Author Topic: '82 cb650sc cafe project (Read 13048 times)

kerryb · « **on:** November 18, 2018, 06:37:30 AM »

Building this with a friend, he wants a cafe racer with just the right "look" (kids these days!). I've already told him we will find an intake solution that dosen't include pods. We have mocked up a 78 cb750 tank, and ideas for a fiberglass seat hump. The aluminum passenger peg brackets are gone and it came with a usable 4-1 exhaust. Staying with the comstar wheels and the dual-disc front brakes.
The opinions I'm soliciting are whether to try hiding the frame shape under the seat, or cutting the rear section off and replacing it with a more period looking shape including a seat hoop.
The bike is a good running driveline needing only a starter clutch repair. The body panels, tank, and seat are in pretty good condition, so I struggle with cutting the frame resulting in no possible return to stock anytime in the future. Are these considered future collector items, or red-headed stepchild best used as parts donors?

Note: the bike pictured is not the one, but same year, model, and color as what we are working with.

kerryb · « **Reply #1 on:** November 18, 2018, 07:39:13 AM »

These pictures describe our progress so far. These are the actual bike.

kerryb · « **Reply #2 on:** November 18, 2018, 07:55:27 AM »

If I cut out the top tubes of the seat area, add a seat hoop W/upsweep, and relocate the upper shock mounts a little further back, that will stand the shocks up at a more vertical angle. If I use longer shocks, then the seat could be raised and the head tube rake angle shortened up a little from the current 30 degree rake. I haven't run the rake and trail numbers yet, but I think there is plenty of room to play with while retaining good handling.
your comments are welcome. yay or nay.

seanbarney41 · « **Reply #3 on:** November 18, 2018, 08:05:37 AM »

Don't over think it. How about seat and tail section from a DOHC era F bike? No idea what it might take to fit but it would be a slick way to get to AMA era superbike.

kerryb · « **Reply #4 on:** November 18, 2018, 08:21:25 AM »

Half the fun for me is over-thinkin' it. When I can't be out there working on it, my brain is keeping busy thinking of interconnected ways to achieve the goal without screwing something else up.
Your idea is actually quite good, that tail would cover up all the frame and intake parts in one neat package, but alas this picture is the goal the designer is shooting for. Since time is of no consequence, the designing and building is the major part of the journey. Aaaand, the kids father is in no hurry for him to have a bike to ride!

seanbarney41 · « **Reply #5 on:** November 18, 2018, 08:44:57 AM »

I am really hoping the young man is not dead set on that totally unrideable front end set up.

kerryb · « **Reply #6 on:** November 18, 2018, 10:39:06 AM »

It's been 30 years since I rode a bike of that style, but my memories of it are good. While I couldn't ride it today, I'm not seeing what makes it unrideable for a younger man. Please enlighten me on the aspects of that one to avoid this time around. Thanks in advance.

seanbarney41 · « **Reply #7 on:** November 18, 2018, 12:01:32 PM »

look at the front forks...it has maybe 1" of suspension travel? That bike has never been ridden more than a putt putt up and down the driveway or someone got very hurt.

And to top the icing on the cake, low clip ons without rear sets is just physical torture.

kerryb · « **Reply #8 on:** November 18, 2018, 12:14:39 PM »

Good eye, that won't be the case with this build. He has requested mid-mounts, but rearsets are on the design table. Bars will be above the top triple and forks on this model are longer to achieve cruiser look from the factory.

seanbarney41 · « **Reply #9 on:** November 18, 2018, 01:20:17 PM »

I was pretty sure you had this stuff under control, you just gotta watch these kids looking at the internet and going "I want that"..."Oh? really? You don't actually plan to ride it then?" lol

kerryb · « **Reply #10 on:** November 18, 2018, 01:24:05 PM »

You make a very good point, come to think of it, I never see those being ridden...just parked! Lol.

SOHC4 Cafe Racer Fan · « **Reply #11 on:** November 19, 2018, 10:08:10 AM »

You'd make life much easier on yourself by using a 500 or 500 frame or 1979 CB650 -- and corresponding fork lengths. The 1980-82 650 is set up for cruiser riding and has that awful dipped seat. The other frames will eliminate the need for cutting off the back frame rails and trial & error to make shocks work.

kerryb · « **Reply #12 on:** November 19, 2018, 11:44:19 AM »

So true, but...I rode this bike when it was in good working order and was impressed with it. I helped the po get it to that state (we solved it's running issues by putting a stock intake system back on it ( pods really are a pain!). If I do take the plunge and cut it up, the sale of stock body parts will probably cover the initial acquisition cost. And, if it all goes horribly wrong, the cost of tiution for what we learn will be mercifully low. Lol. Then, after all that we can attack the 550 project waiting in the wings with a deeper insight and adjusted expectations. Isn't it amazing what possibilities we can mentally justify when a new bike drops in your lap. Not my first choice of bikes to work with, but I don't have to search and wait, or call and hope, or spend the high dollar folks are asking for an unknown commodity. We'll just do this one, it'll be fun!

Godffery · « **Reply #13 on:** November 20, 2018, 03:30:14 AM »

I think This may have the potential to be rather interesting.?! $:-\$

SOHC4 Cafe Racer Fan · « **Reply #14 on:** November 20, 2018, 08:16:11 AM »

If you stick with the existing frame, I would think about getting shorter fork tubes (the length used for the CB500/550). I would also think about cutting the rear frame rails and welding new rails parallel to the ground. This will require relocating the shock mounts, too. More work, of course, than simply swapping your engine and other components into a 500/550 frame, but if you are set on keeping the 650 frame so be it.

kerryb · « **Reply #15 on:** November 20, 2018, 05:26:47 PM »

Quote from: SOHC4 Cafe Racer Fan on November 20, 2018, 08:16:11 AM

If you stick with the existing frame, I would think about getting shorter fork tubes (the length used for the CB500/550). I would also think about cutting the rear frame rails and welding new rails parallel to the ground. This will require relocating the shock mounts, too. More work, of course, than simply swapping your engine and other components into a 500/550 frame, but if you are set on keeping the 650 frame so be it.

New frame rails without the complex dropped seat area would be the major consideration. To accomodate the long fork tubes I am considering longer shocks out back and maybe altering the top shock mount location to give the shocks a more vertcal stance. The future rider is tall, so seat height can rise without penalty. Now about those fork tubes...do I just call forking by frank and specify 37mm tubes of my selected length for cb650 lowers? Guess I have to dig out the 550 forks and start doing some comparisons.
I think you and Goddfery are helping convince me to go for it and not just settle for a costume act.

Ya gotta start somewhere...why not right here?

kerryb · « **Reply #16 on:** November 20, 2018, 05:42:36 PM »

This was my previous foray into frame mods. It was fun to create but my back told my brain that trying to ride such a beast was pure folly and would be rewarded with commensurate levels of pain. So I never finished it...part of it became an engine test stand.
Edit: that engine then got painted and went into a titled frame.

SOHC4 Cafe Racer Fan · « **Reply #17 on:** November 20, 2018, 07:29:41 PM »

Quote from: kerryb on November 20, 2018, 05:26:47 PM

Quote from: SOHC4 Cafe Racer Fan on November 20, 2018, 08:16:11 AM
If you stick with the existing frame, I would think about getting shorter fork tubes (the length used for the CB500/550). I would also think about cutting the rear frame rails and welding new rails parallel to the ground. This will require relocating the shock mounts, too. More work, of course, than simply swapping your engine and other components into a 500/550 frame, but if you are set on keeping the 650 frame so be it.

New frame rails without the complex dropped seat area would be the major consideration. To accomodate the long fork tubes I am considering longer shocks out back and maybe altering the top shock mount location to give the shocks a more vertcal stance. The future rider is tall, so seat height can rise without penalty. Now about those fork tubes...do I just call forking by frank and specify 37mm tubes of my selected length for cb650 lowers? Guess I have to dig out the 550 forks and start doing some comparisons.
I think you and Goddfery are helping convince me to go for it and not just settle for a costume act.

Ya gotta start somewhere...why not right here?

Well, Forking by Frank will make you tubes of any length you specify. The trick will be to get springs for the 37mm shortened tubes -- stock springs will be too stiff when shoehorned into a smaller length. Racetech can help with this, if you provide specs -- they can recommend the correct spring. The shocks will be more tricky. It's not as easy as just finding shocks that fit the span between the mounts but the correct spring rate and dampening.

kerryb · « **Reply #18 on:** November 20, 2018, 09:06:46 PM »

[quote author=SOHC4 Cafe Racer

Well, Forking by Frank will make you tubes of any length you specify. The trick will be to get springs for the 37mm shortened tubes -- stock springs will be too stiff when shoehorned into a smaller length. Racetech can help with this, if you provide specs -- they can recommend the correct spring. The shocks will be more tricky. It's not as easy as just finding shocks that fit the span between the mounts but the correct spring rate and dampening.
[/quote]

While I understand what you are advising, and agree on all points, I think we'll do this in stages. First I'll get frame built to accomodate the existing suspension components. Maybe drop the trees down the forks an inch and move the shock mounts an inch lower on the seat tubes. If it handles as well as my 83 goldwing on the twisties of N. Carolina, I'll be thrilled. If it doesn't handle better than my 78 750k then I'll be concerned and have to consider the cash outlay to make the handling at least safe if not good. My disadvantage is that I consider my 2008 FXSTC to be rather nimble and had a blast charging up and down the dragon on it... so my judgement of good handling is suspect to begin with, lol.

p.s. never rode a modern sport bike so I don't know what I'm missing!

calj737 · « **Reply #19 on:** November 21, 2018, 08:01:02 AM »

Quote from: kerryb on November 20, 2018, 09:06:46 PM

My disadvantage is that I consider my 2008 FXSTC to be rather nimble and had a blast charging up and down the dragon on it... so my judgement of good handling is suspect to begin with, lol.

That's the overstatement of the century

You really need to broaden your horizons if you think that pig handles well. Smooth and comfortable, yes. Nimble? Yeah, like a school bus with flat tires.

SOHC4 Cafe Racer Fan · « **Reply #20 on:** November 21, 2018, 09:05:16 AM »

LOL! I would call your FXSTC well-planted but probably not "nimble" in comparison to say a MV Agusta Brutale or KTM Duke 790. But hey, if you can charge through the Dragon on a heavy bike, a lighter bike will be that much more fun!

Godffery · « **Reply #21 on:** November 21, 2018, 09:37:02 AM »

I think you will find that there is ample height potential with the stock rear mounts, (especially after getting the front down to a reasonable level) you just need the right shocks to accommodate the desired result. (Personally, I'm a big fan of the period area Marzocchi shocks. they are tunable, rebuildable & come 13.5" tall)
https://proxy.duckduckgo.com/iu/?u=http%3A%2F%2F1.bp.blogspot.com%2F-WryfMGmCgmY%2FUlUYR_dGqhI%2FAAAAAAAACew%2F4oBc7aoMpZ4%2Fs400%2Fstrada%2Bshocks.jpg&f=1

The quickest solution to that front end would likely be a straight swap with a standard K model 650 forks.
https://proxy.duckduckgo.com/iur/?f=1&image_host=https%3A%2F%2Fs-media-cache-ak0.pinimg.com%2F736x%2Fbd%2F5a%2F93%2Fbd5a935f87051b0e521ee32f4430a088.jpg&u=https://i.pinimg.com/736x/bd/5a/93/bd5a935f87051b0e521ee32f4430a088.jpg

kerryb · « **Reply #22 on:** November 21, 2018, 10:16:09 AM »

Quote from: calj737 on November 21, 2018, 08:01:02 AM

Quote from: kerryb on November 20, 2018, 09:06:46 PM
My disadvantage is that I consider my 2008 FXSTC to be rather nimble and had a blast charging up and down the dragon on it... so my judgement of good handling is suspect to begin with, lol.
That's the overstatement of the century You really need to broaden your horizons if you think that pig handles well. Smooth and comfortable, yes. Nimble? Yeah, like a school bus with flat tires.

Ignorance is Bliss.

.
p.s. the Wilmac handles like a spider on snowshoes!

kerryb · « **Reply #23 on:** November 26, 2018, 02:42:48 PM »

Well...I made my decision and the die is cast. Dropped off my tubing and a drawing to get a custom rear hoop bent up. I'm going to make the frame flat from the tank mount to the hoop kick-up. Now I have to wait a week to get the parts back but there is plenty to keep busy with until then. I won't cut anything till I get the new part in hand. A little bummed at the cost of 5 bends in my tubing, but if it fits good it will be worth it.

On another topic, I also dragged my teardrop trailer through the dragon with my '83 goldwing, but I admit I didn't charge very hard. Don't have much tire-scrubbing nerve with the trailer in tow!

kerryb · « **Reply #24 on:** November 28, 2018, 08:10:21 PM »

While I wait for parts, I'm wondering about the merits of carb choice for the build. Changing the spacing on a set of pd42b carbs would allow getting rid of the cv carbs. Is this a wise goal? I've heard (read)) that some switch to carbs from a cb750, but I'm not sure what the advantages might be after you get past the "style" angle of the switch. Yes, I know the switch would be involved with a lot of details to attend to, but is there any distinct advantage? Engine is to remain stock, and the exhaust is a vintage generic 4 into 1.

all part of the adventure.

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Author Topic: '82 cb650sc cafe project (Read 13048 times)