Multiple 12v ??s cracked valve seats, piston slapped valves..

wpeschel

wpeschel

Psyko
Joined
Aug 4, 2007
Messages
872
I just finished putting a short block in my truck.. We pulled the valves to inpect the head.. There are crackes inbetween every valve, and multiple small cracks in the valve seats.. This head is only 6 months old.. The original head had only one small crack in between the number one cylinder valves.. I went and had the valves cut, and grinded the seats.. I had no other choice but to put it back on and run it.. I was wanting some opinions on what to do.. I dont want to buy a new head just so they will crack again.. I have not noticed any loss in performance in the last 6 months..

I would also like to find out when the thicker head gasket is needed??? I put my new head on 6 months ago with a stock head gasket, the head is decked.. When I pulled it apart you can see imprints to where the exhaust valve slapped the pistons. What caused that?? To be save I went with a 20 over gasket.. Does decking the head affect piston to valve clearance?

Thanks for all the imput..
 
Cracking is normal and is accelerated with high egt's. A #10 plate with DDp3's is really more fuel than a 62mm turbo can cool.

As for the valve to piston issue. Yes decking the head will reduce the piston to valve clearance, how much was removed? Going with the .020 over gasket should help as long as the head is within tolerance and valve lash is set correct.
 
Well the i'm not sure how much the head was was decked, but was told that a thicker HG wasnt needed.. I do plan on putting a s400 under the 62 in the next month or two..
 
If its hot enough to crack like that it may have melted and stretched the exhaust valves, causing them to hang down out of the seat and contact the piston.
 
BigB82789 said:
If its hot enough to crack like that it may have melted and stretched the exhaust valves, causing them to hang down out of the seat and contact the piston.
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Possible, No damage was done the valves.. They were checked and cut.. I think the pistons more than likely swelled, and contacted the valves.. The #6 cylinder, is scored all up.. Also the retainer ring from the crank was found in the oil pan, the crank would slide front to back about 3/16 of a inch..
 
Did ya over rev the mitty 6? Sounds like valve float... do ya have good springs?
 
60lbs springs, 4k gsk.. I was running it at high egt for quite a while when it started knocking.. It has been using quite a bit of oil for the past 4 months, so I kinda have been running the crap out of it..
 
wpeschel said:
Well the i'm not sure how much the head was was decked, but was told that a thicker HG wasnt needed.. I do plan on putting a s400 under the 62 in the next month or two..
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I was told grinding the seats during a valve job will basically cancel out any decreased clearance caused by decking the head.
 
Jetpilot said:
As for the valve to piston issue. Yes decking the head will reduce the piston to valve clearance, how much was removed? Going with the .020 over gasket should help as long as the head is within tolerance and valve lash is set correct.
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Any one who decks a head better reset the vavle recession when they do it. If the head needs decked it more than likely needs a valve job anyway.
So it doesnt alter the valve to piston clearance, Just like it doesnt lower the compresion ratio.

More than likley he was twisting some r's and floated a valve. Or he said he was at high egt's for a long period could have gotten the valve hot enough to become oversized and get stuck in the guides.
 
You may want to look at the saddle where the main thrust sits. The crank may have eat some of the meat out of the saddle. Block may be bad.

Brian
 
Distributor said:
Any one who decks a head better reset the vavle recession when they do it. If the head needs decked it more than likely needs a valve job anyway.
So it doesnt alter the valve to piston clearance, Just like it doesnt lower the compresion ratio.

More than likley he was twisting some r's and floated a valve. Or he said he was at high egt's for a long period could have gotten the valve hot enough to become oversized and get stuck in the guides.
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You are correct but I have seen way too many guys who just shave the head and don't do the valves or check recession.....
 
Jetpilot said:
You are correct but I have seen way too many guys who just shave the head and don't do the valves or check recession.....
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The head was new, I bought it from pure diesel performance, he suggested when it was in the machine shop getting orings to have it surfaced as well.. So will it hurt anything to keep running the head with the crackes???
 
wpeschel said:
The head was new, I bought it from pure diesel performance, he suggested when it was in the machine shop getting orings to have it surfaced as well.. So will it hurt anything to keep running the head with the crackes???
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Run it I have seen alot of them cracked like that and never hurt a thing and for plaining the head they proably did'nt take .010-.020 off so if valve clearence was only .010-.020 to start with you would have had problems before.
 
Ragged Edge said:
Run it I have seen alot of them cracked like that and never hurt a thing and for plaining the head they proably did'nt take .010-.020 off so if valve clearence was only .010-.020 to start with you would have had problems before.
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I didnt think it would hurt.. I have read that it is very common for them to crack.. I went with a .020 hg anyway for the reassurance..
 
the 12v have had problems with the seats for years u can have ur head sent out and have it cut and have seats put in it but if u do make sure whoever does it knows what there doing cuz the last thing u want is to drop a seat and have it hold the valve open i would run the 20 over gasket reguardless this will lower ur compression and let u run higher boost numbers with less of a chance of hurting anything but from the sound of things u better check out ur bottom end and make sure its even worth putting a head back on
 
and even if the head is new u should have it decked ive seen brandnew heads and blocks come from cummins that have been .005 to.007 out
 
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