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 by 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?
I have seen varnish on valve stems, though never to the extent that it stopped a valve closing.
I have always believed it was caused by the oil rather than the petrol.
The exhaust valves get hot when the engine is running and if when the engine is hot it is switched off and it stops with an exhaust valve open, then the residual heat in the valve can be enough to evaporate the volatile elements in the oil lubricating the valve stem, leaving the varnish behind. But this would be a thin film of varnish, and to leave enough to prevent the valve closing when the engine next turns over seems pretty unlikely. Valve springs exert quite a closing force.
What I can't understand is how an engine that was "fully reconditioned" didn't have the valves removed, cleaned of varnish and lapped in when reassembled. I think the workshop is hunting for an excuse so that they don't have to admit it was something they did or didn't do that caused the problem. Has anybody taken the rocker cover off to see if a valve has slipped its cotters and dropped through, or a spring has snapped? That would be my first check.
As for "old petrol", how many collectors who lay up their car to over-winter drain the petrol and refill with new in the spring? I would guess almost none. And how many who don't, then end up with sticking valves in the Spring when they try to restart with the old fuel? None, I would guess.
Your mate is being lied to.
Jim
A while back there was a problem with Lycoming aircraft engines having sticky valves. A number of people consider it was happening because the oil manufactures were using Arabian crude stock and a number of operators switched to oil manufactures that used other stocks. (We switched from Shell to Silkolene) This cured the problem. My old Chief Engineer said it was because Arabian stock had high ash content. Then in the '70s the major oil producers switched to North Sea Oil (a low ash stock) and the problem went away... until in the '90s when they went back to Arabian and lo and behold the problem with sticky valves returned!
So yes I'd say oil not fuel! Try and find a non Arabian sourced oil.
However this fault only occurs after about 400 hours and if this one was just after it was "fully reconditioned" I'd say someone screwed up!
Slatts
Call me old-fashioned about these things, but it is a funny idea of "fully-reconditioned", even in these austere times, which does not include at least one of (a) clean and lubricate valves and replace valve stem oil seals; (b) grind valves,and (c) renew valve guides - in a world of perfection, all three; though I concede (c) raises parts availability issues on old engines.
Any one of these should have uncovered a stuck exhaust valve, even if work undertaken by the apprentice.
Brian
Remove 2001. to reply by email.
It did include both new valves and guides.
Possibly slightly over-sized valve stem or under-sized guide, in that case. Normally should be enough clearance for any varnish formation to be a non-issue shortly after start-up and certainly old fuel would be all used up before it should cause a problem. Saying that, I have several gallons of old petrol I intend to run through a litre at a time, to avoid any problems. It's too much worth to simply chuck away.
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