Thread: 3.3 Blew Up!!!
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TurboKraft TurboKraft is offline
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Join Date: Mar 2005
Location: Phoenix, AZ
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Originally Posted by JFairman View Post
There are lines of carbon from combustion leakage around most of the head to cylinder sealing surface on the top of the cylinder. It would help to see the combustion chamber side of the heads too.

My guess is the head studs were not torqued correctly and they loosened up more over time duting running and heat cycles and this eventually happened.
Combustion pressure was leaking - you can see that from the carbon trace lines going outwards from the center all the way around on the cylnder deck sealing surface.
My thoughts exactly. Same failure I have seen when a head lifts under full boost.

Why would the rocker arm shaft have moved itself?
We have seen a lot more of this in the past couple of years. When these engines are rebuilt or someone's gone through the top end, and they aren't kind in the removal of the rocker shafts, they gouge out aluminum from the cam housing's bore. Same goes for when the shafts get polished to clean them up (better to just replace them).
It doesn't take much additional clearance and the shaft no longer holds tightly in position when torqued to the factory spec. Then the shaft moves, you get oil leaks, and in a worst case scenario the shaft moves over enough that the rocker is no longer properly supported and the rocker comes off. That can lead to a cascade of failures in the valvetrain, killing rockers, cams, valves, cam gears...

We had 2 different engines where the rocker shafts shifted when the engine was hot, full boost on the dyno. Significant oil leaks ensued when one shaft moved, and the drips onto the glowing hot headers could have flashed into a fire. It troubled us enough to come up with our Rocker Shaft Locks. No more migrating rocker shafts, no more oil leaks.
Chris Carroll
TurboKraft, Inc.
Tel. 480.969.0911
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Last edited by TurboKraft; 09-20-2011 at 05:13 PM.. Reason: addition
Old 09-20-2011, 04:30 PM
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