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Discussion Starter · #1 ·
First - to check an assumptio

First - to check an assumption - on a C4 V12, with number 6 at top dead center compression (Valves are both closed) stroke - I blow air in the spark plug hole and it flows freely out the oil filler -

No water in oil -
Piston goes up and down - engine runs but number 6 is dead -

I have a hole in the piston right? Could it possibly be something else?

Any thoughts on what causes holes in pistons - could inadequate fuel flow cause this at a high cruise speed?

Moving forward - KE pistons are good?

Is Bill still out there? Any advice going forward with a short block?

Is there a source for cylinder boring plates - do I need to make one?


Aaron - same guy for several years back who did some writing in buyers guide….

Discussion Starter · #3 ·
"high cruise speed"

"high cruise speed" Low or bad octane gas will cause detonation and burn holes in pistons or can bend the ring lands and cause the rings to seize on the piston. If your leak shows up at the "air filter" (not the oil filter),,, burned valve.If you over rev'ed durning the high speed run ,,,, bent valve. Don't know about KE pistons, but JE pistons make some of the best.

Discussion Starter · #4 ·
Thanks for the feed back –

Thanks for the feed back –

Sorry about the KE – it is JE – have an email into them.

I can’t say that I have ever heard the engine ping, which is not to say that it isn’t’ pinging.
Would I have heard it over the carburetor noise? – carburetor noise swamped out the exhaust at 3300 rpm cruise.

My timing was set at 15 degrees initial and 20 centrifugal for a total of 35 at 3300 RPM.
Bad gas? – happened to be running Gulf regular which uses ethanol. Figured with 8.8:1 it should not be an issue. I do believe what ever happened, happened at cruise, low throttle setting.

If I run compressed air into the spark plug hole, he air flows “volumously” out the oil filler. I can pressurize the crank case by holding my hand over the oil filler port and when I do that there is no indication of air out the exhaust or the carburetor port.

I have tried to see a hole in the piston through the spark plug hole. Being a 4 cam engine, I can see a reasonable amount of the center of the piston, which is puzzling because I would expect the piston to be thinnest in the center.

A friend of mine suggested that it might be a hole in the head – combustion chamber into the valve cover area. I have never heard of this – but there are a lot of intricacies in the casting -


Discussion Starter · #5 ·
It may have a hole in it. I ha

It may have a hole in it. I have rebuilt several ferrari engine due to cracks on the piston crowns. The customers always ask how long will it last? I always tell them, if I knew that I would also know the winnig lotto numbers. The original pistons are cast and should be replace when performing a proper rebuild.


Discussion Starter · #6 ·
Ethanol,,,, its causing proble

Ethanol,,,, its causing problems with high po engines that are near the limit. just for info, Detonation can start any place in the combustion chamber. We have bent and burned the tops of a piston right over the ring lands.It all has to do with where the hot spot is formed.
Low speed cruising with high load, (throttle down and making engine work to hard, in to high of a gear) can start detonation, and the ethanol lowers the octane rating of the gas setting up the right conditions for detonation to occur. Enthanol in gasoline will cause the engine to go lean,producing higher combustion temperature,and would need rejetting to run this type of fuel safely The new formula cars in SCCA had a simliar problem with burned pistons that was due to ethanol in the gas and fuel maps in the ecu that could not handle the lower octane. Damage can occur at levels you may not hear. That is why knock sensors are used today. From what you describe, I think you do have a leak at that piston.
JE pistons are very good pieces. We have used many of them over the years. shipped to you direct, they are weight matched and only a very light final deburr is necessary.
Keep us posted with what you find. We are always interested in learnig new things.

Discussion Starter · #7 ·
365gtc/4 -Hole in piston? --

365gtc/4 -Hole in piston? -- Engine Pull on Sunday.

Used a new tactical plan to pull the engine this time, it worked very well.

I left the transmission and the differential bolted together via the torque tube, and slid the whole assembly back about 4 inches (both the diff and the trans on a floor jack). This allowed the transmission input shaft to clear the clutch plate – from there the engine went up and out.

– the engine is now on it’s stand with one set of valve covers off. I’m still about 45 mins away from having the head off. I think the intrigue as to what happened has out weighed the disappointment. I have no idea what caused this. My plugs have consistently been a light brown – text book. Best I can tell the timing has been correct. If I had a carb float problem it should show up on both number 5 and 6. If it is timing – I don’t really know what to look for.

What ever the case – the OEM cast pistons are going away!

Any one have an opinion on connecting rods – usually the week link in a high rev engine.
Keep them, Check them for cracks and put in new bolts? Through them out and buy Carillo?

Discussion Starter · #8 ·
Carillo's are the best. Th

Carillo's are the best. They do magic in heating treating the metal. Use the recommended new bolts if you can. Use a micrometer to measure the bolt length gain when torqueing the bolts, instead of a torque wrench. If you get with JE pistons and tell them you want to use Carillo's they will know what to do.
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