Oil seal replacement - 650 final drive.
I noticed oil on the underside of the final drive.It appeared to be coming from the pinnion oil seal,so i thought i might as well change all three while i was at it.
The 650-type final drives are quite simple to dissasemble (probably easier than the 500`s) but i had to knock up a couple of `special tools`to do the job;one to lock the gears while the pinnion drive collar nut was loosened and one to extract the bearing retainer/oil seal holder which sits underneath the drive collar.
The lock-up tool pictured is a spare wheel hub drive flange (this one had severely worn splines but was OK to use for this tool) with a suitably shaped piece of steel attatched.It simply fits onto the crown wheel splines and the steel `arm` fixes to the final drive case-to-swingarm studs preventing the gears from rotating.If you do not have a spare wheel flange you could remove the one from the bike and use that.
The bearing retainer/oil seal holder extractor was made from some square-section steel tube with a tooth/peg welded on to each side.Four teeth are enough as the retainer is awkward to get to but not overly tight or difficult to shift. I could of used round section tubing but only had the square,so that`s what i used.Two holes for the provision of a bar were made to get some leverage..(you`ll notice that the crown wheel large oil seal has already been removed in these pics,i stripped the final drive down before i took these pics to clean it in a parts-washer)
Here the lock-up tool is in place and a socket placed on the nut - this one is TIGHT!! (its probably best to get someone to hold onto the case while you hang off the end of the ratchet...) Once the nut is off the drive collar is removed and the bearing retainer can be seen with it`s toothed outer edge recessed into the final drive case.I don`t know what the Honda special tool looks like because i have never seen one so whether it has just a few teeth like mine or a complete set of teeth to match those on the retainer i don`t know.In the pic the oil seal has been removed - it should sit just inside where the teeth are around the retainer.Also the retainer fixing plate and bolt have been removed - you can see the threaded hole to the left of the case where it screws into.I put a permanent-marker dot on a retainer tooth and a matching one on the drive case to ensure on reassembly it went back in the same position/tightness.
The retainer is undone and screwed out,the oil seal fits here;
Once thats done its just a case of removing the eight bolts and separating the two halves of the final drive,there appears to be two prise-points either side of the case to facillitate separation - there is no gasket between the mating surfaces,a sealing compound doing the job of keeping the oily stuff where it should be and this seal needs to be broken to split the two halves - it can be stuck down quite firmly..The crown wheel large bearing will probably come away with the crown wheel - i had to knock it out using a rubber mallet while supporting the case on wooden blocks,the oil seal sits behind and is easily knocked out.The smaller crown wheel oil seal lives behind the outer bearing,i removed the bearing by carefully tapping from the wheel spindle hole (or use a dedicated bearing puller) and then hook out the oil seal.Be careful of any preload shims/thrust washers when handling the gear-sets and note their location well.Some people have read workshop manuals and have been scared of tackling any repairs to final drives because they have seen references to bearing `preload`,backlash,and the involved method of re-setting and checking using specialist equipment(note that i made reference above to marking the position of the pinnion wheel retainer to ensure it is refitted to the original postion/torque level) If the final drive was working perfectly well before dissasembly (albeit with an oil leak) and you had no reason to suspect any re-adjustment was required to the gear-sets why would it need attention just because new oil seals have been installed?The backlash was set at the factory using shims and would not require any setting/checking unless they have worn to a degree where adjustment is necessary or a new gear-set is fitted.Just make sure it goes back together the way it came apart and it should be fine - i have done two 650 final drives now with no problems after several thousand miles. 
It`s not unknown for a CX final drive - either 500 or 650 to suddenly suffer a massive oil leak.This can happen when the large crown wheel bearing fails (this large diameter bearing operates at high speed) and the disintegrating ball-cage shreds the oil seal - see pic above.I would be a good idea if you have stripped a final drive down to this stage to replace that large bearing while you`re at it,it should be trouble-free for the next 20 years then!The pinnion and bearings look more involved to remove;a puller may be needed to attatch to the threaded part of the pinnion and then extracted out of the case using a screw-type arrangement.It does not need to be disturbed to replace the oil seals and crown wheel bearings so i have never attempted removal...
The 650 final drives are simpler and have less parts than the 500`s.The main problem on the 500`s is the crown wheel large bearing is kept in place with a similar toothed (but much larger) retainer which makes it difficult to adapt/improvise a removal tool for,but of couse there`s always an engineering detour around such things...... ;
When you replace the final drive onto the swingarm,do not do up the mounting bolts until the wheel spindle is in place to ensure everything is square and lined up.If not,undue strain on the final drive may result with resultant bearing failure...
