Honda CB750K Cafe Racer project about to start with a monoshock??

[rohalloran]

Can you verify that the linkage and mounting points were installed in the exact location that they were in on the donor bike? If not, then no way to tell how good it is until it's ridden. Leverage ratios are important on those setups.
It looks like they added the top mounting point directly from the donor right?

Sent from my SAMSUNG-SM-G930A using DO THE TON mobile app

It does look like that alright but I have no way of knowing for sure. All I know is the guy who did the work was extremely talented at this kind of work. He passed away a few years ago which was a real loss to the biking community as he could turn his hand to anything on a bike.

 

[rohalloran]

If the motor is stock, I agree that a set of bigger pistons and a mild cam would wake it up. I just looked at teh intake manifolds and someone spent a lot of time on the conversion.

What have you been able to find out about its history?

Leave the frame color if it's not too chipped or pitted and get the wheels powder coated in Silver or white. You could maybe get away with bright yellow wheels if the tank and seat picked up the yellow in some way. Subtle? Maybe not so much, but could look bold.

So the aluminium intakes were custom made you think? Not stock? I haven't been able to find out too much more really although I was told by a friend the carbs might have been off a ZXR 750. It's goign to be a fun project! The frame needs a to be redone but I won't go near any of that till I can get the engine running. Lots of ideas though!

 

[sebwiers]

Can you verify that the linkage and mounting points were installed in the exact location that they were in on the donor bike? If not, then no way to tell how good it is until it's ridden. Leverage ratios are important on those setups.

You can make a good guess if you work out the setup in software or even just start with a shock that is appropriate to the bike (from bike with similar weight) and work out a location that fully compresses the shock after an appropriate amount of travel. The later is all I did for the back of my bike. I ended up with a rate that is perhaps overly progressive, but the ride is fine. As you say, the leverage is important, but its not to hard to work out, either with a lot of test measurements at different wheel positions or with a good diagram / software package.

 

[rohalloran]

You can make a good guess if you work out the setup in software or even just start with a shock that is appropriate to the bike (from bike with similar weight) and work out a location that fully compresses the shock after an appropriate amount of travel. The later is all I did for the back of my bike. I ended up with a rate that is perhaps overly progressive, but the ride is fine. As you say, the leverage is important, but its not to hard to work out, either with a lot of test measurements at different wheel positions or with a good diagram / software package.

Thanks sebwiers. When the time comes I might be back to you on this one 8)

 

[clem]

Looking at pics of gpz900's online show the lever very close to 90 degrees with the shock. The one on this bike is way past that angle and you will have a very stiff ride as it sits.

Sent from my SAMSUNG-SM-G930A using DO THE TON mobile app

 

[rohalloran]

Been looking at a good few pictures on line over the last 2 days and I now think the swingarm might actually be off a GPZ 750 because of the way the rear brake caliper is held on via the support bar. Plan to dump this and make a small bracket to attach to the swingarm like most modern bikes. Get a nice master caliper then to suit the back wheel that goes onto it. Thinking a GSXR 600 or SV 650 if there is the room.

 

[rohalloran]

Managed to get the head and barrels off today. Found out why it was seized and would not kick.. Outer 2 barrels had built up a layer of rust. On close inspection though I get the feeling the engine might have had been had a rebuild before it got left aside to ruin..

 

[BenHolmes21]

Looks a good base to get started on! I’ll be keeping my eyes out for this!


Sent from my iPhone using DO THE TON

 

[rohalloran]

So gave the barrels a light hone this eve to see what kind of condition the barrel walls were in. They are going to need a rebore for sure. The rust has left some wear on the walls so might as well do the job right.

Where to people suggest going for an oversized piston kit? The current pistons have a .75 stamped on top of them so I'm guessing that means they are oversized already? I see some people do an 836 upgrade but I'm not sure if i want to go that far with it.

Any suggestions are greatly appreciated.

 

[rohalloran]

Managed to get the gearbox and crankshaft out of the engine casings this eve. One step closer to getting it ready to be soda blasted.

 

[rohalloran]

Have decided not to go down the USD fork route now due to costs. I came across this bike over the weekend and I think it is the way to go.
Thinking of putting an F series front end on the bike and MAYBE changing the backend to the F series also. Will see what mods are needed to the Kawasaki swingarm to take the Honda Comstar wheels first. Anyone any experience fitting F series front/backend to a K series, your thought and opinions are welcome.

https://www.youtube.com/watch?v=IxHadZ6a0KE

 

[teazer]

Just a thought, but there is nothing particularly special about that bike in the video, and your bike is unique and appears to have been thoughtfully modified. I would be tempted to rebuild the motor, take care of any consumables such as chain, cables and tires and ride the thing. An F tank and suitable seat might look nice but I's avoid changing anything substantial until you have chance to ride it and see how it works.

If you would prefer to have a bike more like the sample, maybe it would be better and cheaper to sell what you have and buy something that will take way less work to get it to look like that.

 

[irk miller]

I agree. The frame, swing arm scenario looks great. Nothing to gain from F components except a rear disc, which you already have. You also have a sought after swing arm because it allows you to adjust the geometry by rotating the axle mount and essentially raising or lowering the axle location. It's also a lot lighter than an F swing arm. I personally love those mags, but you can easily swap to Kawasaki KZ mags to give you more of a Lester-like look.

 

[rohalloran]

Just a thought, but there is nothing particularly special about that bike in the video, and your bike is unique and appears to have been thoughtfully modified. I would be tempted to rebuild the motor, take care of any consumables such as chain, cables and tires and ride the thing. An F tank and suitable seat might look nice but I's avoid changing anything substantial until you have chance to ride it and see how it works.

If you would prefer to have a bike more like the sample, maybe it would be better and cheaper to sell what you have and buy something that will take way less work to get it to look like that.

Thanks for your comments. Definitely food for thought. Perhaps a rolling chassis to fit my current motor would be a better option to get a big like this example and then overtime build out the current bike with all the mods. : The bracket for the mono shock can stay on the frame so can always swap between the 2 once I get wheels I like for the current swingarm.
There is just something about the look of the bike in the video I like.

 

[rohalloran]

I personally love those mags, but you can easily swap to Kawasaki KZ mags to give you more of a Lester-like look.

So you reckon KZ mags like this would spap in handy enough? The current front-end has a 16 inch front wheel so would need to make a 19 inch fit. Most likely change the whole front-end?

https://www.ebay.ie/itm/KAWASAKI-Z750-KZ750E-1980-ON-REAR-WHEEL-J18xMT2-15/372293541321?hash=item56ae6c9dc9:g:CwMAAOSwo9Fa6OZt
https://www.ebay.ie/itm/1980-KAWASAKI-750-LTD-KZ750H-FRONT-WHEEL-RIM/272912831105?hash=item3f8adf5281:g:4YYAAOSwSrNZ-6JU

 

[canyoncarver]

I agree with Irk and Teazer on the chassis swap. It would be far easier and less expensive to find a good stock CB750 chassis if you really want a bike like the one in the video you posted. The front end could be as easy as find a KZ front end with the same diameter forks as the CB and bolt it into the stock CB triple clamps. The rear will be a little different but there are plenty of KZ rears with disc setup. Look for late 70's, early 80's KZ1000 rear with a disc.

 

[rohalloran]

I agree with Irk and Teazer on the chassis swap. It would be far easier and less expensive to find a good stock CB750 chassis if you really want a bike like the one in the video you posted. The front end could be as easy as find a KZ front end with the same diameter forks as the CB and bolt it into the stock CB triple clamps. The rear will be a little different but there are plenty of KZ rears with disc setup. Look for late 70's, early 80's KZ1000 rear with a disc.

I came across this today when searching and now has me thinking the Kwacker front and rear could actually work really well if I can get the lines right.

http://raggedmoto.com/kawasaki-gpz750-retro/

 

[canyoncarver]

IMHO. It's a good looking bike but it needs honest street tires. That bike is only "posing" as a tracker. Dirt tires and cafe clipons just do not go together. "cafe/tracker" isn't a thing. my .02.

 

[rohalloran]

IMHO. It's a good looking bike but it needs honest street tires. That bike is only "posing" as a tracker. Dirt tires and cafe clipons just do not go together. "cafe/tracker" isn't a thing. my .02.

Yes I agree on the tires. It does give me food for though now on the monoshock.

 

[rohalloran]

Took off the remaining items from the bike last night. Looks much better now without the handlebar risers, clocks etc. First up, different Kawasaki wheels.