Seized Engine

Has anybody had any luck in bringing a seized engine back to life without a major overhaul of the engine? I don't know the history of this KZ750F other than it has 25K miles and the guy say he was just accelerating from a stop sign when he said he heard some noise and the engine seized. The rear wheel locked up and he skidded about 5 ft. An ideas on how to approach the repair?

If you haven't done so already, I'd suggest checking to see if the drive chain broke and is the culprit and not a seized engine.

However if the engine is indeed seized, tearing it down to see how extensive the damage is would be the best course IMHO.

Post edited by: RetroRiceRocketRider, at: 2007/11/14 22:42

I've had luck with getting a reluctant engine to return to normal operation BUT this was from long duration sitting in unfavorable conditions NOT from a PO's description of a driving lock-up.

Generally speaking (I'm hoping for your sake for the disintegrated drive chain too) when an engine "locks-up" while it's being operated... it's not likely to recover from it without a tear down.

I'm in the same boat by the way... Just figured this out today while cleaning and dismantling my "new" '79 650c and discovered the engine would lock-up within a 360 degree rotation of the crank (at the generator). So I'm expecting a full tear-down at this point

Hey, If its not the chain, tear it down. Think about it, how could you enjoy a ride (even a short ride) knowing that the rear wheel could lock up at any given moment. And another thing to check... Make sure the rear caliper didnt stick the pads to the rotor. I say this because my front pads seized yesterday while going 45mph. This bike had 3075 miles when I got it and its a 82 so it sat most of its life. I took all the brakes apart and flushed the systems and all was working fine untill she started slowing down and then I forced it off the road. Thank goodness there was no traffic behind me! I took the pads off and drove straight home. Play it safe, its your skin.

with dirtbikes it's common to pull the head off then beat the piston down by placing a block of wood on the piston and hitting it with a BFH.

But they are single cylinder and 2 stroke....

I would try it anyway, the worst you could do is damage a piston; with the motor likely needing so much help why not??

Face it, you are going to have to remove parts to see what is causing the lock up. Can you rotate the engine in either direction? Just pull the engine and take it apart. It is not that hard. Pull the head and cylinders first, They weigh alot. Then, you can see if the pistons are frozen and what shape the rod bearings are in....chris3

Will I be able to see the primary drive chain by dropping the oil pan? I would think that with the primary drive chain gone, the engine would turn; jsut that you wouldn't have any drive since the secondary shaft would be disconnected

No, you only need to remove the left side engine cover (pictured below) to examine the drive chain.
It's not that common, but sometimes the chain guard (also pictured below) behind that engine cover will come loose and drag/bind against the chain. Although I doubt that this small guard would be enough to actually prevent the engine output shaft from turning - stranger things have happened though.

With simple hand tools, you should be able to pull the left side engine cover to check it all out in about ten minutes.



Post edited by: RetroRiceRocketRider, at: 2007/11/15 21:23

Um, 4R, I believe he said "Primary drive chain", as in the primary chain that runs between the crank and the secondary shaft and drives the clutch basket.

Yes you can see the primary drive chain by dropping the oil pan.

I have never heard of a primary chain on a 650/700/750 breaking, but there's a first time for everything

I have a 750 twin motor that locked up while being ridden, (not mine at the time), and the reason it locked up was overheating causing the pistons to seize, and it freed up when it cooled down. It is a bear to turn over (even with no plugs in it) now.

Post edited by: steell, at: 2007/11/15 21:23

You are correct steell.

I was refering back to my first post where I mentioned the drive chain. I really should have noticed he said primary drive chain. :whistle:

I think working two jobs is rotting my brain and is the cause of this. :S

That's my story and I'm stickin' to it! :laugh:

Post edited by: RetroRiceRocketRider, at: 2007/11/15 21:40

Since this is a shaft drive bike, why does everyone keep referring to the drive chain?

i locked one once.
take off the oil pan and look at the rods.
i am willing to bet it is locked there.
i have never heard of a primary chain breaking.