The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Truckedup on 19.04. 2021 01:11

Title: and then the headbolt strips
Post by: Truckedup on 19.04. 2021 01:11
 so I am installing the alloy head, threads chased clean ,new UK made headbolts and an accurate torque wrench....Second go around a 20 ft lbs when the bolt goes soft....Threads torn off, expensive scrap..UNF 3/8-24 Heli coils, grade 8 bolts,replace all 9 bolts, back in business...
  Actually all the various bolt and studs that have same thread as US fasteners have been replaced..
Title: Re: and then the headbolt strips
Post by: orabanda on 19.04. 2021 03:28
Oh dear!
The standard thread in A10 barrels is BSF (20 tpi).
Were the new UK made headbolts supplied as BSF or UNF?
Richard

Title: Re: and then the headbolt strips
Post by: Black Sheep on 19.04. 2021 06:56
Just to add, no threads on A series BSAs were UNF.
Title: Re: and then the headbolt strips
Post by: Truckedup on 19.04. 2021 16:14
The headbolts are British thread...It gets worse, there's a long internal crack in the stripped bolt hole.... the cylinder is scrap.....looking for a .020 thick flange barrel....
Title: Re: and then the headbolt strips
Post by: muskrat on 19.04. 2021 21:18
the cylinder is scrap.....
G'day Truckie.
A good machinist would be able to make an insert like a timesert (bugga they don't come in BSF). Basically a sleeve threaded on the OD and ID.
Which hole is the offending one?
Cheers
Title: Re: and then the headbolt strips
Post by: Truckedup on 19.04. 2021 23:41
It's a center hole .It's cracked vertically, I believe the crack will continue to spread even with the insert...Timeserts are readily available in UNF, but a set is near $100...
Title: Re: and then the headbolt strips
Post by: muskrat on 20.04. 2021 10:39
G'day Truckie.
There's plenty of meat around the center holes, the outer holes might be a worry.
$100 is better than a few hundred but it's still not BSF. A good machinist should be able to make one and fit in 2 hours.
I doubt the crack would continue once the stress is relived.
Cheers
Title: Re: and then the headbolt strips
Post by: Truckedup on 20.04. 2021 13:09
  I bought a set of Time Serts, both normal wall thickness and extra wall thickness..All the head bolts will be 3/8-24 UNF grade 8 ....I pulled the cylinders and have a junk iron head as a guide ....Do it on the drill press..