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Tolerance when getting head skimmed - 1980 GS550ET (CV carb)

ukjules

ukjules

Forum Sage
I may be asking a question that is not even a factor but is there a tolerance
when skimming the head ?

I cant find such a fact in the service manaul and wanted to be prepared when
I take to the engineering works.

There must be a limit but what is it ?

Thoughts be appreciated,

Jules. (My rebuild is coming on - Cylinder goes on today hopefully)
 
You raise a very good question, one I had not given much thought to. I can't recall ever seeing a head drawing with flatness, perpendicularity and surface roughness specified.
This is going to sound weird but.................... If you have selected the right shop, they already know. Or if a shop I brought it to asked little old me to specify the flatness and roughness I would be thinking about bringing it elsewhere. Limits are different. How much is too much , guessing but .040" or thereabouts.

Reminds me of a wonderful story about a Japanese engineering company visiting Ireland with a view to setting up a plant. They politely inquired what tolerances local machinists typically worked to. At first the head of the local Chamber of Commerce had to have the concept of tolerance explained to him. The Japanese gentlemen were horrified as their host was clearly insulted. " We don't do any of that plus or minus stuff here. When you ask us to do something it's spot on or nothing."
 
Last edited:
Just read the updates.
Love the japanese story !!!!

I did look at the service manual but overlooked that page. You are right there it is in full view
as you state.

Trust me I am no expert but this is the stats from my machine shop when I took my second hand heads in
to be checked (without the spec you informed of). (They are a very very very good machine shop - and this reflects in their price .... !)

Both my heads had a distortion of 0.008 (Madly I didnt find out if this was " or mm) - lets assume it is " ! (will update)
These they inform me need a skimming - and that is to be done.

My Cylinder - had a distortion of 0.001 or 2 (assume "). This they said was ok and could be taken out by the gasket no problems.
 
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