Topic: CB550 Intermittant Seizing.

[HoboJuanKenobi]

i am a new mechanic who just started working on a '75 CB550 rebuild and am having an odd problem with the bike.  It seems to seize sometimes when trying to start it by either the kick or electronic starter.  It will just stop turning over and the kick has no give at all.  If you adjust the crank backwards manually it frees back up the engine and the kick and electric starter work again for a while.  There doesn't seem to be any pattern to the seizures.  Any ideas on what could be causing the engine to intermittently seize up?

Thanks!

[OldSchool_IsCool]

I assume the engine is cold, not seizing because of running lean for hours on end.

My first guess is a loose part floating around in the crank case or tranny that jams up the works until you free it up by the reverse rotation.  Pull all the tappet covers and inventory the adjuster screws and lock nuts.  If you are missing one, that may be the culprit.

Are you ever successful in getting the engine to start?  If it is a loose part and it jams up an engine at speed... well... anyone's guess as to what will happen.

[hymodyne]

could be a broken valve spring.

hym

[HoboJuanKenobi]

I am going to pull it apart this weekend, and hopefully find the root cause.  If it is some loose piece jamming up the works I would rather know right now than later.  Thanks for all the replies.

[rhinoracer]

When I was putting the oil pump back together I noticed that sometimes it locks up, rotating the gear backwards will free it. When assembled to the kickstarter gear it did the same thing.

One more thing to look for.

[merc2dogs]

I am going to pull it apart this weekend, and hopefully find the root cause.  If it is some loose piece jamming up the works I would rather know right now than later.  Thanks for all the replies.

    That's the best way to go. Tear into it before a possibly minor issue becomes major.

  girlfriend one day called me up said her truck died. Went to pick her up and it was seized up solid, and still hotter than crap (45 minute drive) she said it read real hot for a minute, then a big cloud of steam came out and it dropped back down so she kept going.....


 Check to see if it works correctly when you hold the clutch in, that will eliminate the tranny side, watching the valves can help eliminate the top end.
   
    pulling plugs and slipping a drinking straw into the holes can indicate if you have smooth piston movement, inconsistant movement in relation to the other pistons may be an indication of trouble related to piston/con rod.
 
  using a wrench with the piston at half stroke to rock it back and forth can indicate how much play is there, normally shows if shells are worn, but can indicate a pin/piston pin bore problem. 

[HoboJuanKenobi]

Well, I took your advice and I am glad I did.  Turns out the cam shaft was snapped right where the sprocket connects and the bolt that used to be holding it together was wedged in the sprocket at an odd angle making it grind against the cylinder head.  I was able to replace the cam shaft with a spare and am putting it all back together tonight.  I am really just glad I found it before something happened down the road, so I appreciate all the help.  Now on to troubleshoot the other issues with the bike.   

[TwoTired]

You might want to investigate WHY the camshaft broke.  This often happens when there is an oiling issue for the cam bearings, allowing them to sieze.  If the oil supply is not restored in such an event, the replacement cam will likely repeat the failure of the former.

Also, when the cam stops turning it can leave valves open that can be hit and bent by the piston movement.  Bent valves won't seal on their seats properly or move properly in their guides.  A compression check will give you an idea about the valve seating.  And, if the valves suddenly snap closed during a slow crank revolution, this is an alternate sign of bent valve stems.

Cheers,