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Discussion Starter · #1 ·
Hello, hello.

I'm beginning to prepare, or more accurately, research my preperation for
a new 'head' for my 1969 Unit Bonneville 650.
Likely that by the time I get my act together it will be a rebuild, from
'sludgy' up...

I'm after some expert/experienced advice on what type/year 9-bolt,
twin carb head to use (find) to get best results.

any, and all information appreciated...
Thanks in advance,
Paul...
 

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I'd go for a '69 or '70 head.They will have 1/4" UNC threads to hold the rocker boxes.

'68 could be your next best,but you may have trouble with the fit of the pushrod tubes,and the threads are 1/4" X 26 BSC
 

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like Mr Pete said you will have issues with the push rod tubes but it can be corrected, you can mill cut the pocket deeper with a 1-3/16" bit about 100 thousands and it will accept the 69 push rod tubes and "O" rings.
There are some other differences in the intake area, the intake manifolds are smaller in diameter and so are the intake tunnels, the good news is it probably makes more torque from this.
 
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