Topic: CB550 Engine locked up?

[mgalyan]

HI All - New to this forum and am hoping for some advice.
I have a 76 CB550K I "found" last fall and have been restoring to operating condition.  I had it running pretty well but had low compression on #1 so I tore the engine down to install new rings.
Everything went well when putting it back together.  I cleaned up the pistons, installed new rings and wrist-pin clips, and reassembled the engine.  When I had the cylinders on and the head torqued down I cranked the engine using the kick starter to make sure everything worked.  Verified it was pumping oil, etc.  Put the cam back in, adjusted the valves and verified the engine still turned over, etc.
I decided to run a compression check before installing the plugs or firing it up.  I had checked #1 and #2, both were at 126 PSI and then ran into my problem.  I had the compression gauge on #3 and was starting to crank the engine when it locked up.
It would not crank with the starter or the kick starter, acted like something was jammed.
I put the transmission in 5th gear and was able to turn the engine backward using the rear tire to crank it.  It seemed to turn backward OK but it would only crank about a half turn forward using the tire or the kick starter and them jam again.
Thought maybe the problem was with the starter as I could hear it spinning when I turned the engine so I pulled it out but it seems to be OK.
I know the logical thing to do is start tearing the engine down again but hoped someone could suggest something else to look for or what to check before pulling the whole thing apart again.
Thanks for any insight or advice.

[number13]

Can you see all the valve ends with the
adjustment caps off?
Perhaps a valve has fallen into a cylinder?

[bowhunter]

Half turn of the crank indicates something broke/fell off in one of the cylinders. You need to pull off the cylinder head at least to see what's up.


Bowhunter

[seabird]

Valve timing OK?

[bwaller]

Could the camchain have been slack so it jumped a tooth or two to throw the valve timing off?

[cadler]

you have to go on in!

[mgalyan]

Thanks all for sharing.

Pulled it apart last night and found the cam chain guide had dropped into the sump and was getting caught in the chain.  I guess I was careful to do everything right except that one small detail.  So, I am glad it happened before I fired it up but a little pissed that I messed up something as simple as that.

Thanks again for sharing, and letting me vent.

It is nice to know I am not alone in this lunacy.