Milled head need shorter pushrods?

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oregonfj

oregonfj

Joined
May 5, 2007
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Eagle Point, OR
Ok you 2F guru's out there. I've milled .100 off the head and .010 off the block. Should I get .100 shorter pushrods to keep the valvetrain geometery in sync? Or is there enough leeway to not worry about it? The cam and lifters have been reground also.

Thanks,

Curtis
 
Once assembled, I would check where the rocker tip wipe across the valve stem. Noemally they are designed to wipe across the center region. From there it would be a judgement call. Too far to one side of center or the other will cause stem/guide wear, but keep in mind these are not high RPM engines. also make sure your rocker faces are smooth - a honing stone can address the arced surface if need be. Good luck.
 
That seems like a lot to mill off, but I would think that there would be enough adjustment in the valve rail to accomodate it.
Alan
 
Splangy said:
Where are you going to find shorter pushrods?
Click to expand...


My machinist uses a shop out of Bend, OR that will build them to any length you want. I'll try to get their number. I know Summit Racing stocks about any size also from when I built my SBC.
 
Last edited:
For what it's worth, I milled 0.080" from my head, used the stock push rods, and haven't had a problem in over 5 years. Milling the head was the best bang-for-the-buck performance improvement for my 40. I have to use 89 octane gas now.
 
76FJ40 said:
For what it's worth, I milled 0.080" from my head, used the stock push rods, and haven't had a problem in over 5 years. Milling the head was the best bang-for-the-buck performance improvement for my 40. I have to use 89 octane gas now.
Click to expand...

I was hoping to not run premium.... My CR calculations come out to 9:1.
 
The higher octane costs a buck or 2 a tank, well worth it for me.
 
FJsnoozer said:
you milled .1 and you are only estimating a 9:1 compression?

how low is factory compression and the CC size?
Click to expand...


Factory is 7.8:1. Combustion chambers came out to 89cc after a milling, pistons are .005 below the deck, ITM domed pistons are + 7cc, guesstimating .040 for the head gasket....
 
Increasing the compression ratio increases the "theoretical" thermal efficiency of the motor. Going from 8:1 to 9:1 compression ratio results in a approximate gain of 3.5% horsepower. You can increase this a little bit more if you install a cam that breathes better at higher RPMs, but you'd lose some low end torque. The nice thing about increasing the CR, is that you increase power at all RPMs.
 
I'm probably the least experienced in this area amongst you guys but I'm wondering, If the adjusters on the rockers don't run out of adjustment and you can adjust to the proper valve gap, wouldn't the position & angle where valve stem and the rocker tip meet be exactly as it was before the milling? I could see the angle where the adjuster meets the push rod changing ever so slightly but would it matter? Regrinding a cam has the same effect but in the opposite direction. Do we need longer pushrods for reground cam? I would think that if the adjusters can give the right gap, all should be good. But I'm just asking. I don't know. Also if shorter rods were needed, could the lifters be machined down instead?
 
Steamer said:
I'm probably the least experienced in this area amongst you guys but I'm wondering, If the adjusters on the rockers don't run out of adjustment and you can adjust to the proper valve gap, wouldn't the position & angle where valve stem and the rocker tip meet be exactly as it was before the milling? I could see the angle where the adjuster meets the push rod changing ever so slightly but would it matter? Regrinding a cam has the same effect but in the opposite direction. Do we need longer pushrods for reground cam? I would think that if the adjusters can give the right gap, all should be good. But I'm just asking. I don't know. Also if shorter rods were needed, could the lifters be machined down instead?
Click to expand...

You are milling .1, your pushrod tip height and rocker angle are that of your stock setup with .100 lift. So its really the sweep across the valve that you must be concerned with. Ive seen rocker adjustment so bad that it was halfway hanging off the valve stem. Now the fj40 overall cam lift is probably not high enough to really matter, but you should always check.

On the last v8 motor we did, My stock length pushrods were quite a bit short after the valve job. We put the head on and ordered the pushrods after the lifters never pumped up enough to get even close.

. I think he'll have to assemble and see. Even thou it will probably be fine. Its not like the cam has .600 lift
 
Short Pushrods.

You shaved the block you shaved the head, you didnt touch the top of the head where the rocker arm sits.
THEN what are the ajusable rocker arms for.
You could take 3mm off and still have ajustment.
Shaving the head doesnt ajust where the rockers hit the valves
:bang: :bang:
 
maybe no, but it could affect the position of the face of the rocker that rides on the valve tip. .110 is not much, and I believe that there may even still be clearance with some adjustment room as well, but without assembly, there is no way to know for sure, unless someone has already done this. And I don't see them posting their results here. I think its too close to call from my kitchen table.....
 
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