Engine becoming noisey

Rasputin

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During the last couple of rides I have noticed a clattering noise from the engine around 3000rpm and above, it starts and idles like a Swiss Watch, quiet as a mouse, no smoke at all, but when the revs rise and under load it starts to clatter. The noise is getting worse for sure, but can be controlled with the throttle, back of and it quietens down. I’m thinking it maybe a little end problem, or worse Big End.
History of the engine is unknown to me, showing 36,000mls but who knows? It’s a 75 bike, I have read that some early engines suffered from little end issues but not so much later engines.
I am going to drain the oil today to see what’s in it, to verify that it may be the cam chain guide or not.
The chain tension was checked last month when I first noticed a small noise, and was OK.
 
... around 3000rpm and above,
... can be controlled with the throttle, back of and it quietens down.

3k rpm is that magic zone where the decelerating piston's pull on the conrod matches the combustion pressures as it approaches TDC. (What GM called the "detonation prone zone"). At that point, the wristpin's force on the small end is indeterminate, and the conrod (due to its angularity) could be pushing the piston either fore or aft, oppositely from what normally occurs at lower rpms. All this exacerbated by throttle position.

Translation: Piston slap and/or small end wear.

Try retarding ignition timing a couple degrees...

http://www.xs650.com/threads/xs650-ignition-timing-revisited-are-we-too-advanced.45197/
 
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Update. Drained oil looks clean, no debris. Suction screen, as you would expect, except for the piece of gasket, don’t know where that came from wasn’t any evidence last oil change, pressure screen clean as, valve clearances, perfect, plugs look good. I have noticed two things, when winding the engine over the chain tensioner plunger doesn’t move, when I put my finger on it and wind the crank can’t feel anything moving. Looking up into the crankcase I can see what looks like a broken stud, should there be a stud and nut in there?
Thanks Twomany. I will have to put it back together and check the timing, checked it a while ago it was fine.
 

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have you tried backing off the cam chain adjustment to see if the pin starts moving again ?
Any chance you can identify where the piece of loose gasket.came from .? .
Might be worth removing the whole chain adjustment assembly and checking it ;)
 
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Update. Cleaned screens added fresh oil. Checked the cam chain tensioner and found this, see photo. It’s a metal rubber metal sandwich washer. Should it be in there? The adjuster was screwed up tight that’s why there wasn’t any movement. When the rod end was flush with the tension screw the washer thing was trapped solid to the abutment on the tensioner. In the video the clattering is worse since removing the washer, the rod is moving now as it should but it’s noisier, when I press my finger on the end it quietens down. I’ll put the washer back in.
The old bits of gasket are probably from the cylinder base, from a previous repair maybe.
 
excellent video ! you've pinpointed the source of the noise for sure . :)

That small rubber washer is it part of the tensioner assembly ? I am sure I saw an exploded view of the tensioner assembly somewhere the other day I'll see if I can find it again.
8BqahOY.jpg
 
Yes. Thanks for the diagram. As I understand the metal rubber washer is to stop the plunger clattering on the adjuster. The TX750 had an early revision on the tensioner to cure a rattling noise, similar washer.
But as I see it, once tensioned the plunger rod needs to be fixed same as most Honda tensioner, if there is any slack in the tensioner ie without the washer and the plunger rod set flush it bounces in and out causing the noise.
We will see once I test ride it.
 
FWIW my understanding - I haven't had my XS very long - is that the tensioner rod is not fixed. When the engine is running, it should move in and out just a mm or so, and at its most 'out' should be flush with the end of the adjuster nut. There are at least 5 designs of tensioner and they had various arrangements of damper washer to cut noise.
 
That's your tensioner not working as it should, don't use it like that in case you get the cam chain jump and create a lot of damage, the rubber/metal sandwich looks to be a dowty washer and as far as i am aware that should not be in there, they go on top of the head cover, was the dowty just inside the big acorn nut, if it was it's a bodge to keep it quiet, i think you may need a new adjuster or re-build on that one.
 
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Yes I see which part it is now, that's cleared that up, so do you just need to adjust it, or is the guide breaking up causing extra slack in your chain?
 
Yes. Thanks for the diagram. As I understand the metal rubber washer is to stop the plunger clattering on the adjuster.
But as I see it, once tensioned the plunger rod needs to be fixed same as most Honda tensioner, if there is any slack in the tensioner ie without the washer and the plunger rod set flush it bounces in and out causing the noise.
We will see once I test ride it.
NO!
The later tensioners used the rubber washer, but all MUST have that bit of slack movement as the motor spins.
Photo By or Via 5Twins.
TensionerID.jpg
 
My tensioner is type C. When it is assembled as it’s shown it effectively becomes a solid tensioner if the plunger is flush. So I’m going to set it 2mm below and see what it sounds like.
My original diagnosis of the the recent developing noise hasn't changed, I still think it’s a little end problem.
The way the noise reacts to the throttle eliminates the cam chain scenario as that would be constant.
 
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