OT: Help me diagnose this engine trouble

 

Semi OT, because it is regarding a dual sport, used mostly on street
however. It's a friend's 2001 XLR125, push rod 125cc engine. He rides
trails with it from time to time.

When in third gear, it makes a gentle rumble, barely noticeable only
on third gear, no matter if engine hot or cold, but the noise is
there, if you know what to listen. Other bikes with same engine does
not make this noise.

After rode-like-you-stole-it for over half an hour it makes a *loud*
metal rubbing against metal noise. Noise goes away if you calm down
and ride slow with low revs. It never produces the noise if you ride
gently, which is almost impossible on a 10hp engine.

top end is ok, was rebuilt a few weeks ago. I did that myself (not
that this is a signal of good quality job, but anyway...)

Main suspects: broken teeth on third gear cog, bent third gear shifter
fork, main bearing spinning on the case.

No noticeable metal shavings on oil, so I could almost rule out
bearings spinning on the case.

Has been doing that since it was just over the 1 year warranty period.
Problem is worsening, friend says it's getting scary. Bike has over
100,000 miles (yes, miles not kilometers) on stock everything except
piston rings and clutch disks and springs.

Pulling clutch does not change noise, which is worse in third and
fourth gears (5spd transmission)

I plan on splitting cases next friday night, so I could run for parts
saturday morning and hopefully reassembling it before next monday.

Anything I might want to look into? I'm aware that noise can't be
diagnosed through written media, but I know some folks here are top
mechanics... :)

thanks for any insight!

-- T

 

In article


Is this rode-like-you-stole-it noise *only* in 3rd gear as well?

--
Charles
'99 YZ250

 

Tiago reports:


Only in third but worse in 3rd or 4th.  I'm missing something.

If it's speed related, only happens after getting up to third gear
speeds, are you sure it's not wheel (bearing?) noise?

I doubt it's a broken/worn gear or shift shaft if it does it in 3rd
and 4th AND pulling the clutch doesn't change noise.

Check also the output shaft for leaks/looseness that would indicate
bad bearing there.

Good luck!


Go fast. Take chances.
Mike S.

 


I didn't made myself clear, sorry for that.

There is a rumble in third gear, all the time, no matter engine cold
or hot.

There is also another noise, loud, like metal rubbing against metal,
in all gears including neutral, that gets louder with engine speed
(not related to bike speed, I mean, it's on the engine). This noise is
worse in 3rd and 4th gears, but always there. This noise only starts
if you ride-like-you-stole-it for half an hour and goes away if you
let engine cool, either by shutting off or by riding gently for some
time.

No leaks whatsoever.

Clutch doesn't change noise. Aren't all the gear cogs turning, no
matter what gear is engaged? That's why I thought broken gear teeth,
but doesn't make sense if the loud noise only when engine is very hot.
The low third gear rumble made me suspect shifter forks...

Quite a mystery. I guess that I'd have to split cases to find out...

-- T

 

Time for exploratory surgery!

Mike Baxter


On Mon, 1 Feb 2010 07:59:31 -0800 (PST), Tiago