Skip to main content
Collection, Preservation and Display of Old Lawn Mowers

Villiers 150cc Lightweight - valve grinding/adjustment

I've got a problem where the plug keeps fouling, with a black/oily residue.

I thought it was running too rich, so replaced all the jets and needles etc in the carb, lowered the slide needle to it's lowest, and ran without the gauze air filter. But it's still doing it (maybe not so often).

I read somewhere that a lot of problems with these engines can be due to the valves (clearances or grinding needed?).

Can anyone please explain how to grind and set the clearances? I've seen the fiche but don't see any way of adjusting. I'm more used to adjustable tappets or shims on motorcycles! Or am I barking up the wrong tree? The piston doesn't appear too slack in the bore, so I don't think it's letting oil past the rings.

Apologies if this question is answered somewhere, I have tried searching first - honest!


BTW what's the recommended oil for these mesh/wire-wool type air filters? Seems to me that SAE30 would be too thick - maybe I should thin it?


wristpin Thu, 20/05/2021

Your issue is more likely to be the result of worn valve stems and guides rather than valve sealing. Valve clearance ( assuming that they are too tight) is achieved by the removal of metal from the end of the stem, either by grinding or careful filing.  It may be worth checking the condition of the crankcase breather, a ball and sponge installed between the valve chest and the magneto backplate. Correct operation of the breather maintains a negative pressure in crankcase which helps in keeping the engine oil tight. Tappet clearances are shown as 2-6 thou” for both valves.

The recommended engine oil of the day was Castrol XL SAE 20W-50 and the air cleaner maintenance was, wash, dry, immerse in engine oil and allow to drain before refitting .

DJD Thu, 20/05/2021

To grind the end of the valve accurately, I used my pillar drill to make a hole that gave the valve a snug fit into the small 2" X 2" block of pine. With valve sticking out a few thous, I simply rubbed it back and forth on my oilstone, not grinder.Doesn't take very long.

IanC Sat, 22/05/2021

Thanks all, I'll take a look next week, breather first stop.

Oil leakage around the guides makes more sense than leaking valves. Are the guides replaceable?

wristpin Sat, 22/05/2021

Yes, the guides can be replaced but whether they are still available is questionable. Try Paul Child at Meetens.  Bear in mind that there will be wear in both the valve stems and the guides.

IanC Thu, 28/04/2022

Only just got round to investigating the crankcase breather!

I have been sent a plastic ball, and very flimsy small sponge by L&S Engineers. George didn't have them.

But not sure these are right? From memory, there was a far more solid black plastic plug with two 'fins' originally. Difficult to tell exactly as the one I have is in a very poor state (and no ball).

wristpin Fri, 29/04/2022

The ball and sponge sounds correct. Did LS put part numbers on their paperwork? I think that they are 25946 and 25947.



Series3boy Mon, 09/05/2022

I have a similar issue with a Villiers light weight 50cc. 

I have oil on top of the piston. The oil fouls the plug, over time.

Other than that the engine starts and runs well.

I have been told it might have a broken oil scrapper ring. As the compression is good.

Did you solve your issue?

wristpin Mon, 09/05/2022

Broken scraper ring; very unlikely, but worn, almost certainly.

If the breather is in good order the oiling up is probably due to years of wear and tear. You either live with it or strip the engine , measure everything and compare with Villiers’ dimensions listed in the manual. Then when you know the worst, you are probably no further forward as you will probably find that oversize /  underside parts are unavailable.