Generation III Internal Engine - Head milling question...




View Full Version : Head milling question...


alamantia
04-29-2010, 08:50 AM
I have a set of 241 heads that I have read have 66.67cc combustion chambers. I also read that for every 1cc of volume you want to reduce from the combustion chamber you would have to mill 0.007" from the deck of the head.

Well lets say that I want the combustion chamber to be 62mm on my 241 heads. I would have to mill 0.040" from the deck. Would this be too much? Would I run into any issues like piston clearance or intake ports not matching up? Has anyone here had their heads milled more than the typical 0.010"?


Jon@Texas-Speed
04-29-2010, 11:46 AM
You'd have to mill about .035" or so off the heads. Your intake and everything will still bolt up just fine. You could run into PTV problems depending on what cam you are running. Best bet is to check to make sure you have enough. We have cut heads WAY more than that and been fine on intake fitment!

Jon

alamantia
04-30-2010, 07:47 AM
What is the rule of thumb for how much shorter of a pushrod you need per 0.010" of milling. In other words, if I have the stock pushrods (i think they are what 7.400"?) and I mill 0.040 off the head. I assume I have to buy shorther pushrods. Would the length be shorther by the same amount I mill.


In short, If the car currently has 7.400" pushrods and I mill off 0.040" the head to I have to locate 7.360" pushrods?


djfury05
05-02-2010, 09:29 PM
bump for this guy

chrs1313
05-03-2010, 07:29 AM
yup you are right you will need shorter pushrods...use a pushrod checker at zero lash and then add your preload to that number...you can probably get away with .050 shorter pushrods since these will save you more money being a standard size...otherwise trend or manton can make a pushrod in any length...even down to .001

alamantia
05-04-2010, 10:15 AM
I guess i could just turn down the stock pushrods in a lathe, probably cheaper than buying new ones.

Irocss85
05-04-2010, 10:52 AM
I guess i could just turn down the stock pushrods in a lathe, probably cheaper than buying new ones.



I would never try it. the pushrods are hardened. I think the heat generated from that could damage the heat treatment, even if you could get the end to have the proper shape. which im not sure if thats a stamping procedure of if there just turned down? whatever . Id just buy new ones and have some piece of mind.

btw, I milled my 241's .033" and no issues with intake fitment/exh fitment. but did have to flycut the pistons. I wrote a thread about doin it its not hard and the gains in compression (read: more efficient engine, HP, torque, overal driveability) are well worth the extra time/money invested. plus it opens up your choices of whatever cam you want to an extent. I went with a custom grind 235/242 .650/.612 lift. its nice P)

chrs1313
05-05-2010, 02:52 PM
agreed pushrods are a hair over 100 why risk it...plus you can sell he old ones and it might cost you around $50 or less when you are done