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Primary drive housing broken, need some insight please.

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 And the new 300FW is already wounded. Something got in a bind and blew the whole chunk of case out around the primary drive gear at the back of the motor. In the pic you can see the crack along the top...there is a big chunk missing from the bottom. And it won't roll....but the front and rear diffs both seem fine. Unfortunate. This looks to be a bit of a project. Still feels like it will shift through gears so i'm wondering if the ring and pinion just jumped a bit and blew something to pieces.  I have a parts bike.  But will this require the case to be split and transmission completely disassembled?  I assume you can't just slide the broken primary drive out and slide the replacement in?


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To update this thread: Pretty sure it's going to be the one and only u-joint in this bike...the one in the axle tube.  Apparently it's not unusual to grenade the u-joint and when it does it blows the side out of the primary output shaft housing.  My oldest picked up a complete parts bike for $50 and last night i picked up the housing without the gears on feebay dirt cheap so we have some options.  The trick here is going to be getting the broken shaft out and inserting the new one without having to split the case.  I've read you can lay it on it's side and slowly slide the old one out and new one in.  Or possibly backtrace the old shaft on it's way out with thin tubing.

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  • 2 weeks later...

@Frank Angerano Picked up a good used primary drive on feebay for $26 or so.  Also bought a complete parts bike.  Ordered a new drive yoke and clutch cover gasket from partzilla.  When parts come in we'll work on switching out the drive housings...hopefully with the motor still in the bike.  As long as the transmission gears don't fall it'll be a simple switch and put back together.

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Further update: back together and rode yesterday. I replaced it back tracing the shaft with PVC so the gears wouldn't drop sitting on all 4. Unfortunately this requires pulling the side of the motor. I'm told you can lay the bike on it's side and carefully lift the output shaft out and slide the new one back without taking the clutches out. I didnt trust that and did it the hard way. $70 or so in parts and the 300FW rides again. 


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I primarily did it the hard way so I could see the transmission gears inside and maybe get a finger on them should they slide.  It turned out that it was good to stick a finger in and roll a gear to get it to mesh with the splines on the drive shaft.  First 300 i've been into.  While it's quite a bit different than the Yamaha and Kawa's I've been in, it's normal Honda.  Simple and utilitarian.  Not overly complicated.

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  • 2 weeks later...

So the 300FW saga continues.  Back together and rode 2 weekends and it turned into a mosquito fogger.  Dude is burning oil by the mouthful.  After further consideration, i figure this is about normal.  Blowing the output shaft housing interrupted the oil flow to the head and thus overheated and softened the rings in the 10 seconds it ran with the side of the motor broken.  Woops.  New OEM rings came in the other day and we pulled the motor to give it a good once over.  Should be back together and back to normal by the weekend.  Funny how one problem can cause so many issues down the line.


Edit: yes i know you can change the rings with it in the frame.  But a half dozen bolts and a strain on the ole lower back and the motor is completely accessible on the floor.



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