Topic: 550 cam chain prob.

[Killer Canary]

Hello,
I've finally gotten around to installing a new cam chain in my '78 550.
I backed off the tensioner ( though the blade still had some tension on it), installed the cam through the chain and then put the sprocket on the cam where it belongs between cyls 2 and 3.  After a major struggle, I got the chain onto the sprocket but the sprocket just doesn;t have the movement available to install it on the shoulder of the cam where it mounts.
In the past, I've re-installed chains with no problem ; this is a new chain on a complete engine rebuild. The cam is from a '79 650 but from what I've heard, the 550 sprocket should mount on a 650 cam in the usual manner.
The head is torqued down and the bottom of the tensioner sits in the bottom case where it's supposed to. The front guide is also installed right side up and in it's proper place at the top and bottom of the cylinder block.
If anyone has any insights for me, I'd love to hear from them.
Thanks in advance.

[BomberMann650]

The tensioner works in a counterintuitive way.  "Tightening" or turning the adjustment screw clockwise, actually brings the bow inward, lessening the tension.  Release the adjuster screw and the bow springs outward (screw turns ccw).  Applying tension to the cam chain.

As for getting the cam chain onto the sprocket, and sprocket onto the cam.  Yes, the 550 sprocket does bolt directly to the 650 cam.
When I was installing my last camshaft (550 replacement) I bolted the sprocket to the cam first.  Slipped it through the chain and into its tunnel.  Then, through process of trial and error.  Relied on the slack point in the chain drive at 15deg post tdc.  To walk the chain onto the sprocket.  Its just enough slack to make it doable with some  coaxing.
The trial and error part was getting the timing marks dead on each other.  I was off by one tooth in a couple of tries.

[Killer Canary]

Before I installed the tensioner into the block, I turned the screw clockwise and then tightened the locknut but there was still some spring to the blade.
I don't remember if this is normal or not.

[RAFster122s]

You are using a 650 cam chain in a 550?  Who said that would work?  Are the DID part numbers for a 650 and 550 cam chain the same?  If they are that would guarantee their interchangability, otherwise they are not interchangeable.  A 550 and 650 can exchange cams freely but there are changes in the internals for crank and few other items that can impact this swap for other parts.

[BomberMann650]

Raf - i understood the op as just installing the 650 cam, keeping the 550 sprocket and chain.

Killer, iirc the process to do the "auto adjust" of the cam tensioner was a few steps.
First, set engine to 15deg after tdc (the slack point i mentioned). The auto advancer has a point of reference for this, I think it's the stud for the springs.  It shows it in the manual.
Then loosen the lock nut, using a flathead screw driver after that to turn the adjuster bolt clockwise, then remove screwdriver - this lets the bow spring forward into the cam chain, then use the screwdriver to hold the adjuster bolt in position while tightening the lock nut.

Some guys prefer to do this adjustment when the motor is running to ensure the quietest operation.  That method means you'll have to loosen the lock nut, use the screwdriver to turn the adjuster bolt counter-clockwise (forcing the bow into the cam chain) then again, hold the adjuster in the optimum position while tightening the lock nut.  This method has the obvious advantage of being able to use your ears to tell when the tensioner is doing it's job.  I've done it both ways.

[jonda500]

Sounds like you're doing it right to me! The tensioner spring bows the tensioner blade in towards the chain when you loosen the locknut (and the screw turns anti-clockwise), this tightens the chain. To completely back off the tensioner, you need to turn the screw clockwise against the spring tension until the tensioner blade is completely straight and tighten the locknut to hold it there. Then you should be able to slip the sprocket (with the chain around it) onto the shoulder on the camshaft.
John

[Killer Canary]

Thanks for the replies!
I don't see how the 14 degree setting will make any difference to chain slack without the valve train in place.
Maybe the tensioner is cacked. As I said, adjusting the tensioner for max slack before I installed it into the block, I could still press in on the slider against the spring even adjusted for max slack and with the locknut tightened.
Does anyone have a tensioner kicking around that they could try this on and confirm whether it's normal oor not?
Thanks.

[calj737]

The proper technique for installing the chain onto the sprocket is:

Cam installed. Slide sprocket onto cam, do not bolt down. Loop chain over sprocket, then raise sprocket into place and bolt up.

If you bolt the sprocket down first, the chain is "tweaked" to an angle and won't be long enough. Looping the chain onto the sprocket first, allows the chain to be lifted into place (sprocket) without creating the offset angle. This is very poorly documented in the manual, but makes perfect sense when you examine the chain and sprocket during install.

[bwaller]

Can you rotate the sprocket so that part of the widest part of the hole allows it to sit lower on the cam to ease getting the chain over the top?

Remove the blade from the tensioner just to be sure neither end of the blade is broken. I'm not sure why but I was breaking one every race while I used the stock part.

I don't need to tell you how to adjust the tensioner so I'm not sure what you meant exactly. With the tensioner removed you can't compress it to hold...the bolt needs to be through the cylinder to tighten the nut. BUT when you adjust it so it is completely compressed the only spring action is from the bend in the blade itself, otherwise nearly flat. This make any sense?

Something else to check is whether the flat washer under the nut is thick enough to allow the nut to cinch down without running out of thread on the adjuster screw. Use a thick washer or add a second washer.

[BomberMann650]

The cam chain system does have a slack point at 15deg past tdc.  I swear I'm not making this up!  There is just enough of an eccentric ellipsoidal shape in the design to slack the chain on and off the cam sprocket when fastened in place.  This aspect of design is the reason we need cam chain tensioners!

[DaveBarbier]

The cam chain system does have a slack point at 15deg past tdc.  I swear I'm not making this up!  There is just enough of an eccentric ellipsoidal shape in the design to slack the chain on and off the cam sprocket when fastened in place.  This aspect of design is the reason we need cam chain tensioners!

Are you saying the cam and/or crank sprockets are an ellipse instead of completely round? Is this true?

I was under the impression that the reason for the tensioner was to compensate for chain stretching, not an aide for when the chain system is at 15° past TDC.

Site examples you cow!

[BomberMann650]

The cam chain system does have a slack point at 15deg past tdc.  I swear I'm not making this up!  There is just enough of an eccentric ellipsoidal shape in the design to slack the chain on and off the cam sprocket when fastened in place.  This aspect of design is the reason we need cam chain tensioners!

Are you saying the cam and/or crank sprockets are an ellipse instead of completely round? Is this true?

I was under the impression that the reason for the tensioner was to compensate for chain stretching, not an aide for when the chain system is at 15° past TDC.

Site examples you cow!

I suspect it's the crank gear that has the slack relief.  I've relied on this slack point during disassembly of both my parts engines, and when replacing the damaged cam and rockerbox in my bloo bike.

I'll try to make a vid when I get the garage next.  I'll have to set the top end on the studs and demonstrate this elliptical effect.

[BomberMann650]

Another example are the fellers who have the cam chain skip a tooth or three on the sprocket when the tensioner is loose and they smash their valve train apart at high rpm.  Its happened to a few sohcheads here.

[calj737]

I suspect it's the crank gear that has the slack relief.  I've relied on this slack point during disassembly of both my parts engines, and when replacing the damaged cam and rockerbox in my bloo bike.

I'll try to make a vid when I get the garage next.  I'll have to set the top end on the studs and demonstrate this elliptical effect.

I'm not sure I understand what you're positing here, Bombs? Are you suggesting the crank sprocket is not truly circular? If so, the cam chain would constantly be undulating and it's tension forever changing during the rotation of the crank. I have never heard of such a thing in an engine; not that you can't be right, just never heard of such a thing.

And I sure can't imagine that Honda designed such a system into their bike... I might just have to break out the calipers and Verniers and measure each sprocket to discover this 

[BomberMann650]

Its a very small window of opportunity this slack point in the cam chain.  And a very small decrease in the radius at that.  Mostly inconsequential in the operation of the motor unless the tensioner fails at its job.

[bwaller]

It's December, not April 1st Bomber. 

[jonda500]

+1 to what killer canary said - the position of the crank wont make any difference to chain slack without the valve train in place! It's the valve spring pressure on the cam lobes that can either help hold the chain slack on the back side of the engine to help the tensioner work or on the front(wrong) side if you don't set the crank at 15 degrees past TDC.

I have a rather old worn tensioner that I just checked and when held tight by the screw and locknut, I can still push the blade straighter by about 4mm. Have you turned the crank back and forth while holding the chain to make sure it's positioned properly on the crank?
John

[jonda500]

It's December, not April 1st Bomber. 

[DaveBarbier]

Ok, someone needs to measure a crank to get this straightened out. Even if it's very small of a decrease, it'll be measurable.

I'm not buying it! Though you are selling it pretty well.

[calj737]

Ive got a 550 crank sitting about 7' from me. How do you want it measured, and what exactly do you want measured?

[bwaller]

Guys, this is nonsense, both sprockets are completely round.

[Killer Canary]

At the very least, I'll have to try to get the cam and the chain out of the head to check the tenioner for the max 4mm movement when locked down that jonda mentioned.
First thing though, I'll try the 15 degree crank position, just to be sure.
The only thing that COULD be wrong is an ill functioning tensioner.
I didn't count the links on the new chain and compare to the old one as I assumed that I'd been sent the correct item, and it's too late now because I'm wearing part of the old chain on my wrist.
Don't throw anything out, I say.

[calj737]

Guys, this is nonsense, both sprockets are completely round.

I would certainly think so,it I was willing to entertain an obscure element I had never encountered. You never know when you don't know something.

[BomberMann650]

Guys, this is nonsense, both sprockets are completely round.

I would certainly think so,it I was willing to entertain an obscure element I had never encountered. You never know when you don't know something.

I know I'm a cow and I consume a lot of grass, but guys, It's been a reliable trick for me.

[calj737]

I know I'm a cow and I smoke a lot of grass, but guys, It's been a reliable trick for me.

That clears things up 

Hey, I'm not doubting you, I only say I've never heard of it. And I'm willing to measure one up to verify or clarify.