Author Topic: and then the headbolt strips  (Read 255 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, 79 Triumph T140D, 96 Ducati 900M

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....
1961 Super Rocket, 79 Triumph T140D, 96 Ducati 900M

Offline muskrat

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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 now A10CR,  '83 CB1100F, 88 FXST .
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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...
1961 Super Rocket, 79 Triumph T140D, 96 Ducati 900M

Offline muskrat

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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 now A10CR,  '83 CB1100F, 88 FXST .
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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, 79 Triumph T140D, 96 Ducati 900M