MZ250 motor slowly seized.. Is there any way back from this?

[AlanJ]

Hi Carlos,
First thing the bracket is a connecting rod or con rod, and the size of your piston is punched into the top of the piston, often called the crown of the piston. There is a bearing at top and bottom of the con rod but if you can first tilt the piston back and forth freely then the top bearing is probably ok next move the piston and con rod back and forward (called the big end) and if that's ok then it might well be a main bearing problem, If that is the case sad to say it will be an engine rebuild, and even sadder to mention that from your posts giving not too much knowledge of these things you are going to need some local expert help I would think. Anyway Carlos, power to your elbow for having a go.
Wish you well, Take care Alan.

[breakwellmz]

You won`t see much oil in there, it`s only the oil in the petrol that lubricates the engine.
Don`t bother about rings yet if at all, it sounds like a seized big end to me.
Glad you took it apart though, well done!

[AlanJ]

Hi Carlos,
The con rod with the piston attached flops about backwards and forwards if the big end and small end bearings are ok then it's probably the mains, but what I can't quite understand is why the piston dragged as it did and the only thing I can think of is you had a lack of oil problem, it's starting to look that way. The only good part in all this is there are brilliant posts on u-tube from the old MZ company on engine build etc and the Z's are so easy to work on. The parts are easy to come by and cheap.
Wish you well Carlos Alan.

[DAVID THOMPSON]

i think you have lost the bearing on the rod in the crank end
and the whole thing needs to come apart

[AlanJ]

Hi Carlos,
If it's the big end bearing that seized on the up stroke then it could be the forces trying to turn the flywheels are directed up the con rod and pushing the piston hard against the front of the bore and dragging it. Anyway you should be able to tell if the big end has seized and as Dave has said if it has it's a strip down, and if that's it you will need a new flywheel/crank assy and you might as well do new bearings and seals etc.
Anyway that's enough of me, I hope you get it sorted Carlos, Take care Alan.

[Carlos]

Hey guys,


I have the motor free and spinning with the connecting rod doing full revolutions with the crank. However, I need to know how tight the connecting rod is on the crank.

It feels really tight and on any website I can not find or see how free it is supposed to be. Using Gabors MZ laden and their technical parts drawings I can not see any needle bearings (like the ones that locate the piston, I assumed their would be similar ones).

Now im really confused. I really do not want to strip apart the crank and the rest because that is a bit far past my expertise, just to find out it was normal all the same. I see there are bearings on either side of the crank, however It does not feel like that is the problem. It's when I hold the motor still and move the connecting rod. That's when i feel resistance.



Thank you

[Carlos]

Hi Carlos,
First thing the bracket is a connecting rod or con rod, and the size of your piston is punched into the top of the piston, often called the crown of the piston. There is a bearing at top and bottom of the con rod but if you can first tilt the piston back and forth freely then the top bearing is probably ok next move the piston and con rod back and forward (called the big end) and if that's ok then it might well be a main bearing problem, If that is the case sad to say it will be an engine rebuild, and even sadder to mention that from your posts giving not too much knowledge of these things you are going to need some local expert help I would think. Anyway Carlos, power to your elbow for having a go.
Wish you well, Take care Alan.

Hey Alan,

I think we found the problem then. The connecting rod does NOT flip or flop back and forth on the big end. It is tight as I easily turn the rear wheel while the bike is in gear.

Next step is to change that bearing i gather. Now that I know what we are dealing with I can look more precisely on YouTube etc for guides... Fingers crossed I don't need special tools :/

If you have any advice I of course would be happy to take it in.

Thank you

[Carlos]

i think you have lost the bearing on the rod in the crank end
and the whole thing needs to come apart

I think you are correct. Thank you for your replies. I look forward to pulling apart this beast and getting him fixed.

[Carlos]

Hi Carlos,
The con rod with the piston attached flops about backwards and forwards if the big end and small end bearings are ok then it's probably the mains, but what I can't quite understand is why the piston dragged as it did and the only thing I can think of is you had a lack of oil problem, it's starting to look that way. The only good part in all this is there are brilliant posts on u-tube from the old MZ company on engine build etc and the Z's are so easy to work on. The parts are easy to come by and cheap.
Wish you well Carlos Alan.

Hi Alan,

I found those YouTube old school German videos. Really good stuff.
However they use special tools.
I do not have any.
Right now I'm stuck on removing the clutch unit. Is there some way to lock that outer sleeve with the fine thread so I can free up the clutch without a special tool?
Would some careful use of some jimmy bars so the trick?

Here are some updates for the rest of you guys. Thanks so much for ask your help.

[Blurredman]

Hi there. You need a circular clutch puller (do not use the armed ones!) to get the clutch off the crank.

This is the only special tool you actually really need..

[alexxx]

At the very least you need a new piston and rings, that piston is useless now.

[Mzts125]

Im rebuilding my ts125 and i did not have the puller but 2 big flat head screwdrivers and a hammer got it off without damage... i guess i was lucky...

[therealche]

TS125 has a totally different clutch arrangement to the 250. If you don't use a proper puller on a 250 you run a 99% chance of screwing up the clutch