Bike is a â63 650ss.
The oil feed union that screws into the top of the cylinder head has an oil-feed bore of approx. 3/32â.
I have measured the bore where this screws into the head at approx. 3/16â.
I always thought that the oil-feed bore in the cylinder head was slightly smaller than the bore of the union. I donât have another head to compare it with, so, am I correct?
Iâm wondering if some previous owner has drilled this out in an attempt to increase oil flow.
I hope you can understand my dribble.
Are you measuring the tapp…
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The tap size is 5/16. I'm…
The tap size is 5/16. I'm measuring the oil feed bore at the bottom that the tap size feeds into. On mine it's 3/16. Is this standard/correct? Or has it been drilled out to this size?
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The tap drill size for 5/1…
The tap drill size for 5/16 BSF is 6.8 mm. Less than 1mm bigger than what you are measuring. That is a small change.
It would not make sense to enlarge these holes since the main restriction is the very small hole in the rocker spindle as well as the rocker to spindle clearance. Maybe they didn't realise this.
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Are you measuring the tapping size for 5/16 BSF where the thread ends?