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Blood Sweat Tears and Grease => Projects => Cafe Racers => Topic started by: rohalloran on Jun 08, 2018, 17:14:52

Title: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 08, 2018, 17:14:52
Hi All,

Long time browser of the forum but this is my first post. I have to say to all, some of the bikes showcased on this forum are amazing. Great inspiration.

I picked up this bike earlier in the week. The engine is seized due to sitting up but as you can see someone had started to do some decent mods before it got pushed aside. The front and rear end are off a Kawasaki GPZ 900 I'm told and the tank is from a CB900 (or is it standard does anyone know)? The engine will be getting a complete rip down and rebuilt and I suspect I will go for the Cognito Moto GSXR front end conversion but I have to say I do like the monoshock conversion that was done (bar the wheel used). Love to hear what people think and their thoughts on the Monoshock / swingarm used. Hope to keep the thread updated with the progress as I go.

Thanks for looking.

(https://farm2.staticflickr.com/1726/41960615824_92fcae97f8_b.jpg) (https://flic.kr/p/26VV8cw)
(https://farm2.staticflickr.com/1732/27809964477_6720de88f2_b.jpg) (https://flic.kr/p/Jntkya)
(https://farm2.staticflickr.com/1755/41779066255_2ba0f123e8_b.jpg) (https://flic.kr/p/26DSCQx)
(https://farm2.staticflickr.com/1742/27809963917_bdc9de90f1_b.jpg) (https://flic.kr/p/Jntkov)
(https://farm2.staticflickr.com/1722/41779065485_4707fd1c94_b.jpg) (https://flic.kr/p/26DSCBg)
(https://farm2.staticflickr.com/1723/27809963477_eba5f8f8cb_b.jpg) (https://flic.kr/p/JntkfV)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 10, 2018, 16:24:12
Managed to get the engine out yesterday. Now its time for an engine stripdown and rebuild.

(https://farm2.staticflickr.com/1753/40907910560_9e36590b71_b.jpg) (https://flic.kr/p/25jTJAL)

(https://farm2.staticflickr.com/1727/41999911914_2b54ecf5d8_b.jpg) (https://flic.kr/p/26Zowyj)

(https://farm2.staticflickr.com/1741/40907910060_ab990c7477_b.jpg) (https://flic.kr/p/25jTJs9)

(https://farm2.staticflickr.com/1734/40907909840_d8373f2404_b.jpg) (https://flic.kr/p/25jTJom)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: irk miller on Jun 10, 2018, 17:06:01
Holy crap, that motor looks toast.  Is the aluminum broken down as bad as it looks?
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 10, 2018, 17:43:08
Hey irkmiller. It's only some corrosion on the casing. Looks worse than it is (so far...  ;D)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: cardinal on Jun 10, 2018, 17:44:18
lemme guess... you live on a beach somewhere?
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 10, 2018, 17:58:11
lemme guess... you live on a beach somewhere?

Yes  :D It was left outside too which didn't help. Picked it up cheap so hopefully the internals are not too bad.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: trek97 on Jun 10, 2018, 18:07:07
Holy crap, that motor looks toast.  Is the aluminum broken down as bad as it looks?

Haha, I thought it was foaming engine degreaser.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: The Limey on Jun 10, 2018, 18:24:14
Spoked wheels from a Zephyr?
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 10, 2018, 18:37:43
Spoked wheels from a Zephyr?

Now there is an idea.. I like the simplicity of the GSXR conversion Cognito moto offer but have mixed thoughts on the rear end. Leave as is or switch back to the twin shock  ::)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: brad black on Jun 11, 2018, 08:32:39
fix the old style forks and keep the 16" wheel for some wacky retro cool.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: The Limey on Jun 11, 2018, 11:16:16
I was thinking the Zephyr wheels would, hopefully, mate up well with the Kwak rear end.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: teazer on Jun 11, 2018, 12:53:51
I'd be tempted to leave the chassis alone.  Just rebuild the motor and fit a decent looking tank and seat - Maybe an F2 shape.  Dump the K tank.

Wheels are old Kawasaki and actually look good in that set up.  Forget the redesign.  Just get it running and ride it. :-) 
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: doc_rot on Jun 11, 2018, 20:52:15
+1 for keeping the ninja wheels. Different and unique. How many CB750s are running USD cognito setups? Plus the ninja 900 wheels would be perfect for a vintage race vibe.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: irk miller on Jun 11, 2018, 21:06:20
I'll also add that the Ninja wheels give off a Euro Comstar vibe, which is an excellent look and appropriate.

(http://www.cbxclub.com/forum/gallery/image.php?image_id=3590)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 12, 2018, 05:38:41
Thanks all for your input. It will be a while before I make a call on the wheels and suspension but some food for thought there. Need to get the engine completely ripped down first and start that rebuild. I have since found out that the carbs that came with it are also off a GPZ..  8)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: teazer on Jun 12, 2018, 10:36:03
I noticed they were CV flatslides and assumed they were off a GSXR slingshot.  If they are jetted well, they should be a significant improvement on the street compared to stock carbs.  Will be interesting to see what's inside that motor in terms of cam and pistons.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: canyoncarver on Jun 12, 2018, 13:15:44
The mono conversion looks good ( so many are shite ), so does that front end.  I dig the Kawi wheels and forks.  Build that motor into an 836 and go hoonin'.   
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 13, 2018, 13:25:50
Thanks all. I must admit, there was a good job done on the monoshock conversion so part of me woudl like to keep it. I know the fabrication shop that did the work also so I know it was done right. I think what's putting me off currently is the colour of  the wheels against the frame and swingarm.

Taking off the head this weekend to see what lies beneath! Pictures to follow.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: clem on Jun 13, 2018, 14:02:29
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?

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Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: teazer on Jun 13, 2018, 14:29:25
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.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 13, 2018, 17:50:45
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 (http://r.tapatalk.com/byo?rid=89466)

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.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 13, 2018, 18:04:15
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!
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: sebwiers on Jun 15, 2018, 11:16:34
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.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 15, 2018, 11:51:39
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)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: clem on Jun 15, 2018, 12:29:55
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.

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Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 15, 2018, 13:36:13
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.
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 16, 2018, 16:13:29
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..

(https://farm2.staticflickr.com/1744/42121558904_10c78ec2bf_b.jpg) (https://flic.kr/p/27b8ZYd)

(https://farm1.staticflickr.com/891/42121559224_e73a087ac4_b.jpg) (https://flic.kr/p/27b914J)

(https://farm2.staticflickr.com/1723/42839402671_7ebc135c65_b.jpg) (https://flic.kr/p/28gz8UT)

(https://farm2.staticflickr.com/1782/42121559614_65326a0584_b.jpg) (https://flic.kr/p/27b91bs)

(https://farm2.staticflickr.com/1725/42839403091_ef383e5186_b.jpg) (https://flic.kr/p/28gz938)

(https://farm2.staticflickr.com/1768/42121560064_83c5205d9a_b.jpg) (https://flic.kr/p/27b91jd)
Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: BenHolmes21 on Jun 17, 2018, 06:21:37
Looks a good base to get started on! Iíll be keeping my eyes out for this!


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Title: Re: Honda CB750K Cafe Racer project about to start with a monoshock??
Post by: rohalloran on Jun 19, 2018, 16:37:52
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.