My first top end rebuild and it runs like crap........video included

[djmartin]

Hey guys I just finished rebuilding the top end on our 2003 RM85. I bought the bike for $200 and when I purchased it I was told the top end needed work and it wouldn't run.
So I took off the cylinder and it was pretty scarred up the head was also pitted where somthing had been hitting it. So I had the cylinder honed, new piston and rings, head etc... COULD NOT WAIT to fire it up to see how I did.
Once I got her together she started right up but I let her idle as I don't want to rev it to much breaking it in. The top of the motor sounds really good but there is a really bad sound in the lower end. Of course this is far beyond my skill level so I took a video and posted it here so maybe you guys can listen to it and give me some suggestions.
My CR125 which is next to the RM runs so quiet and smooth and I guess that I was expecting the same from the 85?
ANY suggestions would be welcome.
I don't even plan on riding the bike much i just wanted to learn how to do rebuilds.



http://www.youtube.com/watch?v=qcI0tAAZl1U

 

[rmc_olderthandirt]

It's hard to say from a video, can't really separate the sounds and establish where the noise is coming from.

If there is a hard sound coming from the lower end then my guess is that the rod journal bearing is bad. Unfortunately, just about anything wrong in the lower end is a fairly major rebuild operation.

Another possibility is that you put the piston in backwards. Are you aware that there is a front/back to the piston? Did you get it in right?

I would recommend popping the cylinder back off and attempting a few checks on the bottom end. The connecting rod should have a small amount of play side to side, but no noticeable play up and down. If you can feel ANYTHING irregular in the rod as you rotate the crank or if there is any up/down play then the bearing is certainly toast. Even if you can't feel it the bearing can still be bad.

There are similar tests to check the main crank bearings. Pop the clutch and flywheel covers off, remove the clutch and flywheel and see if you get any movement of the crank in the bearings. With the flywheel and clutch off I would expect a little bit of motion in / out, but nothing noticeable side to side.

Rod

 

[arnego2]

+1 good advise :)

 

[jason33]

maybe the main bearings are bad pull up and down on the crank/magneto see if it moves, +2 on the piston check lol