Topic: Motor locked up...first project...

[brycegp]

Ok...i know there are a lot of questions and answers on here regarding Motor Lock Up....

But most of these are when the bike is built and running then dies suddenly.

My CB750 was running several months ago...then I tore it down to mod, resto and rebuild. Here is a vid of the last time it ran about 10 months ago.  I ran ok...not the greatest...but solid.

http://www.youtube.com/user/brycegp#p/a/u/1/dQiIXKv9k0o

About 5 months ago, I drained the motor, removed all the casing pieces and shipped them off for polish while I painted the engine block.  Work, wedding and life has gotten in the way so the motor has sat without oil all that time.  But I plugged up the intake and exhaust ports with rags...

Now I pieced it back together, still drained cuz I haven't put the oil tank back on yet.  I just remounted it into the frame tonight.  Just out of curiosity, I gave the kicker a push to see if it would move and it went half a kick and stopped.

NOW IT WON'T BUDGE.  How much trouble am I in??  Will it loosen up once I get the oil back in?  Should I be very concerned?

What should I do NOW...so it doesn't get permanently locked?

[dave500]

having no oil with half a turn shouldnt hurt anything,is the cam timed correctly?try turning the motor in reverse.

[Lars]

+1, the oil is not your problem. If the cam is not correct mounted, you might have the situation that a piston is hitting an open valve. Not an expert, but it happened to me on another model. Whatever you do - do not use force!

[kslrr]

Or the rags stuffed into the ports are jamming a valve.

[brycegp]

the motor was never disassembled other than the casing pieces.  so the cam should be in exactly the same place as it was. nothing has changed there.  or will tilting the motor around to get it in and out of the frame shift some stuff around???

No rags in the ports now.  the rags where removed already...and I sealed the ports up by covering them with duck tape...for painting...

i'll try turning the wheel in reverse when i get some wheels on it...but that might be a couple weeks...cuz they are torn down too.

should i put something in the cylinders or just get some oil in it??

[brycegp]

update...

it shifts just fine.  and the drive sprocket spins in neutral. 

now I'm just second guessing my self. 
1. when putting on the stator cover, did i put the stator / starter gears in right?  I followed my pictures...but if not would that be jamming the motor?
2. did I put the clutch cover on right?  if I didn't would that cause a problem?

I mean its not that hard to get the covers back on.  I can't imagine I messed it up...but now I'm just trying to think of anything.

[Whaleman]

I can't imagine a running motor locking up solid from rust in a matter of months sitting inside. This is unbelievable to me. Something else is going on. Dan

[Frostyboy]

Not that I know anything much about a 750 engine, but did you also remove the cylinder head cover for polishing?
There's been a few engine problems lately regarding bent valves from incorrect assembly procedures.

[jacquesleclochard]

A couple of days ago I read a post about a guy with the same issue. His problem was solved when he figured out that, like you assume, his stator was blocking. Try that.

[brycegp]

The stator is the first place I'll check...fo' sho'...

Question....Are there any bolts on the CB750 motor that if TOO LONG might penetrate into a cylinder or crank shaft or something like that?

I've heard of this kind of thing on car motors.  I used a stainless bolt kit and hoping that the bolts are all correct lengths.

[Derby City]

I had a locked up motor at the start of this year.  Turned out to be vapor lock (I think that's what Two Tired called it).  I'd forgotten to shut off the petcock while it was in storage over the winter, and gasoline seeped into one of the cylinders.  When I kicked the engine over, the gasoline wouldn't compress, thus the motor wouldn't turn.  I pulled the spark plug, kicked it over, and the gas blew out.  Motor was good as new after that.

I'm wondering if your duct tape job over the intake and exhaust ports are creating a similar problem.  Air has nowhere to go, so it locks up the motor.  You may try poking holes in the duct tape and see if that frees things up.

[justind511]

thats more of a hydro-lock not a vapor lock. that is when lets say your fuel cap isnt venting so when all the air is taken out (from gas going to carbs) it wont let anymore gas in. it is possile if the motor was tilted a certain way oil could have gotten into a cylinder.

[brycegp]

UPDATE:

so I removed teh stator cover and tried to kick it over and still wouldn't budge.  BUT...  then I took a 19MM socket and attempted to turn the stator rotor by the big bolt in the middle (see pic below).  and the motor turned easily NOT PROBLEM.  valves were freely moving (I removed the tappets to see).  i could hear air going in and out of the ports.  ALL GOOD, Right??

BUT the kick start still wont budge the motor.

So I removed the clutch cover thinking maybe the problem was with that cover. 

BUT STILL the kick starter wont budge the motor.

WHAT GIVES???  What could cause the kick starter to be stuck?