M44 head skim cam timings and compression ratio's

[joey]

I know!


what a question,

we have a spare cylinder head that has been skimmed, the bentley manual apparently gives a max of .3 mm
or 11.8 thous, that does not seem like much at all! anyways the engineer who did the head skim said he has taken off .4 which is 15.7 thous..in my limited experience under 20 thou is acceptable in most engines..

so my question is are we ok with .4 ? what will our compression ratio end up at and will it affect the timing?..

I understand the M44 is a high compression ratio already at 10:1...if it needs adjusting I have a guy who can do it but need to be sure i am not storing up problems for further down the line...

thanks all


joe

 

[joey]

answered my own question I think but would help if I get a "yes you right joe" from someone in the know...rich?

just looked on real OEM and found part number 11121433951 which is a thicker head gasket (+.03) this would bring the overall height to within .01 of the original intended and therefore leave timings and cam adjustments much the same..?

thanks

Joe

 

[joey]

Sorry Gaz..shoud have put this here originally..

 

[zedonist]

Hi Joe,

Sorry, about delay, last few days have been hectic would be putting it mild, I have tried to keep up, any way, timing and compression are not related, timing is related to cam and crank position, valve opening and closing. Compression is about the amount of squeeze put on the mixture, a greater degree of mixture and squeeze which means the mixture burns at a hotter temp, gives a bigger bang.

The issue you have with the head being skimmed is the valves crashing with the pistons, because you have removed the tolerance gap, now on flat top pistons this is quite critical, on pocketed pistons not so much, but head space. Still needs to be calculated.

I think you have answered your own question, which is fit the thicker head gasket which puts you back or close to standard limits.

Hope it helps

 

[joey]

will do that rich,

unfortunately the thicker gasket is only available from BMW....

£108..where as the aftermarket standard thickness is £36 at ECP...it is however not worth the risk as I would imagine at very least the cylinder head will need .3 off.

its still not a lot..but if i get .3 off of my head and get the thicker gasket its all as intended by BMW.