Crf450r broken jackshaft

[cmello]

I have made a lot of 450 jackshaft’s and broke them I did not see a pic of where it broke if it was in the keyway on the clutch side and has a drilled and taped hole to hold it on that is the problem send me a pic and I will send a pic of what the fix is

 

[ECkarter]

I have made a lot of 450 jackshaft’s and broke them I did not see a pic of where it broke if it was in the keyway on the clutch side and has a drilled and taped hole to hold it on that is the problem send me a pic and I will send a pic of what the fix is

Chris, picture looks like it was at the bearing race. Looks like the bearing seized there. OP please post more photos…

 

[cmello]

Ok was it the bearing by the clutch or the smaller one on the inside? Is it a chain or belt drive jackshaft ?

 

[Ted Hamilton]

I would be inclined to leave 3rd-4th gear in, use spacers in place of the other gears, and run without the jackshaft at all. The 420 chain conversion using PBI sprockets will ensure you never snap a chain but it's lighter than 520, and the rotating mass of the j/s is probably the same as the output shaft. To add to that, the option of being able to slip the clutch (or install a Hinson) is nice in some situations too.... Just a thought.

 

[Sjg22]

We had those failures switched to higher grade metal

 

[2Pricey]

To that point, what about switching to something like 9310? Is there a reason M100 (mentioned in earlier posts) is preferred by some over say 4140 or 4340?

 

[Jim46]

I run a 3rd bearing on my Taft 250

 

[Compu-kart]

Ok was it the bearing by the clutch or the smaller one on the inside? Is it a chain or belt drive jackshaft ?

It's a belt drive from the crank to the j/s and a 428 chain to the axle sprocket.

 

[Compu-kart]

Chris, picture looks like it was at the bearing race. Looks like the bearing seized there. OP please post more photos…

I'll see if I can find it in the shop and take more pix

 

[Compu-kart]

We had those failures switched to higher grade metal

Any problems afterwards?

 

[Sjg22]

Any problems afterwards?

No

 

[Jim46]

take a picture of the end of the break , where did it break , between the bearing and the clutch ?

 

[tecbigdog]

Guys, Do yourself a favor, use a good hardened tool steel for your jackshaft like Sjg22 mentioned. We have used the 4140 ground and polished (what we preferred) that you can get from Alro Metals, (a little pricey) on nearly every engine combination from Jawa's to Sudam's with no failures.

Now, regarding the Sprag hub question. We tried it about 10 years ago on a UAS setup and quickly abandoned it, but not for the reasons mentioned. If you use one on a large engine, it will give you the most unpredictable and wild ride you have had in a while and yes, it does affect your braking. Oh, and by the way, the hub will require more than one bearing..... Hope this helps your decision making........