Topic: 74 CB550 Cam Chain Adjust Screw Broke

[scubes]

Hey everyone, as the title says I've got a 74 CB550 with a small problem. The cam chain adjuster screw is broke, not seriously but enough for me to view as annoying. I am the 3rd owner and only the second one to actually ride it. Never paid much attention when I first bought it but when I went to do some routine maintenance I found that the slot in the head for a small flatblade one side was broke off. Anybody know if this will cause a serious problem, as just loosening the locknut is supposed to adjust the cam chain tension, am I correct? If it needs replaced I never had a tensioner out so I'm not sure how the adjuster screw is attached, will I have to pull the tensioner to change it? I'm pretty mechanincly inclined but I hate having to think of pulling an engine apart to change a stinkin bolt. Thanks for any info in advance.

[bryanj]

As long as the nut tightens its no problem as the slot is only for use when rebuilding engine (and then not necessary). You can not change just the screw you have to change the whole assembly and that means head and barrels off, so wait till it leaks at the head gasket as they all do eventually and do it then. In meantime get another assembly, still available new from Honda or ebay (any 500/550 is the same)

[mikethejeepguy]

A broken wall on that adjuster is pain because it makes it hard to eventually either loosen or tighten the adjuster nut (depending on which side it is on). The screwdriver will just torque out and the nut will end up turning the screw which will affect the tension to either too much (counter-clockwise) or too loose (clockwise). I had a similar problem, and eventually the screw did nothing whether done by me or the PO. There is a little cam gear on the other side of the screw that fits into a metal track with teeth cut out from it. Also, check out this post. I made a little video on how the tensioner looks and works before it went in the engine.

http://forums.sohc4.net/index.php?topic=55569.0

If you have room, you could take a hacksaw blade, or a Dremmel with a cutting disk and cut further into the peg so you can get more grip with the screwdriver. Also, it helps to grind the screwdriver down until it fits snugly in the slot. I use a little ratchet with a flathead screw attachment (because of lack of room and ability to hold it) and a ratcheting 10mm wrench really helps too so you don't have to regrip. JB Weld unfortunately will not hold up to the torque of the screwdriver if you wanted to build up a new side. I also thought about having a friend weld a bead onto the screw and then slot it with a Dremmel, but in the end decided to just put in a new tensioner which was a two day job. You can actually do it without taking the head off. You will however have to pretty much disconnect the whole motor, exhaust etc. because you have to tilt the motor to the side to be able pull the tensioner past the top bar of the frame (and push a new one back in).



If you need details and pics... let me know. I am thinking of doing a write up on it.

Hope it helps!

Mike

[scubes]

Mike, thanks for the post your video was very informative, I have wondered how that tensioner works and now I know. I did think of cutting the slot a little further with a hacksaw blade but wasn't sure. But in theory I should be able to spin that nut off of there to cut the slot deeper if I need to, spin it back down and bring cylider 1 to TDC, hold the screw and loosen the nut to adjust the tension, then tighten the nut back down correct?

[mikethejeepguy]

You're welcome. Glad it helped someone taking the nut off shouldn't be a problem Just gotta make sure the threads are burr free. As long as your motor doesn't change position I think all is good. Maybe you could ultimately get a thinner nut on there if you can find one? It's not like it holds much force from torquing.

[scubes]

Either get a thinner nut or grind down the existing one and run a tap through the clean the threads. But that will only be if necessary. But am I understanding the theory on this, that you hold the screw in place while breaking the nut loose, let go of the screw for it to adjust, then hold the screw while you tighten the nut? I've only had this bike for about a year and a half, and it's a bit different from my DOHC CB750. That one I just loosen both nuts while its running and everything sets itself.

[mikethejeepguy]

Yup... you got it! The screw will likely only move a tiny bit. Likely, considering it's placement (read... no place for sausage fingers), one would hardly notice it adjusted. But yeah, that's the way it should work, so that nut only needs to be snugged down to keep the tensioner in it's adjusted place. Yeah was thinking maybe grinding the nut would work too.

And don't forget the 15 degrees past TDC.... but you probably already knew that.

[scubes]

Glad to know somebody else caught that in the owners manual. Most people say TDC and even some of the repair manuals (including the  Cb500-550 Maintenance Manual on this site)only say TDC, but the I have the original owners manual and a hard copy shop manual a buddy gave me that say 15deg ATDC. I did not see a post "no place for sausage fingers" but even with my 750 I know all about that. Thanks for the help again Mike.

[Deltarider]

To adjust Bryanj's way is best.

Loosen the nut and then put pressure on the crank so its just about to turn, either with the kickstart OR with a big spanner on the big nut on the auto advance so that all the camchain "slack" is at the back and then, whilst holding the pressure get your mechanically trained spider to tighten the locknut. Been doin that on ALL OHC hondas for 30 years and as long as the tensioner moves and the chain aint worn out its guaranteed to work.

It's the same method I've learned from an old mechanic.