172 clyinder head flatness tolerance

[ben_g40]

Hi guys.
Just in the process of refeshing my engine for my 172. The head is off for a bit of work on the inlets/exhaust.

Ive just measured the flatness of the head and its 0.05mm out .
Does anyone know what the tolerance is before it needs skimming?

Cheers

 

[ALD]

How did you measure the tolerance?

 

[Mr R.]

By eye.

 

[ben_g40]

How did you measure the tolerance?

I measured the flatness with a CMM machine. it apears to be a bit bannana shaped with a 0.02mm rise in the middle of the head.
also measure the surface finish at 0.30 Ra. is there a spec for that?

 

[Matt@codered]

(Carrying on from phase1sr post)
....and a straight edge, plus some feeler guages.
Normally.

 

[sprintcup]

In fairness he's asking the tolerance for run out on the head, he obviously knows how to do it either with a straight edge and feelers or a CMM machine:S

Regards Russ.....

 

[Matt@codered]

Thanks Russ, it was an answer for ALD. (Post number 2).

 

[Matt@codered]

This might help........

 

[ALD]

Thanks Russ, it was an answer for ALD. (Post number 2).

I just wanted to make sure he was doing the right way

 

[Fred@BTM]

CMM to measure a head, where you work, NASA?

that sounds ok, don't forget when it's torqued down in the right order it'll deform to an extent anyway

 

[ben_g40]

This might help........

View attachment 108007

thanks mate, just what I was looking for.

 

[ben_g40]

CMM to measure a head, where you work, NASA?

that sounds ok, don't forget when it's torqued down in the right order it'll deform to an extent anyway

Yep,
With the tightening order should pretty much square back up.

Thanks

 

[andy-reid]

Hi guys.
Just in the process of refeshing my engine for my 172. The head is off for a bit of work on the inlets/exhaust.

Ive just measured the flatness of the head and its 0.05mm out .
Does anyone know what the tolerance is before it needs skimming?

Cheers

acording to renault litrature the elimit is .05mm for asembly!
but i would skim it after the valve work was done incase you scratch the surface again