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CB750 sohc K5 head skimming?
martin_uk:
Helping a friend with his bike and depressions have formed where the head gasket combustion rings contact the head.
I have not come across this on my CB750 bike rebuilds and would appreciate views and experience.
Is it OK to lightly skim head and what is limit?
Has anyone experienced this before and likely cause?
The combustion rings on new gasket will help seal the extra gap caused by grooves, but what is the limit?
Views and thoughts appreciated.
Bryanj:
To me that has been overtightened, personaly i would ask Mark Paris(hondaman) on the us forum as to maximum skim
martin_uk:
--- Quote from: Bryanj on October 13, 2026, 03:28:37 PM ---To me that has been overtightened, personaly i would ask Mark Paris(hondaman) on the us forum as to maximum skim
--- End quote ---
Thanks Bryan
McCabe-Thiele (Ted):
There were some marks on my 500 cylinder head, difficult to measure the depth of the imperfections, one was where the main seal ring is for the cylinder head.
Local machinists said they would take the minimum required to remove the marks. When I picked up the head the finish was like a mirror.
I asked how much material had been skimmed, less than 5 thou of an inch!
The firm are known locally primarily as diesel fitters & engineers.
Service Garage Borrowash.
They have a website now.
martin_uk:
Thanks to Bryan's suggestion, asked question on US site.
General consensus is that original head is 72.2mm (also 72.18 mentioned) thick and light skim would not be an issue.
Cylinder original thickness 84.78mm
However, careful measurements of locating dowels (knock pins) and seals needed, with reductions as necessary.
If after skim the dowels are then longer than total recess (cylinder + head), plus compressed head gasket it would stop head fully seating.
Also potential cam timing issues if more head face or cylinder top removed.
Please double check from other sources before relying on this.
See post here https://forums.sohc4.net/index.php/topic,207323.0/topicseen.html
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