Old petrol and sticking valves.

Mate in my car club had his engine fully reconditioned, and on starting it soon had a nasty noise, which turned out to be a valve hitting a piston. Workshop says it was cause buy a valve sticking due to using old petrol - varnish on the stems.

This is well reported across the pond if you Google, but I've never heard of it here.

Any comments?

Reply to
Dave Plowman (News)
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Petrol varnish on valve stems means by definition that the engine has not been "fully reconditioned" Either the valves would have been replaced, or at the very least reground and cleaned up.

My money is on the valve timing being out.

Steve

Reply to
shazzbat

Self evidently it was not fully reconditioned. Varnish on valve stems does not just instantly form, it would only cause sticking if the gases had been blowing up the sides of worn valves/guides/valve seals for quite a while. I have never seen it and have run many ancient engines on ancient petrol (sometimes having to start them on some fresh since old petrol does not fire up from cold as easily as new.)

As to reports from abroad, I imagine that side valve engines (more common in the states) would be more subject to the problem than an OHV engine due to unburnt fuel being able to run down the valve by gravity and evaporate/turn to varnish.

The only time I have had problems with petrol turning to varnish has been inside carburettors when it can restrict or block jets and glue down the float valve

Reply to
Mrcheerful

He says it was - all new valves and guides. Which had to mean the varnish set very quickly indeed. Would be a very useful adhesive that grips steel so well and sets so quickly. ;-)

And perhaps different additives in the fuel?

This one is injection - yet the injectors seem to be not effected. Or the high pressure fuel pump.

Reply to
Dave Plowman (News)

Yes. Complete bollocks.

Reply to
Dave Baker

Whatever that may mean.

Very, very, very quickly...

Easy enough to diagnose if it IS a valve sticking open - just remove the cam cover, and see if one's wide open when the cam lobe isn't telling it to be.

What's causing it to be wide open is another question - although now it's probably bent as well. Whatever. The head's gotta come off.

Reply to
Adrian

Surely, anything sticky enough to stick a valve wouldn't get through a carb jet or fuel injector, and anything that was already there should have been cleaned off?

Reply to
Chris Bartram

Heh. Short, to the point, and as you'd expect, correct :-)

Reply to
Chris Bartram

Well you can have resins dissolved in solventsthat evaporate when they hit hot things like valve stems. But I'll bet that's not what happened to that engine.

Reply to
Duncan Wood

Especially as Dave's OP suggests this was from a cold start :-)

Reply to
Chris Bartram

+1.

Just a comment on the varnish-like thin brown deposits which are often seen on various things like valve stems, these are polymers formed by oxidation of the lube oil, nothing to do with petrol at all.

Reply to
newshound

What engine? Side valve? OHV? OHC? DOHC? Shim/screw/hyd tappets?

It would take 1000's of miles to build up any deposit that could possibly cause sticking valves. Not the 400 miles you can do on one tank of "old" petrol in a freshly rebuilt engine.

He needs the bits back and a lawyer.

Now if they had said it was due to contaminated fuel and offered to give "expert" evidence to support your claim [1] against the fuel supplier, that might be believable. [2]

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[1] Their claim really, a rebuilt engine should have some sort of warranty on it. They would need the receipt for the fuel to support their claim.

[2] Supermarket fuel fuel doesn't come out of the same tanks as Shell/BP/ESSO etc. It seems a lot came/comes out of the tanks of Harvest Energy in Essex
Reply to
Peter Hill

Rover V8, so pushrods and hydraulic tappets.

Reply to
Dave Plowman (News)

I bought a new lawn mower recently: it has a 4-stroke petrol engine by Briggs & Stratton.

Instruction book insists that preparation for disuse over winter should include emptying fuel tank and refilling with fresh fuel PLUS their recommended anti-ageing additive - otherwise it won't start properly the next season.

Does petrol really degrade over a period of months?

Reply to
Graham J

I would leave it full of fuel over the winter, then drain it and refill with fresh before an attempted start. Not sure about an additive; smacks of 'snake oil' to me, but maybe worth it if not too expensive.

(Old Briggs and Stratton engines used to seize their exhaust valve open during the winter; standard practice was to use upper cylinder lubricant in the last tank of fuel before the winter.)

IME, yes.

The situation is much worse with oil-mix two-strokes, of course.

Chris

Reply to
Chris Whelan

I leave my mower full over the winter without problems, it reduces condensation inside the tank. Petrol does degrade after a year or two, you can smell the change. The thing to avoid stuck valves (on a single cylinder) is to turn the engine to compression and leave it there so the valves are closed. When I was in the Royal Observer Corps we had petrol electric sets to charge the Nife cells, SOP was to run the gennie till completely empty and turn to compression before storage, never any problems on next use.

Reply to
Mrcheerful

No. I have a ride-on with a B&S engine and a push-about with a Tecumseh, both at least 20 years old, and I have never pissed about with "winterising" either of them.

Reply to
Huge

Ditto. Our old B&S engined mower starts every spring without too much bother. No special precautions taken.

I suspect the fact that it *hasn't* got a fuel tap helps to prevent the float chamber & carb drying out/gumming up but that's just a guess.

Tim

Reply to
Tim+

Sorry, but you're wrong.

You don't even know if a branded station is getting fuel from their own bunker or someone else's - depending on local supply availability.

Reply to
SteveH

I usually run the petrol down towards the end of the year then top up with fresh at the start of the next year - have done this for nearly 30 years (B&S and Tecumseh engines). Up until this year have never had a problem, but this year it refused to start. Stripped the carb down and it was blocked with a greenish gunge. I've had my present mower for over ten years, so whether this is ten years gunge or not, and whether it is due to leaving petrol in the tank over the winter is debatable. Still, only took about 20 mins to fix.

Biggles

Reply to
Biggles

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