My first impression was that the keyway is still ok, I might order some larger key stock just in case the stock part seems too loose when I reinstall it.

Will keep updating ...

Update - keyway slightly worn
 

Well upon closer inspection I think the keyway is worn.
http://i1237.photobucket.com/albums/...ider/image.jpg

It is not so so bad but I won't really know until the parts arrive.

My research led me to think that I might be able to fill the gap in the keyway with a product called loctite 660. There is a bit of www documentation of it being used to repair worn keyways and fills gaps up to .5 mm


Anyone ever tried this product? Feedback ? Advice?

I've used the Loctite product in industry on pumps etc with good results.

The thing you need to consider is the key is not designed to take shear forces (ie to stop the balancer rotating on the shaft) but only to provide the correct location. The rotation is prevented by the nut being done up to the correct torque.

I'd be checking that the balancer is still a snug fit on the shaft and that the movement in use hasn't caused any slop when bolted up. If there is any doubt there are various other Loctite (and others) products that can help. Loctite have a product called "Bearing Fit" ( or something similar - sorry can't remember its number) designed to stop bearings spinning in their housing. If there is any doubt I would assemble the balancer onto the shaft with some of this before torquing the nut to the correct figure.

Hope this helps.

I agree, make sure everything is spotless clean and degreased. Make sure the nut is well tight then the key as no stress on it. It's only worn the keyway because the nut was loose, allowing it to move.

play in balancer shaft
 

still awaiting parts (key and breather plate) but started to wonder if this "in and out" play in the balancer will be remedied once i torque the nut to spec. Is the balancer supposed to have all this movement in and out? or is the bearing shot or is the balancer shot? I will probably wait to reassemble and see how it moves afterwards. but if this is obviously a problem i guess it would be good to know at this point. split the cases and get the wallet out again. check this video to see the play. The bearing itself appears to be in good shape and there is no movement in any other direction just the bit of play in and out.



not sure if the embed will work ... if not here is the link. xt550 balancer play - YouTube

as always, thanks for the advice everyone, much appreciated.

If it was me I'd build it, torque it, and check the end float again, I don't know but it will most likely remove most of it. It looks like a roller bearing in there, they have no means of controlling axial float, but are very strong radially.

The bearing will be fine as theres only lateral play. If you were to split the cases you would find only that the balancer shaft will be very slightly mushroomed out where the spinning forces have bashed it around and wear will have occured. With the nut back on some of the play will disappear as it is now limited to the amount of free movement between the gear wheel on one side of the bearing and the inner race face on the inside.

As this is something that is set by design I convinced myself that this was to allow for either mechanical expansion through heat. Its one of a kind in the engine, the other side is just a small common ball race so they must have designed it like this for some purpose.:mchappy: (or so I'd like to think.)

I know I gave it lots of thought when I had mine apart. One idea was to space it out with shim washers on the other end of the shaft. In the end I did replace the bearing to gain no difference what so ever. Shied away from shimming it out as assumed there must be a reason for it and slightly to lazy to take it apart again.No engineers blue either!

update
 

hey A.L.F.
Curious to know if your efferts reduced any sort of knocking noise.
If yours remained with a bit of play - could you still hear this play in the engine while running?

Anyhow, here is the balancer with new parts installed. Installed a new key and used that loctite 660 to make up the small wear gap on the side of the keyway, new breather plate and new lock washer. Torqued to spec from the manual but there still is a little play in there. Guess I'll have to get it running again to see if this solved my problem. Crossing my fingers.


I should have the rest of the motor back together next week. New 1st oversize Yamaha piston, cyl rebore and recut valves by mongoose in poco, bc.

Hope the weather here holds (ie no snow) so I can get the old girl out for a break in run.

Looks O.K. to me, run it and see......

fixed the knock - but more new problems
 

thanks again for all the advise everyone.
the new parts for my balancer have indeed stopped the bottom end knock. I will post another vid soon.

i got the bike all back together and it ran great for the first warm up run anyhow.

now i am having issues with poor running condition, won't idle and a lot of backfiring.

if you have any advice check my new post out.

http://www.horizonsunlimited.com/hub...963#post361102

thanks.

XT550 Service Manual - Index of /josip/manuali/yamaha/xt550 (Long download be patient).