weird knocking noise

[farmerj]

Hi all,

I have an '01 txt 321. I love this bike! I do not love the knocking noise that I hear in certain circumstances. This seems like a weird one, to me - when I lean the bike over to the right, it knocks. Straight up, or leaning to the left, no noise. I have looked for loose or rattling components to no avail. It sounds like what I would imagine a piston knock to sound like.

Any thoughts?

Thanks,

Jeff

[dombush]

Hi farmerj

puzzling one this.... i have had one experience that may be relevant.

My sons KTM80 had too much crankshaft float (side to side) in the main bearings and used to do exactly what you describe.

You can determine this by removing the flywheel cover and push/pull in/out on the flywheel.

some float is normal (fractions of a mm), however this bike had 1-2mm.

This was down to worn crankshaft journals (high milage bike). i ended up making some shims but i dont reccomend this.

Dom

[legionnair]

Clutch ingaged or not ?,

[farmerj]

Clutch ingaged or not ?,

Thanks for the response, guys.

Clutch not engaged. (So I'll try pulling it in and see if there is anything different?)

I read this on the GasGas.com website in resonse to a "knocking" question, which made me wonder...

"I've got a couple of ideas. Check the float level and make sure the carb vents are open. If the level is low and/or the vents are clogged or there is an obstruction in the float needle assembly not allowing fuel to flow into the carb, when you hit fourth gear the carb may have run out of fuel, going lean on the mixture just before sputtering, spiking the combustion chamber temperature, thereby causing the knocking symptoms."

...but it happens to me when the bike is not hot, and idling. I need to go play with it again and see if the knocking persists at higher revs, I can't remember.

Dombush - interesting idea, I'll try checking flywheel play. This bike is different, however, in that it doesn't have very many hours on it.

Jeff

[jse]

Thanks for the response, guys.

Clutch not engaged. (So I'll try pulling it in and see if there is anything different?)

I read this on the GasGas.com website in resonse to a "knocking" question, which made me wonder...

"I've got a couple of ideas. Check the float level and make sure the carb vents are open. If the level is low and/or the vents are clogged or there is an obstruction in the float needle assembly not allowing fuel to flow into the carb, when you hit fourth gear the carb may have run out of fuel, going lean on the mixture just before sputtering, spiking the combustion chamber temperature, thereby causing the knocking symptoms."

...but it happens to me when the bike is not hot, and idling. I need to go play with it again and see if the knocking persists at higher revs, I can't remember.

Dombush - interesting idea, I'll try checking flywheel play. This bike is different, however, in that it doesn't have very many hours on it.

Jeff

Jeff,

When I wrote that answer years ago, it was for a different set of symptoms/circumstances, so I doubt it applies to your problem. I know from answering about 4000+ questions since those first 84 on the website that a lot depends on the nature of the "knock". If it's a heavy, deep metallic sound, it's probably a major component like a crank, with a lot of mass. If it's a light, short click, it's probably something like a kickstart idler gear. I've found diagnosing engine sounds by e-mail is an "interesting" process....

I'd start by a process of elimination, with the easy-to-get-at, less expensive components first. That means taking off the clutch sidecover and carefully inspecting all the various things in there. The 321 is a very stout engine and unless abused, rarely has any major component problems. We have a bunch of them running around here and all have never even had the head off.

Jon

ps. And try pulling in the clutch lever, it may just be the primary/clutch hub gears normal clacking while not under load. Cranks do not rotate at a uniform rate but speed up and slow down slightly each revolution and the gear tooth faces engage and disengage when not under load (more so with straight-cut gears as helical gears have slightly more than one tooth engaged at a time) which causes the rattle/knock in some engines.

[farmerj]

Jon,

Thanks for your reply! Fun to hear from the guy who has answered so many questions! On behalf of many, I thank you for sharing your expertise. I took your advice on jetting settings from the GasGas.com website tech articles. That was really helpful!

My own tech expertise, at least in this case, is embarassing. First off, my description was inaccurate. I hear the noise when I am on the right side of the bike leaning it left. I kept wanting to grab for the kick lever, it was like a noise I've heard when that's partially engaged. But I found something different in playing around.

I started the bike between gears.

I must have done the same thing a couple of times, finding a false neutral (say, between 3rd and 4th gear.) Bike straight up - no noise. Bike leaning right, no problem. Bike leaning left, with me on the right - a knocking, tapping noise. I assume it's from the nature of the position of the gears while in the "false neutral."

I'm grateful for this forum where guys are willing to help us work through to solutions, even when the guy with the problem hasn't been too 'bright!"

[jse]

Jon,

Thanks for your reply! Fun to hear from the guy who has answered so many questions! On behalf of many, I thank you for sharing your expertise. I took your advice on jetting settings from the GasGas.com website tech articles. That was really helpful!

My own tech expertise, at least in this case, is embarassing. First off, my description was inaccurate. I hear the noise when I am on the right side of the bike leaning it left. I kept wanting to grab for the kick lever, it was like a noise I've heard when that's partially engaged. But I found something different in playing around.

I started the bike between gears.

I must have done the same thing a couple of times, finding a false neutral (say, between 3rd and 4th gear.) Bike straight up - no noise. Bike leaning right, no problem. Bike leaning left, with me on the right - a knocking, tapping noise. I assume it's from the nature of the position of the gears while in the "false neutral."

I'm grateful for this forum where guys are willing to help us work through to solutions, even when the guy with the problem hasn't been too 'bright!"

Hi Jeff!

Hey, no problem, I know it's tough being accurate when describing sysmptoms on a forum (like what constitutes a "knock").

What is "clacking" is the pins (called "dogs") on the shifting collar rubbing against the milled shots in the gear body itself. Motorcycle transmissions are what's called a "constant mesh" transmission and the gears are always in the same position relative to each other and do not move, contrary to what most riders believe. Power transmission is done by splined, sliding collars with pins that engage/disengage with slots in the gear bodies.

If the edges of the dogs and/or the edges of the slots are worn, the dog may not slide into the slot easily but bounce back as the two radiused edges meet. The problem can be exacerbated by worn/bent shift forks. The "cure" is to replace the parts but that is expensive, and focused, deliberate shifting will help avoid the problem in most cases. Another thing that might help is to replace the tension spring on the roller detent that drops into the cutouts in the "star" on the end of the shift drum. You can get at the spring by taking off the sidecover. Look for a short arm with a roller on the end that engages the shift drum. There is a good possibility that replacing the detent spring may fix the problem completely and your tranny parts are o.k.. While you are in there, carefully inspect all the exposed shift parts. I'm not positive, but the earlier models had a rivit on the shift arm (that arm attached to the shift shaft that has a "claw" looking attachment) that acted as a built-in "breakaway device" to protect the transmission components if the shift lever got hit by a rock. If that rivit is loose, it could also create your symptoms.

Jon

Edited August 17, 2011 by JSE

[farmerj]

Thanks again for the good information, Jon. If the problem persists, I now know which direction to look for solutions!

Jeff

[jse]

Thanks again for the good information, Jon. If the problem persists, I now know which direction to look for solutions!

Jeff

Jeff,

If you need to split the cases, I'll give you some pointers as to what to look for.

Cheers.

Jon