The Stovebolt Site Forums The Shop Area The HiPo Shop milling the head

How much can I shave off? The old Mcgurk-hotrod article says I have to move the valve in however much I take of the head.
Oh yeah I guess I should tell you what engine it is!! 1959-62 261

Why not just flycut the piston for valve clearance? I'm sure there's a logical reason why it's not done on a stovebolt, but it seems like it would work the same way we do it on a V8. Somebody enlighten me!
Jerry

First make sure the casting number is 3836848 which has the smallest combustion chamber and second check what is possible by zero decking. I can remove .060” from the top of the 261 blocks I have to make the pistons flush gaining compression without polluting valve train geometry. Bear in mind that much of the improvement of milling the head to make the combustion chamber smaller is taken back by having to move the intake valve back by the same amount (1.875” diameter). When it comes to cutting seats on these old heads I like to think take as little as possible to preserve service life.

If you use the 848 head on a 261, remember to drill the extra holes to allow coolant flow past the siamesed cylinders. Use a 261 head gasket for a drilling template, and angle the holes slightly to intersect the coolant passages properly.
Jerry

In Canada those heads will have the holes already if they left the Oshawa factory in a Pontiac car but if not they can be drilled as per Jerry’s instructions. Although generally considered a 235 head the 261 torque pattern should be used (which is different than a 235) as the block determines the torque pattern and not the head itself.

Curt, after decking the block do you run into valve-piston interference? Seems to me that it moves the valve closer to the piston either way.
Is the 235 head really that much better, I just paid to mag the 261? Thanks for the torque pattern info, I thought I had read that somewhere.

What about the push rod length, it should be to long if milling the block or the head.

Joe

Slight differences in pushrod length can be adjusted out with the rocker arm adjusting screws. If it's too far off for that approach, most of the hot rod camshaft grinders have semi-finished pushrod sets that can be cut to length. I just built a set for a Plymouth 383 engine because I installed a set of roller rockers and the pushrods had to be custom-made.
Jerry

The McGurk article explains that you would have to mill 1/8” off the 261 truck head to match what taking 1/32” off the 848 one would do for compression but personally I would never go there and as stated that might even require custom pushrods. The presence of interference is a possibility that is dependent on several variables like camshaft lift, deck or head milling, head gasket thickness, and previous valve reseating. I will nick the pistons for clearance if necessary in my case but one should always pay attention to “cause and effect” when making modifications.

I just looked at an 848 head I've got stashed away, and I can see why notching for valve clearance is not an option- - - - - -A large part of the intake valve overhangs the block, not the piston crown! It would be necesary to flycut a big area of the top of the block beside the piston, and blend that area over into the cylinder above the ring travel with a die grinder to obtain any meaningful valve relief. That's the same problem we encountered many years ago on the flathead Ford- - - -a relieved block made for better breathing, but it lowered the compression ratio. There would probably be a net gain in compression pressure with a radically milled head and a relieved block, but it would be pretty labor-intensive and it would involve some pretty sophisticated volume-checking procedures to equalize the size of the dimples cut into the block.
Jerry

I'm starting to think that leaving the head alone, except for some port work, might be the sensible option!