Topic: Help with new CB650 Project

[76 Supersport]

Hi all, I recently picked up a 1982 CB650 (C?).

This thing is very custom/ Frankenbiked.

PO said engine was seized. Pulled plugs put ATF down all cylinders, and trying from either side of the crank this thing isn’t budging! Next I thought I’d try and put it in gear and give it a rock back and forth. (Till this point I hoped I could tear down the top end, hone cylinders, new rings and might get lucky.)

In gear, clutch out and bike glides forward with no resistance, attempt to roll back and bike gives resistance and an audible whine of an electric motor sound (I assume the starter) so now my question is what else is broken?

Additional information: I tried rocking in all gears. Pulled clutch cover everything looks normal and rotating from the clutch basket the rear wheel wants to spin forward, but wheel won’t spin clutch. Rotating back seems to engage starter motor. Oil seemed to have a metallic swirl indicative of a thrashed clutch and oil was black.

Looked like it was a real labor of love for someone and a pretty unique neat bike. Hope to make this a project with my little brother and get it back on the road.

Thanks in advance for your help and suggestions.

[newday777]

Howdy 76 Supersport
That is unique with the added upside down forks.
As to "what else is broken "? The clutch plates may be stuck together from old oil left in the motor too long, so you may need to open the clutch and clean the plates of gunk and rust(on metal plates).
I'm not familiar with the 650s so I'll defer to others.
Do you have the Honda Service Manual for the bike?? #1 tool. There is download manuals in the manuals section
http://manuals.sohc4.net/cb650/

Go to the new members section and introduce yourself and your bike (I looked through your posts and see you haven't done that since you joined in 2019)

[76 Supersport]

Thanks Stu! I’m already studying that manual and looking at the diagrams the primary is free wheeling either way you spin the clutch basket.

I’ll also head over and give another little introduction as it has been a while since I last posted.

Edit: Tried posting to new introductions, but it just resets my text window and doesn’t post. (Same with a for sale post I tried to make)

[bryanj]

Its possible but not common for either the cam chain or primary chain to snap and lock the crank, unfortunately either will cause a lot of damage

[newday777]

Its possible but not common for either the cam chain or primary chain to snap and lock the crank, unfortunately either will cause a lot of damage

I was just thinking primary chain as a possible culprit.
Remove the oil pan to see if the primary chain is whole or not.

[bryanj]

In over 40 yrs i havent seen a primary break but anything is possible, have seen many cam chains go

[76 Supersport]

Just want to be clear in the attached photo. The magnified gearin the photo  is the primary that engages the clutch basket, correct? That primary gear freely spins in 1st- 5th gear forward and backwards.

Is there a “quick/ easy” way to check cam chain? A adjuster I can remove or one of the top covers to inspect chain? If not, I’ll get to removing the pan to see the state of the primary chain.

[calj737]

You can pull the valve cover and inspect the cam chain. I doubt your issue it there. It sound much more starter clutch/trans related.

[fizzlebottom]

Pull the clutch. You'll need the clutch nut socket or you'll have to fashion one yourself. After that's free you can try to spin the crankshaft nut to see if the motor turns without the clutch pack present. Don't forget to either make or buy a new clutch cover gasket too.

Rebuilding the clutch is cake if that's the problem.

[76 Supersport]

Adjustment covers and breather cover removed. Only 2 out of the 8 rocker arms have a tiny bit of movement.

[newday777]

Adjustment covers and breather cover removed. Only 2 out of the 8 rocker arms have a tiny bit of movement.

That is typical of a frozen motor as you cannot spin it to the required timing mark to have half of thr valves in closed position.

[76 Supersport]

Removed cylinder head cover. Would cam chain be loose/broken, or dangling? Everything appears tight.

[Tracksnblades1]

If your starter motor is turning when you push the bike backwards you found the problem…

You’ll have to determine why and how the spag unit works in a 650 and why its not functioning properly.

I’m not a 650 guy so I’d have to look at the manual here on line but I’m sure it is a bit different but not for sure..both are similar that they only engage one way..

[76 Supersport]

Pulled the carbs, figure need to get them out of the way sooner or later. Then was eyeballing the starter.. why is it not disengaging? Nothing. Till I happen to notice this!

[Tracksnblades1]

Pulled the carbs, figure need to get them out of the way sooner or later. Then was eyeballing the starter.. why is it not disengaging? Nothing. Till I happen to notice this!





         l
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There is an overrunning starter clutch. It is a sprag unit type, rolls a roller up a ramp to lock up and then turns the motor over. If it won’t disengage, it’s stuck or defective…

[76 Supersport]

I guess my question is, now what? What else at the very least is broken? I did see a case on eBay for 60-70 bucks. If it seized at the bottom maybe the head and valves are still in good shape?

It seems odd to me the hole is between the two intake ports. I would think it’d be in line with the cam chain or in line with the primary chain. Could it be a rod cap or something?

If it was sitting in your garage what would you do with it? I’ve got more time than money and don’t mind a project.

[bryanj]

Pull it out, strip it and find what broke, i have seen a socket left on a big end nut do similar

[76 Supersport]

PO said he was riding when it seized, went down at low speed (low sided) and then it seized. Seemed a kind of minute detail cause I’ve never heard of that causing a seize.

The manual I’m reading says to remove the cam sprocket since I can’t do that would I go about disassembling the bottom end?

Once I get this all part are the odds good I’ll be able to find all the parts I’ll need to reassemble?

[calj737]

Slow down. You’re all over the place.

The crack in the case is the indication your issue is with the starter clutch. You can remove the cam chain without cutting it by rotating the crank to access the 2 bolts holding the cam sprocket to the camshaft. Once you’ve done that, release the tension and slightly raise the chain straight up, then slip the cam to the left to clear the sprocket.

Before removing the camshaft, tie up your cam chain with some zip ties to prevent it falling into the cavity.

Then you can start removing the oil pan and looking up to understand more of the damage.

You can’t buy “cases” unless the bearings match your crankshaft. But whole cases as a matched set (or another motor) are in your future. Sorry about your bad luck 

[Tracksnblades1]

Slow down. You’re all over the place.

The crack in the case is the indication your issue is with the starter clutch. You can remove the cam chain without cutting it by rotating the crank to access the 2 bolts holding the cam sprocket to the camshaft. Once you’ve done that, release the tension and slightly raise the chain straight up, then slip the cam to the left to clear the sprocket.

Before removing the camshaft, tie up your cam chain with some zip ties to prevent it falling into the cavity.

Then you can start removing the oil pan and looking up to understand more of the damage.

You can’t buy “cases” unless the bearings match your crankshaft. But whole cases as a matched set (or another motor) are in your future. Sorry about your bad luck 

Can you “not” remove the oil pan without first removing the cam and/or cam sprocket ..

It looks like the grenade went off down below unless I don’t have all the pictures…?

[Tracksnblades1]

I guess my question is, now what? What else at the very least is broken? I did see a case on eBay for 60-70 bucks. If it seized at the bottom maybe the head and valves are still in good shape?

It seems odd to me the hole is between the two intake ports. I would think it’d be in line with the cam chain or in line with the primary chain. Could it be a rod cap or something?

If it was sitting in your garage what would you do with it? I’ve got more time than money and don’t mind a project.

Picture of this hole…?

[76 Supersport]

I’m goin crazy is it obvious? Seriously though, I’m actually really excited!

Although the extent of my engine work was a top end on my Xr80 I think I’m up for the task.

I really don’t want to sink a ton into this, but since I got it for 100 bucks I don’t mind putting a little into her to get it going.

I’ll continue disassembly tomorrow, but I think I’m a little confused. Currently I can only access one cam sprocket bolt and since everything is seized I cannot rotate for the other. I’ll drop the pan tomorrow and maybe I can pick out whatever is in the way. 

Thank you again for everyone’s suggestions and input thus far!

[calj737]

Can you “not” remove the oil pan without first removing the cam and/or cam sprocket …

You certainly can. But he was asking about the cam chain so I added that procedure.

[76 Supersport]

I guess my question is, now what? What else at the very least is broken? I did see a case on eBay for 60-70 bucks. If it seized at the bottom maybe the head and valves are still in good shape?

It seems odd to me the hole is between the two intake ports. I would think it’d be in line with the cam chain or in line with the primary chain. Could it be a rod cap or something?

If it was sitting in your garage what would you do with it? I’ve got more time than money and don’t mind a project.

Picture of this hole…?

Reply post 13 has original picture, but I’ll attach another.

[Tracksnblades1]

Thanks 737. I haven’t ever owned a 650…

76, I’m thinking your original owner hasn’t told you the whole story..

I think you’ll find the (Paul Harvey’s) “In a minute the rest of the story” then you’ll tell us “Now the rest of the story” under the oil pan…

Something wanted out. If it wanted out at 10,000 rpm, it won’t be good…

Best of luck..