Topic: 1981 CB650 Barn Bike....Phase 1: enthusiasm.

[CCMcC]

Well, so someone gave me an '81 CB650.  At the time, I determined that it would not turn over. After some fruitless tinkering, I secured an '82 Suzuki GS850G and left the poor CB in a barn for about 10 years.

The original owner said the CB650 (18K Miles) ran fine until the bike went down on a patch of sand. There are minor scrapes; the frame seems fine.

I assume the bike ran on its side for a while and one or more pistons seized. PB Blaster notwithstanding, putting a socket wrench on the flywheel nut delivers abut 20 degrees of back and forth play and no more.

Clymer in hand, I am filled with enthusiam for bringing the old gal back to life.

I have some noob questions.

1) Does the diagnosis of seized pistons sound plausible?

2) If so, any advice on disassembling a seized engine?

3) Assuming the problem is seized pistons, should I also wade into rebuiling the crankshaft, shift drum, and transmission, etc.? 

2) Does the flywheel nut have standard or reverse threads (Clymer is silent on this--I ask because my old Husqvarna 4-stroke has reverse threads on the flywheel nut).

Many thanks,

Caleb

1981 CB650
1982 Suzuki GS850G
1988 Husqvarna 510TE

[mrbreeze]

When a bike has gone down and the motor don't spin....I'm always wondering if one of the side cases is bashed in and holding up the crankshaft. When they go down and sit for 20 years...its anybodys guess!!!! Take all this into account as you figure out how to get it to spin. You HAVE to be a detective!!! Good luck...post pics....ask more questions.

[TomC]

Hi Mrbreeze & CCMcC
     I had not thought of accident damage. 20 degrees is to much for a stuck piston. Maybe a stuck cam and a lose cam chain. A cylinder 3/4 full of Or anyone of a number of things that I have not thought of.
          TomC

[mrbreeze]

Well Tom.....Its like I say....you HAVE to be a detective!!!!....if not....play dumb and pay someone else to figure it out. They might be straight up and do you right but then on the other hand...... ......Just git it running by spring!!!!!!

[turtle]

My CX engine did this - the big end was TOAST!!!

[paulages]

Hi Mrbreeze & CCMcC
     I had not thought of accident damage. 20 degrees is to much for a stuck piston. Maybe a stuck cam and a lose cam chain. A cylinder 3/4 full of Or anyone of a number of things that I have not thought of.
          TomC

not necessarily true. my friend brad (southbound) has a cb550 that he bought with a siezed engine. it would rotate quite far in either direction, but would always stop at the same point either way. uopn disassembly, we discovered that one (and only one...someone left the plug out?) cylinder's rings had rusted quite badly to the cylinder wall. when the piston broke free (probably from someone just trying to move it in gear), it left a serious rust ring on the cyllinder wall that the piston wouldn't clear, even after a week of pb blaster soaking. in the end, we got the cylinders off of the pistons by hammering on the piston with a plastic deadblow handle while pulling upward on the cylinders. needless to say, the piston was trashed.

a wreck would obviously not cause a rusted piston, but it is possible that some other aberration could be doing the same thing. bent rod preventing full travel?

[jreich]

I ran into the same situation on a 550 engine I recently pulled apart.

It initially had some play, like what your describing. It turned out to be two out of the four pistons were seized.

You might want to shoot some pb blaster or similar down in there initially, if your goal is to get it unstuck. Let it set for awhile, then rock the bike back and forth to get that crankshaft moving

My advice, however, would be to start taking it apart. I can speak from the 'noobs' perspective, that it is quite rewarding to disassemble and correctly fix the problem on your own.

Your Clymer should describe how to take the head off. Just in case it doesn't,  I've been looking, but can't seem to find a shop manual for the 650 online in pdf format for you. Perhaps someone else has a link

Cheers

[CCMcC]

Enthusiasm continues...

Thanks for the replies. I have the cylinder cover and the carbs off. I was able to remove one bolt from the cam sprocket, but the second one is just out of reach due to the limited range in turning the crank. I loosened the cam chain tensioner, but still don't have enough play to get at that second cam sprocket bolt.

I don't see any other way to get the cam chain off the cam sprocket.

I am contemplating sawing through the cam chain (taking on board the commitment to split the cases) so as to be able to proceed with disassembly. Is this a crazy idea? 

[DammitDan]

If you can't rotate the crank around to get to the 2nd bolt, then it may be necessary to cut the cam chain.  But there's no telescoping or bendable socket wrenches you can get down in there?  Ya just need to break the bolt loose, after all.  Cutting the chain might be excessive, though there are new chains available.

[jreich]

Someone else with more expertise can chime in here, but when removing my cam I ran into the same problem, except I couldn't get enough play in the chain to remove either bolt.

I ended up taking a link out of the cam chain to get the cam out

If all else fails you, this might be a better approach then attempting to saw the chain. Don't want those nasty metal bits down in your engine anyway

Have a good one!

[CCMcC]

A different tool is an approach to take. In order to get the bolt out, I would most likely need to let it drop into the crankcase.

JREICH: How did you remove a link from the cam chain? Did you use a file?

Thanks for weighing in.

Caleb

[jreich]

I used a bicycle chain tool.

It mounted perfectly onto the cam chain, and pressed the rivets through the outer plate. Then just pull it apart.

When you are putting everything back together, don't use the same link you pulled out. Perhaps a master link could be supplemented so you don't have to buy a new chain.

[R. Hykawy]

Hj,I had the same problem on a 76 550 engine. the bolts for the camshaft sprocket were at the 12 & 6 o' clock positions. What i did was loosen the bottom bolt using a really cheap/thin overseas wrench, my snap on wrench wouldn't fit. However even after loosening the bolt, I still could not remove it as there is not enough clearance to fully remove the bolt. So I then took a hacksaw blade and cut the bolt, I was then able to remove the cam & sprocket. Just have to purchase a new bolt. I do not know if the 650 will have the same clearance problems. Hope this helps,or at least it's an alternative to cutting the chain.
Richard

[CCMcC]

Jreich and Richard: Thanks for the good advice. Thanks to you, I have some options.