Re: Thanks Guys Heres a picture. Re: Hole in Piston, Expert Opinions Please !?!?!


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Posted by Alan Bowes on February 19, 1999 at 10:40:58:

In Reply to: Thanks Guys Heres a picture. Re: Hole in Piston, Expert Opinions Please !?!?! posted by Sean Butler on February 18, 1999 at 21:02:37:

The little light specks on the piston appear to be a combination of shallow pits and places where the carbon has flaked off. This is typical damage from the intense shock waves caused by preignition/detonation. A loose, hot plug could easily be the cause of detonation. A plug depends on heat transfer into the cylinder head to run at its correct temperature. If it's loose and rattling around, it won't be able to transfer the heat very effectively and it may end up glowing brightly, pre-igniting the fuel too early on the compression stroke. It could also be that this is the leanest of the cylinders due to manifold design, which would make it run hotter and be more prone to pinging. A large percentage of the fuel in the fuel-air mixture remains in the form of droplets, which, due to their greater density, don't follow the air very uniformly through the intake manifold and some cylinders simply get more of the fuel than others, especially with a single-carb, six-cylinder manifold with unequal-length passages.

The hole looks fairly hard edged, as if it were severe shock rather than melting, although it would be easier to evaluate this in person.

I'd say check for damage (oil pump and bearings), clean the crankcase of any debris, replace the piston, check for any manifold leaks, and go have some fun with it.

Alan



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