What does this spark plug tell me?

[eltax91]

Got an old push along mower which I rescued from storage in my mother in laws garage. I had it for a few years before, but a move to a small garden temporarily meant it wasn’t touched for 3 years. She stored it spark plug down unfortunately and all the oil leaked out.

It’s worked all summer, was very Smokey, but getting progressively better. Now it only smokes a little when switched off.

So, here a picture of the plug. Further strip down to follow. But first impressions, what’s the grey ash tell us about the running state of the mower?

[996TT02]

Good, if anything a smidgen lean

[Boosted LS1]

It's fine, maybe running a tad cool but that's all. The colour depends on the fuel used. Dry and fluffy light grey to light brown's within range.

[Shadow R1]

996TT02 said:

Good, if anything a smidgen lean

Nothing to worry about with it.

[Jimmy No Hands]

[eltax91]

Ok good news on the plug.

The piston and valves now visible. Nothing to scare me in hear to my eyes. The valve is slightly open as per picture when the piston reaches tdc. Anything here that may suggest why it’s smoking?

I did have the exhaust off and fully cleaned last year. The oil that has come out is rather black and thick like syrup. Which was fresh oil in spring (sae 30 mower oil)

[Boosted LS1]

It's slightly rich or has only been run for short periods and hasn't warmed up properly. If the clean oil's turned black it's probably excess fuel mixed with carbon/soot deposits from the combustion chamber being washed down past the rings. Does the oil smell of petrol?

Or given that it was stored upside down oil may have entered the cylinder and that'll take some time to finally clear/bake off the piston. You may as well check the valve stem seals now it's in bits and inspect the valve seats.

Edited by Boosted LS1 on Monday 28th December 14:55

[rxe]

Is that something embedded in the piston, top right?

Other than that, the plug looks fine and the piston looks fine. Regular oil changes will help, note that some of these small mower engines are very sensitive to angle - I have one that smokes like a bd if I’ve tipped the machine more than 45 degrees. Change the air filter as well.

[eltax91]

Valve slightly open at TDC

[eltax91]

rxe said:

Is that something embedded in the piston, top right?

Other than that, the plug looks fine and the piston looks fine. Regular oil changes will help, note that some of these small mower engines are very sensitive to angle - I have one that smokes like a bd if I’ve tipped the machine more than 45 degrees. Change the air filter as well.

Good spot. No it’s not, photo doesn’t show it but it’s where I scraped away some of the carbon build up to see how bad it was

[Etretat]

If its a Briggs & Stratton motor and has been tipped sideways with the air cleaner down the oil floods the air cleaner. It will smoke a lot if you can start it and soot up the plug. Clean the air filter and the plug and see what happens then

[eltax91]

Valves up close

[eltax91]

Boosted LS1 said:

It's slightly rich or has only been run for short periods and hasn't warmed up properly. If the clean oil's turned black it's probably excess fuel mixed with carbon/soot deposits from the combustion chamber being washed down past the rings. Does the oil smell of petrol?

Or given that it was stored upside down oil may have entered the cylinder and that'll take some time to finally clear/bake off the piston. You may as well check the valve stem seals now it's in bits and inspect the valve seats.

Edited by Boosted LS1 on Monday 28th December 14:55

I’m not a DIY novice by any stretch. But this will be my first time have an engine in bits. Any good guides out there on how to inspect the seats?

[Boosted LS1]

You'll need to compress the valve springs in order to release the collets. Then the valve should push out by hand. Expect the exhaust valve seat to be a bit horrid.

[eltax91]

Etretat said:

If its a Briggs & Stratton motor and has been tipped sideways with the air cleaner down the oil floods the air cleaner. It will smoke a lot if you can start it and soot up the plug. Clean the air filter and the plug and see what happens then

It’s a ‘GGP technology sv150’ which I think is basically mount field. Air cleaner sponge is in soak already.

[A1VDY]

The oily deposits are either a bit of bore wear or the bottom oil control ring not quite doing its job anymore or valve stem seals.
If it starts well and runs okay I wouldn't worry about it.
Our groundsman runs an old Kohler 10hp engined mower which is around 40years old, smokes really well but never fails to start..

[littleredrooster]

As with all plug/piston/carbon diagnoses, looking at any of them only really tells you what was probably happening for the last 10-15 seconds of that engine's life. This is why the old-fashioned 'plug-chop' was so important; engine was warmed up, run at full throttle under load for at least 30 seconds then ignition was killed and the engine stopped quickly by pulling the clutch. The colour of the plug then gave an indication of how it was jetted and whether it was burning oil etc.

Plug and piston in the OP's pictures look fine for a lawnmower to me.

As an aside, many years ago I attended a lecture by a Castrol oil expert who said that if an engine consumed one pinhead sized droplet every power stroke, it would be doing about 20 miles per pint and the local neighbourhood would be invisible!

[eltax91]

Thanks folks. Couple of new gaskets ordered. I’ll clean it up best I can, check the valve clearances and button everything up again and see how it runs. Since it’s smoking habit is probably it burning oil, then I guess that saves me an annual oil change as it’ll be constantly being topped up.

[Boosted LS1]

Strap yourself to it, on a skateboard and do a 10 second plug chop flat out across an uphill field.

[donkmeister]

eltax91 said:

It’s a ‘GGP technology sv150’ which I think is basically mount field. Air cleaner sponge is in soak already.

Check if the air filter sponge is meant to be oil-coated. No big deal to re-oil one, just pop it in a plastic bag with a little splodge of clean engine oil and squish it around before fitting to the engine.

Judging by how a dirty air filter looks, the oil is there to catch the fine particulates and the sponge is there to catch the big things.

I would say that given your spark plug isn't showing signs of incomplete combustion, being oil-soaked previously wasn't choking the engine, so it certainly works with an oil-coated filter even if that isn't standard spec!