Home » Public Forums » GMCnet » 455 heads from swap
| 455 heads from swap [message #145459] |
Tue, 04 October 2011 08:10  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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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.
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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
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| Re: [GMCnet] 455 heads from swap [message #146033 is a reply to message #145459] |
Sun, 09 October 2011 23:34  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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I am coming in a little late to this party, but I used to machine cylinder
heads in my business. When I set up the broach, I would place a .010" ribbon
gage under each corner of the head after first retracting the table. This
would space the head away from the table a known amount, .010" I would then
clamp the hold downs to the head, and then give the ribbons a slight tug to
verify that the head did not move when the clamps were tightened. I would
zero the scale, back the table away far enough to remove the gages, re
adjust to .010" and take a cut. If the head is flat, all that should be
heard is an occasional contacting from the broach cutters. Then I would
retract the cutter and use a mirror and check the surface. If there were any
low spots, they would be un touched. Then I would set the depth at .015 and
make another pass, and check again. This is the best way to take only the
minimum amount off the head that I ever found. Takes longer, but it worked
for me. In a production machine shop, they don't want to spend that much
time so they just hog off .015" on the first pass.
Hard to find a good careful machine shop.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 4, 2011 at 6:10 AM, Matt Colie <matt7323tze@gmail.com> wrote:
>
>
> 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
> '73 Glacier 23 Chaumiere (say show-me-air) Just about as stock as you will
> find
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Unsubscribe or Change List Options:
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| Re: [GMCnet] 455 heads from swap [message #146046 is a reply to message #146033] |
Mon, 10 October 2011 06:35 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Good machine shops are out there, just like good transmission shops and good mechanics. And, they're like good barbecue joints around here - they got more work than they can handle. Look for the one with the line out front. And ask. And be prepared to pay a fair price - two passes on the heads takes longer than one.
--johnny
________________________________
From: James Hupy <jamesh1296@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Monday, October 10, 2011 12:34 AM
Subject: Re: [GMCnet] 455 heads from swap
I am coming in a little late to this party, but I used to machine cylinder
heads in my business. When I set up the broach, I would place a .010" ribbon
gage under each corner of the head after first retracting the table. This
would space the head away from the table a known amount, .010" I would then
clamp the hold downs to the head, and then give the ribbons a slight tug to
verify that the head did not move when the clamps were tightened. I would
zero the scale, back the table away far enough to remove the gages, re
adjust to .010" and take a cut. If the head is flat, all that should be
heard is an occasional contacting from the broach cutters. Then I would
retract the cutter and use a mirror and check the surface. If there were any
low spots, they would be un touched. Then I would set the depth at .015 and
make another pass, and check again. This is the best way to take only the
minimum amount off the head that I ever found. Takes longer, but it worked
for me. In a production machine shop, they don't want to spend that much
time so they just hog off .015" on the first pass.
Hard to find a good careful machine shop.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Tue, Oct 4, 2011 at 6:10 AM, Matt Colie <matt7323tze@gmail.com> wrote:
>
>
> 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
> '73 Glacier 23 Chaumiere (say show-me-air) Just about as stock as you will
> find
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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