This restoration is still fighting back. The four outside studs holding on the rocker cover are causing problems. I ordered a set of four studs from a well known BSA spares shop. These studs have a course thread one end and fine the other. The fine thread will wind into the head but are very sloppy. The coarse thread will wind in a bit, but feels like it will split the casting if force is applied. The first company described one of the threads as cycle thread ? I thought these bikes were UNF ?
I ordered another set of studs from another well known company and have exactly the same problem, in fact exactly the same studs. If I knew which thread was in the head I would be tempted to just put four bolts on the rocker cover to hold it down. Can anyone help, two famous BSA shops can't. Thank you.
I am surprised but they are actually 3/8 BSF and BSC rather than UNC and UNF.
Is that the coarse end or the fine end and who might sell them please. Certainly don't want to damage my newly rebuilt head. Thanks.
Just noticed Draganfly list them as 5/16 UNF / UNC 14-1623 ? I assume that my head is the one that came out of the factory in 1971-2.
:)
It is just possible that those studs have been wound out unintentionally on several occasions cos the nuts are stuck. I have had the same problem on my A50.
So I tapped it 1/4 unc??I think and I now use allen bolts. Does the job perfik. Its not as if it needs massive torque, so be careful not to overtighten.
Mike
Thanks Mike. I wish I had the old studs which I could replace with new and loctite back in. My engine is now almost new so I don't want problems for the next owner.
Hi Colin,
It sounds like you have one of the late pre OIF heads fitted, which were also 5/16 studs but curiously used UNF threads in the head instead of the later UNC. I've got one fitted to my 1971 Firebird.
I got some double ended 5/16 UNF studs off ebay, around 2" long I seem to recall. Just make sure they screw in right to the bottom of the thread in the head to maximise 'purchase' so they don't pull out. I probably wouldn't go down the route of using UNF bolts, as the threads are only going to get slacker with repetitive removal of the rocker box cover.
Jim
I've always used set screws. The stud idea goes back to pre oil in frame days when there was plenty of room above the head to get the cover over the studs. As you will know the OIF frame leaves little space there as the head steady bolts onto the cover.
Well I have tried every spare bolt I have in my box of many other restorations, none of these fit the four threads in my cylinder head. By the way the 4 threads look fine. It is frustrating parting with money with well known BSA people and the parts simply don't fit. Even the locking nuts with the last set of studs were so tight I could judge how tight they were. I have tried a 5/16" W bolt in the threads, don't fit ? At least the bike is running nice ( So far ) :'(
According to my '71 spares book. #39 are 4 x 14-1623, 5/16" UNF/UNC x 2".
The coarse UNC end screws in to ally head.
Hope this helps.
Just had a good look at the threads with my magnifying glass and they are in fact Helicoil inserts in each corner. Obviously this was done by the previous owner who is now RIP. What is the best way forward now. I have no experience with Helicoils, were they made to replace the original thread ? Now I don't have a clue what size stud to put in. Thanks.
Update.. The Helicoils are M8 and I will be collecting the studs tomorrow, job done I hope. Easy trap to fall in.
One of the hazards of old bikes I'm afraid. Whichever previous owner did this probably had access to metric helicoils so used them. Look on the bright side, at least they have good threads in the holes. So many of the threads I have come across lately on my two projects have been idiots screwing BSF nuts on Cycle Thread studs taking the thread with it as it goes.