ZB locked up

ChrisQ

Member
I bought a ZB last week that the engine was loose on. Turned over fine by hand. I hooked a battery up and the starter turned it over fine. It didn't have spark, so I resolved that issue, and put some gas in it. It backfired twice and blew a mouse nest out of the muffler. Figured it must have a stuck exhaust valve, and sure enough #3 was stuck. I got that coming around but when I went to hit the starter again it wouldn't turn. I figured the starter jammed with the ring gear so I pulled the starter out. The engine will not turn either direction with a pry bar on the ring gear. Next I took the plug out of the side cover to see the hydraulic pump gear. The gear rocks back and forth, so that eliminates the theory of the hydraulic pump locking up. Pushing the clutch in or out does not make a difference either. I suppose next will be to pull the side cover. I should add, with the valve covers off to fix the stuck valve, everything appeared it was getting oil. I really find it hard to believe a rod or main went tight turning it over for maybe two minutes intermittently with the starter. Has anyone ever seen the engine oil pump lock up? My other thought is if the front main (roller bearing) is shot and decided to lock up. I guess I'll figure it out as I dig in deeper. This just seems very odd. Any ideas?
 
Pull the plugs out and make sure you do not have a cylinder full of gas or oil or coolant. Any of them will cause a hydro lock
 
I don't know how your weather has been, I had a U once that had been
sitting and water was in the oil pan, just from condensation, but it was
enough to freeze in the oil pump.
 
I appreciate the help guys, but forgot to say the tractor is in a heated shop with all the spark plugs out...
 
I don't know the design of the ZB but it would not surprise me if a roller bearing locked up. They can be perplexing as a few days without stress might allow it to free up albeit temporary.
 
I know at this point you'r grasping at straws. check the rocker on the valve that was stuck to make sure it wasn't broken and a piece logged in the cam shaft.
MMDEL
 
Since you said it blew a mouse nest out the muffler, you may have debris in a cylinder causing problems.

Do you know any of this tractor's history? How was it stored?
 
Spark plugs are out, and the best I can see, the bores and valves are clean. The tractor was stored inside before I got it. The battery in it was from the mid 2000's. It's probably safe to say it sat 10 years or so. Just thought this was odd. Not the end or the world. I bought it for a parts tractor, then decided it was maybe too nice, now it's working its way back to being a parts tractor..
 
Our old Za has a pretty bad ring gear on the flywheel. Sometimes when you try and start it the bendix on the starter will jam and not start. When we'd try and crank it she was locked tight. After years of pulling it to break it free I got older and wiser and realized all that was needed was to remove the starter and make sure it was free. Slim chance for you but might be worth looking at.
 
If you said it sat for 10 years. There is a possibility and I have had this happen
before. There could be a ring of rust where the top of the piston has set and made a groove
where the top ring is now stuck into. Of course you will need new pistons and a bore job.
Just a thought. Let me know what you find/
 
I would pull the head and look closely to see if part of your mouse nest or other debris has gotten tamped in between the top of a piston and the cylinder block. On a ZB, the piston comes very close to the block and something the thickness of a piece of cloth can cause the engine to bind if it gets wedged in there. Won't cost you anything to look, and the head gaskets are usually reusable.
 
Use logic. If you were a mouse where could you go and to where. If muffler opem you would
go down to head and look for hole in. Exhaust valve open makes a path. Usually on 2 or 3
hole. Where exhaust valve that was stuck is where you will find problem. I always look at
plugs on motor that seizes. Where stuck valve was will have a rusted looking plug.
Had a U diesel few years ago that was running and just stuck for no reason. Critters had
piled up buckwheat on top of #2. Just enough that when piston hit TDC that was it. Would
not move either way.
 
I can't believe all these guys giving you advice on something on top of the piston!!!!!!!!! They didn't read your posts very carefully. #1 The motor turned freely with a crank. #2
The motor turned freely with a starter. #4 The motor made an effort to start. then blew out the nest. #5 You already took the starter out. #6 You took a bar and tried to move it in BOTH directions. IF SOMETHING HAD BLOWN BACK IN TO THE COMBUSTION CHAMBER WHEN IT BACKFIRED you would be able to move it in the opposite direction!!!
My five cents
MMDEL
 

I agree that a locked up mag can sure happen!!

I was running a 605 MM stationary engine one time on irrigation well - went over and it was dead... The old black Bosch mag was pooched apart like it had exploded slightly... And it was just a shambles of broken parts inside...

But to my amazement - I couldn't time it with a new mag - I finally found that when the mag locked up - with the engine at pumping at full load - it shelled the teeth off the cam gear for about half the entire gear! There were two cups of broken teeth laying in the oil pan...


Howard
 
Not necessarily. If something got sucked back in during the backfiring episode and got tamped into place on top of the piston at TDC, the thing will be locked into position and will not want to turn very easily in either direction. I have seen this happen on a ZA. Read his description of events again. It did turn, then backfired, now is locked up. I had a similar thing happen with a ZA and there was just enough debris on top of the piston to put everything into a bind.
 

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