Ok so having completely stripped my 4rt intending to put new crank bearings in due to a knock I have found a little wear on the crank, flywheel side..... is this terminal and a new crank or could it be replaced? Also does any one know of an alternative CRF250 crank possibly ?‍♂️

Whilst the CR conrod works I suspect the CR crank will have much lighter flywheels.

Unfortunately the 4r crank is a one off. I would suspect any wear there to give a "rumble" rather than a knock. How does the small end of the rod  measure up in relation to the piston pin and piston? Check both ends of the pin where the piston sits  and centre of the pin

Thanks both, piston and pin are all ok, to be fair it was more of a rumble than a knock so I suspect the bearing. I can’t find any tolerance measurement for the crank so will replace the bearing and keep fingers crossed. I have a video of the play I found before the full strip but it won’t let me add that.

I'm sure there are others, but a firm near to Nottingham called SEP have a large press and some tooling with which they can squeeze the crank and lobe it such that the bearing grips and remains concentric. They have done a couple for me over the years

How much wear are we taking about?  Does the new bearing just drop on to the shaft / did you have to pull the old one off or did it come off easily?

If it feels like just a transition fit then Loctite 641 Bearing Fit would be worth a go.

P.S. You could upload the video to Youtube and put the link on here

Craig

hate to be a spoilsport, but you cant buy the inner race for the bearing, you have to buy a new crank

i found this out when mine started to vibrate, (must admit it had run fine for a full 12 months) but when i stripped engine i found no inner race had been fitted to crank

bike had been running with just the support of the small needle roller in generator.

much to my disgust honda completely rejected my request for goodwill warranty, 

 

 

Thanks for the help, I’m going to put the new bearing in and see how the crank sits and judge any play, unfortunately due to the make up the loctite won’t be an option.  I’ll see if I can sort out the YouTube link and post as well ?

Thanks for the help, I’m going to put the new bearing in and see how the crank sits and judge any play, unfortunately due to the make up the loctite won’t be an option.  I’ll see if I can sort out the YouTube link and post as well ?

edited post with link ?

Ok I get it now, it's a roller bearing and the inner race is on the crank, can certainly hear the knocking in the video.  I thought it would be a ball race like the old motors hence the Loctite suggestion.

Not that many options as it would prove difficult to remove the inner race from the shaft without damaging it although I've seen similar drop off getting quick heat into them.  It may be worth measuring up the race or take the crank into your local bearing factor to measure it to see if they can get you anything similar but it may be that Honda have their own unique sizes.

As you say, probably best to try a new roller first before going down the rabbit hole...