Topic: 1974 CB550K Cam Chain Adjustment Question

[Dr. Frankenstein]

After the 1972 JDM CB500 valve debacle, I went back to work on my '74 550 today; got the electronic ignition dialed in, the bike starts right up (yay!), idles great, etc. but the cam chain is (to me) rattling more than it should. I have not replaced the cam chain (yes, I probably should have when I rebuilt the engine), but I'm wondering how much rattle is too much? It rattles less when I turn the screw to the left, and more when I turn it to the right (I assume that loosens it), but is there a sweet spot in the adjustment? I'm following a Clymers manual, which says to set the points at 15 degrees after TDC and simply loosen the nut and the cam chain will tension itself - and I did that - that's where I have it set right now - but you can still hear it. And I'm not sure how much is too much, if at all.

I've been reading up on it and the procedure in the forum, but like oil, it seems everybody has a different opinion. Is some cam chain rattle normal, and more importantly, what effect will this have on the engine leaving it as-is, tightening it up, or loosening it - although I'm pretty sure you don't want to loosen it and risk engine damage...also, any comments on doing it with the engine running, or not...?   

[bryanj]

As an ex Honda mech who talked face to face to the travelling techs paid by Honda they told me you should NOT use a screwdriver in that slot as it is too easy to overstress the rack and gearwheel in the tensioner.

I have posted before the way i was told and shown that works for all Honda non auto tensioners and that is

1 loosen the locknut/bolt

2 put pressure on the kickstart so that the crankshaft is about to turn, this pulls the front run tight leaving all slack in the rear where the tensioner sits. In this instance you can CAREFULLY load the big nut on the advancer.

3 whilst hold the pressure on crank nip up the locknut/bolt.

This, if the tensioner is working and also not at its limit should remove all slack that can be removed from the camchain. It is possible for the chain to have tight and slack spots, same as drive chain so if you still get a rattle possibly try in 2 or 3 places

[Dr. Frankenstein]

Hi Bryan - just to be clear, "In this instance you can CAREFULLY load the big nut on the advancer. 3 whilst hold the pressure on crank nip up the locknut/bolt."

So, again, just to be clear - put pressure on the kickstart and then tighten up the nut on the advancer?? The spark advancer? ("In this instance you can CAREFULLY load the big nut on the advancer.") 

So should the advance be set at TDC on 1 and 4, press/hold the kickstart and THEN rotate the engine to 15 degrees past TDC, while keeping pressure on the crank and then tighten up the cam chain tensioner nut/bolt?  Is that the way to do it?

And as I mentioned, all things being equal, is some cam chain rattle normal? Or is it supposed to sound like a sewing machine?

[denward17]

I think what Bryan is saying is:
Use kickstart pressure to tighten the chain (just before moving crank); Then while holding kickstart, use a wrench on the spark advancer nut to keep tension (DO NOT Tighten the spark advancer).  While keeping tension on the spark advancer nut, tighten the locknut on the tensioner.

[Dr. Frankenstein]

But still have the spark advance set to 15 degrees past TDC, yes? As it's described in the manual?  I've never done it this way before; I just want to make sure I know what I'm doing.

[HondaMan]

While I've done a bunch of these, and found sometimes they vary in how well their tensioner's spring actually works (they get a little 'bent up' in use sometimes), the way the 750 works seems to have a higher success rate with the 500/550 design than some other methods. But, it is very close: I use the #4 intake valve (the rocker cover cap off to watch) to tell me when that valve is starting to open (15 degrees past TDC), and stop [slowly] turning the engine right there - then i release the tensioner's locknut. Essentially it's the same way Bryan notes, and his advice about how fragile the tiny gears are is paramount to success with this gizmo.

But - if I'm working on an engine that I haven't been inside to see the condition of said tensioner, I've had to sometimes do other things to get there, like:
- loosen the locknut for the tensioner's screw and wiggle the screw's slot back & forth a little to free the [stuck] plunger inside.
- loosen the locknut for the tensioner's screw and kick over the bike a bunch of times (5 or 6?) to make it 'let go' of the plunger enough to apply tension, then set as above.
- worst one ever: loosened the locknut (on a warmed-up engine) and started the engine, ran it a few seconds (like 5 or 10) and shut it off, just to loosen up the tensioner. This one was sorely over-locknutted by the PO and the little gears on the tensioner didn't want to move, as the housing was bent a bit (I found that out later when the engine had to come out anyway for a bent valve, rusted from having no pipe on it, sitting outside, etc., etc.). I ended up just replacing the tensioner because it was not straight anymore.

[grcamna2]

Subscribed

[bryanj]

Perhaps i worded it wrong
You are not supposed to turn the crank using the advancer nut as in the 750 it bends the shaft and in 350/400/500/550 it can damage the locating pin and ears, having said that in this case you are not trying to turn the crank mearly put tension into the chain hence the CAREFULLY remark.

Like Mark i have seen several damaged tensioner mechanisms, usually caused by attempting to over tension the unit using the screw to the extent that the pressed steel assembly opens up enough that the gear is not in mesh with the rack so not holding it in one place.

If you use this method you can do it at any point of rotation it does not have to be in a spacific point

[M 750K6]

On my 750 I couldn't tell whether the tensioner was moving or not. I removed it and found it was seized. It had small damage on the plunger shaft. I lightly filed a burr, then I polished it, first with fine wire wool, then metal polish and it was free again.

Bike still sounds like a bag of spanners below 1200rpm, so I set tickover just higher than that!