| 455 heads from swap [message #145459] |
Tue, 04 October 2011 08:10  |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma:
|
Senior Member |
|
|
E-mail readers, you don't see the swap side of the forum, so this is a cross post from same.
George Groth thought he had (a)cracked head(s) and was about the repair.
| ggroth wrote on Tue, 04 October 2011 00:03 |
I have the heads off and find a blown head gasket on both sides of engine. There is a slight depression between the bad cylinders, just a few thousands, but that's where the gaskets blew. Now, off to a head shop I suppose and get the heads milled enough to take care of that problem. Hopefully, not as bad as I thought.
|
George,
At the shop, tell them only to cut enough to clear the bridge area. They may have to cut a little more as the head may also have warped a little. Many shops like to mill 0.015 just for starters, that will probably be more than is needed, it may require that the valve train be modified and the intake will not fit as well.
Now,
I will bet that it was the center two (2-4 & 5-7). . I think I have seen this a few (maybe quite a few) times before.
Your base assumption is probably good, but what you have missed is the root cause.
At one time, the head was flat and the gasket was intact. Probably what happened next was an overheat. Between the exhaust valves, it gets pretty hot even when everything is good. But when it gets real hot, three things happen. The cylinder head expands more at the bridge elsewhere. That crushes the gasket that has probably already lost some strength because of the high temperature. But the failure probably could not yet be detected in an operating vehicle. At some later time, the engine was asked for more power (BMEP) than the damaged gasket could hold. It blew through, some power loss might have been noted at that time. That caused the temperature in the bridge area to rise very fast. Then, and what you now see, is that the cylinder head casting actually softened and then failed in compression so that when it cooled, it was no longer flat.
Why do I bother to tell you this now??
Because if you did not already fix the cooling problem, you need to think about it NOW. If you remember the circumstance that caused the overheat, that may guide you to the fix. If not, you will have to look at everything involved.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
