Poor compression Villiers engine

[basil]

Allen Sythe Villiers 25 c four stroke.

Hi
I am trying to start the above engine but it won't keep running. I think the compression is too low as there is hardly any resistance when you turn the engine over by hand. Can anyone tell me what the valve gaps should be, at the moment the inlet is 0.004" and the exhaust is 0.010".

Any suggestions please
Thanks Basil

[Kev]

Basil,
It should be between 6 and 10thou for both valves.
Sounds like you should pull the head off and check the bore, piston and valve seats.
On the positive side all parts are available but you need to be quick because the weeds are growing fast now!
Kev

[pockets]

Allen Sythe Villiers 25 c four stroke.

Hi
I am trying to start the above engine but it won't keep running. I think the compression is too low as there is hardly any resistance when you turn the engine over by hand. Can anyone tell me what the valve gaps should be, at the moment the inlet is 0.004" and the exhaust is 0.010".
Hi if you have a mk25c its 2 stroke?, 4 stroke is just mk25?, poor compression just as the chap says below if its 4 stroke, GL, George. at. www.villiersparts.co.uk


Any suggestions please
Thanks Basil

[pockets]

Allen Sythe Villiers 25 c four stroke.

Hi
I am trying to start the above engine but it won't keep running. I think the compression is too low as there is hardly any resistance when you turn the engine over by hand. Can anyone tell me what the valve gaps should be, at the moment the inlet is 0.004" and the exhaust is 0.010".


Hi if you have a mk25c its 2 stroke?, 4 stroke is just mk25?, poor compression just as the chap says above if its 4 stroke, GL, George. at. www.villiersparts.co.uk


Any suggestions please
Thanks Basil

[basil]

Thanks for the replys.
How do I adjust the valve gap?
The valves have been decoked/ground in.
Basil

[pockets]

Thanks for the replys.
How do I adjust the valve gap?
The valves have been decoked/ground in.
Basil

LOOK UNDER THE FOLLOWER CAPS U MAY FIND SOME SMALL CIRCULAR DISCS EITHER REMOVE SOME TOO LOWER A CAP OR ADD THEM (if u have spares?) TOO RAISE A CAP & CLOSE A GAP.
THATS IT.
GEORGE.

[basil]

Ahh I see,like bucket and shim adjustment.Are the discs all the same size or is it guess work
Basil

[Kev]

Basil,
If you have ground the valves in and you have a gap even if it is only 4thou then your lack of compression is not valve related.
Face it, you need to look at the bore and piston.
Kev

[pockets]

Ahh I see,like bucket and shim adjustment.Are the discs all the same size or is it guess work
Basil

mostly all same, you may find one or more thinner because of wear. yes trail & error work

[basil]

Update.
I had another look at this engine ,did a cold compression test ,less than 50 psi
So I took the barrel off to look at the bore/rings/piston.All looked good so I looked at the valves.Although I had been told that a decoke had been done the exhaust valve seat looked black.So out with the valve and the valve seat was black and pitted After an hour of grinding in with paste a very small area of seat appeared.So reassemble and test again but still less than 50 psi.
Any ideas on cost of getting the seats reground,or a second hand/recon barrel ?
Thanks Basil

[landie57]

The fact it starts suggests whatever compression you have is enough. I have various machines with Villiers Mk 10, 12 and 15 engines and some seem to have very little compression, but they all run. An engine that starts but fails to keep running may have a faulty condensor in the magneto.