Hi I'm just wondering if anyone can help, im after replacing the 4 long studs which takes the barrel on my bultaco, as it looks like someone has replaced mine with some threaded rod! This has worked but I'm after doing it properly as im guessing they should be a high tensile steel because of the heat maybe??? Can you actually buy these, I'm also after the studs which go in the barrel to take the head? Any advice would be great, thanks

Almost any steel will be stronger than the aluminium, if you have a problem it will be the aluminium female threads that strip.

A4 (316) stainless steel studding is probably as good as anything for this job.

Bultaco UK (In Motion)

JC Motorcycles, Port Talbot

Sammy Miller Product

Any of the above may have new or used.

Anyone on ebay with parts for sale from breaking Bultacos may have some

The head doesn't have studs, it uses the four cylinder studs and in addition there may be two or four bolts that locate into threads in the cylinder (two or four depending on which model you have)

had the same problem only mine had snap at the base.so had to drill it out then i had to put a hellicoil in it bought a new studd from inmotion this was a few years ago. they may still have some if not you should easy get some made. make sure the rear leaft hand studd needs to be slightly longer to take the headsteady as woody said depends on what model you have.

They don't all have a head steady, only '76 on.

My '75 159 has one

woody i was just pointing this out has we don't know what model trum has.

Threaded rod is available in different strengths and harnesses. Regular hardware store rods are usually pretty soft and can stretch when heated. The original bolts are probably the best choice but if unavailable get some heat treated, high strength threaded rod to make your own.

Hi I'm just wondering if anyone can help, im after replacing the 4 long studs which takes the barrel on my bultaco, as it looks like someone has replaced mine with some threaded rod! This has worked but I'm after doing it properly as im guessing they should be a high tensile steel because of the heat maybe??? Can you actually buy these, I'm also after the studs which go in the barrel to take the head? Any advice would be great, thanks

Hi trum,

not sure if i am using the correct format for replying to your post, I am sure the experts will correct me, apologies in advance for any wrong doing!. I have a large stock of Bultaco parts mostly used, as my father and I have been riding, repairing and restoring these excellent bikes to what our budgets will allow for the last 10 years or so, as anyone knows if you have a penchant for a particular bike the collection of parts just seems to grow. If you get stuck please message me I am sure to have a set or two lying around.

kind regards

hencam

Typical "hight tensile" steel for threaded fasteners has a yield strength of 635 N/mm2. A 4 Stainless has a yield strength of 600N/mm2. Sheet and structural steel is anywhere between 250 and 430 N/mm2 and aluminium quite a bit weaker than that.

Coefficient of thermal expansion. Aluminium expands a lot more than steel when it is heated. When your barrel heats up it has the same effect as applying excess torque to the fasteners, this distorts the barrel and fatigues the studs. This is one of the reasons the studs snap. A4 stainless has a coefficient of thermal expansion much closer to aluminium than high tensile steel and it a better material for the job. Manufacturers do not use it because of initial cost, but a metre of threaded rod is only a £few.

The matching of components thermal coefficients of expansion is only really critical on high performance "on the limit" engines.

My '75 159 has one

The 159 is the one I meant as it's generally referred to as a '76 bike, even though it was introduced in '75. But I think I was wrong anyway as the previous model may have been the first with the head steady

Hello all, my running mate and I just finished up on (74) mod 125 & (75) mod 151, these are of the early bored out

250 cases & therefor do not have a head steady, they have a very thin-wall liner and are known to leak causing the

most frustrating time to sort.

Regards Larry

Hi chaps thanks for the reply, mine does have a head steady on it, I've given in motion a call and hopefully they have sourced them for me, bottom end is nearly rebuilt?, new piston kit and rebore next week, then I'm nearly there!!! Expensive game but want to start trailing again after it's been in the garage over 8 years!!

it would be worth while welding a bit off steel rod down the back off the headsteady they do crack on the weak pot my 199b has the rod welded on it you can easy make 1 out off tubing make it flat on bothe ends and shap it drill the holes in the flat ends job done.

Ok thanks for the advice bondy, can't wait to get it back together to be honest!