A10 front fork slider repair

[Lannis]

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

[RichardL]

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.

[Lannis]

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

[RichardL]

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.

[Lannis]

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

[groily]

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 . . .

[MikeN]

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

[LJ.]

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' 

[Lannis]

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' 

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

[Lannis]

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

[RichardL]

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.

[groily]

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.

[Brian]

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.

[beezalex]

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

[RichardL]

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.