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GS850 Engine Noise

  • Thread starter Thread starter sztandanga
  • Start date Start date
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sztandanga

Guest
Hey guys,

I bought this bike back in August in a not running condition. So far I've done valve clearances with a new gasket, took apart, cleaned and dipped the carbs, and put in a K&N insert and weather stripped the airbox. I finally fired the bike up from its long sleep and at first, and while cold, wasn't making any noise. Once warmed up, it'll make this noise intermittently in varying lengths of thunking, and sometimes it doesn't even make the noise. It seems to be coming from the intake side on the valve cover, 3rd or 4th cylinder.

Can anyone help diagnose this? Is it valve chatter from too much clearance? Is it cam end float? Piston slap?

If it helps, I did a compression test after the valve clearances and was getting around 125 in each cylinder.

Here's a video I took of the noise: https://www.youtube.com/watch?v=MpWPK8CF6ds
 
Sounds a bit like the infamous "cam end float". Increase engine speed slowly, see if it goes away at about 1500 RPM. If it does, don't worry about the noise. MANY bikes here have had tens of thousands of miles put on them after hearing that noise. It never gets any better, but it doesn't get any worse, either.

Question about your valve adjustment, though. How did you position the cam lobes to check the clearances? The correct procedure is to position the cam lobes properly, then check BOTH valves on that side of that cam before proceding to the next pair. Many 'newbies' try to change the cam lobes for each valve or they try to check the clearance with the lobe pointing away from the valve. You MUST follow the procedure outlined in the FACTORY service manual, not what you see in Haynes or Clymer.
 
I followed the directions from Bikecliff's site. I made sure I read it a couple of times and understood it. I'll rev slowly and check. Thanks for the quick reply.
 
You can hear it go in and out, which to me means it's probably nothing too serious. It doesn't sound like anything to do with the valve train or pistons. Have you messed with the cam chain tensioner at all? I think I've heard of a loose cam chain sounding like that.

Other possibilities are something loose in the clutch or starter clutch but I think those would be a more consistent rattle and problems with those are rarer on the 850 than the bigger bikes anyway.

I didn't think the 850s made the cam float noise. (But it does sound similar.)
 
Revving a bit did make the noise go away. Or at least I couldn't hear it with my ears or through a stethoscope.

I also decided to check the cam chain tensioner. At first I didn't want to take it out because I didn't want to wait for a gasket, but it came off super easily and the gasket stayed intact. When I took it apart, the spring was only wound half a turn. So I gave it 1.5 and then put it back together. I haven't had a chance to run the engine for too long as it's late, but from a cold start it sounded a bit quieter already. It didn't get warm enough to be at the point where the knocking starts though, so I'll report back tomorrow.
 
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Be sure you understand how the automatic cam chain tensioner works. Check the service manual and this page: http://www.bwringer.com/gs/camchaintens.html

Basically, there's a set screw (inside the lock nut) that when tightened, locks the pushrod in place. This set screw is only tightened against the pushrod when removing and installing the tensioner. The pushrod has to move freely out against the chain in order to do its job. Which means when you install the tensioner, you back off the set screw, hear a little thunk, then lock the setscrew where it is using the lock nut.

You might already be aware of all this, just want to make sure it isn't missed.

Edit: and if you did need a new gasket, it's extremely simple to make one out of a sheet of gasket material from the auto parts store. Probably the easiest one on the whole bike to make.
 
Thanks eil. Yeah, I made sure to mess with it for a few minutes to understand how it works before putting it back in. Bwringer's tutorial explained everything really well.

Well, it looks like I'm waiting until the weekend. I work until 7pm and by the time I get home it's 9pm, dark and cold, making working with the garage door open not very fun.
 
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