Oil Mist from Suffolk engine

[vhgmcbuddy]

Just acquired a 1965 Atco lawn mower with the Suffolk 75 G engine.
Was suspicious because it looked in remarkable condition due to being smothered in oil and dead grass.
However have had it to bits and cleaned everything up and checked that everything worked.
Sealed all the joints,decoked the engine and got it started and running really well,cuts grass like a new one, no oil leaks from joints, however a fine oil spray on my boots from the exhaust pipe suggests a problem.
I guess its the piston rings that must be worn, The bore was lovely and smooth and there didn’t appear to be any piston slap. So fingers crossed it only needs new rings.
Can anyone tell me what the tolerance gap of the rings in the bore is? There are no marks on the piston so I reckon it’s a standard original piston.

[wristpin]

Would have thought that if the oil is coming from the exhaust you would be enveloped in white smoke! Are you sure that it’s not coming from the crankcase breather in the valve chest?
The breather is a small poppet valve installed in the floor of the valve chest and held in place with a spring hooked over the stud that holds the chest cover in place. If you remove the cover you should find a tin shield. Fiddle that out and you should see the breather valve which consists of a small circular casting (the body) with two lugs to locate it. Also a fibre washer between it and the valve chest floor.Within the body is a paxolin disc and over the top a steel cap all held in place by the spring.
The disc is free to rise when the downward stroke of the piston displaces crankcase air and should seal against the casting on the upward stroke and by so doing maintain some negative pressure in the crankcase to retain oil.
Both the disc and it’s seat in the body wear and the valve looses effectiveness.Sometimes turning the disc over to present an unworn face to the body helps.
Of course, there is the possibility that someone has been in there and either assembled it incorrectly or left a bit out!

[vhgmcbuddy]

Thanks for that Andrew, have taken it to bits and turned the disc over, will reassemble and test tomorrow. Think it probably fooled me as the hole in the valve chest cover comes out close to the exhaust also the plug was badly oiled up when I first took it apart.Plug looks dry now but probably over rich mixture as it is well sooted up.
I note from an exploded diagram I have found that the valve chest cover should have a baffle or is that the tin shield you mention?
Thanks anyway for pointing me away from the wild goose chase I was probably about to start.
Best Wishes,
Keith

[wristpin]

Shield/baffle , one and the same!

[vhgmcbuddy]

Hi Andrew just returned from holidays and tried the mower.
Your recommendation did the trick. Engine now tuned and runs smoothly with no trace of oil where it shouldn’t be, Thanks for your help.

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