Topic: cb550 cam chain tensioner

[valleycb]

Hey, I'm just wrapping up a rebuild of a 78 cb550 engine.  Among the standard rebuild stuff, I replaced the cam chain just for peace of mind.  I'm trying to do the cam chain tension adjustment and it's acting weird.  I thought I'd see if anyone has any insight.  Normally, you can loosen the locknut and the screw can turn counterclockwise and it'll kind of spring back into adjustment.  After loosening the locknut, my screw won't turn...either way.  Could this just be that it's a new chain and there's just no adjustment travel in it? 

When I was assembling the engine, I had to turn the screw and lock it down with minimum tension in order to get the chain onto the cam gear.  It was certainly tight.  That's why I'm just wondering if there's no play in the new chain.

I checked at other engine rotations just for kicks and the screw never turns. 

If I take the head and cylinders off again to investigate further, I assume I'd have to replace the head gasket, right?  I'd rather not have to.

Any advice would be appreciated!

[strynboen]

thek that the tensioner have seated korrekt in the bottom.(crankcase(..look inside from the oil sump..and have some light on..often it jumps aut of the groove and Places vrong..and mess up...give a bad adjusting feeling

[BomberMann650]

Just remove the valve cover and try to look down the cam chain tunnel.
A long flat head screwdriver will allow some manipulation of the tensioner bow.
With the locknut loosed, you should be able to press on the bow and see the adjuster rotate.  Let it slap back and set the locknut after positioning the crank past tdc.

If none of that works.  Disassmble and inspect might be the next move.

[BomberMann650]

thek that the tensioner have seated korrekt in the bottom.(crankcase(..look inside from the oil sump..and have some light on..often it jumps aut of the groove and Places vrong..and mess up...give a bad adjusting feeling

That too.  The angle on the adjuster screw could be binding in it's hole.

[strynboen]

dave 500 have some good Photos..try to seargh(if it vorks)

[valleycb]

Thanks for the suggestions folks.  I popped off the oil sump cover and had a look.  I couldn't see much.  I took off the cylinder head cover and couldn't see much there either.  I popped the cam chain gear off of the cam shaft (which makes the cam chain go slack) and in this state, the tensioner feels normal.  I can turn the screw clockwise and it springs back.  But when I put the cam gear back on the shaft, the screw doesn't turn clockwise at all again.

So I'm thinking that either the chain is just really unstretched and there is no adjustment left in it.  Or there's something else up, like it's not seated at the bottom like was suggested above. I tried to find dave500's photos, but I haven't been able to yet.  Can you post a link?

If I take the cylinder off , do I need to replace the head gasket again?  Or can I just torque it back up again?

Thanks again for the help!

[BomberMann650]

Don't take the head off yet.

Quick question; when rebuilding, did you install a brand new tensioner bow or are you reusing an old one? 

I ask because an old bow doesn't adjust as well as a new one.  There have been side by side pics taken of new and old.  New bow curves out much farther into the tunnel.
Old ones reach their max adjustment without as much reach.  As a result, there is no more clockwise turning of the adjuster screw, the mechanism simply doesn't have enough teeth for that.

Word of warning; trying to force the screw to turn clockwise will damage the gear teeth.  Counter-clockwise is the only way the screw should be turned.

[goldarrow]

thek that the tensioner have seated korrekt in the bottom.(crankcase(..look inside from the oil sump..and have some light on..often it jumps aut of the groove and Places vrong..and mess up...give a bad adjusting feeling

+1 here

Check against these top two photos Marissa's 1972 CB500

https://r.tapatalk.com/shareLink?share_fid=13548&share_tid=166160&share_pid=1951622&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D166160%2Emsg1951622%23msg1951622&share_type=thttps://r.tapatalk.com/shareLink?share_fid=13548&share_tid=166160&share_pid=1951622&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D166160%2Emsg1951622%23msg1951622&share_type=t

[valleycb]

Bombermann650, I already pulled the head off unfortunately.  Yes, I have a new cam chain but was reusing the tensioner.  I just had everything apart and now back together with the same result.  With the tensioner removed, it functions smoothly.  And it's only when I pull the chain and cam gear onto the cam shaft that screw doesn't turn (clockwise).  I actually have tried turning the screw counterclockwise also...seems to tighten the chain.  And I don't think it caused any damage yet.  I'll avoid doing that any further I guess!  So do you think I'm just out of travel?  And if so, as the new chain stretches, there might be some travel down the road?  Or is my tensioner just spent?

[BomberMann650]

The tensioner bow has probably lost its shape and strength. 

Turning the screw ccw sucks the bow in (iirc) which does feel "tight" on the screwdriver.  Because you're working against the spring that makes the mechanism work.

The engine can run fine with a worn bow, but it's not great in the long run.  It will be many many miles until your new cam chain presents any remarkable amount of stretch.
A worn bow can still keep the chain on the sprocket.  And a proper carb sync can keep it from getting overly noisy. 

But since you already took the head off, why not order a replacement bow from ebay?  Get a fresh guide too if possible.  I learned the hard way what happens when the guide falls apart and a piece of it goes somewhere it doesn't belong.