Mower engine - issue found?

[NT]

stripped the engine back down and removed the snapped head bolt.

k smoke at initial start up otherwise run fine but with the odd "cough" and= now visible smoke. =A0I let the engine run for around 1 min maybe 2.

ne over a could of times, there is a little oil again on the cylinder.

is a little oil normal. I don't think it can be using oil as I haven't add= ed any oil for around 5 years and have been having the issues for at least = a year.

I wouldnt lose sleep over black smoke at start up. Similarly a little oil leakage into the cylinder, as long as it starts ok, is fairly harmless, deposits soon get burnt off during use. Not ideal, but mower engines are crude things.

AIUI black smoke is carbon, meaning unburnt anything, and plenty of CO. Fully burnt oil gives grey smoke.

Oil getting past worn parts can always be much reduced by switching oil grade, eg from 10/30 to 20/50, and it sounds like that would be a good plan to reduce temporary valve fouling.

NT

[The Natural Philosopher]

Oh dear. com[pare a diesl exhaust (oil burning) with - say an over rich petrol engine to see the difference.

[The Natural Philosopher]

stripped the engine back down and removed the snapped head bolt.

smoke at initial start up otherwise run fine but with the odd "cough" and now visible smoke. I let the engine run for around 1 min maybe 2.

over a could of times, there is a little oil again on the cylinder.

a little oil normal. I don't think it can be using oil as I haven't added any oil for around 5 years and have been having the issues for at least a year.

Fully burnt anything gives NO smoke.

The black is carbon, the white is more or less water vapour. Longert chain hydrocarbons (kerosenes and oils) have less hydrogen per unit carbon and therefore burn blacker.

[Tim+]

That's as may be, but in the real world (at least the pre-cat world), a petrol engine running rich produces black smoke but a petrol engine burning engine oil produces whiter smoke (blue/grey/white).

Tim

Tim

[Grimly Curmudgeon]

Both black.

[The Natural Philosopher]

Never has in the real world tim.

[The Natural Philosopher]

Smoking disel : black

petrol is white

because ofte over rich mixture misfiring and shoving steam and unbirnt fuel oput.

[The Natural Philosopher]

And this is the best example of white petrol smoke

> Tim

[Tim+]

petrol lawnmower (possibly burning its own engine oil).

Um, didn't sleeve valve engines go out of fashion due to lubrication problems with the valves? They need a lot more lube that a poppet valve and hence more oil gets burnt. You can clearly see puffs of black smoke coming from the exhaust during start up until the engine warms up and the mixture is leaned out.

Hardly a good example to support your case.

Try this.

no more than your clip but is at least based on a conventional poppet valve petrol engine and is typical of an engine running rich.

Tim

[Gary]

The text for the Bristol engine by the owner says 'The rich mixture produces the thick black smoke but clears as she gets above 1300rpm. I hope to get to the bottom of the fuel mixture problem soon as she makes for an expensive hobby guzzling about six litres per minute at present - at idle.'

and the tank engine from a comment 1 0f many similar 'Maybe if he? didn't rev the life outta it the piston rings etc would not pass buckets of oil!'

I personally can only look on in awe

[Huge]

Please don't.