Topic: Valve help..CB550

[RK550]

Hi everyone! I have a 1978 CB550 that I did a rebuild on about 1500 miles ago. The bottom end is from the 1978 and the head, and cam cover are from an earlier (74-76) model. I installed and did the 650 cam mod at that time and it ran well until just recently when it developed a "clacking" from either the #1 or #2 exhaust valve after really opening it up late one night, I can't exactly tell which valve it's coming from. Everything else on the bike is stock. I did a valve adjustment after I started to hear the noise thinking they were out of spec. Ran it after and the noise was still there. Is it possible to burn a valve from a little bit of hard riding? Is it possible to bend a valve that way at all? I checked the tappets thinking maybe they weren't contacting the valve correctly and noticed that the #2 exhaust tappet was a little "chewed up"..as in not smooth with little divits in it (photo below). Would this be a sign of the rockers being worn and wandering?

I'll attempt to post a video of the bike running so you can hear the noise. Any help or insight would be greatly appreciated!!

Thanks!
Ryan

[Greggo]

Those tappet screws are toast if they have deep pits.  Did it run smoothly with the new set up for a while?  How many miles after the rebuild are we talking?  Has your cam chain been properly adjusted?

[RK550]

Here's the video. It was running well before really getting on it that night for about 1500 miles. I did the cam chain adjustment as well and just changed out those pitted tappets and adjusted. No luck

VID-20120504-00006.3GP

[Greggo]

Is it getting enough oil up there?  Also, check behind the end caps to see if the rocker shafts sit centered.  Search 'rocker shaft wear' to see what I'm talking about.  I wouldn't run that motor much more until you find the problem.

[lucky]

What you have is a possible broken valve spring.
If you removed the valve cover you can get a tool to fix it. Just buy some
1/4 inch braided nylon line and stuff it in the spark plug hole,then you can remove the keepers and springs without taking the head off.

Put a new valve guide seal on while you are at it.

[TwoTired]

Did you check the cam cover aluminum bore for the rocker shaft wear?

Are your tappet adjusters, or rockers hitting the inspection plugs?

[That 70s Bike]

http://www.sohc4.net/?p=324   read Service Bulletin #8

[RK550]

No signs of the tappets or rockers hitting the inspection plugs. I haven't measured the bore (what do I measure that with?), but looking through the rocker shaft access holes there doesn't appear to be any wandering or gap.

I haven't pulled the cover yet, but when I do I'll do the rope trick and check the springs for the exhaust #1 and #2 valves.

[dave500]

remove the rocker caps and pull the plugs out so you can use the kicker by hand to turn the engine over,remove those end cap retainers then screw a 6mm bolt into one of those shafts end,,dont pull on it!try to wiggle that shaft around with the screw,rotate the engine so the spring load comes of that shaft as the rockers close the valves,check all four this way,,you might not sight the wear unless you try this.

[TwoTired]

No signs of the tappets or rockers hitting the inspection plugs. I haven't measured the bore (what do I measure that with?), but looking through the rocker shaft access holes there doesn't appear to be any wandering or gap.

I haven't pulled the cover yet, but when I do I'll do the rope trick and check the springs for the exhaust #1 and #2 valves.

Check this...
http://forums.sohc4.net/index.php?topic=20408.msg212239#msg212239

[That 70s Bike]

Whoever removed the '78 head (valve guide issue?) should've re-installed the '78 improved valve cover as it would've fit & avoided shaft rotation damage. I'm thinking of drilling & tapping these damaged covers from top then putting 2 long set screws per shaft w/loctite to push the shaft back downward.

What's interesting is each steel shaft is pressured to "rock" only during 1/2 of the cam rotation (when the lobe is compressing/uncompressing the valve spring) whereas the steel cam's 4 bearing areas are pressing on the aluminum head continiously while loaded by 1 or more of the 8 compressed valve springs. Same steel on aluminum but there not equal wear to the aluminum head. Ahhh.. because oil is pumped to the cam's bearing area but not to the isolated shafts, as they were not intended to rock!

[RK550]

No broken springs, so that's good! It has to be rocker shaft wear. Looking for an updated valve cover. I think that should do the trick (fingers crossed). I'll update when I receive and install.

Thanks everyone!!!