it did ocur to me that this may be a factor?

Jon
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PostPost by: rgh0 » Fri Jul 21, 2017 12:39 pm

The suction into the airbox in an Elan is not significant as the restriction of the air filter is close to zero. The crank case blows into the airbox in the same way it blows straight to open air.

Later systems used a PCV valve where the crankcase is vented via the valve to the low pressure intake manifold down stream of the carb or fuel injection butterfly. These systems have a controlled suction on the crank case via the PCV valve

Many years ago i did some interesting dyno tests on one of the first generation engines to incorporate a PCV valve system. The impact of the suction into the inlet manifold of blow by gas was to increase total emissions more than just venting the blow by direct to atmosphere would have. It had to be done due to regulations but the technology of the time could not manage the impact on combustion it had. That's the difference between bureaucrats and engineers

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PostPost by: jono » Sun Jul 23, 2017 1:10 pm

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?

I do drive the car hard so now wondeirng if I should just rebuild it very carefully (using your recommended aviation gasket sealant) and fit a second breather.

I've checked the dip stick for accuracy and overfilling does not seem to be an issue.

Would appreciate your views.

Cheers

Jon
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PostPost by: rgh0 » Sun Jul 23, 2017 1:18 pm

compression seem fine.

Have you checked to see if your breather is clear and venting OK

where is the engine leaking from ? The front pulley seal seems to be the biggest leak problem on my race engines when the crank case pressurizes. Leaking out elsewhere from fixed joins is really an assembly problem

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PostPost by: jono » Mon Jul 24, 2017 9:50 am

Thanks again Rohan.

I'm going to remove the carbs and check the breather for blockage but it seems to be okay as it leaves a small puddle of black oily gunge on the garage floor when I park the car and you can see a vapour plume emanating on tickover from start up.

The leaks appear to be largely the front cover, mainly the right hand side when viewed from the front, possibly also from the front crank seal, but definately from the cork gasket between the head and the chain housing. There are also a few drips from the bellhousing.

I have a short std bore 1600 cross flow engine and may use this instead of the Lotus bottom end when I strip and rebuild the current motor for no other reason that I like the idea of a bit more torque (given also that I'm swapping to a new gearbox with a tall first).

What do you think about such a conversion and will the character of the engine change significantly, is it a worthwhile mod?

Cheers

Jon
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PostPost by: jono » Mon Feb 05, 2018 10:59 am

I've now stripped my engine to get to the bottom of this oil leak issue:

The bores and rings all look good as new (rebored and new pistons 15k miles ago). No broken rings or similar. Normal 'coking' to the combustion chambers and piston tops. Head an block faces excellent (Ajusa gasket used - will use the same, new, gasket again)

The cork gasket to the top of the timing case and almost disintergrated to the front section (rear part okay) to the extent that only the tin foil sandwich if left (a major cuplrit as suspected)

There seems to be some evidence of leakage between the back plate and block on the alternator side. I used wellseal on the paper gasket but there was a film of oil between the block and back plate in this area.

Crank seal area - all looks good, no evidence of leaks here

One surprising finding is that the rubber oil drain tube has swollen like a banana to over +50% of it's original size when comparing it to an original old tube I had lying about. This has caused the orifice at both ends to close to around half the original size - has anyone else experienced this, dodgy Chinese part I am guessing?

I hate the timing case cork gasket - recently there were some musings about using a rubber/neoprene substitute material. Were there any developments on this?

Jon
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PostPost by: david.g.chapman » Mon Feb 05, 2018 11:44 am

If you replace the rubber down tube with another one, make sure that it fits tightly into the holes in the head and block first - I have had two different sizes of tube, one of which was too small!

They should all be the same!

As for the cork timing cover gasket, it might be worth rtv-ing (or your favourite sealant) it to the timing case first and letting it set. Then use rtv on the other side and fit the head, as these gaskets tend to squirt out of position.

Do not be tempted to overtighten it, although you might need to nip up the bolts to the correct torque a few times.

You could also try another gasket material, but I am not sure which one.

Cheers,

Dave Chapman.
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PostPost by: el-saturn » Mon Feb 05, 2018 12:51 pm

rocker cover gasket: no rtv etc... NOWHERES - i'm using a burton composite and a thick payen cork gasket - no leaks AND can check valve clearance as often as i want to - the simplest solution i've ever used!! sandy
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PostPost by: jono » Mon Feb 05, 2018 12:52 pm

Sandy,

What are you using between the head and top of the timing chest?

Jon
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PostPost by: el-saturn » Mon Feb 05, 2018 3:32 pm

that's exactly I T: nothing, just these 2 gaskets: even NO rtv where we have our semicircular cam gaskets!! sj
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PostPost by: david.g.chapman » Mon Feb 05, 2018 4:30 pm

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PostPost by: rgh0 » Tue Feb 06, 2018 1:12 pm

So Sandy you fit the semi circular hard rubber seals dry in the head. i am sure you can do it but why is the real question ?

The cosmetic gasket versus a cork gasket for the cam cover is a personal choice as both should work. I find a cork gasket stuck down to the head with a gasket sealant of choice ( not TV or other silicone gasket formers) and greased on the other surface so the cam cover can be easily removed when need good enough for me.

Fitting the cork gasket between the head and front cover can be done dry as you imply it is just harder to get it to stay in place as you tighten down the head. It helps if you have a range of thickness to match then space after the head gasket being used is compressed so the cork gasket is compressed just the right amount, it also helps to use a gasket sealant of choice (not RTV again) to stick the cork gasket so its less likely to squeeze out IMHO

The real challenge in a real 9000rpm engine is the front pulley sea,l how do you centre that and keep it central overtime is the challenge as crank vibrations mean the seal is operating at its maximum deflection limits. Keith of Sidedraft central fame has gone to the extent of building a frame to hold the front cover in place so it does not move overtime with the vertical bolt tensions and relative thermal growth of the cover versus the block in his quest to build an oil tight 4 bolt crank engine

cheers
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PostPost by: Craven » Tue Feb 06, 2018 1:47 pm

The cork gasket between the timing cover and cylinder head slowly extruding out over time is a common but well known problem, in a factory service bulletin Lotus recommended using a suitable adhesive on one side and a normal sealant on the other.
Sorry can?t recall the products recommended.
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