KV75 gearbox expert?

tony_d123 · KV75 gearbox expert?

I need a KV75 gearbox expert, so I guess that means Stale!

Had a proper look at my KV gearbox today. Both selector forks are 5.0mm thick (when I fit the NOS one) and the groove in the shifter or slider is within standard limits.

Everything else looks OK apart from the dogs on the 2nd gear (output shaft) and the corresponding ones on the shifter are worn, mainly on the faces where they slide across each other. The sides are still fairly square, although slightly rounded at the top.

If I cannot get a replacement, I was thinking of dressing the dogs and trying to square them up, but as the sides are not too bad and the faces now have a matching profile I may do more harm than good as I will reduce the height. Do you agree?

Why are they worn so much on the faces rather than the sides, has something (other than a boot!) been putting pushing them together? Is this why the selector fork was so badly worn on one side and broke?

tony_d123

Has anyone had dogs welded & re-ground to the correct profile?

180kid

have you got the part number ?

The Wolfman

Worn?? one of those dogs looks to have a big chunk missing or is it a trick of the light?

looks like 13131-032 has it got 26 teeth?.....any advance? Also used on the MT1 series.

The gear will probly be case hardened which is why once the surface is penetrated the metal disappears at a rate of knots. Any work on the gears will then need the surface hardening again, if you look in your local Yellow pages there wil probly be gear engineers around you, but their work will be pricey.

A good S/H or NOS is a good start.

ståle

This is common, Tony. You'll need a new or at least a good 2nd gear. The 2nd gear is the weakest link in the KV tranny. What usually happens is that if the engine has too much rpm in 1st before changing to 2nd, the 2nd gear dogs will take a good beating when changing gears. Over time this will result in rounded dogs on 2nd, that will push 2nd and the shifter away from each other. This again will result in the gearbox locking up between 1st and 2nd, then with the shift fork in tension, and it breaks. Mine was excactly like yours.

You have a new fork, get a good 2nd gear and a good shifter. Then have them undercut on the 2nd gear side (recommended !!) My mate has undercut all our KV's using an angle grinder and cigarette paper

Works great !

tony_d123

Thanks Stale, you confirmed what I feared. These KV gearboxes must be made of really crap metal, considering the relatively low loads going thro' them.

ståle

That should be it, Gra. Same on all the 75's.

ståle

The ratio gap between 1st and 2nd, combined with a centrifugal clutch is a disaster waiting to happen.

g6mow

So when are you getting the gears repro'ed Stale

, think I'll need some too.

ståle

Here's a used shifter. Cheap too:

http://cgi.ebay.com/ebaymotors/TR...MotorcyclesQ5fPartsQ5fAccessories

ståle

g6mow

ståle

tony_d123

180kid

thought it was the big' 26t cog thats fooked, that where your main wear is,..not the part in the link,...

tony_d123

Bri, it is the 26t gear that I need, but that link is the shifter that the fork sits in and meshes with it. Looks like I need both.

ståle

Yes, looks like you need both, but if you're shifter can be saved by undercutting it you'll be fine.

ståle

Did you get your parts, Tony ?

tony_d123

180kid

have found some on the net 26t one, but $67,...

tony_d123

Bolted the KV engine back together today. Success! Just had a quick ride up and down the street, all three gears, nice smooth change (considering the auto clutch).

I tried buying a second hand transmission from the US but it was well worn and almost as bad as mine, despite getting loads of hi-res pics.

In the end I had to buy a NOS 2nd gear, slider and fork selector, cost me plenty but at least its done.

Can pull it to bits now and start on the cosmetics, now where did I put those rattle cans?

kas750

Nice one Tony.If you are short of any bits you are welcome to have a look here.BTW are you gonna do it standard or use a bit of artistic licence?

tony_d123