Topic: how to put 160 rear on 78 cb750f easy sprocket line up

[samm_j2]

I figured I would write a post showing how I put a 160 tire on my 78 cb750f. I of course did this with help of the forum. I could not find an exact procedure outlined so here is my attempt. Here is a list of everything I used and it all bolted right up. I have done a monoshock conversion to my bike so there is some extra tubing. I can not see any reason this would not work had I left the original shocks on the bike...?
 
I am having trouble trying to put photos inside of the post rather than at the end. If the photos don't post I hope the links work...

I think part of the reason this worked out is the 78 has an offset on the transmission output shaft. there is a step of about 7.5mm that the front sprocket will rest against. Since this output shaft does not use the locking tab and is just held in place by the bolt a thicker washer was used to take up the extra gap as the output shaft came through slightly. I used a wheel spacer that I had lying around to fill the gap.

https://photos.app.goo.gl/cgwjq43uhmyKn5yFA

https://photos.app.goo.gl/JRvEv3JnsqzV6eV36

https://photos.app.goo.gl/1oKhSrbdoYe64soQ6

 The 78 cb750 f also has a wider swingarm, it is roughly 10 and 1/4 inches. I am not sure what other models have this type of output shaft and the wide swing arm but if you have them you can easily put a 160 tire on the rear.



The rear rim I am using is off an 03 Suzuki sv650. This rim uses a 20mm rear axle and because of this the stock Honda axle will be reused.

In order to gain clearance on the frame and engine case I switched to a 530 O-ring chain. The sprockets are set up to take the 530 chain.

The front sprocket I am using is made by PBI and as a 1/4 inch off set.

https://photos.app.goo.gl/ga6uXkx6smw2sju1A
https://photos.app.goo.gl/WVcpWjsJZfMHtrok8

The rear sprocket is made by JT Sprockets. the part number is JTR829-48

I am going with a 16 tooth front and a 48 rear. I am not sure if a larger front sprocket will have clearance as things are pretty tight...

The sprocket side spacer off of the 03 sv650 will be used and this actually centers the wheel perfectly. it measures at about 18.5mm

https://photos.app.goo.gl/w9Zo66X3Cas71hsV7

https://photos.app.goo.gl/MYzCLvKpm3Ma6s1A8

Here is a machined straight edge to show the back face of the sprockets lining up.

https://photos.app.goo.gl/QEGV5cZh1V1KUJgc6

Here is a photo showing the chain alignment.

https://photos.app.goo.gl/ScwXczoyatnN8gaVA

The rear axle needs to sit towards the back of the adjuster range to the sprocket bolts don't hit the swingarm. There is still plenty of room for chain adjustment.

I started with a 120 link chain and shortened it about 6 or 7 links.


Here is a photo showing clearance on right side between tire and swing arm. It is close but there is still plenty of room.

https://photos.app.goo.gl/d5F7q6ycPhHN4aps6

The chain also clears all of the tubing on the frame with this set up. It is close in some areas but no rubbing and a few mm of space.

As far as the sprocket cover goes there was a "post" in it that I had to cut out when I was trying various sprockets. I had ordered a a front sprocket form cognito moto. They advertised a 3/8 offset sprocket (9.5mm) to do a wide tier swap. This DID NOT work for the 78 cb750f as the output shaft has the step mentioned earlier. And it did not measure 9.5mm offset but actually more like 11.5mm... the extra 2mm also caused the chain to hit the case. I am not ragging on cognito, they are a great company and I have used many of there products. It was when I was fitting this sprocket that I cut the post on the sprocket cover, This may or may not need to be done.

https://photos.app.goo.gl/mManZvo9VJsQfcaa8

This post was originally made to show just the sprocket side as there are a variety of ways to do the caliper depending on what you chose to run, but I will outline what I did.

As far as the brake side goes that will be depending on what you choose to run for a caliper. I am sure that the caliper off the 78 cb750 could work but a bracket for it will need to be fashioned OR a custom rear rotor that is larger than the sv60. I can definitely say the arm that holds the caliper will not clear the tire. I have seen some people bend the arm to clear the tire but I went a different route.

I am using a brembo p34 rear caliper and a bracket I made for it, I am not going to write about this unless someone asks as you may have a different caliper you want to run. I basically used a plasma cutter to cut an outline...

I kept the sv650 stock brake spacer for my mount to sit against. And then filled the rest of the gap with what I think was originally a spacer for the 78 cb750 honda.

I hope this helps someone put a wide tire on their Honda.

[robvangulik]

I'm just wondering why you would like such wide tyre on your bike, it will only make it heavy to steer and cumbersome to handle.

[754]

It will probably fit without an offset sprocket, i put 150 on a K6 which is narrower, but admit it waz ona standard rim.
 The post or pin you cut on the cover, is a 77 and 78 only thing, due to tge single mount bolt system. Earlier covers do not have that...

[samm_j2]

Rob, I am going to disagree with you on that. This is not some 280+ tire that lacks a profile. The only down side for a wider tire is more lean angle for a given radius at a given speed. The wheel set up weighs about half as much as the OEM set up so it will feel lighter and turn with more ease, accelerate and stop faster as there is less rotating mass.

I have changed the geometry of the bike completely and have a cbr1000rr front end including the 17x3.5 front wheel. The 17in front wheel with the stock rear left tire options lacking. The reasons mentioned above plus tire options are why I switched.

754, It probably would have fit without an offset sprocket but then the chain would not have lined up with the rear sprocket. I could have milled the rear sprocket carrier down to get things to line up. I thought an offset front would be easier.

[754]

Well I am not a stranger to modifying or building any of the parts..
 Hard enough to get z chainguard on there past the shock, witout moving chain out further...

[Alan F.]

Did somebody say 280+ tire?

[Medyo Bastos]

I figured I would write a post showing how I put a 160 tire on my 78 cb750f. I of course did this with help of the forum. I could not find an exact procedure outlined so here is my attempt. Here is a list of everything I used and it all bolted right up. I have done a monoshock conversion to my bike so there is some extra tubing. I can not see any reason this would not work had I left the original shocks on the bike...?
 
I am having trouble trying to put photos inside of the post rather than at the end. If the photos don't post I hope the links work...

I think part of the reason this worked out is the 78 has an offset on the transmission output shaft. there is a step of about 7.5mm that the front sprocket will rest against. Since this output shaft does not use the locking tab and is just held in place by the bolt a thicker washer was used to take up the extra gap as the output shaft came through slightly. I used a wheel spacer that I had lying around to fill the gap.

https://photos.app.goo.gl/cgwjq43uhmyKn5yFA

https://photos.app.goo.gl/JRvEv3JnsqzV6eV36

https://photos.app.goo.gl/1oKhSrbdoYe64soQ6

 The 78 cb750 f also has a wider swingarm, it is roughly 10 and 1/4 inches. I am not sure what other models have this type of output shaft and the wide swing arm but if you have them you can easily put a 160 tire on the rear.



The rear rim I am using is off an 03 Suzuki sv650. This rim uses a 20mm rear axle and because of this the stock Honda axle will be reused.

In order to gain clearance on the frame and engine case I switched to a 530 O-ring chain. The sprockets are set up to take the 530 chain.

The front sprocket I am using is made by PBI and as a 1/4 inch off set.

https://photos.app.goo.gl/ga6uXkx6smw2sju1A
https://photos.app.goo.gl/WVcpWjsJZfMHtrok8

The rear sprocket is made by JT Sprockets. the part number is JTR829-48

I am going with a 16 tooth front and a 48 rear. I am not sure if a larger front sprocket will have clearance as things are pretty tight...

The sprocket side spacer off of the 03 sv650 will be used and this actually centers the wheel perfectly. it measures at about 18.5mm

https://photos.app.goo.gl/w9Zo66X3Cas71hsV7

https://photos.app.goo.gl/MYzCLvKpm3Ma6s1A8

Here is a machined straight edge to show the back face of the sprockets lining up.

https://photos.app.goo.gl/QEGV5cZh1V1KUJgc6

Here is a photo showing the chain alignment.

https://photos.app.goo.gl/ScwXczoyatnN8gaVA

The rear axle needs to sit towards the back of the adjuster range to the sprocket bolts don't hit the swingarm. There is still plenty of room for chain adjustment.

I started with a 120 link chain and shortened it about 6 or 7 links.


Here is a photo showing clearance on right side between tire and swing arm. It is close but there is still plenty of room.

https://photos.app.goo.gl/d5F7q6ycPhHN4aps6

The chain also clears all of the tubing on the frame with this set up. It is close in some areas but no rubbing and a few mm of space.

As far as the sprocket cover goes there was a "post" in it that I had to cut out when I was trying various sprockets. I had ordered a a front sprocket form cognito moto. They advertised a 3/8 offset sprocket (9.5mm) to do a wide tier swap. This DID NOT work for the 78 cb750f as the output shaft has the step mentioned earlier. And it did not measure 9.5mm offset but actually more like 11.5mm... the extra 2mm also caused the chain to hit the case. I am not ragging on cognito, they are a great company and I have used many of there products. It was when I was fitting this sprocket that I cut the post on the sprocket cover, This may or may not need to be done.

https://photos.app.goo.gl/mManZvo9VJsQfcaa8

This post was originally made to show just the sprocket side as there are a variety of ways to do the caliper depending on what you chose to run, but I will outline what I did.

As far as the brake side goes that will be depending on what you choose to run for a caliper. I am sure that the caliper off the 78 cb750 could work but a bracket for it will need to be fashioned OR a custom rear rotor that is larger than the sv60. I can definitely say the arm that holds the caliper will not clear the tire. I have seen some people bend the arm to clear the tire but I went a different route.

I am using a brembo p34 rear caliper and a bracket I made for it, I am not going to write about this unless someone asks as you may have a different caliper you want to run. I basically used a plasma cutter to cut an outline...

I kept the sv650 stock brake spacer for my mount to sit against. And then filled the rest of the gap with what I think was originally a spacer for the 78 cb750 honda.

I hope this helps someone put a wide tire on their Honda.

Where did you find the pbi front sprocket? Do they carry a 17T?


Sent from my iPhone using Tapatalk

[samm_j2]

Alan F that thing is awesome!!!

Medyo Bastos, I got it off the ebay:

https://www.ebay.com/itm/OFFSET-SPROCKET-1-4-16-TOOTH-530-WIDE-BIG-TIRE-DRAGBIKE-HONDA-CB750-SOHC-/254984241449?_trksid=p2349624.m46890.l49286

seller also had more teeth options and different offsets.

[Alan F.]

It was an old thread, I dunno 2005? 2007? I'm uncertain if it was a real bike or not, there was the idea of it being a Photoshop mockup. I can't seem to find the thread based on the search criteria I've used, maybe someone else remembers more. I think it'd be a neat idea to revisit in real life, especially now that it's easy to post a video and link it to a build thread. I'd start by building it around a stock bike, maybe using a stock frame and a custom swingarm, I have enough projects.