Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Stretched head bolt

When I removed the head from my 71 A65 one head bolt was seriously stretched.
I believe that it's the TS rear bolt, but I might be misremembering.
Any idea on what caused this, just one bolt?

What about it tells you the bolt has stretched?

If the bolt is indeed stretched, it would be most likely from over-tightening or poor metallurgy.

Perhaps its appearance?

Well, I have never seen that before. Even when I have threaded up my own headbolts. They must be made of some real shite steel and just black jappaned to make them look like decent high tensile bolts. I have had barrel threads fail (which is what made me wonder if the bolt was the issue or not), All the non stud threads on my 68 barrel have got helicoils in, (I think about 3 were bad and I did those and the other 2 as a matter of prevention over cure)

There is some rubbish on the market which is why I started doing my own... Till I found the SRM ones were better than what I was threading up...... Now I use theirs.

MY money would be on it being an aftermarket bolt not made out of high/medium tensile steel ?

compare any markings on the heads of the good bolts to this one and see if they are different, a pic of the head of the stretched one and a good one side by side would be interesting

but you were lucky it didnt bust off inside the thread ...the way it has necked down it was sure close to doing that

by the way the necking is typical of freemachining / mild steel that has passed its yield point in tension

another quick (not definitive ) test is hold the bolts lightly by the head and hit the bolt lightly with another piece of bar ....an high tensile will give a pinging type sound and mild will give a deader almost thud sound ....if the sounds are different you can be 90% sure they are different material

I'm pretty sure that the bolts are after market, they have the correct BSF thread but the heads are 9/16" AF. I never thought twice about that because I wrongly assumed that BSA changed to Unified, as did Triumph.
I've bought new head bolts, but it looks as if I will need to repair the threads. The holes are wallowed out at the top, even with the new bolts fully in I can wiggle them about.
Are the coil type inserts adequate for this?

Well the helicoils would be going into cast iron so they SHOULD be ok .... it sure isnt ideal unless you can get nice long ones ....i have no idea if you can get them in different lengths. only ones ive seen are quite short.. i never use them, but thats only cause im too mean to buy the whole kit just to do one thread....are all of the threads "wallowed " ?

My 70 is BSF so yeah after market 'soft " bolts is the answer ...dont be tempted to re use the "good" ones save then for a less important application that needs a BSF bolt.

Off the top of my head (pun intended ) i dont think thee will be enough metal between the edge of the bolt hole and the pot to accommodate a tread insert so you might be stuck with helicoils ....... shop around for some LONG ones .... some one here will know where , i dont

As mentioned earlier I helicoiled mine. Since doing that I haven’t suffered with any oil weeps from the head gasket after wringing its neck. It did when it was just threaded directly into the cast iron.

I used standard length helicoils and a drop of locktite when installing them.

I mounted them on the pillar drill table, ensured it was dead plum and by hand only threaded into the barrel just using the Chuck as a guide.

Hi All,
Helecoils come in 3 standard lengths , 1D 1.5D and 2D where D is the bolt diameter
Timesert solid inserts are the same outside diameter as helecoils

John

There you go David P ........go with the 2D that would give you plenty of threads engaged

so 20tpi x .375 = 7.5 threads engaged , rule of thumb is MIN of 1.5 x nominal diameter but more is always better

check out the lengths u can get the "timesert" solid ones in , never heard of those i always just make my own like i said to mean to buy a kit for just one thread

I assume the "timesert " ones are hardened as the helicoils are ? .........

top info Chaterlea

David, I recommend British Tools & Fasteners.
https://britishfasteners.com/
They have most every size coil spring thread repair kit, British nuts, bolts, screws, taps & dies imaginable.
Fullminator.

I just looked and the Timeserts are only available in 3/8x16 or 24tpi. The solid insert seems to be more suited to high-torque applications, but the kit is at least $80.
I have found coil insert kits in 3/8" BSF for less than half that much. So far the only threads I've repaired on this bike is one rocker cover stud. I just used a UNC coil for this, I put the coil in with red Loctite.
Thanks for the clarification of the length specification, I'll look for at least 1.5D. In any case, the barrels must come off.

Actually, if the outside threads are the same, I could just buy some Timesert inserts and use the Helicoil tap which I already have for 3/8"x16? Just need to countersink the holes.
Just buy some grade 8 bolts. Don't know what that would do to the torque settings using a different thread pitch though.

Just buy some helicoils David and don't over complicate life. Im running 10:1 compression in my a65 and they have held up fine for about 4 years.

with helicoils your coming very close to the wall of the bore, espeically if your already running over sized pistons... Add the top hat of the timesert in there as well and you might be very close or broken into the cylinder wall. You might not be too bad if its the one behind the pushrod tunnel but your not really gaining anything. If it was a spark plug thread, I would say fit a timesert.... But it isn't.

in any event get the longest ones you can ..........dont worry about different pitch and torque settings it wont make any practical difference , the amount of pull down will be the same regardless of pitch , they wont loosen of that's what spring washers are for , flat washer on alloy head spring washer under head of bolt

David - I have seen new (after market) head bolts that were very sloppy. I would try a known good bolt before going to any helicoiling.

Regards

actually that is a really good comment ! i hadnt even though of the possibility that the aftermarket bolts could be undersize on the effective (pitch) diameter ....definitely try a known good one! and see if it is loose

Might be worth adding to the good comments above that BSA increased the washer thickness to a shade under 3mm from the original 1.5mm. This was to address oil leaks.

Allan, how did using heal-a-coils alleviate your leaking problem?

Thanks, I had not thought of that. I'm at +0.080, so that might be an issue.

50 year old engine from a company which went out of business 48 years ago makes it kind of difficult to find anything but after market bolts. The only other 3/8" BSF bolts I have are the old head bolts. The new ones came from Steadfast.

At this point my only other option is another set of cylinders. I have a set with one broken fin, which might be 20 over. However, they're early so I would need to resize and relocate the holes for the base studs. Add to that new pistons, rings and machine work.
Quite frankly the bike is not worth it to me to spend too much time and money on it.

If you are going to replace and helicoil all 4 i would use 3/8 UNF as you can
buy either grade 8 or allen bolts (grade 12 or 14) easily.
The engine i did for the race bike i prepare had good threads so i just bought
grade 8 3/8 unf bolts which were plenty long enough then cut them and ran a
3/8 bsf thread on them. The heads are unf but they are good quality bolts and
that's what you are after. I too have come across crap bolts/studs.
If you are replacing the studs as well, use the 71/72 type they have much longer
threaded ends on the barrel and are shaped to bottom properly. The kits that are
sold now supply shorter studs like the earlier ones.
Just my 2c

30lbs is fine on them.

The helicoils provided a decent thread for the bolts to lock in to.

I took a closer look at two of the old head bolts. One, which has the proper 3/8"W head, is marked Rubery Owen T55-65 on the head. After researching the company, I presume that this is OEM, as supplied to BSA.
The other has a 9/16" AF head. It has a raised place in the center with two ovate stampings which might have originally been numbers? It's the correct thread but a mystery as to who made it.
The new ones from Steadfast have no markings.
I got a Recoil kit in BSF. Got the cylinders waiting on my drill press. Must be careful to get the bit Concentric with the original hole. It's a bit frigid in the shop these days.

Right David, original bolts are Rubery Owen. The two marks on the other bolt may be just hash marks, as appear on much ordinary hardware.

Can you use the cylinder head to make a drilling template, to then bolt to the barrel? Just a thought...