Yamaha TRX850 Enthusiasts Forum

I have an engine rattle which happens at mid-throttle between 2500-3000rpm. Rattle completely disappears above 3000, doesn't make any difference engine hot or cold. TIming chain/tensioner was renewed only 48000km ago (first one went for 129000km). Doesn't sound like big ends or gudgeons, could be piston slap? Anyone got ideas?

you sure its not something simple like loose header clamp bolts?

I had an annoying intermittent rattle that turned out to be stones being flicked up and hitting the header pipes

Keep it above 3000 rpm

@ 440kms to a tank, re your other post, I would suggest that noise is your engine begging for more fuel.

funny you should say that, thought maybe it was fuel related but it has been rattling for the last 20000km, before I changed the jets. I nhave tried high-octane, standard, ethanol blend fuels. Got the smoothest performance when emulsion tubes/needles were worn using e10 ethanol blend. Worst running on high octane.

Now with new needles etc it runs better on 91 than e10. Haven't tried 96 yet.

For the noise I have thought of header pipes/clutch/final drive/big-ends/gudgeons/piston slap/timing chain/something loose inside the motor.
Am thinking maybe timing chain and/or guides, maybe it gets a resonance at 2500-3000rpm. Was hoping someone might have had the same problem and fixed it.

brenyw

How often do you change the oil???and filter...

54,000km out of a chain and sprockets and the noise started 20,000km ago round abouts.... are you sure it's not from the gearbox

20,000 for a chain is good. 54000 is waay too long imho.
i only ever run premium (98) .
perhaps its pinging?
cheers
fung

brenyw wrote:......Am thinking maybe timing chain and/or guides, maybe it gets a resonance at 2500-3000rpm. Was hoping someone might have had the same problem and fixed it.

brenyw

Mine has always had a bit of a 'resonance' rattle between about 2500-3000rpm. In fact it was more of clatter when I bought the bike about 3 years ago.
It was definitely coming from the camchain area so I replaced the camchain and the tensioner. Out of interest, the new camchain was exactly the same length as the old one, the old tensioner seemed to be in good condition and there was plenty of adjustment left (bike had done 30,000km at the time). I suspect that the tensioner may have seized, although I was able to get it moving freely once removed from the bike.
After replacing the chain/tensioner it wasn't clattering but there is definitely still a vibration in that rev range.

My theory is that as the camchain stretches over time it gets a slighty looser and more rattly until it gets stretched enough to engage the next ratchet on the tensioner - then the whole cycle starts again.

Maybe you could try removing the tensioner and make sure it's working properly?

My theory is that the camchain doesn't stretch (as you said yourself) but the neoprene tensioner blades wear until the next ratchet "tooth" is reached.

dandywarhol wrote:My theory is that the camchain doesn't stretch (as you said yourself) but the neoprene tensioner blades wear until the next ratchet "tooth" is reached.

Good call!

Excalibre wrote:

dandywarhol wrote:My theory is that the camchain doesn't stretch (as you said yourself) but the neoprene tensioner blades wear until the next ratchet "tooth" is reached.

Good call!

My chain had streched 2,5 links when i changed it...

Can't believe a camchain can "stretch" 2.5 links - if it was measured against the new one then the new one is too long................

Chain's don't stretch - the pins can wear but if worn 2.5 links the chain would've broken in that time IMO

dandywarhol wrote:Can't believe a camchain can "stretch" 2.5 links - if it was measured against the new one then the new one is too long................

Chain's don't stretch - the pins can wear but if worn 2.5 links the chain would've broken in that time IMO

Yep, a high tensile metal as in a cam chain would snap instead of expanding under load to the value of 2 or so links length..
I am under the understanding that the cam chain tensioner mechanism can become hesitant..[stuck] on the way to its next ratchet point, making a chain slap noise..and as the chain tensioner is on the back of the load in the direct line from the crank to the cams..its job is to maintain a direct line of tension to cams and crank...the tensioner is on the return side to the crank..yeah.?
As in the old TT600s and i have heard from other trx owners..it is possible to loosten the cam chain tensioner mech..on the back of the right hand cylinder near the oil filler...then give it a light tap or so...better have a look at an exploded diagram of it first or ask a mechanic as i really havent done this...and it might loosen or move up a notch..
But i have heard of tensioners becomeing frozen..good luck on this.

dandywarhol wrote:Can't believe a camchain can "stretch" 2.5 links - if it was measured against the new one then the new one is too long................

Chain's don't stretch - the pins can wear but if worn 2.5 links the chain would've broken in that time IMO

Not only that, it was impossible to set all markings correct and i thought i´ve done something stupid and then a forum member said to change it....after that all marks lined up superb.
The stretched one was the original one.
Might be my memory and it was 1,5 links then...if that sounds better!? Think i wrote about in here a couple of years back.