MZ/MuZ Riders

Whilst cleaning the TS125 yesterday, I noticed that the rear chaincase was cracked from below the speedo drive, right up to the top flange, with the broken-off part being held in place by the upper boot. No problem, I have a spare. But looking at the spare I have found a hairline crack in exactly the same position.

Has anyone else seen this crack, or had their chaincase crack similarly? Anyone know the cause? I'd really not like to have another break!

(sorry no photos, I didn't take any at the time and it's not so convenient at the moment)

Can you show pictures please?

In my experience with Mz Ts 125/150 chaincases, age and a incorrectly tensioned chain slap is always the problem. Or the rear wheel or how it situated on the swinging arm is crooked
Everytime I cleaned the chain, or replaced it, I would measure the chain slide adjuster's and turn them equally.. just like my handbook informed me.

The TS 125/150 chaincover does not have this bush.

I've had a chance now to get some photos.

The fitted one is at the top, my spare is at the bottom. As you can see, similar damage to them both.

The chain was a bit slack, but not in the slap-zone, wheel aligned nicely. I haven't checked the spacer yet. As the barrel's off at the reborer's, I'll have plenty of time to do a very careful assembly to check clearances etc.

Of course, it could be an old hairline crack which chose this time to open up.

+ 1 to Puffs' comments. I don't think this particular plastic was ever of that good a quality - or flexibility.
Keep us posted with how the rebore job goes. (I've had 2x 125 standard barrels rebored to 1st. o/size, and problems with both.)

That plastic is quite akin to a bakelite sort of feel. I have no idea how resistent to breaking they were when brand new, but I've also had to replace two of mine (one on an ETZ250 the other on an ETZ251). My brother's ETZ250's one also broke and was replaced. I think it's common. Rocks, road debris etc can bump up perhaps from the road? Knocking them with removing/installing the wheel perhaps? Of course chain binding up in the back there is a likely cause too if ever the engine is removed and the chain slips back in through the chain gaitor and then the bound up chain puts pressure on the case.

Thanks all for the input.

I'm leaning towards this having been damaged due to the machine having been rolled back with the chain disconnected. As earlier photos seem to show a small crack before we had to remove the engine, I assume it's damage inherited from a PO. Unfortunately, there's a chunk missing on the broken one, so I'll have a bash at repairing the spare. Puffs' silver one looks really smart, I may well crack open a rattle can. I have a replacement part on the way for the bike.

Don't know why these weren't alloy - Zschopau seemed to have a good supply and the Russian stuff I used to run had nice alloy chaincases.

Rebore: I'm expecting to pick up the rebored parts tomorrow PM. Will keep you posted on progress, JayBee. What issues did you have with your rebores?

The chaincases were made from alloy on the older models. But they changed it to bakelit in case the chain broke it should leave the bike without blocking the rear wheel...So it needed to be "breakable"...

They don't like being stood on either, they are quite strong for what they are. A chain does revolve in them. So you would expect micro cracks with use and age. Much better to have the Honda Yamaha steel type. As they can be manipulated by a small hammer/ piece of wood and the reform quite well.