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

[Carlos]

Today I ran my MZ250 about 200km at 100-110km. At the end of my trip I was slowing down from the highway and my bike started to lose power... I thought it was a fuel thing.

Eventually it rolled to a complete stop and turned off.

When I tried to kick it the kick starter lever was rock hard. The motor seized. (in a very non dramatic fashion)
When i rock it in gear forwards the wheel just slides, reverse however the engine gives a "CLICK" sound and doesn't move.

How do i unseize it! I can trouble shoot the cause of this later I just need to run her 10km to my friends house.
What I think is i har to buy some cheap crappy oil from a petrol station, this and high revs on a warm day lead to overheating.

I would really appreciate any advice as I'm 200km away from home!


Any ideas that have worked for you guys?

[DAVID THOMPSON]

take the top a part and clean up the mess with emery paper and a fine file
hope no broken rings
and get some good chain saw oil and give it a try

these things are big mopeds and every one runs them at 750 cc speeds
i am surprised we do not see more it blew up stories

what most of us need is a bmw r60/6 (a daily driver)

being in NZ i would travel with a spare piston and barrel and some ring sets
as spares are long on arriving

[Carlos]

An update to add to further attempts-

I waited all afternoon and half way through the night till it was nice and cool and went back to check the engine. Still rock hard.

Same clicking noise when rocking it back.

I was near a small incline so I pushed the bike up it and did some nice reasonably fast attempts and jump starting. The rear wheel just locked up and I skidded to a stop.

I have not tried yet to remove the plug to see if there is a pressure build up as I'm not at home my tools :/

Im getting worried

[DAVID THOMPSON]

sounds like a broken ring forcing things will just ruin more things
stuff it in the back of a van and take it home

[Carlos]

take the top a part and clean up the mess with emery paper and a fine file
hope no broken rings
and get some good chain saw oil and give it a try

these things are big mopeds and every one runs them at 750 cc speeds
i am surprised we do not see more it blew up stories

what most of us need is a bmw r60/6 (a daily driver)

being in NZ i would travel with a spare piston and barrel and some ring sets
as spares are long on arriving

Cheers Dave for this straight to the point advice.

One quick question, I assume I am applying chainsaw oil directly on the piston to let it soak into and around etc?

When this works I will not run him so hard. I just hear stories from all the older German men saying they used to run their 250 with a side car and their wife with saddle bags etc etc... Running down the autobahn at 110km.

Gave me false expectations I guess. Tho I have a really strong gut feeling about this crappy no name brand 2 stroke oil.

[Carlos]

sounds like a broken ring forcing things will just ruin more things
stuff it in the back of a van and take it home

Just noticed this comment now.

I have decided to drag him home... He has to sit for a few days unfortunately in a supermarket carpark while I organise things. I'm really sad to hear your opinion, worst case scenario am I looking at a new motor?
The bike only cost me 750... Don't want him to vanish

[DAVID THOMPSON]

i pulled a 125lb fiberglass sidecar with a bmw r60/2 1962 motor never ran it what i felt was hard
and it was trash in 15,000 miles
but it is very Hilly here the local joke is when you go some where your always going up hill

[AlanJ]

Hi Carlos,
I bet Dave is right about the seizure and if it's the top ring and it has broken through to the top of the piston there is only just over 1mm clearance in that area so that could be the reason why it won't turn over. You might be lucky and only need a new piston and rings and a bit of cleaning up. Just had a thought, if it is a ring problem how ever it is, make sure you can account for all the bits before you fit the new piston.
Wish you well Alan.

[DAVID THOMPSON]

pull barrel up a bit and use a clean shop rag in between barrel to case opening to catch the junk that may fall into the case

but there may still be some junk all ready in there if piston broke or hole in top

[breakwellmz]

Have you had a look down the plug hole hole/exhaust/inlet ports/head(?) by taking off bits? It`s pretty basic and easy to take these things apart.
It won`t heal itself unfortunately.

[Carlos]

Thank you for the replies.

These pictures show great encouragement... Please give feedback to the next step.

Obviously cleaning and removing the small particles is a must.


Carlos

[DAVID THOMPSON]

see post above about use of good shop rag and take the barrel off

[Carlos]

So after the a top cleaning of the piston and am overnight soak I am able to apply a gentle - moderate blow to a piece of wood and have the piston move down.
More soaking some permeating oil and the kick starter won't move. Even tried putting it in gear and turning the rear wheel by hand. This however gives that clicking sound i mentioned earlier.

The piston bore is spotless, not a mark, I travelled the plus piston down 9mm. The piston was sitting at 17mm approx from the top of the bore, is that top stroke? I can't find that in my MZ manual.

Is the next idea to keep pulling bits off? I inspected the mechanical ignition side of the engine to see the chain and sprocket, all looks great.

Thanks in advance

[Carlos]

So, as you can see I made some headway.

Even tho the piston is free the rear wheel STILL WON'T TURN IN GEAR. I have noticed that the bracket the piston is attached to its stuck in place. It does not move and this is stopping the full revolution of the engine. It looked pretty dry in there, have not checked the oil yet tho it was topped up a month ago.

How would you proceed? Can I lubricate round the seized bracket? (please someone tell me the correct term for this) could I use WD40 or go with chainsaw oil? I do not have any gearbox oil on hand you see and I don't know if that penetrates.

Ideas please guys we are nearly there i feel.



Carlos

[Carlos]

You guys still with me?

When I order new rings where do u take the measurement for ordering? On the piston I assume. And my piston ranges from 71.2mm - 71.5mm do I assume that this is a 71.5mm ring i must order?

Also the connecting rod has slowly started to free up, does anyone know a way to lock the motor so I can gently nudge the rod free and move it round a full revolution eventually?

Thank you

Carlos