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Warped head milling allowance

  • Thread starter Thread starter Zimmy
  • Start date Start date
Z

Zimmy

Guest
Took a 82 GS1100GKZ head into a machine shop to do a valve job. Turns out the head is a little warped (7 thousands might be a little more that a little warped) and the shop needs to know what the limit is that can be milled off the head in order to get it straight once agan. I have checked around alot & no one seems to have this information. Please help

:confused:
 
Zimmy said:
Took a 82 GS1100GKZ head into a machine shop to do a valve job. Turns out the head is a little warped (7 thousands might be a little more that a little warped) and the shop needs to know what the limit is that can be milled off the head in order to get it straight once agan. I have checked around alot & no one seems to have this information. Please help

:confused:
Click to expand...

You can true that up with a 10 thou cut. Your increase in CR will be minimal and in fact benificial. Your cam timing will be slightly retarded from stock after the cut, unless you find a thicker head gasket or fit slotted cam sprockets and degree your cams.
 
Here is something you need to consider. When these heads are made, the cam bores are bored parallel to the head surface. If you have the head off of the motor, and find that the mating surface is warped or bowed, so are the cam bores. If you put this head back on the motor, and clamp it down with some good studs, it gets flat again, and the cam bores are once again straight.

If you take this head and machine the mating surface flat, you have just rendered the cam bores permanently warped. Now they won't straighten out when you bolt it back on the block.

Many an ohc cylinder head has been ruined doing this.

If the head surface has surface flaws that need to be machines out, that is a different deal.

What should you do? If it is bowed ( high or low in the middle ), we would put them in the press and flatten them back out to within a couple of tho, then surface it.

Jay
 
Big Jay said:
Here is something you need to consider. When these heads are made, the cam bores are bored parallel to the head surface. If you have the head off of the motor, and find that the mating surface is warped or bowed, so are the cam bores. If you put this head back on the motor, and clamp it down with some good studs, it gets flat again, and the cam bores are once again straight.

If you take this head and machine the mating surface flat, you have just rendered the cam bores permanently warped. Now they won't straighten out when you bolt it back on the block.

Many an ohc cylinder head has been ruined doing this.

If the head surface has surface flaws that need to be machines out, that is a different deal.

What should you do? If it is bowed ( high or low in the middle ), we would put them in the press and flatten them back out to within a couple of tho, then surface it.

Jay
Click to expand...

Jay,
I bought a ported head off of ebay. The receipt that came with it said it was milled .015, but it sure doesn't look like it. How can I now tell if it's warped?
 
Big Jay said:
Here is something you need to consider. When these heads are made, the cam bores are bored parallel to the head surface. If you have the head off of the motor, and find that the mating surface is warped or bowed, so are the cam bores. If you put this head back on the motor, and clamp it down with some good studs, it gets flat again, and the cam bores are once again straight.

If you take this head and machine the mating surface flat, you have just rendered the cam bores permanently warped. Now they won't straighten out when you bolt it back on the block.

Many an ohc cylinder head has been ruined doing this.

If the head surface has surface flaws that need to be machines out, that is a different deal.

What should you do? If it is bowed ( high or low in the middle ), we would put them in the press and flatten them back out to within a couple of tho, then surface it.

Jay
Click to expand...

Good point Jay.
I have seen Ali auto heads pressed straight after radical chamber reshaping following Tig welding. This was done prior to milling for the same reason.
 
Acording to the manual you are still within tollerance for head flatness. Just torque it down per manual.
V
 
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