Hello everyone, I am certainly new to these forums but have been involved in a project with a 1996 CBR600F3. The engine had a knock when I bought it and I prepared myself for the grueling journey that is engine disassembly. Currently, the engine is in pieces and the case has been split. I have the fortune of having access to micrometers and other specialized tools. After taking a look and measuring a few things I have determined that Piston #3 had a smeared connecting rod bearing. After further investigation, it became clear that the crankshaft had been ground where the big end of the connecting rod attaches. I am having problems determining exactly what bearing replacement I need to purchase to match this now non-factory crankshaft. It appears to be 150mm over or 31.5 radially but it is difficult to get extremely fine measurements around the crankshaft itself. I have however done specific measurements of ID of the connecting rod. They measure as such in inches, #1-1.3382 #2-1.3378, #3-1.3378, #4-1.3383. I'm not sure if this helps or if anyone will be able to give me and advice but I was hoping to find a definite answer on which bearings I need to purchase. I also have the option of possibly purchasing a slightly used (can't verify any measurements) crankshaft that has not been ground. Also, a general question, would the ID of the big end of the connecting rod also be ground or just the crankshaft itself?

The image included comes from the service manual that I am working from. It shows that if you add the specified bearing (factory) to the connecting rod big end ID it comes within proper clearances. I just don't know how the ground crankshaft will affect the selection of the bearing. The original factory bearings were as such: #1-B1, #2-B2, #3-B1, #4-B1.
Thanks,
W

 

I'm probably just gonna end up making this an informational guide about the process if I can. After taking apart the engine and doing further testing I found that the crankshaft had already been ground prior. !@#$. I didn't know what to do at all. I looked at alternatives such as buying another crankshaft, used but in "good condition" as for how good, I didn't get the chance to test. I opted to look for other methods because not only would I need new connecting rod bearings but I would also need new main crankcase bearings. (expensive) Anyways after doing some digging, and thinking that someone has got to have done this before, I found oversized bearings. That being STD - 25 - 50 - 75 - 100 - 125 - 150 - 200 These designated the (mm) smaller than standard ID bore meaning that you could take material off the crank and use these bearings. After doing some calculations and modeling everything in CAD I found that using the 200 series oversized bearings would allow me to have the crankshaft journals ground to a smaller dimension such that it was a perfect fit. After looking at the engine more I believe that the original knock came from an incorrectly ground journal from one of the previous owners. It measured, strangely, much smaller than the rest of the journals which were all within a 1-2 thousandths and this was the proven bad cylinder due to smear marks on the removed connecting rod bearing. As for the connecting rods themselves they might need minor regrinding but the shop that I took my crank to said it was relatively cheap. I'm going to have done this entire job for somewhere around $600. Alternatively, for ($650-700) I could have bought a used engine off of ebay and slapped it in but I wanted something trustworthy. I have done a ton of measuring and this job has been very interesting (first complete engine rebuild)! If anyone is doing something similar and needs information I'd be happy to help. While everything not completely done with the job and all of this is still somewhat unproven I am for once confidant. I will be sure to post pictures once I reassemble the bike and maybe a video of it running. Love them CBRs.

 

Sounds like an interesting project. Yes, pictures of the progress would be cool.