what causes a hole in a piston

[pvaman]

85FJ60 - 200K miles. Pulled the head and one of the pistons has a fairly good sized (1/2 sq cm) hole in it. What can cause this...a vacuum leak? ???

 

[Degnol]

Pre ignition, timing too far advanced, will burn a hole in a piston. Vacuum leak isn't a big problem unless you're trying to get a smooth idle. A big vacuum leak would make it run lean and hot, but I don't know if it would burn a hole in a piston.
Ed Long

 

[Gumby]

A vacuum leak can cause pre-ignition.

 

[woody]

#5 or #6 piston? IIRC, a bad vacuum booster can cause enuf of a vacuum leak to trash a piston...

 

[pvaman]

#6 it is.

 

[CruisinGA]

Normally bad boosters are pretty obvious though. Hissing like a pissed snake. How are your brakes pvaman?

 

[hammerhead]

Do any other pistons show signs of pitting?

 

[dd113]

I would bet it was a bad booster or even a good booster drawing on the back 2 cylinders. I have no idea why this happens. It might be that the vac for the booster causes it to run lean but I cant see why this would hole the piston. Could also be a small part of a plug that got in there.

 

[bobrose]

Don't remember off the top of my head what symptom points to what but the type of hole it is can be telling. A hole that looks like it was punched out (fractured edges) vs. a hole that looks like someone took an acytelene torch to it.