engine and drivetrain Cylinder head milling

[darrinos]

Just wondering...it's time to do a rebuild on the cylinder head on the little '02. Thinking of raising the compression a bit by milling the head...what is a safe or max amount that can be removed? Other than the issues that come with higher compression, namely fuel, are there any dangers of doing so? Thanks for the help....

 

Darrin

[KFunk]

You can lose some tension on the timing chain and also throw off the cam timing.  These can be fixed by getting an adjustable cam sprocket and a better tensioner mechanism (think you can get both from IE).

These wouldn't be really that necessary for a light skimming, but a light skimming probably wouldn't do much for compression.

[darrinos]

I was thinking that the chain tensioner would allow for this, but you bring up a good point. Thanks for your input.

[jimk]

Your machine shop SHOULD know the minimum head height that is allowed.  If they don't know, take it to another place.  Somebody here will jump in with the dim, I'm not enthused enough to look it up.  The head may already been cut.

 

Your valve timing will go late because the center to center dim between the cam and crank got reduced and when the chain lengthens from wear, the valve timing will go laterrrr.  You can correct with an adjustable cam timing sprocket.

[airborne85]

Try some liquid engine restore..

 

Check it out on Youtube......Unless there's an extreme mechanical problem....It may be a waste of time.  However, I now use this stuff at every oil change and even before I changed my oil, just as a try....I found a good and noticeable difference in the way that my car performed.....

 

Top end speed went up.  Throttle response was better. Response in every gear was super noticeable......I thought it was snake oil, but I was proven wrong..

 

Just my experience.  It comes in 4 cylinder and 8 cylinder sizes.  Yesterday I put the 8 cylinder size in just for boo-boos and giggles...I was not let down..

 

 

Just a thought

 

ira

[carlkkreienkamp]

Macartney's  Restoration Guide says that "BMW says that thickness of std. head is 129 mm +/_0.1 mm , not to be reduced by more than 0.5 mm". Macartney says "in my opinion max removal for raising c.r. is 1.5 mm.  He further says "on an E 12  head removing 0.5 mm will +c.r. by 0.435, 1 mm + c.r. by 0.87, and +1.5 mm will  + c.r. by 1.305".....

[TobyB]

I agree with Macartney's numbers.  But I'd say that 1mm is about what I'd be comfortable with on the street.

 

Measure your head first- I have only found 2 or 3 that were uncut... 

 

If you're adding cam lift or duration, keep in mind that cutting the head brings the valves closer to the

piston crowns, so, as they say, "check your work"

 

And after about .75mm, advancing the cam's worth the effort. 

And you then get the added tuning 'benefit' of being able to adjust the cam timing...

 

Finally, don't underestimate the effect that valve seated height has on compression....

 

t

[Conserv]

....Measure your head first- I have only found 2 or 3 that were uncut... 

+1

Everyone likes to believe their '02's odometer is on its first trip around, and their head's never been off, but that's just wishful thinking!

Regards,

Steve

[darrinos]

Thank you all for your input...on this particular car, I'd say nearly all of the 9's have shown on the odometer at least once...

[Preyupy]

At a 90mm bore with flat top pistons set at a 0 deck height , 1.5 mm thick head gasket with a bore of 90 mm.

A 121 head has a combustion chamber volume of 50.6cc at this would give you a 9.27:1 compression ratio, if you shave 0.010" from the head you will raise the compression to 9.5:1.

A E12 head has a combustion chamber volume of 62.2cc which would give you a CR of 80.9:1 with 0.010" off the head it would be 8.25:1

A E21 head has a combustion chamber volume of 58.9cc which would give you a CR of 8.27:1 with 0.010" off the head it would be 8.44:1

A stock piston is not usually right at the deck height but this gives you a good idea of what you can get by just cutting the head. I don't recommend shaving the head just to increase the compression ratio, as you can see by the time you have taken enough off the head to really make a difference you have taken so much off you will have trouble with the cam chain tensioner (you can always use an adjustable cam gear to get the timing correct but that does not compensate for the decrease in distance between the cam and crank centerline change)