1G Head resurfacing limit valve interference

[97egl]

I have a car that I am wanting to fix up for a winter beater. 91 FWD turbo. Its got like 204k miles on it. Compression test 25-50 psi. Head gasket looked brand new but was blown between all cylinders. First thing I checked was the head for warp and its got about .016 warp. I know the service manual says .008 is the limit to machine it and I searched and found guys saying you can go as far as .015 but nobody ever says why that's the limit.

I am not worried about the compression ratio going up. I am not going to be racing it and will barley ever get into any boost maybe a few psi taking off from a stop. I don't care that that cam timing will be slightly off. My only real worry is possible piston to valve clearance issues from milling the head down. I'm guessing I'll have to mill .020 to fix the .016 warp that is has. I know every engine is slightly different and there is not "set" maximum number that you can take off but there has to be an acceptable range. If after .015 the engines may have piston to valve clearance issues I will clay test to verify but I would rather not if the accepted .015 "limit" is for any other reason.

FYI I have already verified the cams spin freely in the journals with the rockers off and I know the head needs to be leak tested but that's just not possible to do with this much warp so I'll have to test it after milling it

 

[dustyboner]

you could have it surfaced, then measure it and use a thicker head gasket to make up the difference.

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[1990TSIAWDTALON]

Check the "limit" indicators on the head and see how much room is between the bottom and the head surface. There are 3 of them on a 4g63T head.

 

[97egl]

you could have it surfaced, then measure it and use a thicker head gasket to make up the difference.

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Thanks for the idea. If I could find a cheap composite gasket I would be all for this option but for a cheap beater I'd rather not spend 100 or so on a gasket plus have to pull the block to get it resurfaced and pay for that too. But if you know of a thicker composite option that would be great!

Check the "limit" indicators on the head and see how much room is between the bottom and the head surface. There are 3 of them on a 4g63T head.

They read .035 - .040 but I was not sure if that meant the head can be cut that far with no issues as long as the block hasn't been cut?

 

[DSMPT]

My only real worry is possible piston to valve clearance issues from milling the head down.

Generally you wouldn't need to be worried about that neither. You would probably still have the piston to valve clearance much more than you imagine. But this is something very hard to tell because like you said every engine is different, it really depends on your setup, what cams, springs, pistons, valve size, age of valve springs, engine speed, how much already been resurfaced etc. In case if you are still worried after claying to check the minimum clearance, you can add the clearance by using a slightly thicker head gasket or adjustable cam gears. (In this case it would affect the valve timing, so the car would run a bit differently)

 

[1990TSIAWDTALON]

To add, the head can be cut down to the limit markers before it is salvage.

 

[97egl]

Generally you wouldn't need to be worried about that neither. You would probably still have the piston to valve clearance much more than you imagine. But this is something very hard to tell because like you said every engine is different, it really depends on your setup, what cams, springs, pistons, valve size, age of valve springs, engine speed, how much already been resurfaced etc. In case if you are still worried after claying to check the minimum clearance, you can add the clearance by using a slightly thicker head gasket or adjustable cam gears. (In this case it would affect the valve timing, so the car would run a bit differently)

Engine is 100% stock so that's good news there. The car seems like it was poorly cared for so I seriously doubt that the block was ever resurfaced.

To add, the head can be cut down to the limit markers before it is salvage.

Thanks for clarifying