The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: RichardL on 16.06. 2008 05:03

Title: Stripped Barrel Stud - Total Frustration
Post by: RichardL on 16.06. 2008 05:03
So, everything was going along fine. The first six nuts tightened down perfectly. Then, the dreaded "snug snugger, loose." A good mechanic would not even ask the question I am about to ask: Does anyone have a feeling for how much trouble I will be in if I run with eight, instead of nine, barrel studs? The offending stud is the first one forward of the socket-accessible studs at the rear. I have a feeling this discussion will lead to my removing the barrels and doing the helicoil. The next question I will ask you and myself is: should I just do them all? I can't wait for the joy of trying to keep the chips out of the crankcase.

Title: Re: Stripped Barrel Stud - Total Frustration
Post by: fido on 16.06. 2008 07:27
I suppose the thing to do is ask yourself "what's the worse that can happen?". Depending on how badly stripped it is I think I would initially try either loctite, araldite or chemical metal on the stud threads after degreasing the hole as best you can. If you then leave the stuff to cure before tightening the nut you will know if it has held.
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: Brian on 16.06. 2008 08:12
At this stage you only have to remove the barrels to fix this stud. If you leave it and it causes a problem then you have to dismantle the whole top end. A lot less work to fix it now. While you are doing it take the rest of the studs out and have a look at them and helicoil any suspect ones.
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: a10gf on 16.06. 2008 11:32
When encountering destroyed threads in alu I got it alu-welded, then drilled, then fresh threads. Helicoil is of course also a good possibility.

Fido's option may work if there is a little sign of threads still there, in addition you may want to try a slightly longer stud, in case there are some intact threads a little deeper down.

A 'quick fix' I've used sometimes is to find the nearest larger mm thread tap and make some fresh mm threads, and use a mm bolt cut in length to suit. Mixing metric and withworth or inch is of course not the perfect solution, but one can get some solid and lasting results.

My impression, if you have the barrel with 8 studs solidly tight and 1 somewhat looser, I would not believe any damage will occur, except if one starts overtightening studs next to the the damaged one...

But it's always nice to know problems have been fixed properly, so if time permits, get it done the best possible way.
Anyway, just some ideas to maybe help you along.

Title: Re: Stripped Barrel Stud - Total Frustration
Post by: groily on 16.06. 2008 15:20
Ooops Richard. . . .  very bad luck. We know from this forum that 'helicoils are good'. We don't know much about the engineering properties of araldite and other glue, although they may very well do it as per Fido's thoughts if the ali is better than the stud and there is still a fair bit of thread there. To check, regardless of visible signs, I'd take a tapping-size drill for the hole (the thread's minor diameter) and see if it wiggles appreciably in there - if it does, the thread's dead.
If it were me, I'd whip the barrels off and do the job properly, while also extracting all the other studs to check. To illustrate: only last Tuesday I had a similar crisis with an AMC twin I was rebuilding, where one stud that held the centre main bearing web into the crankcase stripped on reassembly (below the level of the top of its hole in the case, naturally). . . I pulled out the rest of the studs, and found three of the remaining 5 were not good - waisted, bad threads and/or plain bent. One had busted before and was only screwed in about 3 turns of 1/4 whitworth - the rest was down the 'ole. Lot of work to fix, and a fair bit of fitting afterwards to get things straight and perfectly aligned but peace of mind is more important . . . Back to BSAs, and another instance - I once had some A10 barrels fly off and wreck all the holes in the crankcase and much else besides, the memory is vivid. Reason was dodgy threads in the crankcase. Lucky the head steady hold the thing in the frame! So I would say it is definitely worth the effort to do the thing the hard way. After all, you don't want to be worrying every time you open the gas. As I recall there is plenty of ali there to do a helicoil job - all round in my case at the time. There's probably enough to make stepped studs with fat bottoms, pardon the expression, if you had to. And the welding route would be maybe the best of all if things are truly horrible down there. One of those options is what I would do, definitely. Many of the problems I have had over the years have arisen from things just like what you are facing, some being bodges of my own which I thought might just 'do', others of other people. Good luck in whatever you decide!
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: RichardL on 16.06. 2008 15:41
Thanks, all, for the comments and implied empathy.

I suppose if I had discovered this when doing a tightness check after some running, I would have have put some epoxy between nut and barrel flange to keep it from rattling, then, just wait for it to be a winter project.

Even if a chemical approach were possible, by the time I remove the barrells to get to it I would feel committed to the helicoil, which I have resolved to be.

A bit longer stud with the correct threads on each end might be as time consuming to find as doing the helicoil, but the idea of threads deeper in is interesting. I think I will forego metric, as once there, returning to 5/16-18 BSW would be difficult. I don't know that welding while the case is assembled and in the frame is really an option. I think it would cost a lot of money to get a mobile unit to my house, and the potential disassembly would feel like soul-destroying torture.

I think everyone will agree with the point of fixing it now while it is still just the barrels that must be removed. One thing I am going to do while the barrels are off is test the studs for taking the typical torque for the 5/16-18 thread in aluminum. This should let me know if any others want to let loose. Then, I am going to do the fish-scale-on-the-end-of-the-wrench approach for doing the assembly. I know I should be expereinced enough know what is about right when hand tightenting, but the saying is, "Once burnt..."

Groily, your reply came in as I was trying to post this. Those are some important examples, especially the one about the barrels coming off. That is exactly the kind of example that makes the choice of a good fix a no-brainer. The Helicoil kit will be ordered today.

Anyway, thanks again for responding and giving me a place to discuss it. You might might not believe this, but my wife is not fully up on helicoils, torque, welding and Loctite.


Title: Re: Stripped Barrel Stud - Total Frustration
Post by: groily on 16.06. 2008 18:09
My wife isn't either Richard, which is why I come here for it! She's more into tennis which is not my dish of tea. I've learnt more about tennis players over the decades than she has about camshafts, though, I have to say!
Hadn't realised the cases were back in the frame - that is a bore. However, with care, loads of clean and as they used to say 'lint-free' rag round the opening and the rods, and a very careful approach to drilling and tapping, I reckon you'll be OK. The toughest thing to ensure is 'verticality' if there is such a word. To try to ensure that, I have been known to make silly little bits of metal to bridge from A to B or a triangle even (whatever I can get a good fix on) directly above the hole to be dealt with, and use a precisely drilled hole in the bridge piece as a guide for drill, tap, whatever. A bit of a palaver to get the hole in the right place, and requires some mental exercise, but it can help a lot. To get your hole straight and where it's needed I'd put a good-fitting drill or bit of steel in the hole to be redone, check it's vertical with a T square or something else with a true rt angle on it, assemble the bridge above it, put something  sticky on top of the bit of steel/drill, raise it till it touches the bridge and leaves a circle of yuk, withdraw bridge, drill hole, reassemble bridge, etc etc . . . There's nothing worse than crooked holes, as the nuts don't go down right on crooked studs. Friend of mine did a wrecked Velo Venom crankcase-to-cylinder thread this weekend with the motor in the frame - no hassle. Started mid-am and was out and about on it mid afternoon. So no worries, as they say down under. And you are definitely doing the right thing in my opinion.
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: RichardL on 16.06. 2008 19:00

Thanks much. The drilling fixure is a great idea. I had figured to just follow the line of the existing hole with the hand drill, but the fixture is well worth the time. You can count on a picture of it once it's made.


Title: Re: Stripped Barrel Stud - Total Frustration
Post by: LJ. on 17.06. 2008 10:05
Good Luck Richard, take your time with it, sounds like no second chances here. I'd even treat myself to a new drill for what they cost.
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: RichardL on 19.08. 2008 05:20

It has taken a long time for me to get around to posting these pictures showing the fixture I bodged to keep the bit vertical when drilling the tap hole for the barrel stud helicoil. Thanks to Groily for the suggestion. It worked out fine and the rebuild has gone well beyond this (rocker-box on and valves adjusted), but I am just catching things up with posting the pictures.

The taped-wrapped pin in the top photo assures alignment of the existing hole with the oversized fixture hole as the fixture is anchored.

The case is dammed with tape to keep out chips.

I hope you find this mildly amusing, and thanks to all for the continuing support, advice and encouragement.

Title: Re: Stripped Barrel Stud - Total Frustration
Post by: groily on 19.08. 2008 08:39
Very pleased to see that worked so well Richard. Proper result by the look of it and you needn't worry about failure on what looks to be a lovely engine that should serve you well after all the trouble you've taken.
Apropos nothing at all, I have to say I haven't had to touch my A10 for a month or two now - it just seems to work. Been sharing the mileage with other bikes, particularly since putting together a single of the marque which is just fantastic - if you don't want to go very quickly (or even a little bit quickly!) But still knocking up a few hundred A miles a month, every one a pleasure despite lousy European summer. Perhaps you'd ask the weather gods to send something a bit better for September and October from your side!?
Title: Re: Stripped Barrel Stud - Total Frustration
Post by: LJ. on 19.08. 2008 10:20
Thanks for those pics Richard! Each one tells its own story. Good reference for others who suffer stripped threads.