Yet a few more possibilities...


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Posted by Alan Bowes on February 19, 1999 at 12:03:25:

In Reply to: Re: Thanks Guys Heres a picture. Re: Hole in Piston, Expert Opinions Please !?!?! posted by Alan Bowes on February 19, 1999 at 10:40:58:

Just to cover some more bases, here are a few other things that could cause preignition:

-- Excessive carbon buildup as a result of running too rich for a long time can result in hot spots that can pre-ignite the fuel-air mixture.
-- An exhaust valve that is not seating properly will be running too hot and pre-igniting the air-fuel mixture. Even though it may be seating close enough that there is not much compression loss, it only takes a minute gap to prevent heat transfer from the valve into the seat and block.
-- Timing is advanced too far. This would tend to affect leaner cylinder(s) first.
-- As mentioned, a spark plug that is either loose or an overly high heat range can act as a 'glow plug.'
-- Air leaks in the intake system. These tend to affect multiple cylinders, but if there is a leak directly next to an intake port in the head, it could affect that cylinder somewhat more.
-- An overheated engine, due to cooling system problems, can cause pinging.
-- Running 100 percent antifreeze can reduce heat transfer efficiency.
-- A bad water distribution tube, a blocked water passage, or excessive rust around a cylinder can make it run too hot, causing pinging.
-- A coolant leak into a cylinder can, if large enough, cause pinging, although you'd probably notice the smoke/steam in the exhaust. Check the head gasket pattern on the head and block for any tracks or discontinuities. Check for cracks in head or cylinder walls.
-- Overly low-octane fuel will cause pinging under load.
-- A milled cylinder head and the resulting higher compression may require higher-octane fuel to avoid pinging.
-- A bad batch of gasoline, or winter fuel used during the summer, may cause pinging.
-- Sometimes a cracked porcelain insulator in a spark plug will still allow a plug to fire, but the end of the electrode will get much hotter than usual, due to the thermal break created by the crack.
-- An incorrect metal head gasket can extend into the combustion area and act as a glow plug.
-- An overall lean condition caused by carb problems or incorrect jet(s) can cause pinging.

I could probably think of a few more, but those should give you some ideas about things to check.

In addition to checking and cleaning the crankcase, oil pump, and bearings, while you have the cylinder head off, you should thoroughly flush out the cooling system and check the water distribution tube, if used.

Good luck,

Alan



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