Comp Cams Extreme 4x4, Mopar valve springs and .040" off, will it work?

I picked up a 7120 head yesterday form the JY for $40 and took it into my machinist to have him work on it. Can't find any 0630 heads anywhere for cheap.

My machinist suggested I take off .040" off the head and run a cam with matching springs. Bumping the compression.
Comp camps extreme 4x4 cam, 68-232-4, look like the winning cam. They suggest using their own valve springs, CCA926-12 but these have a heavy spring rate and the spring retainers wont work either.
The only winning valve springs are the Mopar P4529214 but those bastards are $15 a piece!!!

My question is: Will I have valve issues if I mill off .040" and throw in the cam plus valve springs on a stock bottom end block? My machinist is going to work on the valve stem seals and such to match it up.

I ended up milling off .030", we'll see how it runs this weekend.

the comp cams springs are for 4.2 retainers and locks.

my machinist ended up using GM performance beehive springs for my comp 231 cam, but had to mill down the head for them to fit. with a short rod stroker, i went with .020 off the top

Your going to have to check your preload with that much taken off the head.

Your pushrods will now be effectively .030" longer then they were. You need to check for coil bind at full lift.

jeeperjohn said:

Your pushrods will now be effectively .030" longer then they were. You need to check for coil bind at full lift.

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That is not how a hydraulic lifter works. It won't cause more lift on the spring just because preload has changed. What it will do, if preload is more than spec (.030"-.060"), is hold the valves open. The piston would bottom out in the lifter and effectively make it a solid lifter.

However coil bind should be checked for regardless, either by using a solid lifter or testing springs.

Talyn said:

That is not how a hydraulic lifter works. It won't cause more lift on the spring just because preload has changed. What it will do, if preload is more than spec (.030"-.060"), is hold the valves open. The piston would bottom out in the lifter and effectively make it a solid lifter.

However coil bind should be checked for regardless, either by using a solid lifter or testing springs.

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Right, I wasn't thinking about the lifters being hydraulic. Another issue could be poor oiling of the top end due to the lost stroke of the pistons in the lifters.

jeeperjohn said:

Another issue could be poor oiling of the top end due to the lost stroke of the pistons in the lifters.

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Good point. However, how much do they actually need to move?

Talyn said:

Good point. However, how much do they actually need to move?

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Not sure, it would be interesting to find out.

jeeperjohn said:

Right, I wasn't thinking about the lifters being hydraulic. Another issue could be poor oiling of the top end due to the lost stroke of the pistons in the lifters.

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the lifter piston is not responsible for oiling on the top end, it is provided by the oil pump, which is why you can prime your oil system with just the oil pump