Milling head

[PeaveyBassist]

My head has 185,000 miles on it and I am getting it machined. How much can you safely take off without getting valve -> piston contact. I have the timing issue covered but I wanna make sure it doesnt get machined too much. Isn't there a line on the d/s front of it to where it can be machined down to? If not, how much material can be taken off?

Will

[Sean]

It should be in the Bentley. It's not a matter of shaving before piston and valve contact - cause if you shave that much, the head will warp instantly when it gets hot. There's a certain tolerance, listed in the bentley.

Which I just so happen to have next to me.

A stock head is: 125.1mm (+/- 0.1mm) (4.925in +/- .004in)
After machining, the minimum height is: 124.7mm (4.909in)

Going beyond that can and may cause the head to warp faster than if it's not. So, I'd reccomend just shaving off what's needed to make it flat, and then some.

Just tell the machinest that. ;)

-Sean

[Super Eurobeat]

on my heads ive taken off up to .030 of an inch, you can take off more though.
.020 seems moderate of a resurfacing. You will notice a big difference of power around .025 though.

[Sean]

on my heads ive taken off up to .030 of an inch, you can take off more though.
.020 seems moderate of a resurfacing. You will notice a big difference of power around .025 though.

Good or bad - since timing will be off?

[PeaveyBassist]

I can get timing taken care of no problem. A little changing of the stock cam gear can give me a set advance to compensate.

Will

[Super Eurobeat]

you dont even need to worry about your timing being retarded when decking the head cause its so small its not a big deal...the tensioner takes up the slack in the timing belt anyways....
Dont waste your money on the adjustable cam sprocket, like 279 bucks.... ouch

I know all the specs from my legendary stroker so i know what is too extreme or too much machining.
Make sure to put at least a 284 cam in there, or 272 if your State is NAZI like California here! You will gain a lot of torque with the cam, intake side port work, especially the upper entry corners, and where the valve guide is.
You can get these 325i heads to flow 16 percent better with port work...exhaust side is a piece of cake to try and port match to the exhaust manifold.
I bored out the throttle body like 5 thousands of an inch but because it was free :P

[EtaSport]

Going off by one tooth on the cam gear will change the timing by 9 degrees, when milling the head down you only need about 2.5-3.5 degrees difference. Cam timing is important to the engine's performance, so yes it will have an effect on how it runs if it's too great. If you open the intake valve too soon you won't be able to get full mix into the chamber for the power stroke decreasing performance, since the valve will also close too soon.

[PeaveyBassist]

The cam will be advanced 4 degrees after the head has been milled. Etasport, can you mill off 0.025" and be safe? I'm sure you have done a lot of headwork before.

Will

[EtaSport]

I see no issues with a .025" cut. And 4 degree should be about right from what I've heard. I've not actually done it, but I know sean ran a slightly greater cut with his seta head, and I have also talked with a guy on e30 tech who ran .020" *EDIT* it was .025 cut and something like 2.5 degrees altered cam timing (which supposedly sets it back to stock). He stated it bumped compression from like 9.0 to 9.2:1 and gave him some gains after he dyno tuned it.

I found the thread, its here:

http://www.e30tech.com/forum/viewtopic.php?t=24107&highlight=

bottom of post

[Super Eurobeat]

My stroker i did for my friend was 9.4:1 compression, i think we decked it like 35 thousandths.
The head becomes physically stronger when decking it.
When you advance your timing, your lower RPM power increases and you lose some up top, and vice versa with retarding...more top end.
Cause you are changing specifically when the valves are opening in comparison with the crankshaft.
Progressively....if you could find a system that advances or retards the timing as RPM increases (i have NO idea how spark is controlled in these cars), then you can gain some power additionally.
You can even deck them 45 thousandths, though, thats a lot.
I would do like .025 myself for a performancy resurface.
Then if you need to do it again in the future, just machine off like 2 thousandths.
When doing a 3 angle valve job, make the first top cut at 34 degrees, thats the best for a 3 angle job, you can find out the rest for yourself....
When you put in a aftermarket cam, or a reground cam from www.racetep.com or www.bmw2002.com, you will need oversized eccentrics.

I have done about a dozen strokers so far.....
The next one we are shooting for will be 250 foot pounds of torque. It all depends on how many sponsors we can get to help us out...normal people, not business' though.

[Sean]

I hope to do some headwork in the future.

EtaSport - I actually just had the head flattened (not even sure how much he took off - probably no more than 1-2 thousandths)

I did have my block decked .015", which actually could be the cause of my low compression readings due to the altered timing.

My car runs good though, and the grunt down low is pretty damn sweet. :) Can't wait to do some headwork though!

[PeaveyBassist]

So 30 thousandths would be a good compression bump? I might just tell them to mill it flat right now (whatever is needed) then build a head later on.

Will

[Super Eurobeat]

Do 25 right now
if you are running higher compression after market pistons, disregard what i said about milling entirely
the setup i was talking about is for super eta pistons, i am too lazy to read the rest of the thread though.
Just mill off .022 for now.

[PeaveyBassist]

I think they are just going to mill whatever is needed to make it flat and then later on I am going to build a head. Thanks for the info guys!

Will