Tappet Mis Aligned


XS650 Enthusiast
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Missoula, Montana
Bike Engine: 1979 650 XS, Stock as far as I know
About a month ago my engine started knocking like a jackhammer, I adjusted the cam chain tension and valve clearance and the sound went away. Then I went on a 50 mile ride with a buddy and by the end of it the sound was back. Checked the cam chain tensioner and the valves again and the only thing that was off was the right side intake tappet. Checked the lock nut and it was still secure so I readjusted and the sound was gone. About 35 miles of in town riding later and I could hear the sound coming back, so I again checked all the tappets and sure enough the right side intake was off. I checked the spring and looked at the bottom of the adjustment screw and everything seemed in order and I was really stumped. When I came back to the bike a few hours later I realized what was up, the adjustment screw is not making contact in the center of the raised area on the valve side (sorry I don't know the technical term!) It is making contact on the side of it (hitting the corner where the raised part flattens out) So I figure that the misalignment is causing something to wear improperly and that is what is causing the horrible sound. Sorry for the noobish explanation, I can certainly try and get pictures if that would help explain.

I checked everything around the area but I can't see anything amiss, is there anything obvious I might be missing or an easy fix that doesn't involve pulling the engine? Or do I need to pull the engine and check the rocker arms and valves for wear?

Oh and yes I let the bike sit overnight and cool down every time I adjusted the valve clearance.
Kk so I took some pictures and here is as good of shot as I can get.


By salchite



By salchite at 2010-06-25

**EDIT** if you click on the hyperlink under the images you can get a much bigger shot

If anyone can tell whats goin on here (idk if the pictures are clear enough) how serious is this misalignment?

I popped to tappet cover off to show my mechanic buddy (10 years at a BMW bike shop) and we were playing with the rocker arm and noticed that it had some side to side play, not a lot, certainly under a half cm. Is this anything to be concerned about or normal for a bike with 12k miles on it?

Next I turned the engine on so he could hear the noise but the bike sounded great. So we sat there bsin while the bike ran and in about 5 mins the noise started to come back and by 10 mins it was really noticeable. So we are both pretty stumped at this point, but I had stopped riding just when I could tell the noise was coming back the day before. I think I'll go ride it for like 15 miles tomorrow and have him listen again.


  • Tappet Misaligned 1.jpg
    Tappet Misaligned 1.jpg
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When you say off, how much off is the valve adjustment? The engine has to get warm before the noise occurs? To me, that small amount that the rocker/valve contact is off is nothing. It will change as rocker does down through it's arc. Doubtful it would sound like a jackhammer. Perhaps you have lower end noise? Hard saying without being there.
Ya maybe jackhammer is a bit of an exageration. :yikes: But it does sound horrible. My friend asked that exact question, how far is it off? Being a noob I didn't check but it is supposed to be at .0025 and a .003 went in with almost no drag. Next time I do the adjustment (hopefully tonight) I will see how big a gauge I can get in there. I also grabbed a stephascope to help pinpoint the noise. I guess I'm just assuming it has something to do with the clearence because everytime the noise comes back that one clearence is off. I'll check to see if the lower end is to fault soon.