2-stroke MZ-250 piston reverse-assembled, 4 yrs running !

Can you believe this ?!

4 years ago I bought a MZ 250 single 2-stroke of 1975, which judging
from the original tyres and rust in the tank, had just been parked for
a few decades. I've used it only for 100km per month since then.
And it never ran as smoothly [especially not idling] as I've seen these
east German bikes do.

Recently the engine sounded noisy, so I suspected the small-end
bearing. From the book: I confirmed that I could get a 18*22*24
needle-roller cage before I removed the head.

The 'new' bearing seems no better than the original communist
manufactured one, and the big-end seems also not perfect.

Since the small-end doesn't even rotate - it just rocks back and
forth - I can't see why it needs needle rollers. The force from each
explosion would perhaps be better handled by a brass bush - or a
spring !?

Strange marks on the cylinder wall and a 'tapering' below the one
port lead me to investigate and find that the piston had been installed
REVERSED [back to front] !! I.e the ring gap coincided with port.

I intended to just reverse the piston and rplace the original needle-cage,
because the 'new' one', has single needles over the full length [24 mm]
instead of two sets, offset, like the original.

Obviously the ring which 'shaved the taper' below the port must be
worn; although I can't see anything.

I guess no parts are available, since the factory closed when the
Berlin wall fell ?

Have any other readers had experiences with MZs ?
Comments and advice are welcome.

== Chris Glur. easlab @ absamail . co . za

 

Parts are pretty plentiful - cycle parts for the early ES models maybe a
bit tricky. Still as cheap too.

Try BSA-Regal
http://www.bsa-regal.co.uk/

Burwins
http://www.burwin.co.uk/

and the Daddy of them all:
Fred Rogers (may not be open as he's recovering from a serious illness)
01606 593638

 

not@top-post wrote:

[snip]

Check http://www.mzridersclub.co.uk and contact them.
Very helpful lads, they are...

--
Tom :{)
BOTAFOT#105 COFF#02/ OSOS#15 KwaSoH#2
SR500(.de), SRX-4(.jp)
Make it idiot-proof and someone invents a better idiot...

Hiroshima pics: http://makeashorterlink.com/?C12E12B97

 

Had an interesting reverse issue on an MZ 175 back in the 80's. I was
going along the A13 London bound on the (?Bow floyover?, the one where
Newham meets Tower Hamlets) at about 8.30 in the morning and trying
rather timidly to filter though some tightly packed traffic. Snatched
the clutch but managed to keep it going OK, or so I thought. Cos when
there was space I let the clutch out, a lot more carefully this time,
and discovered that I now had a reverse gear, indeed 4 reverse gears.

Scared me shitless and created much alarm in others. Lots of hooting,
as in horns from the cages and wagons, and laughter from the bikes
ensued. Still it got me there and back.

Brian