Engine Rattle

[pops]

When I got this free '79, I gave it a thorough going over before getting it running. I found the cam chain adjuster plunger quite deep in the adjusting nut. I remember thinking that if it had been run like that for very long, the front chain guide is probably toast. Adjusted it according to spec. and got the bike running pretty good.

I noticed that while riding it, as I go through the gears and approach the shift point where the engine is not loaded as heavily, there's a rattle (quite loud) that seems to be coming from down low. I can instantly eliminate the rattle by modifying the throttle either open or closed. Just changing the throttle a little makes the rattle disappear. Otherwise the engine runs just fine. At first, I thought that it must be the plastic all worn off the chain guide making the noise, but it seems to be coming from down lower than the guide. So I'm wondering if I have a sacked out crank bearing.

Anyone have any experience with worn out crank bearings and the sounds they make?

pops

[grizld1]

Usually you'll hear a loud whirring sound from bad mains. What you're describing sounds more like a rod knock, maybe from big end bearings (not a real common problem in these engines, but with a bit of abuse anything's possible). Couldn't hurt to pull the top end and check for vertical slop in the rods, check side play, inspect small ends and wristpins, etc.

[pops]

Thanks, Griz. I'll be tearing into it soon as I get my mother over the hump from her two surgeries (carotid endarterectomy and triple coronary bypass.) An XS650 overhaul should be a breeze compared to these last four weeks of hospital camping.

pops

[givememytoys]

I have noticed the exact same sound you are describing in my newest XS. I also here it at idle.
Please post when you find out what it is ...

Thanks Kayle

[steveslade]

most likely wrist pins are loose in the rods--only fix is new rods--I had to change mine

[marlboroman]

sounds like mine did.....before I put in new rods.

[Phantom Phyxer]

Hi, did Pops, ever find out what this noise was? I have the same noise with the same indications, change throttle position and noise goes away. Its only when I ride it though. I can run this thing up to 6 grand while sitting in my garage and no noise. If I get on it and go through the gears and really give it the gas, no issue, Its just riding along at about 3200 to 3500 RPM that it starts knocking. And its a low down sound. I can fill the vibration through the foot pegs when it happens and its pretty loud.

[grizld1]

We haven't heard from pops since 2012. The worst thing you can do to yourself is to overthink the problem from the outside--pull that motor and open it up, the grief should be obvious when you start looking.

[pops]

I'm still extant but bikes have been on hold for awhile. I thought retirement would give me more time for the bikes but it's been just the opposite.