Author Topic: 16 inch rear tire to 18 inch switch issues! (Read 1523 times)

Jinsonphoto · « **on:** October 08, 2015, 07:12:51 PM »

So I have 78 cb750k with a 73 motor in it. the bike came with a 16 inch rear wheel that I'm switching to a 18 inch. I already put new bearings and rubber on the 18 inch wheel and now that I went to mount it I realized there is extra space between the swing arm and spacers!

Now after further inspection I realize the flanges are different.

18 inch:

&

16inch:

I'm guessing I could just swap the flanges but I already have the new bearing in the new flange, plus the flange from the 16 inch is in pretty rough shape. Since I've already put the bearings in the new 18 inch flange I'd rather not swap them. Could I just machine a longer spacer??

What do you all suggest?? I appreciate any help I can get!

Thanks in advance!

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goaarongo · « **Reply #1 on:** October 08, 2015, 07:20:39 PM »

Not 100% sure on whats up with your spacing issues, but you do need to make sure you have the right sprocket carrier (flange) for the motor - otherwise your chain will be off kilter a bit... there is a tall and a short I believe. I think the 73 was the short one, but in a 78 frame? I dunno. Spacers are easy to make, and bearings are easy to change. Chain and wheel alignment is what this is really gonna be about.

Powderman · « **Reply #2 on:** October 08, 2015, 07:22:27 PM »

Is the wheel/chain centered when the space is on the right? If so, yes a spacer can fill that gap.

seanbarney41 · « **Reply #3 on:** October 08, 2015, 07:40:56 PM »

First of all, if you really had a '73 engine in a '78 frame with no modifications, your sprockets WERE NOT in line. The CycleX website has a good write up and pictures of what is going on here. Its on the chain and sprockets page down at the bottom I think. The 18" wheel has the correct sprocket carrier to go with your '73 engine, but the 78' swingarm is wider...so you just need to space the wheel correctly. You may be able to use some combination of 77/78 spacers and 76 and earlier spacers. Also, if you are good at measuring, it is pretty easy to take an extra stock spacer and cut it down. You will need an extra 10mm on the sprocket side...or you could swap to a '76k or earlier swingarm

754 · « **Reply #4 on:** October 08, 2015, 08:28:27 PM »

78 needs longer sprocket carrier, AND correct longer inner spacer. (greasyspacer)

Jinsonphoto · « **Reply #5 on:** October 09, 2015, 01:43:21 PM »

Quote from: seanbarney41 on October 08, 2015, 07:40:56 PM

First of all, if you really had a '73 engine in a '78 frame with no modifications, your sprockets WERE NOT in line. The CycleX website has a good write up and pictures of what is going on here. Its on the chain and sprockets page down at the bottom I think. The 18" wheel has the correct sprocket carrier to go with your '73 engine, but the 78' swingarm is wider...so you just need to space the wheel correctly. You may be able to use some combination of 77/78 spacers and 76 and earlier spacers. Also, if you are good at measuring, it is pretty easy to take an extra stock spacer and cut it down. You will need an extra 10mm on the sprocket side...or you could swap to a '76k or earlier swingarm

It is a 73 motor in a 78 frame. The previous owner must have modified it because everything was lined up before I took off the 16inch. I did switch the rear sprocket from the 16 to the 18 so the front spocket matches the one I now have on the 18.

So would it be a bad idea to put two spacers on the left side to make it line up? I do have an extra spacer I could just cut and face on the lathe.
-OR-
I could make a brand new spacer on the lathe?
-OR-
Could i just put the flange from the 16in in this 18in wheel? (this seems like it would be the easiest an most practical if it works)

What do you guys think is the best option?

754 · « **Reply #6 on:** October 09, 2015, 01:47:29 PM »

73 motor uses narrow sprocket carrier.
And I'd you have all 73 stuff there will be a gap as shown... If so just add a spacer, got to figure out which side..starting to learn ok look ke sprocket side

Powderman · « **Reply #7 on:** October 09, 2015, 01:54:01 PM »

You should use everything that fits the 16" swingarm. None of that knows or cares about what size rim they are spoked to. I know you said the 16" part wasn't arnica as the 18". I would clean up that part and swap the bearing back into it and be done with no modifications at all. Ya, it's a pain to have to swap them back but once it's done it's done correctly and you no longer have to worry about anything.

Don R · « **Reply #8 on:** October 09, 2015, 02:15:44 PM »

X2, what worked before should work now.

Jinsonphoto · « **Reply #9 on:** October 09, 2015, 03:07:39 PM »

Okay thanks guys!

However I may have to leave that old bearing in the 16 inch flange for now as the the retainer is so banged up Im not sure I can get it off to replace the bearing. I think Ill just run it until i can get the correct flange that's in better condition.

BPellerine · « **Reply #10 on:** October 09, 2015, 04:58:22 PM »

early brake side spacer,and late sprocket carrier should do it.bill

Jinsonphoto · « **Reply #11 on:** October 11, 2015, 10:34:19 AM »

Okay guys one more question. It may be stupid, but...

So I ended up just making 10mm spacer out of an extra spacer I had. The bearing seal on the newer flange was just too chewed up to unscrew.

Anyways I mad the spacer right at 10mm. I'm able to get it to fit, but it's pretty tight getting the last spacer in. Although I did get it in. Is this okay?

I would figure it would be good for it to be a tight fit, but since the original setup wasn't very tight I thought I'd better double check before I put it on the road.

Any help would be greatly appreciated!!

Here is a pic of the new spacer.

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Powderman · « **Reply #12 on:** October 11, 2015, 11:11:01 AM »

Quote from: Jinsonphoto on October 11, 2015, 10:34:19 AM

Okay guys one more question. It may be stupid, but...

So I ended up just making 10mm spacer out of an extra spacer I had. The bearing seal on the newer flange was just too chewed up to unscrew.

Anyways I mad the spacer right at 10mm. I'm able to get it to fit, but it's pretty tight getting the last spacer in. Although I did get it in. Is this okay?

I would figure it would be good for it to be a tight fit, but since the original setup wasn't very tight I thought I'd better double check before I put it on the road.

Any help would be greatly appreciated!!

Here is a pic of the new spacer.

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Once everything is torqued they are both the same "tightness". Your good to go. How did the bearing retainer get messed up on the threads?

Jinsonphoto · « **Reply #13 on:** October 11, 2015, 11:31:39 AM »

Powderman what I'm saying is the last spacer I put in fits in really tight.
And I'm actually worried because now it looks like the brake panel is not flush. I'm wonder if the spacer is to wide it's causing that? Or is this normal?

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Jinsonphoto · « **Reply #14 on:** October 11, 2015, 11:33:34 AM »

The wheel spins fine though?

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Powderman · « **Reply #15 on:** October 11, 2015, 11:45:58 AM »

The spacer between the swing arm and the backing plate have no bearing on how far in the backing plate goes into the drum. You either need a wider spacer behind the backing plate or your wheel sleeve is not wide enough and the bearing is being pushed in too far. As long as the wheel spins freely you should be okay. Anything you would take off the outer spacer to correct that space should be added to the inner spacer.

Jinsonphoto · « **Reply #16 on:** October 11, 2015, 01:39:19 PM »

Okay so I finally got everything sorted out. the wheel is on. Everything is lined correctly. Everything seems as it should. HOWEVER I took it out for a test spin and it feels really weird. Like the front end feels weird? Now I the only thing I really have to compare it to is my experience with the 16inch rear wheel. Do you guys think it would make that big of a difference in handling?
Switching from a 16 inch rear wheel to the an 18.

Thoughts??

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Powderman · « **Reply #17 on:** October 11, 2015, 03:07:59 PM »

16" tire is usually wider than an 18, and the profile is different also, so yes, you would be able to notice a difference if you've been use to the 16"

seanbarney41 · « **Reply #18 on:** October 11, 2015, 05:03:33 PM »

Quote from: Powderman on October 11, 2015, 03:07:59 PM

16" tire is usually wider than an 18, and the profile is different also, so yes, you would be able to notice a difference if you've been use to the 16"

the taller 18" also changes rake and trail quite a bit,so yeah, you are gonna notice

RAFster122s · « **Reply #19 on:** October 12, 2015, 12:36:09 AM »

The rake and trail vary only is your wheel height changes outer diameter. This can be minimized if the section height is changed to compensate for the tire diameter change. So, the original tire is say something like 140/90×16
So, the replacement might be a 120/70×18.
The 2nd number being the sidewall's percentage of the width figure. The numbers just pulled out of my ; thin air...

The 16" wheel being more forgiving in width, whereas the taller wheel can be narrower with better performance. (Less sidewall flex, contact patch would be a little less, etc.

One thing I think might be affected if your spacers are pushing the swingarm wider would be a little stress on the shock if it were to bind the shock action. Odds are it isn't really a major actual issue as you aren't pushing it way offline. Not going to see stiction of the shock action.

Personally, I might be anal enough to see how much difference in width the 16" assembly had before bolted up snug. You could reassemble the 16" wheel and use feeler gauge to get the amount of free space available. Then shave that much off the extra spacer.

Powderman · « **Reply #20 on:** October 12, 2015, 10:38:28 AM »

If you look at how tall and wide a 16" tire is compared to an 18" you'll find not much different in total height.

754 · « **Reply #21 on:** October 12, 2015, 04:05:51 PM »

1/2 would b a lot, usually. More like 3/8...
The difference. In height is divided in half...... So 3/4 inch shorter is only 3/8 in ride height.

Don R · « **Reply #22 on:** October 12, 2015, 08:33:03 PM »

Just a tire change can make a difference even in the same size. You changed the diameter a little but the width probably more, that will change the way the bike rolls over onto the sidewall. (Tip in? )

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Author Topic: 16 inch rear tire to 18 inch switch issues! (Read 1523 times)