Lotus Elan

Twin Cam engine help

PostPost by: Jonesrp6 » Sat Feb 17, 2024 12:13 pm

Hi and help please
I recently bought a197p plus2 which seemed to be running rich. Also Smokey on startup and under acceleration. Plugs clogging very quickly My trusted garage tried to tune but found . Low compression(sub100) in cylinder 1. Referred me to engine specialist who found low compression(c120) across all. He stripped top and bottom end and replaced piston rings (engine previously rehired one to .20 6000 miles ago only)
All seems fine when back together on idle. Under pressure, oil in cylinders, so stripped and rebuild top and bottom ends again. Still no improvement so stick what to do next

Any recommendations?
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PostPost by: Foxie » Sat Feb 17, 2024 1:42 pm

Your garage found low compression (100psi ) on one cylinder. Your 'specialist' found ~120 psi across all cylinders. One of the two (at least ) got it wrong. This should have been checked.

Were the cylinder bores wear checked ? ( position a piston ring in the bore at different heights, measure the gaps and calculate)

Not clear from your post, but was the engine rebored 6,000 miles previously ?

Were the cylinders honed prior to fitting new rings ?

Were the compressions checked again before and after the rebuilds ? ?

If your garage and/or 'specialist' cannot tell you what's wrong here, you need to find someone who can.

:)
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PostPost by: Jonesrp6 » Sat Feb 17, 2024 1:47 pm

I am not sure if the bores were honed

He has crossed checked the clearances which seems ok

It was reviewed 6000 miles ago by a garage in Bristol which does not appear to still be in business so cannot go back and check what day did
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PostPost by: englishmaninwales » Sat Feb 17, 2024 2:26 pm

Plus the engine should have had a leak down in addition to the compression test. This would help determine if the low compression(s) were rings/bore or valves.
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PostPost by: Jonesrp6 » Sat Feb 17, 2024 2:30 pm

Thanks for the responses so far
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PostPost by: rgh0 » Sat Feb 17, 2024 9:44 pm

Has the low compression been rectified and now its only an oil and smoking issue ?

Was the vavle stem to guide clearance checked and within what is a very tight specification

cheers
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PostPost by: JohnMorin » Tue Feb 20, 2024 4:27 pm

I had symptoms like this a while ago on a low mileage engine and it turned out to be the head gasket. Make sure you can screw in all of the bolts into the block all the way in by hand before fitting the head. Make sure you use alignment dowels when fitting the head then again check all the bolts go right down without their washers by hand before torqueing down. Worth checking the flatness of the head and block as well.

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PostPost by: Jonesrp6 » Tue Feb 20, 2024 7:55 pm

Thanks John

Talking to my engine guy today the cylinders were honed and the head has been reground and piston rings replaced

Compression is now 170 for each cylinder but oil is getting into all cylinders and exiting as smoke!
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PostPost by: Jonesrp6 » Tue Feb 20, 2024 7:59 pm

Will pass all this on to him


Any other thoughts?

Many thanks to all

Richard
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PostPost by: HCA » Tue Feb 20, 2024 10:22 pm

How ‘specialist’ is your engine specialist? S/he should have all the answers and not really have to revert to asking a forum for thoughts. Maybe you need to consider elsewhere?

You say that the head was reground - do you mean the valves and seats or the head surface. I assume the former, in which case the valve guides, as Rohan asked you, should have been checked as a matter of course by any competent builder…

Your opening statement says ‘smokey on accelaration’. Nothing about colour, but the assumption is blue, yes? Basic engine evaluation is: blue smoke on acceleration is oil rings and blue smoke on overrun is valve guides. OK, rings are replaced but you say ‘under pressure’ the smoke persists - is ‘pressure’ acceleration? Then go back to the rings. They are either broken, fitted incorrectly or the piston is too sloppy.

You say ‘oil is getting into all cylinders’. How do you lnow it is all and not just one or two?
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PostPost by: nmauduit » Wed Feb 21, 2024 9:21 am

HCA wrote:You say ‘oil is getting into all cylinders’. How do you lnow it is all and not just one or two?


yes, this struck me as odd... I certainly who dig into this by all increasingly invasive means (up to head removal, which is not that bad of a job if one takes his time, and nothing beats direct scrutiny when in doubt)

good luck!
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PostPost by: Jonesrp6 » Wed Feb 21, 2024 3:02 pm

Thanks again for the thoughts

Origially the engine exhaust was smokey on start up but black, so I put that down to being set muc too rich, which is was. Compression issues was raised by the tuner who could not tune due to low compression in cylinder one

Engine guy (he is a specialist engine guy, although not a specific Lotus specialist) then recorded low comproession of c 100 in all 4 and took off top and bottom ends and replaced cylinder rings, regound head etc, new gaskets etc.

On rebuild, idle ok but under acceleration blue smoke
He stripped and rebuilt both top and bottom again and still the same. So now somewhat unsure were to go next

Any suggerstions of twin cam specialists welcome.
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PostPost by: mbell » Wed Feb 21, 2024 3:50 pm

Do you have a brake booster? The seals in them can fail and allow brake fluid to be sucked into the engine causing smoke..

As others suggested a leak down test would be a good idea.
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PostPost by: Craven » Wed Feb 21, 2024 3:53 pm

FWIW
No specialist, but you may be jumping the gun here, Twincams are well known as oil burners, modified/added oilways in the piston under the scraper ring is often done. I would give it some miles before condemning the work.
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PostPost by: HCA » Wed Feb 21, 2024 4:39 pm

Jonesrp6 wrote:Thanks again for the thoughts


On rebuild, idle ok but under acceleration blue smoke
.


What about immediately on start up first thing in the morning? What colour?

Underneath the head, the twincam is a workhorse Ford engine, and unless Rohan corrects me, the only causes for oil getting into the combustion chamber are: oil ring issues, valve leakage or head gasket. The old rule of thumb - blue on hard acceleration, rings. Blue on decelaration, valves. Blue on start up after prolonged standing, valves.

Rohan has already told you this re the valves. I think you need to go back to your engine builder. I bet that your head needs rebuilding. Now, this I would advise you to ask questions of the person doing the rebuild...
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