Topic: epoxy limits

[zoomer]

so in the meantime I am rebuilding a wee twostroke scooter. It has a kickstart shaft which passes right through the crankcase, no bearing, just the steel shaft wearing on the crankcase. It is way oval so I am looking to build it back up.

There is less than 0.25" of metal left in the alloy tube.

Option 1: get it drilled out to round and a brass insert made up?
          2: fill it full of what you American guys call JB weld and drill it out myself with a handheld drill??
          3: insert the shaft and stuff the void with jb weld, twist out the shaft before the epoxy goes off?? Might only be a mm or so of epoxy on the unworn side.
I have never used this epoxy stuff before. How hard is it?

[chrisf]

In my experience, JB weld and other mixable epoxies are pretty hard. But it depends alot on how it is mixed as well as the ratio. Personally, I were trying a low cost method, I would drill it out, then hone in with a brake honer, then turn a brass insert. A lot of steps, no doubt, but you would also have a piece of mind knowing it was done properly.

I suppose you could also fill it with TIGed material, then drill it, then hone it as well. That will probably cost as much as the JB weld method.

--Chris

[Uncle Ernie]

A close, clear, in-focus, well lit photo would help. I can't picture what you're talking about. 
Is this repair for esthetics, does it keep dirt out, hold parts together, is it stressed while in use?

[zoomer]

the problem with drilling it out for a bush is that the drill bit will want to wander off centre. It would take a rock solid engineering drill press to hold the bit whie it chipped out the unworn side to the bush radius.

In operation the alloy tunnel through the case holds the shaft while it operates the quadrant onto the 50cc crank on the exterior lft side. Barbaric but necessary. Not a lot of stress but enough to wear out the alloy. With all the slop the quadrant has a hard time engaging the gear. The old models had a pullstarter on the right side. Crafty Italian redesign.

[Uncle Ernie]

I think I might get it... I wonder if you could get bearings to fit the shaft and epoxy them in the case?  Anyway, if the lever is not pushing on the material itself, I would think JB Weld would hold your bushing in there. I don't think it would hole it's shape while trying to pull your tube out- why not leave it in there?  Maybe score the sides first.  JB Weld has metal in it somehow, so it's not just a regular epoxy.

[zoomer]

maybe I'll have to do the whole photo upload download thing, shouldn't be necessary.

There's no "tube" as such, just a hole through the case outside of the crankshaft sealed area. No room for bearings. The extra bit they added to the case design protrudes to support the kick shaft until it clears the frame. Only .75" diameter.

The epoxy stuff I have is "CRC emergency metal repair" you break off a piece and knead it to release the hardener. It hardens in a few minutes.

[Steve F]

I'd try to stay away from the cobble-up method of using epoxy and JB stuff.  If you know a competent machinist, he should be able to bush it quite easily, given your description of the problem.  Is this shaft sticking out of a cover that can be removed?  If it is, that's even better.  The correct method would be to bore the alloy crankcase to accept a light press fit of a bronze sleeve, and then bore out the sleeve to fit the shaft in the same set-up, all done in a milling machine.  No drilling is done, just boring. If you do it right, it'll last for decades.

[zoomer]

did the pic thing, still undecided. How many hours for a whiz bang machinist? It's about 3/4" thick. Other case half is similar.

[kazjim]

As an ex-machinist myself, I'd say if you clocked that up in the mill, got the bore centre-line correct, the total time would be less than an hour ....

Just to bore and ream the hole to a larger size ...

Then turn up a phosphor-bronze bush (self-lubricating... should last nonger than brass or straight bronze...)  - probably another 1/2 hour...

press bush into housing (0.002" fit and Loc-tite probably .. not sure of the grade of the alloy.... 0.001" maybe better ...) probably another 1/2 hour ...

Allow 1 hour for f**kups and smoke breaks ....

3 hours should have it all fixed up ! (here in Oz, thats about $300 .....) whats a new housing worth ?

Cheers, good luck!
J

[Terry in Australia]

None of those epoxy-based products is hard enough, so don't waste your time mate, JB weld is a brilliant product, but it's still just glue.

As a dodgy back-yard engineer, I'd just set it up on a mill/drill and bore the hole larger using a slot drill (don't buy new, I always try to buy them cheap on Ebay) of the appropriate size (a standard drill bit would be no good as it'd "wander" around the existing hole) then turn up an alloy, brass, or bronze sleeve a couple of thou bigger than the hole's ID, that I'd freeze overnight in my beer-fridge and "shrink-press" into the hole.

A quart bottle of Jack Daniels finest "fighting Soup" should cover it! Cheers, Terry.  

[zoomer]

The boatyard across the way might be able to fill it full of tig without melting the whole thing into a blob? I have done a wee bit of stainless tig welding, only with very thin wire, not much experience to go on but I just can't see it working.

I might have to hope some dodgy backyard alcoholic machinist pops up on this side of the ditch.

[Terry in Australia]

I might have to hope some dodgy backyard alcoholic machinist pops up on this side of the ditch.

Don't worry mate, there's plenty of dodgy backyard alcoholic machinists on your side too, we're well spread out, ha ha!

[crazypj]

You clock it on the oil seal bore and, as Terry said,  use an end mill to rough it out round. (as your boring you could use a 4 flute slot drill and step up the sizes if it's a bit too flimsy to take out it one hit or use an adjustable boring head with single point tooling)
 Ream to a known size  and make a flanged bush (with at least 1.5mm wall thickness)to fit into back of oil seal housing (usually there is a least 1mm clearance behind seal)
Set up is going to take far longer than the actual machining, but it should be possible to do it in about 40mins or so.
If you use boring head you may not need to ream hole.
PJ

[zoomer]

Mostly greek to me there mate. I used a mill once in my life, 20 years ago. No oil seals involved btw.

[zoomer]

would filling it up with epoxy make it a home drill press job to "rebore" and then bother the machine shop for some bushes?

[Terry in Australia]

would filling it up with epoxy make it a home drill press job to "rebore" and then bother the machine shop for some bushes?

No mate, the epoxy is softer than the parent metal, and so the drill would just chew through that, further "oval-ing" the hole. The slot drill/ milling cutter had a flat bottom, not pointed like a normal drill, so it doesn't try to find the centre of the hole like a regular drill bit will. Cheers, Terry.