just thought i would let everyone know my miss fortune. my motor blew up on the weekend. the annoying partis that it went because the motor was not built properly by whoever built it. the pistons sit proud of the block by about a mm! they were never decked so it had been hittingon the head. what amazes me is thatit lasts 1 year. pistons 1 and 3 had part of the lip of the dish smashed off. something even more interesting is no. 1 looks like it had been like that for a long time as there is carbon build up there and when i did a comp test 6 monthsago it was low. i think it was like that when i got the car... and it still made150 on 12 psi.

well after a rebuild and a few more mods should be better than ever. they were acl e15 turbo pistons. has anyone been using anything else with good results?

D'oh...

I gave the engine builder on my last engine a bad oil pump... failed messily 6000 miles on right after putting $100 in super expensive oil in too...

these things happen... seems like you just need a little thicker headgasket or a very thin spacer to make it work as is... or get new pistons and have em trimmed a little too...

"about a mm" is no way to measure deck height. clean up the pistons and deck and measure it at TDC with a dial gauge prefferably, or if you don't have access to one, with a straight edge and feeler gauges.

A compressed head gasket will be between .040" and .050" so it does allow you to run a positive deck height.

are there witness marks on the head and pistons - there would be if they were hitting each other. It would also have been pretty noisey.

its more likely to be detonation damage to the piston headland if its cracked above the top ring and taken a chunk out of the edge of the headland. are the compression rings broken too?

it was definately hitting as you can see the marksin the head and the surfaceof the piston is clean in that area. even with head gasket thinknessinto account i prefer not to run positive deck height to allow for stretch at high rpm. these pistons should have been machined. it is easy to miss if you dont how to build and engine but dont really check for tolerences.contradiction in terms i know... but there are plenty of guys outthere that know how to put and engine together in their shed but dont think to check clearences.

as for the pistions. we are not talking about little chips or detonation marks here. a third of the pistion top lip (concidernig it is a dish type de-comp piston) has broken off to the ring lan leaving the in tack all in one go. thatis not detonnation. thats fatigue.

my god it must of been making some nasty sounds......i just pinched a big end bearing and it sounds bad enough...pistons hitting the head with even the slightest touch would have to make alot more noise....you can even hear detonation in most cases!!

good luck with the rebuild tho, hope you have more luck then i seem to have

my money's on detonation. if there was physical interference you'd have done a big end long ago.

its not unusual for detonation to crack a top ring, it overlaps and breaks off a long chunk of headland.

its also normal for the part of a piston under the closed side of the combustion chamber to be clean.

maybe they should have been milled, but you only need .030" static clearance to be safe. you could measure the clearance on the other undamaged pistons if you wanted to be methodical about the cause of the failure.