CR500 - Engine Noise Question

[HomeMadeSin]

I did a search on "gear noise" and it seems there are lots of theories, mostly revolving around piston slap or other components. My 96 CR500 has what I would call gear noise, like that usually associated with straight-cut gears. The frequency seems too high to be piston slap, but I'm new to either so I don't know. I've got good compression (100 psi at 6,000 feet ASL or 13.5 psig or so in). The bike has always done it (bought used 2 years ago), but I can only hear it near idle (pipe noise overtakes at higher rpms?). The engine is un-molested and unless there was a reason to go into it I'd like to keep it that way.

I am planning on selling it and don't like sayin' "its always sounded like that".

 

[SULLY]

Can't comment on 500's, but have had experience of smaller MX'rs and have found that often unexplained gearbox noise is down to the clutch basket. If you think about it it's a large rotating mass that is pretty much unbalanced -the clutch plates are not made to such tolerances that you could call them 'balanced', and they wear anyway which will make them even more unbalanced. The clutch basket bearings are usually fairly sloppy fit - they have to be to allow for some play/backlash and all in all in my experience this adds up to NOISE!, but nothing to worry about. It also tends to sound worse at low revs. when there is less load on everything, allowing for more slop.....could be this is your noise?

 

[marcusgunby]

MX engines make horrible noise at idle, another reason is if they have a metal water pump gear , the plastic are quieter but more fragile.

 

[Studboy]

If you pull in the clutch at idle, does the sound go away?

 

[baxterj787]

CR500s have a lot of piston slap, especially after a few tens of operating hours. The old-style cast iron liner calls for a generous piston-cylinder clearance (around .0035 is a spec, .0050 is the extreme service limit). Honda does not give a cranking compression value, but 100psi seems way too low. Did you have the throttle wide open during the compression test?

The very first time I heard piston slap, I thought either the fuel tank or seat was loose. If the bike is "unmolested" at 8 years old, that is impressive. I'm getting ready to take my 1995 to .060 oversize.

 

[HomeMadeSin]

I didn't have the throttle open during compression test. From what I understand, the ratio is supposed to be 6.8:1. Atmospheric pressure is around 13 psig up here in high country. Thats why I think the 100psi is ok....unless I'm missing something.

No, it doesn't go away with the clutch pulled in. I'd love to hear what piston slap sounds like. It just doesn't strike me as that.

 

[Dirtman500]

Read some of Eric Gorr's comments on engine noise. 8 years is alot of run time on a 2 stroke without a rebuild. 8 years of service tell us something about the CR500 engine! I own one and it made it 3 years. I have is crated and sending it to Eric Gorr for complete engine rebuild.
Check your clutch basket! If it is stock i'll bet it is really worn out!
I'm not favoring any brand of MX bike but i'm very pleased with all of the Hondas that I have owned.

 

[HomeMadeSin]

Years of service is somewhat ambiguous. For instance, I've owned it 2 years and I bet I've put maybe 30-40 hours of run time on it. Pretty sad, huh?

 

[Papakeith]

I experienced a similar noise on my 98 500. It was unnerving to say the least. It was nothing more than clutch noises.
If the bike was used when you got it, and you have two years and 30-40 hours on it; Tear down the top end. My bike gave no warning before the piston cracked and almost took the cylinder with it.
:confused: Of course that was in 2002, and the bike still had the factory piston in it :think:.

 

[jski]

All 500's make noise to a certain degree. My 00 that I bought new made the noise you describe which had me worried at first until I listened to several 500's all of which made the same noise. Now after 100+ hours 2 topends ans a clutch bike still sounds the same as it did when new noise and all.

 

[HomeMadeSin]

I dropped it off at a local shop, just to have another set of ears on it. We'll see what they say. I've never done a top end before, but I guess you gotta start some time.