Cylinder head bolt threads

[WEM]

1974 Commando MK II. Head is RH10. I’m getting ready to remove the three 3/8” studs from the bottom of the head prior to shipping the head for repairs to the exhaust port threads. The three studs correspond to head bolts 2, 7 and 8 I think. I’m wondering what threads these studs have so I can use correctly threaded nuts when double nutting them for removal. Thanks.

 

[L.A.B.]

You mean the outer ends of the studs which were thought to be (60 degree) 3/8" x 26 Cycle thread although they may in fact be (55 degree) Whit form as the rear nut is Whit form according to AN therefore the studs should be too.

Andover Norton - CYLINDER BASE/ HEAD NUT 3/8

CYLINDER BASE/ HEAD NUT 3/8

andover-norton.co.uk

 

[dobba99]

You mean the outer ends of the studs which were thought to be (60 degree) 3/8" x 26 Cycle thread although they may in fact be (55 degree) Whit form as the rear nut is Whit form according to AN therefore the studs should be too.

Andover Norton - CYLINDER BASE/ HEAD NUT 3/8

CYLINDER BASE/ HEAD NUT 3/8

andover-norton.co.uk

That would make the thread size to be 3/8 BSB (British Standard Brass) which is 26 T.P.I. by 55 degree thread angle

 

[L.A.B.]

Yes it should be the same as 3/8" BSB.

 

[WEM]

Thanks for the quick replies. Much appreciated.

I didn’t think to check the AN website.

 

[Tornado]

But you should have the nuts that came off those studs no? Just use them for the double nut removals.

 

[WEM]

I had the same thought but the three studs in question correspond to Bolts 2, 7 and 8 on the head bolt tightening diagram. Studs 7 and 8 are the ones that the unusual long sleeve nuts go on so those nuts are no good for double nut method and Stud 2 is the one in the centre of the back of the head under the fins. The nut for that bolt is too long to allow double nut method. I’m thinking about cutting a spare nut I have for Stud 2 in half, creating two separate nuts and using those to double nut.