Smokes like a two stroke

Hi all, I just had the cylinder heads on my LM2 skimmed and had new valves and guides fitted. I’ve started it up and it smokes badly and oil is coming out the exhausts.
. I’ve attached a pic of the top of my piston and as you can see there is a mark where the inlet valve has touched the piston crown. I suspect, when the engineering firm skimmed the heads they took off too much material, as both pistons have exactly the same mark i’m inclined to think that something has gone wrong.

Anyone had similar probs? what’s the best way to proceed from here?

Check the guides not damaged or valve bent if its clipped piston…estabilish how much they’ve taken off and fit extra base gaskets to suit…
Which will rather negate having them skimmed in the first place alas…
Le Mans run quite close to detonation as standard…

I guess you could take a bit out of the piston to give more space if it is still tight with a second base gasket.
The trick was always re-assempble and cover the piston with plasticine to see how close things get.

brain not working to well (vodka induced)
you say the inlet has touched the piston is not the inlet the bigger valve out the two if so is the piston cut out the other side bigger (looks it on photo) so if correct is piston on conrod the right way round
also was it original rings ? if new rings was barell if cast iron glaze busted ?

now sober
if top end build only
If valve has been tapping piston they need to be checked to see if they are bent at all and what fit they are like in the guides as that’s all that’s changed put valves in a drill and rotate to check

Luckily I photo everything cos it makes putting things back easier, an I’ve just checked the photo’s. this is very embarrassing, piston not fitted correctly doh. best check those valves out. Thanks for the reply’s i’ll re-post any updates.

DOH!! Yes it is! Piston is back to front …

Also have you got O-rings on the six cylinder studs in the correct locations? If not, possible oil can get into a cylinder via one of the stud tunnels. (?)

PS, why were heads skimmed?

Blimey…Ray spotted that after vodka !

These new o rings look worse than the old ones
I didn’t ask to have the heads skimmed, I only wanted the guides fitted and the seats re-cut. I also wanted the Cylinderhead shop to do the work but they were in the process of moving and I didn’t want to wait till the end of November …er but… I spoke to Len the other day and he told me that the moved had been cancelled.


are not the O rings meant to go between base of block and engine crankcases ?

lucky it did not end up like mine where someone put piston in backwards on a spada
sad thing is i beggining to think i work better after vodka

I’m glad I shut down the engine at the first sign of "that smokes’s not clearing’ thought and stripped it again cos I gave the valves a spin in the drill and they seemed fine. I got the pistons round the right way and I replaced the top o-rings (I’m sure 4 o-rings go under the valve train hanger and 2 under the barrel on the short studs) fired her up and still smoking.

The barrels seem ok, no obvious scoring, the rings seem to measure up, I opted to not do anything to the barrels on refitting with the original piston and rings. Do you think its possible that by disturbing the cylinders it reached a tipping point and gave up, or maybe I should scrap them and buy a kit.

I don’t have the tools to really measure heads, but visually they seem ok I’ve tried pooling petrol around the guides and the seats, all ok. I’m starting to think maybe I was a touch hasty in assuming that the engineering firm was at fault.

I’ll strip it again and see what the experts say cos I’m a bit stumped and it’s starting to get cold in the garage.

Cheers! .... now where's that vodka......

Just a thought, what oil are you using?
Synthetics are no good for running in, use a standard 20-50.

when fitting the valves are they a good fit in the guides to the point of if you try to pull out valves with thumb over the end of the guide the vacuum should suck them pack in - or if pulled fully out they should make a popping noise if the pull out without popping they are to loose

Only two of them. The other four go under the rocker pivot blocks.

any updates ?

did it get cured ?

we wait with bated breath! :smiley:


Fixed and ridden off into the sunset I guess.