Author Topic: and then the headbolt strips  (Read 570 times)

Offline Truckedup

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and then the headbolt strips
« 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..
1961 Super Rocket, 89 Honda 650NT

Online orabanda

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Re: and then the headbolt strips
« Reply #1 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


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Re: and then the headbolt strips
« Reply #2 on: 19.04. 2021 06:56 »
Just to add, no threads on A series BSAs were UNF.
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Offline Truckedup

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Re: and then the headbolt strips
« Reply #3 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....
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Re: and then the headbolt strips
« Reply #4 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
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline Truckedup

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Re: and then the headbolt strips
« Reply #5 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...
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Re: and then the headbolt strips
« Reply #6 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
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline Truckedup

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Re: and then the headbolt strips
« Reply #7 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..
1961 Super Rocket, 89 Honda 650NT