Topic: 77' Cb750k -- CAN I UPGRADE TO 18" REAR WHEEL?

[Xander^]

Hey everyone.. so i was riding with some friends and they noticed my rear wheel wobbling a little bit left and right.. talking probably 1/4 inch or so of play. I didnt notice anything while riding, yet at least..

BACKGROUND: rebuilt this bike almost everything was redone, however rims/spokes are original, and wheels were balanced after i put new tires on. I did not ride before tear down because it was not running. I didnt get new rims during rebuild because i wanted to just get it running first, this is my first season on the bike and only on my first 200kms..

(origional rims seemed to have solid spokes and in decent shape. Inside had some surface rust, BUT has some pitting and likely some of the nipples were fused to the rim)

options/ideas of where to go from here:
- i was looking to order a new rim and spokes and start fresh? I was looking for a black or chrome based rim from rising sun or something but i cant find a 77/78, those years they used 17".

- taking it to a shop and maybe it only needs to be trued up again?

- Buying a early model 18" rim which are largely available, new spokes, and i guess i would need a 48T rear sprocket? (Is this possible and what else do i need to worry about if i go with this option)?

PS, i cant find enough clarification on the 77/78 rear rim specs... 17" size but what about the 1.85/2.15/2.25? can someone explain this?

any advice? Thanks

[Xander^]

Also should add the tire im running right now is a 130/90/17.. if that paints a better picture.

[ekpent]

 Do you have a center stand to put it up on to spin the wheel and get a better idea as to what is going on ?

[Xander^]

Do you have a center stand to put it up on to spin the wheel and get a better idea as to what is going on ?

Nope.. will jimmy something up tomorrow though

[Old Moe Toe]

If you had not ridden the bike before you purchased it, it may have already had a dented rim and you did not notice it. A dented rim can be hard to pick up just looking at a bike.
I'd agree with the centerstand as mentioned.

[Alan F.]

If you happen to still have center stand mounts on your frame, you can mount a center stand with its pivot only...for maintenance purposes only, it'll work well and you can take it off when you're done.

[bryanj]

First thing i would check is whether the tyre is square on rim

[Xander^]

I dont have center stand mounts.. I might just take it into a shop this is a bit above my abilities lol..

[BenelliSEI]

Check what Bryanj suggests. Most tires have a raised rib near the rim edge. If the tire was never seated properly, one part of the bead can be too deep in the rim. That vibes exactly the appearance your friends describe......

[rotortiller]

i cant find a 77/78, those years they used 17".

That is an issue for sure  with the 17 inch rear wheel. Make sure the wobble is at the rim by sticking it on a truing stand. You could clamp an indicator to the swing arm and run it to the rim, then slowly spin the wheel and look. That should isolate the rim wobble from the tire. There is sometimes one spot where the rim is welded that you may see a very minor variance which is normal. Side to side wobble is adjusted out with the spokes provided the rim is not bent.

[Erny]

Hey everyone.. so i was riding with some friends and they noticed my rear wheel wobbling a little bit left and right.. talking probably 1/4 inch or so of play. I didnt notice anything while riding, yet at least..

BACKGROUND: rebuilt this bike almost everything was redone, however rims/spokes are original, and wheels were balanced after i put new tires on. I did not ride before tear down because it was not running. I didnt get new rims during rebuild because i wanted to just get it running first, this is my first season on the bike and only on my first 200kms..

(origional rims seemed to have solid spokes and in decent shape. Inside had some surface rust, BUT has some pitting and likely some of the nipples were fused to the rim)

options/ideas of where to go from here:
- i was looking to order a new rim and spokes and start fresh? I was looking for a black or chrome based rim from rising sun or something but i cant find a 77/78, those years they used 17".

- taking it to a shop and maybe it only needs to be trued up again?

- Buying a early model 18" rim which are largely available, new spokes, and i guess i would need a 48T rear sprocket? (Is this possible and what else do i need to worry about if i go with this option)?

PS, i cant find enough clarification on the 77/78 rear rim specs... 17" size but what about the 1.85/2.15/2.25? can someone explain this?

any advice? Thanks

To the rim size - on my stock K7 it is 2.50"

[spotty]

My 2c worth

Check the wheel bearings, if it's wobbling that far in both directions that, to me , indicates something amiss in the centre of the wheel

I have had a rear wheel bearing collapse and ended up welding the centre race of itself to the axle. It had to be hammered forcibly out of the hub, destroyed the hub and axle, not a pretty sight.
It manifested itself as a wobble in the back wheel and as I was usually too stoned to remember there was a problem when I got off the bike , ended up with the bike slumping to the left on acceleration and dropping back to the right when slowing down ( or was it the other way... can't remember, I was stoned)
Anyway, easy enough to check and could we'll save a nasty accident if the wheel seizes at speed

[Xander^]

Thanks guys gonna get some of these checks knocked off the list

[Xander^]

Hey guys can i increase my rear wheel from 17” 2.15 to a 18” 2.15? I have to room for it under the seat, however what else do i need to worry/ take into account of?

[Alan F.]

I'm planning the same move for my K8 and I'm not aware of anything to worry about or account for.

Just use the K7-K8 sprocket carrier with your original spacers and you're good to go.

[Xander^]

I'm planning the same move for my K8 and I'm not aware of anything to worry about or account for.

Just use the K7-K8 sprocket carrier with your original spacers and you're good to go.

So just buy a set of rear spokes for 18” rim and buy the outter 18” rim and keep the original hub??

[Alan F.]

That should work just fine if you keep with stock parts and you can lace and true a wheel.

Some rims will vary in style and dimension from stock. To be sure you order the correct spoke length you need to have measurements from the hub and the rim that you plan on using. Have a look at this: http://earlymotor.com/leon/misc/html/spoke.htm

It works well, I've used it before.

[Stev-o]

Have the swing arm bushing been replaced? 

[Xander^]

Have the swing arm bushing been replaced?

Yes they have!

[Xander^]

just need to know if i can keep STOCK 1977K rear HUB and increase rim to 18" with new 18" spokes. Stock rim is 17" on 77-78. Will this setup work ??

[Alan F.]

Hub should be identical.

[Xander^]

Hub should be identical.

Thank you sir!

[grcamna2]

Have you considered swapping in a rear wheel from a K6? 4.00x18 tire.The hub is the same.

[mrbreeze]

I'm not familiar with 77-78 or F bikes but know some of the differences you might run into. It may or may not make a difference so listen to what others are saying about making the swap. 77-78's had the 630 chains. Earlier had 530 so may have some carrier difference. F's had disk brake and K's had drum. Also swing arm got bigger on 77-78.

[Alan F.]

Yes the sprocket carriers changed for 77-78, they are 10mm wider to the left side of the bike so use the one that came with your bike and your original axle spacers if you change hubs. Hubs and drum brake carriers are the same.