Last Saturday I started a 520 Km road trip from my town to my mothers town in my CRM250R (http://www.flickr.com/photos/julio_costa/2248254144/). After 280 Kilometers of small roads travel, I got into a full speed highway. I drove that highway for 120 Km. with only a little fuel refill and soda drink stop around the 80th kilometer. During the last kilometers (after the stop), the bike had a couple of power loss issues during some left line truck passings (I am not sure if this is the right way to say it in english, but I guess you get the idea). At some point the traditional engine noise became grave (low, deep), so I released the throtle and press the clutch. The engine went dead. I released the clutch and the engine went on again, but still with the new noise. I stoped inmediately since I thought It maybe the piston rings. Once I stoped at the side of the highway, I gived a turn to the start kick and listened a drag noise in the cylinder (The rings I thought).

Yesterday I took the bike to the mechanic and today I saw as he opened the engine. The strange thing is that the rings, piston, and cylinder walls looked alright. The only thing that we found was a movement in the conrod, that the mechanic said was the cause of the problem ("You will need a new conrod").

Now, I really don't see the relation between the wear out conrod and the sudden change in the engine sound, do you? Does anyone have another theory (experience), for this kind of failure, with the rings, pistong and cylinder not being involved? And finally, what other conrod will feet the CRM? since CRM parts are almost impossible to find in my country.

Thank you very much for your help.

agerio wrote:Now, I really don't see the relation between the wear out conrod and the sudden change in the engine sound, do you?

I have far more experience than I would want on the change in engine noise when the big-end bearing of the conrod fails. You will get a _lot_ of noise as the direction of the forces on the bearing alternate every engine cycle, so the con-rod bangs from the top to bottom of the bearing clearance.

It isn't clear from your description if the problem is the big-end or small-end of the conrod. If it is the big end then the con-rod is probably OK, and you need a crank rebuild. This is a big job, and unfortunately one for a specialist. The bearing itself will be fairly standard, but you will also need a set of gaskets for a complete engine rebuild.

If the problem is the small-end bearing then you _might_ get away with just a new bearing, but there is a good chance you need a new con-rod. This requires just the same crankshaft and engine rebuild as the big-end bearing.

Thank you Andy,

Today I took a look at the engine in the mechanics shop, and the movement was only in the lower part (big-end?). Tomorrow I will send the bike back to my town, so my regular mechanic can take a look at it. I hope it can be resolved with a new bearing and new engine gaskets. I will let you know.

Cheers

this can happen if you have had a few top end rebuilds and never changed the conrod. it can suddenly wear out leaving almost no damage to the top end (if you stop in time) Id change the conrod and little end bearing at the same time, then check piston rings and if they havent been done for a while do them while its in bits. Jon