seizing ?

[porka123]

Hi All , anyone got any ideas on this ? Twice now in the last year my ETZ 250 has felt like it has seized . both times it has happenned at high speed and without any warning !!
Once about 6 months ago whilst travelling at 65 mph the back wheel just locked up completely and I quickly pulled in the clutch and freewheeled to the side of the road, rocked it in gear and the engine turned so I left it two or three minutes while I recovered from the shock of it .
Then 2 or three kicks and it started without any trouble and I carefully travelled 6 or 7 miles home at 30 mph, I removed the exhaust and put my iphone to it and videoed the piston through a few slow moves of the kickstart to see if there was any damage. All looked reasonable apart from a little scoring to the front of the piston which was obviously the only side of it I could see. I tweeked the oil cable to make sure it was getting plenty of oil and called it a fluke momentary seizure that might never happen again .
I have only used the bike 3 times since, one was a 200 miler with no problems and all speeds up to 80 mph, the other was a short 20 mile round trip with a break , then just recently I was travelling to north wales which is another long trip of about 130 miles, after about 3 hrs , I was doing 75mph on a dual carriagway overtaking a 40 ft container truck, when it happenned again!! needless to say there were a few skid marks and not all of them on the road !
Instictively I pulled in the clutch and it cruised while I once again avoided death under a truck or the knob in the beemer behind me who tooted at me angrily
probably thinking I was being a tool fooling around .
similarly to the last time I rocked it in gear and then kicked it over and it started and I went on my merry way staying under 50mph
I'm very surprised that the back wheel could actually lock up and there not be any damage to the engine or gearbox or even the chain.
on both occasions there was no warning or no loss of power such as the endine slowing and struggling for a while as if it were slowly seizing.
So with the story related to you all, you can imagine that i'm somewhat reluctant to use it again without checking out why it happenned and making sure it cant happen again.
The rear brake is functioning and applys and releases and I struggle to use it to lock the back wheel on its own even in the wet so its not likely to apply itself in an instant and then release .
Prior to me owning it the bike had done about 3600 miles and then stood for twenty odd years under a cover , the previous owner greased all the chrome appart from the exhaust and the bike is remarkably good considering it has sat outside all its life . It now has approx 4300 miles on it as I only use it occasionally for fun .
any help or comments on this would be much appreciated as im very reluctant to use it now .

[DAVID THOMPSON]

my experience with road 2 smokers was in the mid to late 1960's 65 to 69

bikes 250 to 350 were up to the task up to about 65 mph

i do not run my 500cc rotax powered Saxon Tour over 70 very often

i know the mz 2 smokers are tuff stuff but 65 plus mph is being a bit hard on it

a suzuki T500 will run 80 all day long but you will ware it out in a year or 2

my mz rt125 is a large moped when you try to run it like its a big bike you will blow it up....

make sure your using the correct oil and add a bit of mix to the tank when your going to run it hard
and lots of oil has the effect of a lean mix and messes with the 14 to 1 fuel to air ratio
and could make it run hotter
the burn in a 2 smoker is a complex thing and some times a bit of fun sorting out
check also is it starving for fuel at the carb and going very lean and seizing from the heat that results
when fresh fuel does not arrive to cool off the cylinder and head

running out of fuel at high speed can even make an air cooled 4 stroke seize up
a locked up back wheel is no fun

dave

[arry_b]

Timing - check the points gap, and that the points open at the correct 2.7 btdc. Check you've got the correct plug fitted too, B8HS.

Check the gear oil level isn't too high, too much can overwork the engine and cause overheating.

Carb - check for air leaks around the manifold and that the correct main jet is fitted. It could be worth changing the crank seals (not a bad job on an ETZ250, no engine split needed), as they've sat for 20 years without moving. At such a low mileage, the carb shouldn't be worn, one of my old 251s used to nip up regularly until I swapped the old worn carb out. Check that the fuel tap flows at a decent rate, it should flow, rather than dribble. Finally, check the vent in the fuel cap isn't restricted, you should be able to blow through it without popping your eardrums.

My ETZ250 / 300 bitza is happy to run up to 85 mph in short bursts and will hum along as 75 all day without damaging itself, so you've not been abusing it.

[therealche]

Even though the piston looks OK it is probably worth taking the barrel off. When the engine seizes, you get some ally transferred to the barrel. This needs removing or is likely to pick up again.

[porka123]

Thanks for the info, The tank is very rusty inside and I have cleaned it out once and replaced the tap which was completely clogged,and could need doing again it shows no signs of fuel starvation such as not revving or stop start. The float in the carb is set wrong too as it drips constantly from the overflow if you leave the tap on when its not running, so I had it set at half on , which would have starved it slightly of fuel would'nt it ? but not of oil .
I had no quality two stroke available when I re filled the tank so used a lower grade of oil for a chain saw, I guess that would be a bad move also then ?
I had thought that if it seized instantly and locked up the engine it would have done some untold damage like bent the rod or burnt the piston, how come it still goes afterwards ?
Cheers again for your help, this is my first Mz and Im used to Jap four stroke twins and fours, but I really love the Mz its quirky and carachterful so i'd like to feel safe on it and know it isnt likely to seize again.
Josh

[DAVID THOMPSON]

get its little problems sorted and it will go..
half does like the tap half on can be the source of more problems instead of a fix
dave

[breakwellmz]

Thanks for the info, The tank is very rusty inside and I have cleaned it out once and replaced the tap which was completely clogged,and could need doing again it shows no signs of fuel starvation such as not revving or stop start. The float in the carb is set wrong too as it drips constantly from the overflow if you leave the tap on when its not running, so I had it set at half on , which would have starved it slightly of fuel would'nt it ? but not of oil .
I had no quality two stroke available when I re filled the tank so used a lower grade of oil for a chain saw, I guess that would be a bad move also then ?
I had thought that if it seized instantly and locked up the engine it would have done some untold damage like bent the rod or burnt the piston, how come it still goes afterwards ?
Cheers again for your help, this is my first Mz and Im used to Jap four stroke twins and fours, but I really love the Mz its quirky and carachterful so i'd like to feel safe on it and know it isnt likely to seize again.
Josh

I think you have answered your own question here-fuel starvation and inappropriate oil.

[therealche]

I had thought that if it seized instantly and locked up the engine it would have done some untold damage like bent the rod or burnt the piston, how come it still goes afterwards ?

Josh

The force needed to bend the rod is a lot less than breaking the rear wheels grip on the tarmac! Plus MZ's are built like tanks. You might find the performance down a bit if the piston has smeared and the rings can't move to seal the piston. But if you are lucky, once the engine cools down, clearance is re-established between piston and barrel and off you go!

[Carlos]

Hey guys, just jumping on to this thread.


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.


Any ideas that have worked for you guys?