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
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.
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.
Malcolm
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.
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?
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)
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
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.
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…
Twincam are only smokey when worn or not correctly assembled. What you need is data and expert analysis of that data. Smoke on acceleration certainly suggest rings or very over rich carbs which can affect the rings in turn by washing the oil off the cylinder walls with excess fuel.
The sort of things I would be asking if standing infront of that engine:
Are there any unusual noises, what do the plugs look like and what plugs are you using
what is the actual valve stem to guide clearance and is there any wear on either the guides or stems and is it within spec. What is the state of the cam bearings if excessively worn excess oil can end up in the head, flooding it and causing leakage down the valve stems especially on the exhaust side as it drains poorly
what is the piston to bore clearance, has the bore been poperly honed, have the rings been fitted correctly.
what head gasket are you using, though this is unlikely to be the issue if oil getting into all cylinders
what is you carb setup and jetting
what if any other modifications exist on the engine
Very hard to do this sort of analysis remotely so if you cannot do it you need to find someone with a detailed knowledge of twincams locally
