Jump to content
Sign in to follow this  

Do I need a new connecting rod?

Recommended Posts

Hi guys,

This is my first time rebuilding my top end on my 2007 rm 250 since I bought it. It has also been years for me since i have rebuild a top end.

Anyway, after inserting the new piston I noticed that the piston did not rock back and forth smoothly on the connecting rod. After taking the piston off to inspect I noticed that there are tiny grooves in the small end of the connecting rod where the bearing sits. Is this normal? My gut says no, but they are so subtle and perfectly uniform that I almost think they should be there. Please let me know if this is by design - apologize for the pics it's the best I can do.

Thanks!!

ImageUploadedByThumper Talk1378687653.801612.jpg

ImageUploadedByThumper Talk1378687677.950677.jpg

ImageUploadedByThumper Talk1378687690.901696.jpg

ImageUploadedByThumper Talk1378687702.884964.jpg

ImageUploadedByThumper Talk1378687581.385587.jpg

Share this post


Link to post
Share on other sites

Yes it needs to be replaced! 

 

You could probably "get by" with it but it will put extra stress on the bearings.

Edited by BDubb106

Share this post


Link to post
Share on other sites

Yeah that's what I though - guess I'm not riding next weekend...

Thanks for the reply!

Share this post


Link to post
Share on other sites

if those are indeed grooves where the needle bearings ride  you caught this in time . good job 

you sure wouldn't want to spit any of those out

  • Like 2

Share this post


Link to post
Share on other sites

Rebuild, or replace your crank, I bet the big end isn't far behind. What type of oil, and ratio have you been running?

Owner before me says he's been running 32:1. I have been running the same most of the time. I've leaned it out a bit for a couple hare scrambles I raced this year, but never past 40:1.

Share this post


Link to post
Share on other sites

This is the oil I use. The bike has never used anything else, so I'm told.

ImageUploadedByThumper Talk1378751237.904364.jpg

Share this post


Link to post
Share on other sites

Owner before me says he's been running 32:1. I have been running the same most of the time. I've leaned it out a bit for a couple hare scrambles I raced this year, but never past 40:1.

 

 

This is the oil I use. The bike has never used anything else, so I'm told.

attachicon.gifImageUploadedByThumper Talk1378751237.904364.jpg

That oil is just fine... I wouldn't go past 32:1 in any 125 though. That is just my opinion based on the motors I have worked on. I have never seen a 125 that has sufficient premix in the bottom end when running under 32:1. While you have the top end off. Use a stick of some sort and measure how deep your oil pool is under the crank. That is the only true way to know if you are running a high enough ratio. If you need to lean the bike out slightly do it with jetting, not changing your ratio.

Share this post


Link to post
Share on other sites

It is a 250 - does that make a difference, Or still never go past 32:1?

Do you guys think this is an poor oiling issue? I usually check my spark plugs ever couple rides to make sure it's not running too dry. Ill take a look in the case however, good point.

Share this post


Link to post
Share on other sites

Oh, odds are you are safe then. I was under the impression it was a 125 for some reason. I don't think it is attributed to the oil. Looks like the crank just has a ton of hours on it. Depending on how long the piston has been in the bike, odds are that the wrist pin bearing was in there for a long time as well. Once those bearings wear they will stick and not spin correctly causing the grooves you have.

Share this post


Link to post
Share on other sites

Your oil mix, and brand where just fine. Did that bike happen to sit quite  a while? And can you feel that bearing impression with a finger nail?

Share this post


Link to post
Share on other sites

What is it with RM bottom ends? Every bike I see for sale either has a new bottom end or a whole new motor. Seems kind of weird to me but who knows. I want to get one but it scares me ha.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×