How can i find a squeak in a motorcycle engine?

June 14, 2009 10:31 PM

My 1982 Kawasaki has developed a peculiar squeak somewhere in the engine.

It only shows up when the bike is in gear and moving, and only when the clutch is engaged. It disappears if the bike is coasting AND the engine RPM is above 2k. The sound and frequency of the squeak do not vary with engine or vehicle speed.

posted by casconed to travel & transportation (10 comments total)

From my husband: Is it a rhythmic squeak (i.e. happening at a regular interval) or more random?
posted by amyms at 11:22 PM on June 14

"... It only shows up when the bike is in gear and moving, and only when the clutch is engaged. It disappears if the bike is coasting AND the engine RPM is above 2k. ..."

"The sound and frequency of the squeak do not vary much with engine or vehicle speed." FTFY.
I'd be looking at fork issues, or, perhaps, at rear suspension/sub frame problems. Sounds like the nylon bushings used in a lot of Japanese rear subframes/swing arms of that era are worn past use.

Specifiying the exact model number of your bike would help future AskMe responders help you.
posted by paulsc at 11:28 PM on June 14

What model is it?
posted by Duke999R at 11:29 PM on June 14

From hubby again:

paulsc is definitely on the right track, and his train of thought would explain why it's only happening while the clutch is engaged, or it could be something as simple as a worn-out chain, or some of your plasticworks coming loose.

If you have a bike shop you trust, your best bet is to take it there and let them diagnose it. A bunch of strangers on the internet are going to give you a myriad different possibilities and solutions which could end up costing you more money to investigate than it would cost to take it to a bike shop. Not to mention the fact that your safety is potentially at issue.
posted by amyms at 11:40 PM on June 14

I'm with amyms, but just my two cents:

Possible that a bushing has worn out enough to allow the engine or connected component to flex under power so that something like a heat shield or fairing begins to rub against something. Check for something like coasting in neutral (flexing structures will likely rest in a position similar to parked, so the noise will disappear) vs going downhill/decelerating with the transmission engaged (all the flexing goes the other direction, so the noise will disappear or change).

Since the sound doesn't seem to change much with engine speed, I'm tempted to look outside of the engine block first.
posted by Extopalopaketle at 12:16 AM on June 15

More details please. From the information given it's not possible to diagnose.

Just to be clear; the noise only happens when the bike is moving and the engine is under load but it also occurs if you are coasting at less than 2k rpm.

If you cannot make it happen when you are stationary then it isnt the engine.
If you can hear it when you are riding then it's probably pretty loud and probably important to sort out.
'Not varying with engine/road speed' is very easy to get mistaken about.
'coming from the engine' is also very hard to be sure about; if it's coming from underneath you when you are riding then it could be pretty much anything on the bike.

My random guesses though;
*Lubricate your chain well!
*Bounce up and down on the bike savegely, see if you can hear a creak, crunch or any other noise which might show a damaged bearing. '82 is too early for a monoshock, so I'm going with swingarm bearings needing lubed.
*Check your exhaust header nuts. A leak at the header tends to squeak under load. (Will also give a gruff thrum on the overrun). The nuts up here are invariably siezed but leave overnight with a good dose of WD40 on then and then use a hex socket (not bi-hex, not spanner) to nip them up.

More info please, and let us know how it works out!
posted by BadMiker at 5:09 AM on June 15

The bike is a 1982 Kawasaki 750 LTD. The squeaking is periodic and constant while moving in the described scenarios (moving, engine under load, or coasting and engine less than 2k RPM), and the sound of the squeak does not vary except to be "on" or "off".
posted by casconed at 7:50 AM on June 15

My Road Glide has a similar squeak due to a loose exhaust clamp, only at the muffler. No matter how often I tighten it it eventually comes back and I have learned to ignore it, since I know what it is and it isn't anything serious. BadMiker has a lot of other good ideas, too.
posted by TedW at 8:04 AM on June 15

An inexpensive mechanic's stethoscope can be invaluable in finding/isolating mechanical noises. Even a simple hose can help (perhaps fitted with a couple inches of copper tubing, so you can push it against warm engine parts, too), by narrowing down the scope of the source of sound, and by making sounds at low levels more audible. If you have a gas leak at your headers, you can probably hear it constantly (even at idle, in neutral, on the stand) with such a rig, but it will become more audible to your unassisted ears under conditions similar to what you describe - it is actually always leaking, but passes enough gas at the described conditions to make a noise in the 2-3Khz frequency range, where the human ear is most sensitive.
posted by paulsc at 11:50 AM on June 15

After a bit of investigation i noticed exhaust leaking from one of the exhaust headers. I also noticed the squeaking only happens after i've been riding for a bit so it seems plausible that this is the problem. Thanks for the tips!
posted by casconed at 9:23 PM on June 15