Topic: 1971 CB750 with GSXR Front End

[JohnnyM]

Seeing your problem with the fork hitting the tank and not having a good turning radius, it screams back if it was easy, you'd see a lot more custom bikes than you do.  If you're going to the trouble of having someone make a custom triple tree, have them make one that will actually work on your bike.  I've played around with various forks and found the 89-90 GSXR fork works best at getting the turning radius within reasonable bounds.  You may have to play with the fork stops but that fork is not as radical as the triple tree you now have.   Unfortunately, I've been where you are and learned from it the hard way too.  Good luck
Johnny   

[GNGSXR]

Seeing your problem with the fork hitting the tank and not having a good turning radius, it screams back if it was easy, you'd see a lot more custom bikes than you do.  If you're going to the trouble of having someone make a custom triple tree, have them make one that will actually work on your bike.  I've played around with various forks and found the 89-90 GSXR fork works best at getting the turning radius within reasonable bounds.  You may have to play with the fork stops but that fork is not as radical as the triple tree you now have.   Unfortunately, I've been where you are and learned from it the hard way too.  Good luck
Johnny

I didn't commission the top triple tree to be made specifically for my application. It's a piece meant for these type of "popular" front end conversions.
The turning radius is still in reasonable bounds. Not any worse than my race bike haha.

[SOHC4 Cafe Racer Fan]

Seat/cowl and seat pan also showed up.
I drew a seat design in CAD and had Dave make it for me. His ebay store is located here http://stores.ebay.com/hotrodmetal 



I decided to use an upswept rear hoop after I had already sent off my design for the seat. I'll have to cut the rear of the seat to match the hoop I ordered from Dime City Cycles.

Any chance you can exchange your upswept hoop for a plain Jane horizontal hoop?  I like the seat design, and it would be a shame to cut the curve out of it to accommodate the hoop.  I think it would look better with hoop sitting flush with the seat as designed by you.

[Retro Rocket]

Seeing your problem with the fork hitting the tank and not having a good turning radius, it screams back if it was easy, you'd see a lot more custom bikes than you do.  If you're going to the trouble of having someone make a custom triple tree, have them make one that will actually work on your bike.  I've played around with various forks and found the 89-90 GSXR fork works best at getting the turning radius within reasonable bounds.  You may have to play with the fork stops but that fork is not as radical as the triple tree you now have.   Unfortunately, I've been where you are and learned from it the hard way too.  Good luck
Johnny

I didn't commission the top triple tree to be made specifically for my application. It's a piece meant for these type of "popular" front end conversions.
The turning radius is still in reasonable bounds. Not any worse than my race bike haha.

While the turning radius may still be workable, the trail is now well over 4 inches, thats the main reason triple clamps with a similar offset to the 750/4 should be used, less offset = more trail= slower steering... With the combination of more trail and a 17 inch front wheel the bike will be more stable in a straight line but will feel like it wants to "fall" into or "flop" into corners, this should be more prominent at lower speeds,  the 17 inch wheel is working against the slower steering geometry. The 17 inch wheel steers quicker than the stock 19 inch and now the trail is contradicting this, its trying to work against itself. I am having custom clamps made up for all 3 of my 750's and will run 18 and 19 inch front wheels  due to this problem. For the GSXR front end to work without modification,  the swingarm pivot to steering head measurement would have to be similar to the Gixxer and share its rake, it all gets a bit complicated but thats roughly how it works....

[JohnnyM]

You touched on something no one mentions but again, if you are changing one thing, it affects other things.  I used 17" wheels and GSXR fork and swing arm.  The bigger factor is the shorter modern forks.  Most of the older forks are in the neighborhood of 42-44" and the GSXR forks are a lot shorter, around 38-39"  Add the 17" wheels and you are changing  a lot.  If you are going with twin shocks, make sure you are keeping the geometry about the same as a GSXR, don't push up the rear end too much and don't have the front end too steep.
Johnny

[Retro Rocket]

You touched on something no one mentions but again, if you are changing one thing, it affects other things.  I used 17" wheels and GSXR fork and swing arm.  The bigger factor is the shorter modern forks.  Most of the older forks are in the neighborhood of 42-44" and the GSXR forks are a lot shorter, around 38-39"  Add the 17" wheels and you are changing  a lot.  If you are going with twin shocks, make sure you are keeping the geometry about the same as a GSXR, don't push up the rear end too much and don't have the front end too steep.
Johnny

I'm using the GSXR1100K {1989} 43 mm right side up forks on 2 of them , they are longer than the GSXR750J {1989} forks and have all the adjustment the 750 forks have, i have a set of 41mm forks off a CB1000F 2007 model that are almost the same length as a stock 750 and will carry a 19 inch fr4ont wheel. I have had extensions made up for the 43mm Suzuki forks if i need to alter the ride height at the front, just need to get them hard chromed, they will both wear 18 inch front wheels.....

[GNGSXR]

Test fit with no frame modifications.



The seat Dave made me was great and he matched my cad file perfectly. It still needed some on site and completely expected modifications.




Chopped the rear section of the frame and the passenger pegs. The stock seat hinges were eventually cut as well.


I ended up using the upswept rear hoop. I like the look compared to a straight line from the bottom front of the gas tank all the way back.



The hoop install meant we needed to modify the seat to match. A little more trimming and some runs on the air hammer and it will be set.

[SOHC4 Cafe Racer Fan]

I take back what I said. The trimmed tail looks superb with the upswept hoop.

[Trad]

That really looks great. Seat fitment at the tail is beautiful.

[riverfever]

Man that looks really nice.

[GNGSXR]

...the bike will be more stable in a straight line but will feel like it wants to "fall" into or "flop" into corners...

Great. This is exactly what I want. Ill leave the other cb750 I have with a very lazy, awkward, heavy relatively stock setup.

[Retro Rocket]

...the bike will be more stable in a straight line but will feel like it wants to "fall" into or "flop" into corners...

Great. This is exactly what I want. Ill leave the other cb750 I have with a very lazy, awkward, heavy relatively stock setup.

Thats a strange description of a 750/4 handling, they were quite quick steering bikes due to the small trail numbers from stock {well under 4 inches} and short swingarm, , I always fit a steering damper, thats something thats not needed on a slow awkward steering bike..?
That falling into corners feeling can be a bit freaky as you turn in to a slower corner the bike just feels like its going to fall over, thats what it feels like and you are the first person i have ever heard say that "thats good'...   The tail looks great...

[GNGSXR]

...the bike will be more stable in a straight line but will feel like it wants to "fall" into or "flop" into corners...

Great. This is exactly what I want. Ill leave the other cb750 I have with a very lazy, awkward, heavy relatively stock setup.

Thats a strange description of a 750/4 handling, they were quite quick steering bikes due to the small trail numbers from stock {well under 4 inches} and short swingarm, , I always fit a steering damper, thats something thats not needed on a slow awkward steering bike..?
That falling into corners feeling can be a bit freaky as you turn in to a slower corner the bike just feels like its going to fall over, thats what it feels like and you are the first person i have ever heard say that "thats good'...   The tail looks great...

The stock CB750 geometry and large front tire makes for a very heavy handling feel in my opinion. I am just used to a different style of bike and style of riding. see me in my profile picture for what I am referring to. Reminding myself of the basic laws of physics will keep me confident that the bike won't fall over when I go into a turn unless I make a mistake. The "freaky" feeling is something I am used to but I guess can serve as a warning to anyone else wanting to do modifications like this.
Ill post a full honest description of my thoughts on how this bike handles when completed.

[Retro Rocket]

...the bike will be more stable in a straight line but will feel like it wants to "fall" into or "flop" into corners...

Great. This is exactly what I want. Ill leave the other cb750 I have with a very lazy, awkward, heavy relatively stock setup.

Thats a strange description of a 750/4 handling, they were quite quick steering bikes due to the small trail numbers from stock {well under 4 inches} and short swingarm, , I always fit a steering damper, thats something thats not needed on a slow awkward steering bike..?
That falling into corners feeling can be a bit freaky as you turn in to a slower corner the bike just feels like its going to fall over, thats what it feels like and you are the first person i have ever heard say that "thats good'...   The tail looks great...

The stock CB750 geometry and large front tire makes for a very heavy handling feel in my opinion. I am just used to a different style of bike and style of riding due to racing experience. See my profile picture. Reminding myself of the basic laws of physics will keep me confident that the bike won't fall over when I go into a turn unless I make a mistake. The "freaky" feeling is something I am used to but I guess can serve as a warning to anyone else wanting to do modifications like this.
Ill post a full honest description of my thoughts on how this bike handles when completed.

Its hard to explain a "feeling" sometimes, I have owned Gsxr 1100's and other late model bikes as well, I have a lot of friends that used to race, i've pit crewed for them and have done track days myself, i couldn't compare the handling of the earlier bikes to the later model bikes, i think its the weight difference that you are sort of referring to, the geometry is definitely different. One thing i will say though is that it is entirely possible to make these old bikes handle surprisingly well... Watch the old guys on old bikes, we rode the wheels off these things way before good tires and suspension were ever heard of....

[GNGSXR]

Shaped the front of the seat pan.





Seat pan and cowl mounting.



Offset front sprocket from cognitomoto.com
Cyclex is not making these at the moment.
 



Had a dust cap made.




Shaved off the stock gsxr steering stops on the lower triple. Then drilled and tapped two holes. Turned a couple pieces on the lathe for this strange but very sturdy headlight setup. fyi the damper "cup" mount won't hold water =)



Mounted the gauge to the upper triple clamp.




Headlight mounted. I didnt want fork ears for a headlight mount. Goal was to use a bottom mount to keep the forks clean looking.






I started to really dislike the width of the tank that came on my bike.



So I picked up a '74 CB500t tank that is skinner. I also really like the shape on the sides of it. It is a really beat up tank though and will take some work to straighten out. It also needs to sit forward about a 1/4 of an inch.



Cut open




There was a lot of work done on the CB550 swing arm to allow for a 170mm tire. I'll post more detailed pictures later. We also mounted the rear brake caliper and made some custom axle spacers as well. That won't be the final position of the muffler.

[riverfever]

I like that tank. Bike's really looking good man. Interested to see the pics of the swing arm.

[SOHC4 Cafe Racer Fan]

Shaped the front of the seat pan.





Seat pan and cowl mounting.



Offset front sprocket from cognitomoto.com
Cyclex is not making these at the moment.
 



Had a dust cap made.




Shaved off the stock gsxr steering stops on the lower triple. Then drilled and tapped two holes. Turned a couple pieces on the lathe for this strange but very sturdy headlight setup. fyi the damper "cup" mount won't hold water =)



Mounted the gauge to the upper triple clamp.




Headlight mounted. I didnt want fork ears for a headlight mount. Goal was to use a bottom mount to keep the forks clean looking.






I started to really dislike the width of the tank that came on my bike.



So I picked up a '74 CB500t tank that is skinner. I also really like the shape on the sides of it. It is a really beat up tank though and will take some work to straighten out. It also needs to sit forward about a 1/4 of an inch.



Cut open




There was a lot of work done on the CB550 swing arm to allow for a 170mm tire. I'll post more detailed pictures later. We also mounted the rear brake caliper and made some custom axle spacers as well. That won't be the final position of the muffler.

Great mods on the triples (including the headlight mount) - very clean. 

I was wondering why so much space between the seat pan and the seat?

[GNGSXR]

The pan is flush with the seat. It has a gap just for the picture

[RobbyD]

whats your plan for a tail light?

reason I ask is my seat for my 550 is very similar to yours and im also going with the kicked up hoop.  Been scratching my head over tail light options.

bike looks great

[GNGSXR]

whats your plan for a tail light?

reason I ask is my seat for my 550 is very similar to yours and im also going with the kicked up hoop.  Been scratching my head over tail light options.

bike looks great

I am not sure yet. I am sort of waiting until I pull the trigger on a set of rear shocks which will then help me determine how much clearance I have between the tire and rear hoop.

[GNGSXR]

Rearsets and cognitomoto bracket right side. Trying to figure out where/how we will mount the rear master cylinder and reservoir.




Decided to make a bracket from scratch and add it to the rearset brackets.






Reservoir mount.




The short tail, low stance, low exhaust makes for an unintentional stretched look. I like it. The current wheel base of this bike is about 1/4 inch longer than my GSX-R750 race bike. I may change the exhaust to a different low profile "pancake" collector instead of the bulky one this MAC 4-1 system has.




The CB500T tank was hammered out to clean up all the dents. The C mounts were relocated about 1/4 back. I am not sure if they are called C mounts but they are the brackets located on the front of the tank that slip over the rubber mounts located on the frame. The back of the tank had about 1-1/2 inches removed. This required some heat and time with a hammer to reshape it. I kept the stock knee dents as is after getting the dents out. I want it to look like it was never modified. Sand blasted the inside rust before closing it up. The pictures above were taken prior to the dent removal and modifications on the tank.

[GNGSXR]

I have two remaining BIG things other than paint/powder coat and getting my ass in gear to finish the wiring.

Rear shocks - I have a general idea how this bike will handle when completed. The fully adjustable front end SHOULD be matched to a high quality adjustable rear shock setup but I am not sure if it is worth it yet other than for the cool look factor. I do know that I want a bit more length on the shock setup in the back compared to the stockers. I'd love to have a set of Ohlins H0140's or something similar but I am a cheap ass.

Triangle under the seat - I don't want to use the stock side panels. They will be too bulky looking on here so i may make my own sheet metal side covers that are tucked in further to the sides OR i may completely open up the triangle area.

I am headed to this next weekend along with the MotoGP race http://www.handbuiltmotorcycleshow.com/
If anyone is in the Austin, TX area you should definitely come check out the show. I am pretty excited to see some top of the line builds and maybe get some more ideas for my own bike.

[SOHC4 Cafe Racer Fan]

The bike is looking great.  Nice mount for the rear MC and reservoir.

I vote for an open triangle under the seat.  Maybe you should look into Devin's (CognitoMoto) oil tank to replace the stocker and open up the space. 

As for shocks, I've been told by Buzz at Dynoman that the Ohlins will not fit.  You may want to consider Race Tech, Works and (now) Fox for adjustable good quality performance shocks.

[GNGSXR]

The bike is looking great.  Nice mount for the rear MC and reservoir.

I vote for an open triangle under the seat.  Maybe you should look into Devin's (CognitoMoto) oil tank to replace the stocker and open up the space. 

As for shocks, I've been told by Buzz at Dynoman that the Ohlins will not fit.  You may want to consider Race Tech, Works and (now) Fox for adjustable good quality performance shocks.

Haha I was thinking about posting a link to his oil can but I don't want it to look like I am a huge poster advertisement for him. Here it is anyways http://cognitomoto.com/collections/cognito-moto-designs/products/bolt-on-cb750-oil-can
I've picked up a lot of stuff from him and I'm sure I'll be ordering more. His oil tank is a marvelous piece.
If I do open up the triangle then I will most likely make one myself. Mainly because the other goal of this first build was for me was to gain experience so I'll draw something in CAD and take a shot at forming it out of sheet metal and welding. If I fail then I'll throw more money at Devin for his tank.

I can't find any dimension specifications on the H0140. What exactly about them won't fit on our bikes?
The FoxShocks have also jumped to the top of my list

[SOHC4 Cafe Racer Fan]

The bike is looking great.  Nice mount for the rear MC and reservoir.

I vote for an open triangle under the seat.  Maybe you should look into Devin's (CognitoMoto) oil tank to replace the stocker and open up the space. 

As for shocks, I've been told by Buzz at Dynoman that the Ohlins will not fit.  You may want to consider Race Tech, Works and (now) Fox for adjustable good quality performance shocks.

Haha I was thinking about posting a link to his oil can but I don't want it to look like I am a huge poster advertisement for him. Here it is anyways http://cognitomoto.com/collections/cognito-moto-designs/products/bolt-on-cb750-oil-can
I've picked up a lot of stuff from him and I'm sure I'll be ordering more. His oil tank is a marvelous piece.
If I do open up the triangle then I will most likely make one myself. Mainly because the other goal of this first build was for me was to gain experience so I'll draw something in CAD and take a shot at forming it out of sheet metal and welding. If I fail then I'll throw more money at Devin for his tank.

I can't find any dimension specifications on the H0140. What exactly about them won't fit on our bikes?
The FoxShocks have also jumped to the top of my list

As for the Ohlins H0140s, I've asked Buzz at least twice.  At one time I think he told me the clevis mount on the bottom was not available, but more recently he said that they will not fit (and I'm not sure why).  Like you, I have a sport bike, and I am an Ohlins fan, but I'm not going to throw good money away on something a guy selling 750 parts tells me won't work.  Accordingly, I am somewhere between Works and Fox for my next project with a modern adjustable front.