Belarus 420A motor froze


New User
I have a 420A Belarus that backfired and the motor froze up. We just bought the tractor, it has been consistently run since before our purchase. Everything I have read has been a result of the tractor sitting, anyone have a suggestion for one that s been running?
An engine that is froze up from sitting, usually meaning years of no use, or it can happen in a couple
months if rain is getting in the cylinders, is caused by the rings rusting to the cylinder walls.

One that locks up running is a result of mechanical failure.

If it is locked tight, will not turn either direction, that is typically caused by seized main bearings,
commonly caused from running with no oil pressure.

If it was running and the next time you went to start it was locked, pull the starter. It may be jammed or

If that looks good, try prying on the flywheel teeth, see if it will turn either direction. It will be a
matter of taking things apart until you find the problem. Start with the easy stuff first, the timing cover,
oil pan, gear driven accessories. You'll find it!
Did your 420A arrive from the factory with the Engine Decompression option?

Try turning engine over with the Decompression lever in the start in this shall remove the compression..
Hello AT welcome to YT! First let me say I know
nothing about working on a Belarus. There is a slight
possibility that something happened to the starter and
is now locking the engine, this is what I would at least
check for. Otherwise I think JD D has you going the
right direction to check the valves.
The 420 engine is basically a Deutz copy, and they will run backwards if during a cold weather
start the compression lever is operated at the wrong time of the engine rolling over, but as
said, pull the decompression lever full up as if its was a cold weather start, pull the starter
and try a little bit of leverage against the ring gear.
I have had one that had a stuck pilot bearing also, and maybe this backfire did some damage to
the clutch area? slim idea on that.
but a better description of what the engine was doing at the time of backfire is needed, ie:
rolling over, and the decompression was operated? was attempting to start[ puffing smoke],
grinding noise heard, starter was noisy/operating is somewhat spurts of power. And when they
backfire and run a lot of black smoke comes out of the air intake/exhaust, or any other leak it
can find :) so the actual time/sequence is needed? a backfire as said could be a internal failure
while it was running
hope it helps
Well this a very late reply for sure, but i am curious as to what you have found as a reason for backfiring.. reading that it was running at the time i am leaning towards possibly a broken injector dumping fuel in a cylinder? broken piston? dropped a valve in the cylinder? maybe the backfire didn't happen but massive fuel or breakage is what you heard/saw result of in the exhaust?
hope to put your findings in my file of things about the these machines.

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