HEAD MILLING QUESTION

juggernaught

Thanks for all the input so far, hoping to get this 360 buttoned up this week. I was looking at another post about intake leak problems,when it dawned on me that maybe I should try to find out how much my heads had been milled and if this will cause me any problems down the road. These heads are 1974 dog-leg style that have been rebuilt once before.My machine shop said he took off 0.010 and I believe that as much as 0.024 may have been taken off previously. If 0.034 has indeed been milled off my heads, how much of a problem am I going to see mounting and sealing an aluminum intake? How can I measure this? Do I need to have the intake milled? Can I use different gaskets? I have not yet purchased the intake, but will probably be a PERFORMER. As soon as I can get this resolved, I can bolt my heads back on. Thanks in advance.

kris

Dont know about the aluminum intake, but with mine using the stock intake we took .020" off the deck and "just kissed" (his words) the heads. Im guessing less than .010". Using the fel-pro pan and not milling the intake, it was really difficult to get all the bolts in. If there is a clearance problem you may be able to egg the holes a little, but it would be best to mill it if necessary. k.

juggernaught

Thanks chris.......When you say .020 off the "DECK" you are talking about the top of the block. Correct? There does seem to be about .020 from the top of the pistons to the top of the block. Then there is the gasket thickness. With my valves installed, the edge of my intake valve sits about .020 above the newly surfaced head. How does this compare with a head that has not been surfaced? Can anybody tell me? The COMP CAM that I am using is a 260H, which should be close to stock on duration(260), and has a valve lift of .447. I do not know what a stock cam's valve lift is, although it should be close. This is all a pretty stock set up with the exception of 9.0/1 pistons and the fact that the heads have been shaved. Is ther any one who can give me an idea of how many thousandths these heads can be milled before I need to worry about interference? What would be the best way to go about checking that clearance if necessary?

fifesjeep

juggernaught wrote
Thanks chris.......When you say .020 off the "DECK" you are talking about the top of the block. Correct?

DECK corresponds with the top of the block, ie: Zero DECK.... Pistons sits @ .000" when measure from where the heads meet the block, DECK Height... the distance from the center of the journals to the surface where the heads bolt to the block...

juggernaught wrote
With my valves installed, the edge of my intake valve sits about .020 above the newly surfaced head. How does this compare with a head that has not been surfaced? Can anybody tell me?

About stock distance... that's almost what my 502 heads measure.

juggernaught wrote
This is all a pretty stock set up with the exception of 9.0/1 pistons and the fact that the heads have been shaved.

What casting numbes are those heads? You can have the heads CC'd and then you'll be able to better judge/determine roughly how much has been milled... It's not the most scientific or proper way but it'll put you in the ball park.

juggernaught wrote
Is ther any one who can give me an idea of how many thousandths these heads can be milled before I need to worry about interference? What would be the best way to go about checking that clearance if necessary?

Take some clay/puddy etc put it on your piston bolt the head down without the gasket, install the pushrods, rockers etc and slowly rotate the motor by hand, do two full turns break it back down, what i do is carefully cut the puddy/clay in half with a new razor and i carefully lift/remove one side and I use my dial calipers to measure the compressed thickness... (It's good to try it on a few cylinders)... Once you get that number add the thickness of the headgasket and that will give you a relatively close ball-park figure.

juggernaught

WOW! I ask and I got a very specific answer. Thanks. I honestly thought that there would be alot simpler way, but there is nothing like mock-ups to give you an exact measurement. Do you think I will be any where near my piston with this configuration?

fifesjeep

juggernaught wrote
Do you think I will be any where near my piston with this configuration?

I honestly don't think so... but then again, you have to take into consideration that I am only going by what you say etc. Your piston design could/will also determine how close the valves are to the piston...
Are you able to post pics?

Mudrat

juggernaught wrote
WOW! I ask and I got a very specific answer. Thanks. I honestly thought that there would be alot simpler way, but there is nothing like mock-ups to give you an exact measurement.

That's what happens when you 'talk' to a machinist :lo1l: :t: You'll also need to look at the piston top and see if (or where) the eye brow reliefs are cut. They're put on the pistons to clearance the valves :mrgreen: So make sure they are not in backwards :shock: :idea:

juggernaught

Piston is installed. Cam is installed. Hope to get the timing gear, cover, oil pump, balancer etc. installed this weekend so I can rotate the motor and check preload on the lifters. From what I gather I should have enough clearance. Sorry, not able to post pictures at this time.

AMX69PHATTY

Need to use a pair of Solid Lifters when claying a piston, or full cam lift will not br realized. A pair of old hydraulic lifters can be taken apart and modified to act as a solid lifter. Best to use adjustable length checking pushrods to determine required pushrod length to get correct rocker geometry. Use of low tension "Checking Valves Springs" also makes it easier to clay a piston. Understanding is head doesn't need to be fully torqued down, just a few bolts put in snug around the cylinder being clayed. Textbook is equal amount machined of each head side of the intake to what was machined from the heads and/or block. Then on the front and rear horizontal intake surfaces, machine off 1.4 times the heads and/or heads amount, to maintain the proper end gaps between intake and block. All that's needed to be installed on the front of the block to clay a piston is timing chain set and use a crank turning nut. Understanding is on AMC heads that have not been milled, on the intake manifold side, the area on the outside bottom of the intake runners is "as-cast". If heads get milled, that area becomes a machined surface. Agree, CC'ing the heads is a good way to get an idea of how much they've been milled, and is excellent information for calculating compression ratio.

Mcktiger74cj5

i would diffenitley claly your motor.2yrs ago may had it all put together went to fire her up and that was it. the piston valve relief werent right broke or bent every push rod some broke in 2 spots. but all is good now.