Maximum to shave off the head

[icey756]

I already have .011 of an inch off my 7mgte head. I was wondering how much in total can be shaved off before running into problems?

[ianstaley]

Originally Posted by icey756

I already have .011 of an inch off my 7mgte head. I was wondering how much in total can be shaved off before running into problems?

I wouldn't quote me on this but I have had some experience of shaving the heads on another car that I turboed some years ago. I had a BMW 730 which was a NA carburetor model of some 3.0L. I turboed it using parts from a scraped 745 turbo. Now the 730 normally ran @ 10.5 to 1 and after shaving the head it was brought down to 8.5 to 1 which the engineers that did the job said was risky as there wasn't a lot of meat on the head. Even though the head had not blown a gasket it was warped (ally head). The result was that 3 months after the job was done it blew the HG.

So I would seriously check out the engine has it had a BHG before, if it has I would not be overly enthusiastic in using the head again as you may remove too much that can't be taken up with a thicker gasket.

I would imagine that the factory Comp ratio would be about 8 or 8.5 to 1 MAX. Hope that helps.

[icey756]

I have no idea what those numbers even mean. I'm not doing this to increase/decrease my compression. I just want to know if taking more off the head will compromise it. I bought the car with a BHG and replaced it with a felpro gasket. I now have the engine out because I got the car totally repainted. I wanted to do a MHG since the engine was out and it was convenient. I shaved the block and gave it new bearings and rings. I just want to know how much more I can take off the head if I have .011 off of it already. Along with that, the block has .006 of an inch off. I bought a 1.4mm Titan MHG. Is everything still going to be ok if the machine shop takes off another .006 or so off the head?

[cre]

CR isn't the issue and can be accounted for with a thicker MHG or in the worst case an added shim. As for the maximum allowable cut, I'm certain I posted it here in the past but I'm having trouble finding it and I can't find my notes on it. I'll let you know if I do locate the info.

[ianstaley]

Ah okay, thought you were going turbo sorry. I think that taking a few though shouldn't be a problem , however, there is always one isn't there, the MK3 is a non interference engine but I am thinking that take too much off it could become an interference engine, make sure the company that is doing the shaving can tell you if the valves will interfere, hit the pistons, just incase the timing belt breaks.

[cre]

Coming from Ian, I'd take this as gospel: "20 thousandths" So you'd be effectively doubling the height the piston crown extends past the deck in a clean, stock engine. Then you will want to account for it with your head gasket selection.

http://www.supramania.com/forums/sho...ness-selection

[icey756]

The only problem is that Ive already had the gasket for a while and it's a 1.4mm. Will that still work ok without running into any problems?

[btwilson86]

I understand that this thread is asking about how much physical material can safely be removed from the cylinder head, but since it is somewhat related I'm wondering if anyone on here knows how thick a stock head gasket is when it's properly compressed between the block and cylinder head.

I assume that a 1.4mm metal head gasket does not compress beyond this thickness when properly installed, so that the result would be a 1.4mm gap between the cylinder head and the engine block. If you have .011" off of the cylinder head, and .006" off of the block, then a total of .017" (or 0.4318mm) needs to be compensated for. If the stock head gasket is .9682mm or less when compressed, then your compression ratio should remain the same or be slightly decreased a minuscule amount. If the stock gasket is thicker when compressed, then your compression ratio will increase slightly, and your cylinder head will be closer to the block than stock, which could create interference in a non-interference engine with very close tolerances (I do not know whether or not the 7M falls into this category).

[btwilson86]

Ah, should have read CRE's supramania link first...

So with a stock gasket being 1.37mm, you are losing about .4mm of space between block and cylinder head with your current setup (1.4mm hg, .006 off block, and .017 off head).

In order to be closer to stock compression ratio and clearances, you would need something closer to a 1.8mm mhg.


******EDIT******

After reading quite a bit of the thread linked earlier by CRE, there are several reasons why it would be less than ideal to reduce the distance between block and head. From what I've read, buy a 1.8 to 2.0mm head gasket and do not reuse your existing 1.4mm

[icey756]

I already spent 130 on the 1.4mm gasket. I already unwrapped it and shit got messed up when torquing it down. I doubt they'll take it as a return so I can get a thicker one.