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Posted By: S-NJ-W Stripped A65 Cylinder head thread - 02/08/21 6:45 pm
The front most rocker box cover thread that holds the stud into the head of my '72 A65 is stripped.
However the head is NOT the original head. It's pre OIF modifications, maybe 1966.

The thread I mean is the one that holds part number 65-0876.
Looks like it was originally tapped 1/4" British Standard Cycle - 26 TPI.

Any advice on how to deal with it? I am guessing that BSC helicoils might be hard to find.
Has anyone re-threaded the rocker box stud drillings in the cylinder head ?

Thanks for the help.

Steve.
Posted By: Allan G Re: Stripped A65 Cylinder head thread - 02/08/21 8:11 pm
Originally Posted by S-NJ-W
The front most rocker box cover thread that holds the stud into the head of my '72 A65 is stripped.
However the head is NOT the original head. It's pre OIF modifications, maybe 1966.

The thread I mean is the one that holds part number 65-0876.
Looks like it was originally tapped 1/4" British Standard Cycle - 26 TPI.

Any advice on how to deal with it? I am guessing that BSC helicoils might be hard to find.
Has anyone re-threaded the rocker box stud drillings in the cylinder head ?

Thanks for the help.

Steve.

I’ve helicoiled one of my heads to 1/4 BSF (also 26tpi) then instead of a stud used a BSF bolt.
Posted By: leon bee Re: Stripped A65 Cylinder head thread - 02/08/21 9:03 pm
Lotta bikes running around with some JB Weld in that hole.
Posted By: pushrod tom Re: Stripped A65 Cylinder head thread - 02/09/21 12:05 pm
I have one that I used 6mm helicoils. Good fix and a bit smaller od than 1/4. PRT
Posted By: S-NJ-W Re: Stripped A65 Cylinder head thread - 02/09/21 1:08 pm
Thank you for the suggestions. There is enough 'meat' around the stripped hole to run a drill into it and re-tap it.
I guess I will run it through with a number 7 drill and see if it will hold a 1/4 UNC tap. If not, then a 5/16th F. I think
it's likely to be the latter. So I will wind up with a head with one thread as 5/16th UNC and the rest 1/4 BSC. That
kinda stuff really messes with my OCD. smile
Posted By: Mark Z Re: Stripped A65 Cylinder head thread - 02/09/21 2:37 pm
If you still want to indulge your OCD, I'm pretty sure British Tools and Fasteners has BSC Heal-a-Coils.
Posted By: S-NJ-W Re: Stripped A65 Cylinder head thread - 02/09/21 2:56 pm
Originally Posted by Mark Z
If you still want to indulge your OCD, I'm pretty sure British Tools and Fasteners has BSC Heal-a-Coils.

For the BSC Helicoils, no 1/4" items listed.

However, on BSC-CEI listings, they do have 1/4".
What's the difference between BSC and BSC-CEI ?
Posted By: gunner Re: Stripped A65 Cylinder head thread - 02/09/21 3:01 pm
I've done quite a few recoils on BSA rocker boxes using M6, BSC and other threads and replaced the original studs with socket caps.


Unless youre worried about originality I simply use whatever is easily available, which in my case is M6.


Whatever you do end up using will be an improvement on the original as recoils are much stronger.
They are Both
the same. British Standard Cycle and Cycle Engineering industry if memory serves.
Posted By: Ola Re: Stripped A65 Cylinder head thread - 02/09/21 6:30 pm
As a 72, you should use sturdy 5/16" bolts/studs, due to the "head steady stay" between the rocker box cover and the frame. You do have the cover fitted for this, I hope. As far as I remember, oif covers do not go very well with earlier heads.

Regards
Posted By: S-NJ-W Re: Stripped A65 Cylinder head thread - 02/09/21 7:52 pm
Thanks for the comment Ola and you would be right if the bike still had the single carb head on it that it left the factory with. The previous owner swapped the OIF head for a 66-68 twin carb 'small port' head and just forgot about the head steady. The rocker cover is correct for the earlier head. It's just the one thread that's stripped.

Also thanks Stan about BSC and CEI being the same at 26 tpi. Brit tools and fasteners says on one of it's pages that BSC and CEI are the same, but they prefer to use BSC, or something like that.

Looks like I will be getting a helicoil to keep the OCD daemons at bay.. It's my own fault, I know..
Posted By: Allan G Re: Stripped A65 Cylinder head thread - 02/09/21 9:20 pm
I wouldn’t go any bigger than 1/4, you have a small area on the rocker box that you have to try and seal.
Posted By: Tridentman Re: Stripped A65 Cylinder head thread - 02/09/21 9:46 pm
If you can't get hold of 1/4" BSCy then 1/4" BSF is virtually identical (same tpi).
HTH
Posted By: S-NJ-W Re: Stripped A65 Cylinder head thread - 02/09/21 11:00 pm
BSF = 55 degree thread form.
BSCy = 60 degree thread form.

OCD twitch starts...

I guess I can put a BSF helicoil in the stripped thread, buy a 1/4" BSF tap and recut the rest of the threads and then switch to cap head allen screws for the entire rocker box (6x screws).

There isn't a lot of space with the early head on the OIF frame and it looks to me like I have to unscrew the studs from the head to remove the head in the first place, So, that might be the best thing. I think it was the required removal of the rockerbox studs to pull the head off that may have been the reason why the thread was stripped in the first place.
Posted By: Mark Z Re: Stripped A65 Cylinder head thread - 02/10/21 1:17 am
A side issue: You really should have some sort of head steady. Maybe you could work off the lug on the front of the cyl. head, and fab some sort of bracket off the frame downtubes.
Posted By: Tridentman Re: Stripped A65 Cylinder head thread - 02/10/21 1:37 am
Low OCD threshold IMHO.
Posted By: S-NJ-W Re: Stripped A65 Cylinder head thread - 02/10/21 12:59 pm
Originally Posted by Mark Z
A side issue: You really should have some sort of head steady. Maybe you could work off the lug on the front of the cyl. head, and fab some sort of bracket off the frame downtubes.

Yes, I agree. I have been looking at the bracket welded to the frame under the steering head that the horn was screwed into and wondering if I can fab a 'rod' from that bracket to the drilled lug on the head. The angles are weird.

Originally Posted by Tridentman
Low OCD threshold IMHO.

Celebrate diversity.
Posted By: Tridentman Re: Stripped A65 Cylinder head thread - 02/10/21 1:18 pm
Agreed!
Posted By: Mark Z Re: Stripped A65 Cylinder head thread - 02/10/21 2:51 pm
Originally Posted by S-NJ-W
Originally Posted by Mark Z
A side issue: You really should have some sort of head steady. Maybe you could work off the lug on the front of the cyl. head, and fab some sort of bracket off the frame downtubes.

Yes, I agree. I have been looking at the bracket welded to the frame under the steering head that the horn was screwed into and wondering if I can fab a 'rod' from that bracket to the drilled lug on the head. The angles are weird.

Yes, if you don't have a horn mounted there, that offers possibilities. FWIW, I've found that you can flatten the ends of tube steel without heating it. Then you can drill and angle the ends however you like. When my A65 bitsa was in a hardtail frame, I made the rear fender stays that way. Then perhaps a flat "U" bracket coming down from the horn lugs... or something like that.
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