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I am aware of the pitch angle difference between 1/4 BSF and BSC

From several vendors I was trying to source a thread repair for the primary case screws for a 68 a 65. The vendors have the various BSC and BSF helicoil kits. But for 1/4 they have the same kit. Where you're looking for 1/4 bsc, but when you click on the product it's a 1/4 BSF repair. Are helicoils of that size an in between angle or different profile that will accept any 26 tpi? Any engineers or machinist out there shed some light? I repaired some threads (I think rocker box) on my 65 tr6 with a 1/4 BSF kit which I still have but years ago before I understood the different threads. I certainly don't want to buy a duplicate to repair the a65 primary if there's virtually no difference. Any help appreciated


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I didn't mention the vendors I had checked but that wasn't one. (I'm in US but frequently order from the UK as we don't seem to have the problems with shipping the continent does-items usually get here quicker from Britain than many US vendors, but I'm on the east coast) I didn't want to trash anyone as shishters if helicoils indeed have a rounder or different profile. Between the 55 and 60 26tpi


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Most suppliers just sell 1/4 BSF stuff as BSF/bsc, nuts, bolts etc.
1/4 screws or bolts BSF or bsc will fit 1/4 BSF helicoils no problem.

Same with ww/UNC in smaller sizes.


Personally if i was helicoiling a primary case i'd use UNC or M6 you can
buy them anywhere and they are much cheaper, as are the bolts etc.

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If it’s any help, I have 1/4 BSF coils in my crank cases, the screw sets as your probably aware are (or should be) cycle thread for pre 69. The screws go in no problem. They aren’t loose, but they just fit nicely. I also lock them into place with some locktite.


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Of course they sell them as the same thing. The difference is pedantic. Lets be brutal. You are repairing an unusable threaded hole with a piece of coiled wire. The result will be quite close to original but will not be a perfect replica of a theoretical thread form. You are then fitting a screw made within commercial limitations or possibly even the worn screw that came out of the repaired hole. Neither will have a perfect thread form either.

In this case all 26tpi threads are interchangeable, be they BSF, BSC or BRASS.

Save your money and use what you have.

Cheers,

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Originally Posted by DAMadd
I am aware of the pitch angle difference between 1/4 BSF and BSC

From several vendors I was trying to source a thread repair for the primary case screws for a 68 a 65. The vendors have the various BSC and bsf helicoil kits. But for 1/4 they have the same kit...........
I'm tending to agree with Villiers and Allan G. I've done the same. It's not going to make a real difference ......

But if you simply must, Tracy Tool in the UK actually offers both kits and at different prices so they are probably not the same, so you do have an option if you choose. They are a great company. I've been using them for British taps and dies since the 90's, back when they didn't take credit cards. In those days, you had to mail them a check. Nowadays they have a great website and take credit cards. Surprisingly quick service too.

https://www.tracytools.com/index.php?route=checkout/cart

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Originally Posted by Stuart Kirk
Originally Posted by DAMadd
I am aware of the pitch angle difference between 1/4 BSF and BSC

From several vendors I was trying to source a thread repair for the primary case screws for a 68 a 65. The vendors have the various BSC and bsf helicoil kits. But for 1/4 they have the same kit...........
I'm tending to agree with Villiers and Allan G. I've done the same. It's not going to make a real difference ......

But if you simply must, Tracy Tool in the UK actually offers both kits and at different prices so they are probably not the same, so you do have an option if you choose. They are a great company. I've been using them for British taps and dies since the 90's, back when they didn't take credit cards. In those days, you had to mail them a check. Nowadays they have a great website and take credit cards. Surprisingly quick service too.

https://www.tracytools.com/index.php?route=checkout/cart

+1 for Tracy Tool. Top Notch IMO. Even with shipping added I still think they are the best deal........they carry stuff others don't.

Gordon


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DAMadd Offline OP
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Someone had replaced a few of the rocker cover studs with UNF making for a variety of nuts which I was trying to avoid on the primary. For my own ocd and future owners. It's just one bad position so I'm going to use the BSF ones I have as per advice. Thanks for the replies! On a past thread or maybe a searched topic I had been put on to Tracy tools. Got my bsc tap and die set there.. I thought that might have been one I checked, but no matter. I wondered mostly about the pitch angle of helicoil. Certainly can't discern by eye on 1/4 26 piece of wire
Thanks again


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Another +1 for Tracy Tools.
I ordered a 1/4" BSP die nut from them last Thursday---it arrived yesterday.
Great selection and great service.
Also pretty fantastic for unusual stuff like LH thread dies and taps.
The founder was an old style machine tool guy from Birmingham UK--not far from where I grew up.
Around there babies are not born with blood in their veins --they are born with suds oil in their veins.
Just my two cents worth of course.

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There is an old thread where Stuart insists that the threads in the case of a 60s unit Triumph are in fact 55 degree 1/4 BSF rather than 60 degree cycle. This is because cycle was only used into steel. BSF was used into aluminium. As the threads get larger the tpi drops with BSF whilst the big steel threads on a Triumph remain 26 tpi. apart from the big rear spindle which is 20TPI. I wonder if it is the same for a unit BSA?

dave

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Originally Posted by dave j
There is an old thread where Stuart insists that the threads in the case of a 60s unit Triumph are in fact 55 degree 1/4 BSF rather than 60 degree cycle. This is because cycle was only used into steel. BSF was used into aluminium. As the threads get larger the tpi drops with BSF whilst the big steel threads on a Triumph remain 26 tpi. apart from the big rear spindle which is 20TPI. I wonder if it is the same for a unit BSA?

dave
Yes, in parts books for the Unit Single rocker box studs pre UNF/UNC you see the 1/4 stud is threaded BSF one end which screws into the alloy head and Cycle on the end a steel nut is used. You only know which end is which by looking at the length of the thread. The same stud ends up UNC/UNF on later bikes, showing they finally realised 26 TPI in alloy is not a good idea.

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For case screws I would helicoil them BSW or UNC


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My info came from Stuart. His original post is in the Triumph forum thread. I accidentally restarted by posting what he said at the end of the same thread instead of here! I thought my post had disappeared so I did it again, this time in the right place.

Dave

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If the insert ws made from diamond shaped wire at the correct angle is would make a difference.
Bit most inserts in this size are round wire so if the TPI is the same they will interchange .
Decades ago the different inserts were made with different wire.
Now days they all seem to be the same
One only diamond profie & plain round profile so the actual thread shape is not importaant apart from the fact tat is can damage a soft grade 5 bolt.


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DAMadd Offline OP
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That's where I was going with the question originally. Moot pt now, as it just got simultaneously more complicated then simpler. It was the dowel position at the front so it looked a pretty complicated thread repair if the drill was larger than the dowel. In pulling it and transferring to the cover to not lose it, I noticed how deep into the case it stuck out and after matching the bolt up and checking the depth of the engine realized I had 10 -15 mm of thread deep I could go into the engine with a longer screw. I had dry fit the case and cleaned and chased all the threads previous and picking the bolts from a random amount in bins by sticking them thru the cover to get equal sticking out the back. Guess I need a longer screw. Doh! Still gonna countersink the holes lightly while I have it back open and see if I can true up the cover via a bit of the old glass plate trick as it had a steady annoying drip. Anyone recommend a good aftermarket gasket maker?


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