The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Peter Gee on 19.09. 2018 21:05

Title: A7SS Short Head Bolt queries!
Post by: Peter Gee on 19.09. 2018 21:05
If you Google a bit, you get  many differing lengths for the short alloy head bolts  1" 5/8ths, 13/16"ths(!), 2" and so on. Draganfly even shows a stud in the 67-1114 pic!

Then you get the "waisted" type bolts "suitable for alloy heads" ( my Triumphs have no such bolts..just straight shanks, and do not seem to suffer. Is a "waited bolt" a special chearence in the alloy part?

My estimation is that 1 and 3/4" x 3/8"BSF + washer would be fine...I mention this because I have to have these bolts made up.

Pointers would be of much use. My A7SS is reviving after 40 years as a pile of junk, and is entered in an International Show 10 days from now. Hope to hear.
Title: Re: A7SS Short Head Bolt queries!
Post by: trevinoz on 19.09. 2018 22:29
Peter, apparently waisted bolts were introduced to stop bolt breakages.
Note also that head bolts have a reduced hexagon.
Use high tensile washers under the head and have the holes spot faced if necessary.
Title: Re: A7SS Short Head Bolt queries!
Post by: Greybeard on 19.09. 2018 22:42
Are you sure they are BSF?
Title: Re: A7SS Short Head Bolt queries!
Post by: trevinoz on 19.09. 2018 23:04
They are definitely BSF
Title: Re: A7SS Short Head Bolt queries!
Post by: berger on 20.09. 2018 00:51
trevinoz is correct about the waisted bolt reducing the chance of breakages, the railways first used them and found they could take more load upon tightening and did not tend to loosen under extremes of vibration. well that's the info I took from a south African engineer who did his apprentice time in Rhodesia . sad to say another deceased good man too soon.
Title: Re: A7SS Short Head Bolt queries!
Post by: BSA_54A10 on 20.09. 2018 10:32
Waisted bolts have a rolled thread.
This is a type of forging so does not create a crack initation point as you get from a cut thread
Title: Re: A7SS Short Head Bolt queries!
Post by: JulianS on 20.09. 2018 10:36
Rowland Pike, when at BSA, explained the problems with alloy head bolts breaking in his memoir.

Worth reading this chapter;

http://beezagent.blogspot.com/2009/01/roland-pike-autobiography-chapter-22.html

My spare short bolts are 1 11/16 inch under head with 3/8 x 20 tpi BSF thread.

They are high tensile with rolled threads. Wrong material will allow the bolt to stretch and "neck" and will not hold torque.
Title: Re: A7SS Short Head Bolt queries!
Post by: Greybeard on 20.09. 2018 13:32
http://beezagent.blogspot.com/2009/01/roland-pike-autobiography-chapter-22.html
I read that, (although the text is very small on my monitor). I found it fascinating. Thanks.