Busted Polinis why??

• Author: elliot (---.hsd1.ca.comcast.net)
• elliot
• Date Posted: 01-27-08 00:25

Ok so this just happened to my puch (given i was pushing it and running a bit lean) but here are some photos of other ppls polinis that the same thing happened to, it seems like the bottom of the cylinder crown hits the exhaust port and brakes off, on every one.

this is not siezeing from oil breakdown it seems more like a mechanical failure of parts.

has this happened to you? anyone out there know why this keeps happening, i know there are alot of super techs out there who understand engine dynamics lot better than I do.

another theory is that this occurs actually because ppl chamfer the exhaust port, and that in turn causes a heat build up in that area and warps the metal when under stress. the front of the piston always has wear as well even if the kit never siezed.

Of coarse i did not just throw away the kit after this i installed a new piston and ring, but had to re-chamfer the exhaust and raise the port slightly.

Anyone else have some theory why polini’s bust? there are literally dozens of kits with pistons that look just like these in SF.

we run portmatched bottomends, and 15bings-21mm dellorto 4pedal setups and stock gearing.