The BSA A7-A10 Forum

Technical => Frame => Topic started by: Lannis on 08.07. 2009 15:24

Title: A10 front fork slider repair
Post by: Lannis on 08.07. 2009 15:24
The threads that take the clamp bolts that hold the front axle on my A10 are completely knackered.    I went to tighten them up prior to a 700 mile weekend trip and they just turned.

All four are about in the same shape - 47 years of working in and out of the alloy has finally done them in. 

I replaced a couple of the stripped bolts, swapped bolts and washers around till I could find enough thread in each hole to hold some torque, and was lavish with the Loctite.  I'll be stopping at intervals Friday to see how they're doing, because the last thing I need is for the front wheel to part company 40 feet in front of a big truck at 65 MPH on I-79 around Morgantown.

So as SOON as I get back, I need to fix them.

I did it wrong on a Harley Panhead years ago.  The same thing happened, so I drilled the hole bigger, threaded it for 3/8 - 20, and cut some threaded rod to use as a stud.  That lasted about 10 miles before the whole end of the fork broke, because there wasn't enough material around the bigger hole to hold the strain.

What is the best way to try to save these fork sliders?  Is there a way of providing strong new threads that removes a MINIMUM of metal from what's already there?   Can one of our machining or race shops carefully mill it out and insert a very thin threaded insert that would not take away from the strength of the slider?   Is there something like a Heli-coil that will go into these random buggered British threadforms and be a good fix?  I don't want to bodge it, and the chances of finding another set of sliders with good threads after all these years is pretty slim - I'm sure they're all in the same shape.

Thanks!

Lannis
Title: Re: A10 front fork slider repair
Post by: RichardL on 08.07. 2009 15:57
Lannis,

The Whitworth helicoils are definately availabe. Is it that you feel the tap hole size for a regular Whitworth helicoil is too large? (Actually, they will probably be "Recoil" brand.) I don't have that type slider, or a picture at hand, so I ask, would it be possible to build up some weld on the outside of the slider to reinforce the area in question? You shouldn't need much if just trying to make up for the insert, plus a bit more. Some careful grinding and filing might make it virtually disappear.

Just my thoughts. Hope it helps, or that you enjoy scoffing at nonsense, if such.

Richard L.
Title: Re: A10 front fork slider repair
Post by: Lannis on 08.07. 2009 16:08
manosound -

I think that if I were going to get a MIG welder involved, I'd probably just have him weld up the original holes, and redrill and retap them.

I hesitate to do that UNLESS it is someone who I KNOW understands the type of alloy involved, and what the welding will do to the brittleness of the metal and all.

I don't know how much metal I'd have to take out to put in a "helicoil" or "recoil" type of insert.   I'm not set on having Whitworth or BS threads, as long as its a good thread that will hold; it could be metric or SAE if that's easier to get.

Lannis
Title: Re: A10 front fork slider repair
Post by: RichardL on 08.07. 2009 16:32
Lannis,

You are, clearly, rather internet adept. However, in case it helps, here is a link to the inserts and drill sizes:

http://www.newmantools.com/recbri.htm

I am curious if it is even possible to weld-up a small diameter hole from top to bottom with confidence. The weld on the outside would be far less critical.

Richard L.
Title: Re: A10 front fork slider repair
Post by: Lannis on 08.07. 2009 18:41
Also, I've been reminded that the slider is not alloy, but steel.  Even my old '65 Harley slider was alloy, so I thought this would be, I should know better.  That makes the options a LITTLE more palatable ...

Thanks!

Lannis
Title: Re: A10 front fork slider repair
Post by: groily on 08.07. 2009 19:59
Ah, wondered what forks you had. But no great ideas bar welding as not sure how much steel there is to play with for rethreading. You could have a new lower section turned and milled up to go over the existing slider's amputated lower section as a welded-on sleeve, but it might look a bit odd. Worth a go maybe, if the option is sending them to the scrap-man.
Suppose if you don't fly over hump-backed bridges too much, the force of gravity would tend to keep the wheel on . . . *smile*
Title: Re: A10 front fork slider repair
Post by: MikeN on 08.07. 2009 20:58
Lannis,You may have had trouble last time with the alloy forks .
   But If it were my bike, I would be confident that steel sliders would not fracture if you tapped them oversize to accept a helical insert.
 Oh,and please dont use threaded rod this time,use proper hight tensile studs.
Mike
Title: Re: A10 front fork slider repair
Post by: LJ. on 08.07. 2009 22:29
Why not buy some new bolts? I did this when my threads became worn. This is the trouble with British cycle threads as they are so fine. I gather I was lucky with the new bolts as they hold quite well, but you can bet that I now remove and replace them 'Surgically'  *eek*
Title: Re: A10 front fork slider repair
Post by: Lannis on 09.07. 2009 01:17
Why not buy some new bolts? I did this when my threads became worn. This is the trouble with British cycle threads as they are so fine. I gather I was lucky with the new bolts as they hold quite well, but you can bet that I now remove and replace them 'Surgically'  *eek*

LJ -

New bolts will be part of the picture, BUT the threads are also gone inside the fork slider.   I put thinner washers on, and one longer bolt to catch some good threads at the bottom of the hole, but I can assure you that I'll be stopping regularly on the trip this weekend (700 - 800 miles) to check on things.

I'm feeling better about putting a thread insert like a Heli-coil in there - BSAs are made out of some pretty good steel, and I think it'll be fine.

Now the question is - do I do it myself with a hand drill, or take it to an automotive machine shop .... will they do any better a job than I will?  Maybe they'll actually chuck it in a lathe or a mill and make sure the holes are squared up?

Lannis
Title: Re: A10 front fork slider repair
Post by: Lannis on 09.07. 2009 01:18
Lannis,You may have had trouble last time with the alloy forks .
   But If it were my bike, I would be confident that steel sliders would not fracture if you tapped them oversize to accept a helical insert.
 Oh,and please dont use threaded rod this time,use proper hight tensile studs.
Mike


Absolutely.  I was just a kid at the time (well, 19 years old) with nobbut two pence to rub together, all-thread looked good at .12 cents a foot .... !

Lannis
Title: Re: A10 front fork slider repair
Post by: RichardL on 09.07. 2009 03:46
Lannis,

If it were I, I would do them myself with a hand drill. You already have  rather good pilot holes in the form of the stripped holes. If you really wanted to be fussy about it, you could fashion a guide block that bolts to the half-dead thread on one side while drilling the other side.

Richard L.
Title: Re: A10 front fork slider repair
Post by: groily on 09.07. 2009 06:12
Yup, if you're confident after all there's enough metal (I'm sure there is), then careful drilling out should be fine. I'd probably end up with stepped studs, as that gives the option to use the nearest larger suitably fine(-ish) thread regardless of what form it is (for the thick ends), plus enables the use of a proper taper tap to get things started guaranteed square. Which as you say matters if you want the caps to go on nicely. Not sure what tap/taps comes with the helicoil/recoil kits because I (still) don't have any.
Title: Re: A10 front fork slider repair
Post by: Brian on 09.07. 2009 07:08
Lannis, you have a few options all of which will give you a good result.

As Groily says you can go a size larger and make stepped studs.

You can use thread inserts ( I use Recoil) which is probably the easiest. Dont take any notice of the stories you may have heard about thread inserts, they are easy to put in and will give you a stronger than original thread. Even if you have never used them before if you follow the instructions and use a bit of care you wont have any problems. They are available in cycle thread if you want to stay original or else use UNF. Most recoil kits come with a intermediate tap but plug taps are available, ask at your local engineering shop. Considering the cost of buying a thread repair kit though it may be easier and cost efficient to take them to an engineering shop and have them do the job, they will most likely have UNF kits there.

Whatever method of repair you choose make sure you get some good quality studs or bolts, high tensile, not some from the local hardware shop.
Title: Re: A10 front fork slider repair
Post by: beezalex on 09.07. 2009 15:24
Lannis, here's what I did on a set of my own fork legs (later Triumph type, but essentially the same): Buy the appropriate drill, tap, helicoils (get the longest ones that will fit) and installation tool from Mcmcaster-carr.  It's going to be for a 5/16-24 UNF thread.  Drill the holes with a hand drill, but use the axle caps as a guide by bolting them on with one bolt.  Just be careful that the tap is straight when starting...though eyeballing is close enough.  I ground the tapered bit off the end of the tap so I could run it in deeper.  Install the helicoils with red (permanent) loctite.  Use Grade 8 bolts for your axle cap bolts.  I would be wary of using turned threads in this critical application.  OTOH, if you're running the original full-width SLS brake, a thin piece of string probably would be enough to hold the caps on *smile*
Title: Re: A10 front fork slider repair
Post by: RichardL on 09.07. 2009 16:30
Lannis,

I know that Alex knows of what he speaks from experience, and I respect that, but I do not understand why one would choose UNF when Whitworth coils and bolts are available. I would see it as an excuse to have the Whitworth kit around for other purposes where it is not convenient or you would not want to casually change to UNF.

Richard L.
Title: Re: A10 front fork slider repair
Post by: MikeN on 09.07. 2009 20:00
Lannis,

I know that Alex knows of what he speaks from experience, and I respect that, but I do not understand why one would choose UNF when Whitworth coils and bolts are available. I would see it as an excuse to have the Whitworth kit around for other purposes where it is not convenient or you would not want to casually change to UNF.

Richard L.

Its probably because 5/16-24 UNF is nearer to the correct tpi of 5/16-26  BSCy than 5/16-18 Whitworth (or 5/16-18UNC for that matter).
Which means it (Whitworth) also has a considerably smaller core diameter and is not ideal in this application.
Mike
Title: Re: A10 front fork slider repair
Post by: RichardL on 09.07. 2009 20:13
I used "Whitworth" generically. Perhaps the original is 5/16-22 BSF, for which there is also insert sets. Unfortunately, that type leg is not in my parts book so I can't cross-reference the BSA part number to a parts list on stainlessbits.com, or the like, to know the exact original thread.

A bit of self analysis: Why is it I am politicking for British threads when other threads might do? I think, because I regret replacing 3 of 4 sump-plate threads with 6mm inserts instead of getting the appropriate British inserts.

Richard L.
Title: Re: A10 front fork slider repair
Post by: beezalex on 09.07. 2009 20:35
Well, I go for the more commonly available threads because 1. I can get everything for it in less than 24 hours and 2. particularly for safety-critical applications, I like to get high-strength fasteners and those ARE in fact available at my local hardware store in SAE threadform.  By all means, though, if originality to that level is important to you and you're not in a hurry, spend the extra time and money.
Title: Re: A10 front fork slider repair
Post by: LJ. on 09.07. 2009 21:06
I expect poor ole Lannis's head is spinning by now!  *lol*

Note: Is that correct? Lannis's or Lannisses? I give up!
Title: Re: A10 front fork slider repair
Post by: Lannis on 10.07. 2009 00:06
I think "Lannis's" would be right although I've never really thought about it.  Since it's my name, I suppose I can make up the rules if I like.

I had not thought about the possibility that there might originally have been studs in these holes, and nuts went on them to hold the axle caps on?  Were they originally studs or bolts .... ?

I'm suspecting bolts, since my A65s all had them, but studs would make sense too.

Lannis
Title: Re: A10 front fork slider repair
Post by: coater87 on 10.07. 2009 03:13
 I have found the proper thread inserts from re-coil.

 The problem I see is the lack of insert length, maybe I am missing something in their offerings, but it does not appear they offer longer length inserts. Just what we would call "stubs", which are great for most uses, but certainly dont cover them all.

 Take my barrels for instance, the threads are shot completely. I would feel much more comfortable using a coil for the head bolts if they were deep enough to almost bottom out. But the short ones they offer have me worried to the point I may just have to go with SAE from Heli-coil for piece of mind.

 Anyone know of a place that offers the correct thread inserts in longer lengths?

 Lee
Title: Re: A10 front fork slider repair
Post by: RichardL on 10.07. 2009 04:25
Lee,

Recoil is an Alcoa product. Here is a link to their catalog. I think the British thread listings start around page 46 (or thereabouts)> The trick will be finding a distributor for the size you want. It may take a call direct to Recoil/Alcoa.

 http://www.alcoa.com/fastening_systems/commercial/catalog/productcatalog/Alcoa_Recoil_Catalog.pdf

Richard L.
Title: Re: A10 front fork slider repair
Post by: groily on 10.07. 2009 06:32
Studs and nuts, or set screws/bolts? Both my BSAs have studs and nuts on the fork bottoms - already there, not mine.

I always use studs washers and nuts where I can as the fewer times things come out of critical 'oles the better.
I'll happily make things in metric if that means stealing less metal at the receiving end! But I'm also a big fan of 5/16th 24 and 3/8th 24 UNF - a very useful pair of fine threads and easily obtainable everywhere your side Lannis, in good quality as you say. Just means carrying one extra, AF, spanner from time to time. Per MikeN's comment, I use WW very rarely except into alloy as the minor diameter is so small - which is why BS'Fine' came about.
Title: Re: A10 front fork slider repair
Post by: beezalex on 10.07. 2009 14:33
(http://i206.photobucket.com/albums/bb152/beezalex/Clipboard/58forksbottom.jpg)

In steel, fine thread bolts are fine and the threads should be able to endure many, many assembly/disassembly cycles under ideal conditions.  Unfortunately, dirt and misaligned threads tend to limit this.  With helicoil (or recoil, for that matter) the threads become much stronger since they are now rolled, just like the threads on the bolt, so it should be as good as a stud.  AFAIK, BSA never used studs until the OIF forks.
Title: Re: A10 front fork slider repair
Post by: cus on 11.07. 2009 00:12
G'day All,
I might as well throw my hat in the ring as well. I just re-built my front end, & this is
my opinion only, but I would be replacing those sliders rather than mucking around with
the threads on such a critical part of the bike, it sounds like they are pretty old
& are probably flogged out inside as well. Over here I can get new for about $120 ea.,
then you need bushes etc. but could be worthwhile (Peace of Mind) doing 100kmh down a bumpy road.
Then you are right for another 30 years!

regards, Cus
Title: Re: A10 front fork slider repair
Post by: Lannis on 19.07. 2010 21:52
Here's another thread I never responded to with the solution, despite tons of excellent input.  My apologies.

I made it home fine from the trip I made with the old bolts barely holding the axle on, with a good check-over whenever I stopped.

I ended up taking the sliders to a good machine shop, with directions to remove a minimum of metal from the existing holes, and tap them for high-tensile studs of the appropriate length.  They did, and it works great.   It's nice to be able to tighten down properly on those axle clamps!

Lannis
Title: Re: A10 front fork slider repair
Post by: brackenfel on 20.07. 2010 18:23
Hi Lannis,
I think that bolts are the standard fitment rather than studs..
My '61 Flash had a similar problem when I took the front wheel out to look at the brake shoes.. In my case the bolts were worn as well & there was (I hope!) enough thread left in the legs for new bolts. I didn't overtighten them though, just in case... Check the bolts in there are the correct ones - I've found all sorts of strange bolts on my bike that are "almost" right thanks to previous owners...

I suspect this may be a fairly common problem - good luck with sorting it...

Adrian
Title: Re: A10 front fork slider repair
Post by: groily on 20.07. 2010 20:50
Well done Lannis. Whatever might have been there to start with, there's nothing better than studs and nuts. I keep on wondering why the heck bolts or setscrews were used when studs would've been better if there's clearance. Whenever I can I replace anything that screws into something sensitive (and which has to come off often) with a stud . . . and make it a stepped one if the original hole is doubtful. Might surprise the next owner, but I'll be dead by then, so no problem.