Barrel Stud Tension

[Les Oz]

Could some knowing person out there in cyber space please
abvise me the correct tension for the barrel nuts,, same for
the head studs,(cast iron head) all is going ok with the old B*****,but was there
some B******d bits in there, but still going up & down and doing what they
where intended to do 57 years ago, Be interesting to see how many
current bikes will be around 57 years from now,(I know I won't be)
Les Oz

[RichardL]

Les,

My Chilton "BSA Repair Guide," and Bacon's "Twins and Triples" both list torques for nuts and bolts on A50's and A65's. In the case of the barrel base nuts, Chilton lists 18-20 lb. ft. and Bacon lists 18.  I see no reason why the torque should not be the same as for your plunger (a guess as to your model, based on it being 57 years old). 

I am a little concerned about telling you a torque for the cyclinder head bolts (does the plunger have cylinder head nuts?). Somewhere along the way, BSA changed from uniform diameter head bolts to those with reduced diameter on the unthreaded portion. This was due to the bolts fracturing where the threads ended, which, in turn, was due to that being a weak spot caused by stretching when torqued. By reducing the diameter of the unthreaded portion, they put the stretch there, reducing stress at the point where the threads ended. Having said all that, I can tell you that Chilton lists 28-30 lb. ft. for 3/8-20 head bolts on an A65, while Bacon lists 25 (maybe going with the lower torque is the best idea).

I hope this has been helpful and I also hope others will chime in to correct me if necessary or add certainty where I didn't. This is just the kind of topic that gets a lot of interesting replies on the forum.

My bike is a '55 swingarm, so some of the parts will not be the same, like, maybe, the head bolts.


Richard

[groily]

'Tis a cleverer man than me that can get a torque wrench - or darn near any decent wrench - on the barrel to crankcase nuts. I use a ground-down open-ender to get the awkward ones near enough done up, then mess about  a fraction of a turn at a  time with a v slim ring to tighten them to what I regard as about the right setting. But what that may be, I couldn't tell you! I suppose if one had a set of very fine crow's foot spanners, one could do it - but my crow's feet are as bad as the memsahib's and certainly won't go on (only joking, natch). As for an iron head, a 3/8ths BSF thread ought to take the above-mentioned 28-30 ft/lbs and in many applications hereabouts, including one 72 yr old car cylinder head (iron head, iron block), takes a recommended 34.  . I'm sure there are proper engineers here who can cite correct torques for all and any threads in all and any materials (the handbooks being coyly silent on the subject while enjoining us to do them up in the right sequence) - and I look forward to learning more. Always best to use new studs though, of the right stuff . . . Groily

[RichardL]

I must say, I also tightened the barrel base nuts on my bike by struggling with spanners, and without torque measurement. I can envision the old fish-scale-on-the-end-of-a-spanner method. So, let's assume you had an 8"' spanner, you wouuld need a fish scale that could measure up to around 30 lb. to get 18 lb. ft. on the nut (actually, you would need a reading of 27 lb. on the scale).  All this assumes you could get a right-angle pull on the end of the wrench. Want to figure out your own:

Reading on scale in lb. = (required torque) x 12 / (spanner length in inches)

Note: "Spanner length in inches" is from center of bolt or nut to the point at which you can pull with the scale at a right angle.

[RichardL]

Groily,

What is a "v slim ring"?

Another thing I think worth mentioning is that torque on the barrel base nuts would be far less critical (as long as they are good and tight) than the cylinder head bolts, where the copper gasket is being deformed. I know you know this, but I mention it for any who might not have considered this.

Richard

[groily]

Ah, Richard,  a 'v slim ring' is a very slim ring-spanner - the US equivalent for which I have momentarily forgotten - one of the ones that go all the way round the nut, anyway with, usually, 12 points . . . Has to be v slim for the reasons we have highlighted!

Yeah, I've thought about tying bags of sugar to the ends of spanners of a certain length! Or even using a spring balance with a wire reel attached. But in the end, as we agree, the barrel base nuts just need to be nicely done up. On the later engines with the thick flange I guess it doesn't matter too much, but just maybe with the old thin flange per the plunger bikes there is a risk of some disaster or other if one applies too many bags of sugar? . . . I don't know and probably never will! But I do remember vividly once having a thin flange barrel let go, and having to get home gently with the flange and cylinders unconnected, the engine only held together by the head-steady. Messy and expensive day out . . .crankcase stud work, new barrels, bent pushrods, you name it . . . . but I was a throttle-happy youth then, so it couldn't possibly happen now, could it? . . . Groily

[RichardL]

I believe the equivalent is "box-end wrench."  Like many of us, I have a variety in fractional and metric sizes, but only sockets in Whitworth (soon to be remedied). When I need to, I don't mind grinding down the box height or wall thickness on fractional or metric, but I doubt I will be doing it on Whitworth.

Richard 

[Brian]

I am probably going to get jumped on for this but here goes anyway. I am a bit concerned that the discussion on barrel and head tension is over complicated. Do the barrel studs up tight and the head bolts anywhere between 30 and 40 lbs and they will be fine. To quote a sentence from a  BSA manual I have regarding head bolt tension it says " do the head bolts up tight and then go back over them and do them up very tight". There are probably some members of the forum that have not had a lot of mechanical experience and I would not like them to think that these old bikes are more complicated than they are. I would not like to think that someone was lying awake at night worrying that maybe the tension on their barrell nuts was not quite right and maybe the next time they ride the bike it will blow into a million pieces. Well thats what I think, now I will wait to be lined up in front of the A10 firing squad !             Brian.

[a10 gf]

Yes, all things are not difficult or critical. I use some washers under all nuts, tighten lightly and evenly, using a cross-system like with headbolts, and continue slowly cross-wise until all is "very tight", but far from risking damaging threads, anybody with a little experience will know when to stop. Then retighten after a while in case gaskets have compressed slightly.

e.

[Les Oz]

Appreciate the several responses,was informative and little amusing at the same time,
Yes the bike is a 1951 plunger, 9 head bolts (new) no nuts to aid said bolts,
got the message re head tension, as for the barrels,a ringy was what they were going to get,
and think I will pass on the fish scales,when the spanner bends l know l over did it, (kidding)
Les

[fido]

I have never heard torque referred to as "tension" but then I've only been in mechanical engineering for 32 years so what would I know!  One tip I was recently given about spanners and stripped threads: A friend of mine is a model engineer who is building a narrow gauge steam loco. He once borrowed some spanners from an elderly toolmaker. They were all single ended but had been neatly shortened. The owner explained that he used his hands as torque wrenches, by tightening as hard as he could with the leverage available on each spanner. With the standard length spanners you had enough leverage to strip threads but with his shortened ones this was unlikely.

[a10 gf]

With the standard length spanners you had enough leverage to strip threads but with his shortened ones this was unlikely.

Yes indeed, my experience as well, the use of short spanners or wrenches is an excellent and safe way of controlling torque. F.ex the small wrench on the pic is my choice for keeping control, I recommend to have one in the toolbox.

[RichardL]

Fido, et al,

You note an interesting point about "tension." I, too, have never heard torque referred to as tension. On the other hand, torque applied at the head of the bolt does result in tension in its length, so, maybe, the term is not that far off.

I don't know if anyone here will run off to their sheds (borrowing the Bristish term) to cut their wrenches shorter. I doubt it and I don't think that's what you meant to happen. Considering the gathered experience, I bet we would find that, consciously or unconsciously, we all use "hands as torque wrenches." I sometimes find myself pulling on long wrenches with a given finger, or fingers, with the understanding that a limited and somewhat metered torque would be applied. Of course, just pushing or pulling on a wrench closer to the ring or span has the same affect.

Another point in this ongoing converstaion has been when to use a torque wrench and when to let it go. For me, if it is for significant parts (for example, heads and rod journals), and if I have a logical torque value, and, finally, if the nuts and/or bolts are reasonably accessible (unlike cylinder base nuts), then I will apply a torque wrench.

Les, I told you that this topic would get a lot of action.

Richard