| 455 Heads [message #145305] |
Sun, 02 October 2011 20:49  |
|
|
I haven't got the heads off yet, but indications point toward cracks in the valve area; just looking ahead and wonder who had any. I know "J" heads already have hard seats and that's what mine are. I'd be interested in what anyone might have; mine are coming off tomorrow.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
| Re: 455 Heads [message #145354 is a reply to message #145305] |
Mon, 03 October 2011 10:33  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
|
Senior Member |
|
|
George I sure would like to see those heads. The guy that did the valve job has an excellent reputation ,it will be interesting to see what went wrong. Howard should have some heads in his shop? Most G,Ga,and E heads besides the J heads should be good if they have the hard seats.Superior Machine in Reno did a decent valve job on my heads. If you need a hand lifting them off give me a call.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
|
|
|
|
| Re: 455 Heads [message #145356 is a reply to message #145354] |
Mon, 03 October 2011 10:49 |
|
|
Hi Roy, thanks, I'll get them off today I think; I'll call you and let you know, so I'd like to have you look at them.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
| Re: 455 Heads [message #145441 is a reply to message #145356] |
Mon, 03 October 2011 23:03 |
|
|
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.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
| Re: 455 Heads [message #145458 is a reply to message #145441] |
Tue, 04 October 2011 08:03 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
|
Senior Member |
|
|
| 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
|
|
|
|
| Re: 455 Heads [message #145487 is a reply to message #145441] |
Tue, 04 October 2011 14:51 |
|
|
This is for MCollie. You have attempted to post here and on the GM site, but I see no verbiage. Please try again as I'd like to see what you have to say. tnx.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
| Re: 455 Heads [message #145568 is a reply to message #145458] |
Tue, 04 October 2011 23:08 |
|
|
mcolie wrote on Tue, 04 October 2011 06:03]| 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.[/quote
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
|
OK Matt, I read your info now, and have noted the "stop blocking"
entry. I am baffled because it is the area between #1-3 and 6-8 cylinders that is burned out. I'll take your advice on the machining. I just don't remember any overheating. Thanks for your help.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
|
|
|
|
| Re: 455 Heads [message #145657 is a reply to message #145582] |
Wed, 05 October 2011 21:37 |
|
|
| Hardie Johnson wrote on Wed, 05 October 2011 05:31 |
This is a very interesting, important discussion. But why is it going on in the swap meet, where none of the emailers can read it?
|
Hi Hardie, I originally started this a just a request for some 455 heads; that is why it is here. I later posted info on my problem on the Net.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
|
|
| Re: 455 Heads [message #148635 is a reply to message #148617] |
Thu, 03 November 2011 13:23 |
|
|
Thanks Phil; that's why I'm getting the correct carb and having it overhauled; My timing was spot on, though I can't hear well enough to detect pinging. I think I will get a knock sensor from Jim K. to help me w/that. I just dont' want any more problems.
geo groth '73 260 Sequoia
Carson City Nevada 89703
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
