how much can be removed safely from a 7m block before i run into issues

[queenskid926]

I'm doing a headgasket job, my head had 9 thousands taken off and now its time to bring the block to be decked. The block looks pretty bad on the exhaust side and I'm wondering whats the maximum that can be taken off before i run into problems.

Everything else on the motor is stock, stock rods, stock pistons, How much will have to be taken off to zero deck the block?

And I'm a newbie, the pistons cant protrude past the top of the block right?

 

[jdub]

The TSRM says max warpage is 0.0020"...that implies the max that can be removed. However, I have seen more, it's up to you and your comfort level. In any case, the MHG thickness needs to be enough to make up for the material removed from both the head and block. That will keep your CR (assuming stock pistons) close to factory and will not cause valve timing issues.

Stock piston protrusion above the block deck is 0.020" iirc...yes, they do protrude above the deck


I hope you had the head hardness tested before you Had it decked. I would have the block magnafluxed for cracks before I spent a penny on it.

 

[queenskid926]

The TSRM says max warpage is 0.0020"...that implies the max that can be removed. However, I have seen more,

whats the most or average that you have seen?

And thanks for the quick reply, now i know that the pistons already protrude out from the deck. I thought it was the opposite

 

[jdub]

The most, 15 thou...the motor didn't seem to have any issues. The MHG that was installed did make up the difference....a custom Cometic slightly larger than the cylinder bore and at the thickness 1.37mm stock thickness + head material removed + block material removed (0.38mm).

 

[queenskid926]

ok thanks for the information jdub, and again for the quick responsed

 

[REG8000]

hi
i have rebuilt 13 7m's and if needed i have had the top of the pistons milled the same amount that was tacken off the block . i have not had to go more then .015 and run into no problems. i rebalanced the pistons but they were in limets and used a hks i.2mm gasket, been running for 3 years and still going. the head gasket makes up the differenc.

 

[Adjuster]

Why mill the pistons? Just do the machine work, and buy a Metal Head Gasket that is the right thickness to get back what you lost.

If the gasket is slightly too small of a bore for your motor, have the shop clamp it inbetween the tourqe plate and the block, and then bore for the pistons. (You will get a gasket cut exactly to your new bore diameter that way every time.)

The pistons are supposed to stick up slightly. NO big deal. Just get the right thickness of gasket, and you should be fine.

BTW, if you milled down the pistons, you completely have lowered the static CR of the motor unless you compensated with the gasket or head work.

 

[gaboonviper85]

hi
i have rebuilt 13 7m's and if needed i have had the top of the pistons milled the same amount that was tacken off the block . i have not had to go more then .015 and run into no problems. i rebalanced the pistons but they were in limets and used a hks i.2mm gasket, been running for 3 years and still going. the head gasket makes up the differenc.

LOL you fail!