Engine is seized in my 73 cb750, What is going to need to be replaced?

[sam_watts01]

My engine seized over the winter and I believe that it is probably from water that was in the gas. If I can manage to get it un-seized with some type of penetrating oil, what will need to be replaced? I have been told everything from just sanding down the rings to a full engine rebuild. What do you guys think?

 

[cyclebuster]

heck i have rode dozens of them i did nothing to. unstick it and run it for a day or 2. pull all 4 plugs and spray a whole can of pb blaster into it. put it in gear and rock it hard back and forth, it will come free. likely it will even be fine.

 

[sam_watts01]

Thanks, I'm gonna give it a try.

 

[cyclebuster]

any luck?

 

[MK3Brent]

Yeah, I'm in the same boat. Hahah.

Any luck?

 

[Field]

After pb blaster try to "push start" it, as in get it in 2nd or 3rd gear, run with clutch in, then release. Obivously for this scenerio you can leave it on the "off" position instead of "run".

What'll the condition be like for the engine? I dunno.

Taking it all the way apart, having it honed, and replacing the rings maybe... but I doubt it unless your rings were bad to begin with.

 

[Dave]

My bike was seized when I rescued it out of a snow bank several years ago. I put Coca~Cola in the cylinders about 1/2" deep. Let that sit until it evaporated. Then I squirted in a bunch of ZEP (Industrial version of WD-40) and lets that sit a few days. Then I broke it loose by bouncing on a nice long snapon breaker bar on the alternator nut.

Been riding it ever since.

 

[MK3Brent]

My bike was seized when I rescued it out of a snow bank several years ago. I put Coca~Cola in the cylinders about 1/2" deep. Let that sit until it evaporated. Then I squirted in a bunch of ZEP (Industrial version of WD-40) and lets that sit a few days. Then I broke it loose by bouncing on a nice long snapon breaker bar on the alternator nut.

Been riding it ever since.

glad that worked for you. Was the bolt and crank totally solid before you started that? mine is so tight, I'm worried I'll snap it doing what you did, bouncing on a breaker bar

 

[Field]

Well it is meant to have a load of upwards of 850lbs at the crankshaft (500lb bike, 200lb rider, 150lb rider, any which numbers could be higher) so you probably won't break the bike. I don't know about your breaker bar. You can always put a long pipe on the breaker bar (like 8ft). If you do this you'll be no where near the part that is breaking (that'll be inside a pipe anyways).

Or again try to push start down a little hill or something. Technically even having the rear wheel suspended in gear, and turning it would give you way more leverage. Because of the gearing it is in your favor as you turn the wheel the engine will barely turn at all (allowing more leverage).

 

[MK3Brent]

No, torque on the bolt is not equivalent to the force the bike needs to produce to move a mass. This bolt just holds the rotor on. The axial force on the crank bolt is still limited by the material. In this case,I don't know what Honda uses, perhaps a high carbon steel. Torsion is nasty on bolts, and will definitely snap.

 

[dirtdigger]

That bolt torque is 72 ft/lbs for everyones information. If the motor wont break free at that torque then I would disasseble and rebuild it properly. If this are stuck that bad do you really want to take a chance on running it when parts were obviously rusted that bad? Think of all the expensive parts that can be ruined if you break a ring or score a bearing because things are dry and or rusty. On the other hand it may be a good excuse to take it apart and drop in lightened crank, stronger rods, big bore, cam etc.

 

[Field]

No, torque on the bolt is not equivalent to the force the bike needs to produce to move a mass. This bolt just holds the rotor on. The axial force on the crank bolt is still limited by the material. In this case,I don't know what Honda uses, perhaps a high carbon steel. Torsion is nasty on bolts, and will definitely snap.

I didn't mean at the crank bolt, sorry, I meant applying leverage through the transmission etc, isn't abnormal force.