Just a query. I was making a tool for finding exact TDC on my engine. While doing this I had to try a drillbit in studholes in head . Does anybody know why the centre hole on o/side of head is slightly smaller than the other 8. Thought this was an oddball head, but have three others and they are all the same.
Has anyone else noticed this.
Ian.
Cylinder head stud holes
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wanderinstar
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to be honest, I've never found the urge to measure the diameter of the head stud holes!Has anyone else noticed this.
There probably was a reason - I've no idea, but if I were to guess either it was to help locate the head (one stud hole being a tight fit to the stud to help locate it - more than one tight fit stud would lead to tolerance problems) or because there are ports either side of the stud hole and a smaller hole helped increase the wall thickness.
The other possibility could be that the hole was used to locate the head on a machining fixture (i.e. a special size for manufacturing purposes - pretty unlikely)
Or finally - because it was a mistake on an early drawing which was subsequently copied across to all the other head drawings
(engineering legends of the sacred cow - a drawing which has dimensions which nobody understands anymore but still get copied to hundreds of other similar parts just because thats how they were)
