Possible to repair Tri Z crank?

[poolieZerUK]

Any one had good results getting similar to this repaired?

256678

How was it done?

I was thinking of TIG braze then turning back down to correct diameter.

[yaegerb]

What are we looking at? Are those gouges where the stator side seal rides? Can’t really tell.

[poolieZerUK]

Yeah,

it's off an engine I picked up that had been sat without a stator cover on and corrosion has gotten into the crank on the area around the crank seal.

Decent cranks are thin on the ground and all available seem to be suffering from the same. I have three like this:(

[oldskool83]

Why not buy a new one that's tri. Yz250 is the same.

[3Z with Fangs!]

Actually I don't believe YZ250 Is the same. The flywheel taper is different. You can use it but with the YZ Flywheel and stator, you'd also lose lights going this route.

[yaegerb]

Yeah,

it's off an engine I picked up that had been sat without a stator cover on and corrosion has gotten into the crank on the area around the crank seal.

Decent cranks are thin on the ground and all available seem to be suffering from the same. I have three like this:(

I am pretty sure you could get that tig welded. There’s really only one place I know that could fix that appropriately but it’s in the States and may cost a lot for shipping. I would try crank works in Arizona.

[ponderinjunkman]

Is it heat treated-hardened? I'd be hesitant to weld on it for fear of warping. My inclination would be to turn the bad area down and shrink a sleeve on. Of course, you want to be sure the crank is true before cutting! I also suspect there is a center hole inside the crank cheek, which would guarantee accuracy. So if rebuilding the big end, fix the seal surface before assembling.

[Dirtcrasher]

I had a couple RM125/250 cranks TIG welded when I was in my twenties, both had wear spots where the oil/water/seal had been riding on.

Guy fixed them in about 45 seconds and I ran them for a few years before I moved onto bigger bikes and trikes.

Shouldn't be a big deal...

[El Camexican]

You can weld that and get it turned, MIG, TIG, stick, whatever, but use steel, don’t braze it! Brass is soft. Best done with the crank pulled apart. If cost is no object and you want the best, send it to Falicon and get it balanced at the same time, but any competent custom machine shop should be able to build up the shaft and turn it to size.

[yaegerb]

Why not buy a new one that's tri. Yz250 is the same.

It is not the same

[El Camexican]

RH side is the same as YZ, but the LH side used a different diameter. If he was willing to give up his lights and could find a YZ ignition to go with a YZ crank then I believe it would be an option.

[Gabriel]

I've seen it done. Not a Yamaha, but small crank nonetheless. The welder REALLY needs to KNOW what he's doing. Not some green horn.

I watched an old guy fix one in a machine shop I worked in years ago. The crank was first turned undersize. Then, Tig weld, Air hardening tool steel rod & it was done mostly submerged in a pan of water. Left to cool slowly and then set up on an ID/OD grinder to finish.

Can it be done? Yes, absolutely. Easily....No.

[poolieZerUK]

Same boat for YZ cranks in terms of wear and availability. Not sure whether the YZ cranks are available new but tbh haven't looked though wouldn't have thought so.

No bottom end power with reduced flywheel mass and loss of lighting coil unless you use sought after aftermarket road legal ignition/lighting stator.

The reason I thought about braze was because I have some rods and a machine:lol: I know Mig is tough material to work so in hindsight probably better than braze for friction area.

As for being toughened I put an old file across damaged area and it dug in fairly easily now I'm a carpenter not an engineer so don't know how that compares to the Rockwell scale if it's a useful indicator at all.

[ponderinjunkman]

If you can cut it with a file, it is plenty soft to machine. After looking at the pictures again, I would be tempted to emery cloth it, and see if a new seal will touch all around. May not need more than that!

[fabiodriven]

If you can cut it with a file, it is plenty soft to machine. After looking at the pictures again, I would be tempted to emery cloth it, and see if a new seal will touch all around. May not need more than that!

I just looked again because this was said, and I agree. You don't have anything to lose by trying. It looks like it might be OK.