axle bolts shearing

[bigdalk]

I have the 1-1/4 solid smooth axles and have been shearing the left rear bolt several times. The hole has wollered out on the sprocket and axle so the 3/8" bolt has play. I think that the shock from having play is why. I'm using grade 8 bolts. I have a welder so I could weld up the holes then redrill 3/8" holes or I could just drill out to a 1/2" and use a 1/2" bolt. It would be easier to drill. Anyone see a problem with the 1/2" hole? And yes I have seen the $5 washers that Richards Relics has. Don't plan on doing that.

[Mike]

If it is really bad I would weld the sprocket tube and re-drill it so that you are not increasing the size of the hole in the axle. Then once you get the hole back to stock, you have to make sure that the threads of the bolts go into the sprocket tube slightly so that when you tighten the nut it tightens against the sprocket tube before it bottoms out on the shank. Many people make the mistake of getting a bolt with a shank that is just barely too long and they don't realize that the nut stopped on the shank instead of the axle tube. That leaves just enough play that it will eventually shear the bolt over and over again.

[bigdalk]

Thanks Mike. I appreciate you always offering a quick answer. The nut is going all the way to the sprocket. I think I knew the right answer when I asked the question, take the long road.

For anyone that doesn't know... The easiest way to weld up the sprocket shaft will be to get a piece of copper pipe to slide in where the axle goes and keep it tight against the hole that will be welded up. The weld will not stick to copper.

[LarryW]

Like Mike said but make sure that the threads dont go in the axle either. The threads are a weak spot. It is usually hard to find the right size shank. I just use a longer shank that goes all the way through the axle and sprocket tube(or wheel hub). But I have to use 2 or 3 washers on it so my nut dont bottom out on the shank like Mike was saying. That way you have the bolt nice and tight on the axle tube and the full strength of the bolts shank.

For anyone that doesn't know... The easiest way to weld up the sprocket shaft will be to get a piece of copper pipe to slide in where the axle goes and keep it tight against the hole that will be welded up. The weld will not stick to copper.

Neat tip!!! Thanks

[jerseybigfoot]

I use shoulder bolts; McMaster-Carr
I have also welded richards washers to the sprocket tube which also works.

[Pophamrt1]

Use grade 5 bolts. The more ductile/soft material absorbs shock whereas the harder Grade 8 bolts tend to break under shock load. Grade 8 also wears the axle and sprocket hubs instead of the bolt.

The stock axles are mild steel. Welding them correctly requires pre-heating and post treatment (gradual cooling) to relieve the stress. Simply laying into them with a tig or mig creates some pretty significant stress cracks. If done correctly they’re as good as new. If not, the heat induced stress will be the first area to give.

If you're going oversized, or for an interference fit, use 12mm instead of ½”. It’s the next size after stock and after you mic the actual bolts, it only an increase of about .025" depending on the bolt supplier.

Definitely weld shoulders onto the sprocket hubs to support the bolts and prevent the wear from happening again. Richard’s has some in mild steel. I CNC’d some 1" diameter 12mm ones out of 4130 chromemoly and may have some extras.

Interference fit… if you have the patience and equipment, hone both the axle holes and sprockets with hardened shoulders to an interference fit for the next oversize (12mm). Then press fit the bolts with antiseize. The lack of any opportunity to move prevents initial gap necessary to create the repeated cycles that lead to significant wear (oval holes)—completely.

[onlyonce]

I jumped up to a 7/16 bolt from 3/8. Bought a 11mm drill bit that was one thousands undersized, then drilled both axles and sprockets and reamed hole slightly. Bolt is very tight fit. Mic your bolt first then buy the correct drill bit you require. I would add cup washers or equivalent to add more bearing surface on sprocket hubs. Like has been said before buy a bolt long enough so not much thread is in hole and cut off excess. If not and it breaks it will start gashing the tub as its spinning and trying to work its way out of sprocket. Not as quick a fix as drilling a hole and dropping one in there but it will hold up longer.

[Pophamrt1]

Stock Size is 7/16 not 3/8 right?

Scratching my head about the 3/8" axles bolts being replaced with 7/16" on a Max IV...

Isn't 7/16" the stock size on a Max IV with 1-1/4 solid axles? I just went back and checked the old bolts and the ones I pulled from my Max IV were 7/16". So I checked the catalog and they're consistent with Recreatives part no. 10091: "Bolt Hex 7/16-20 x 2 1/4 (Plated Axle Bolt), All Models."

Going up to 12mm is basically going from 0.4375" to .4625" or only 0.025".

Is there a solid 1-1/4" Max IV version with 3/8" bolts?... Maybe someone used 3/8" by accident or for convenience? I could see now that would cause severe wear/ovaling and snap if in a 7/16" hole. Could that be the original problem causing failures?

[countrycummins99]

i use 1/2 grade nine never broke one yet

[wfo]

I went to the r.i splined axels

[onlyonce]

The reason I was able to jump from 3/8 to 7/16th bolt is due to the fact that I do not have factory axles. Your next jump up in standard size would be 1/2"

[Wobbly]

I've only had my 1991 MAX IV a few months and right away had to replace the left rear axle bolt. -Was able to finesse a replacement into the bolt hole without removing the engine or anything, but was it ever a difficult place to reach! Now that I'm going through the machine, replacing all drive chains, all idler sprockets, and drive sprockets as necessary, I see the left rear sprocket assembly needs some serious attention. The sprockets themselves are in good shape, so I'll weld and drill as necessary to bring the holes to 7/16" or perhaps half-inch. Is there a problem of weakening the axle by drilling it out to 1/2-inch? I see some of the previously offered advice on the topic and will observe it carefully.
I'd include a picture of the formerly replaced axle bolt, but some of you might get sick. It's NOT straight anymore, by a long shot. Shoulder bolts someone suggested sound like a good idea.

[bigdalk]

I ended up welding up the holes and drilling out 3/8". I welded washers on each hole and filled in with metal around the gap. I went with grade 5 rather than 8 on my bolts. Supposedly the grade 8 bolts are too hard. I read not to go up in diameter from somewhere as it weakens the axle. So far, I haven't broken the new grade 5 bolt yet and I've driven it pretty hard.

Now i'm working on fabbing up some headers. I'll post up some pics when I'm done.

[Mike]

Thanks for the update. I'm sure it feels good to be done with that and able to move on to fabbing up something a little more enjoyable.

[Wobbly]

-Should be interesting to see how this works out. I've just ordered the makings to build up my own rear and middle sprocket assemblies for our MAX IV. Rather than the standard 1.25"-ID & 1.625"-OD tubing (3/16" wall thickness), I've ordered tubing from speedymetals.com with 2" OD (3/8" wall thickness.) Found 26T and 34T weld-on sprockets with 2" ID for about $11 & $16 respectively at shoupparts.com.
The end result should be super-rugged assemblies for roughly $50 apiece, including shipping. I'll be drilling 'em to take TWO 7/16" bolts each, which some noble person on this site suggested earlier. (Wish I could remember who, but thanks!) With a little luck, shearing bolts should hardly ever happen again.
One interesting thing I found during disassembly was axle shafts drilled to 7/16" with sprocket tubes drilled to 3/8" and 3/8" bolts installed. No wonder they slopped around so badly!