Topic: 1982 CB650SC, Project: "Black and Blue"

[tourmax]

Well, thats interesting:



Obviously, thats sitting pretty high because the frame doesn’t fit it, but that sure would accommodate a trellis frame.

Time for another photochop methinks… daydreaming of a noce fat aluminum trellis frame again….

[tourmax]

Ah, it's always fun to daydream:



That's within my wheelhouse, but I just don't think I want to put that much work in to it. That would take the project from a couple months worth of work to a couple years......and I just don't think I want to invest that much time and money into this bike to end up with a 60-70 hp bike with 5-10 grand in it that will have a market value around 2 grand at best.

Not to mention, I've got the FJ1200 to put back together and I at least want to get the Mustang back to the point where it can at least move and stop under it's own power.

I think I'll stick to the stock frame for now (probably add some bracing to it) and finish up the engine and suspension. If it hangs around for a few more years, I may look at the full trellis frame treatment in nice,thick Aluminum tubes and plates. But don't hold your breath for it to happen....

[tourmax]

Ohhhh, photshop is evil:



It's sooo easy to draw lines on a picture and it's working to give me a visual strong enough to MAYBE suck me in to a bigger project than I wanted to start with.

One of the issues though is that I got rid of my mandrel bend machine a fair while ago and I'd need one at least to make the tube sections that woudl go from the swingarm pivot, around the engine and to the steering head. I suppose I could just build another one, but that's even more work on top of the frame itself (not to mention the need to cut up the tank to make it fit the bike properly). Soooo much work to get it to where the photochop is......


Must.

Resist.

Urge.

To.

Build..........

[Alan F.]

Yup, the strength and discipline to resist side projects is very important.

[tourmax]

So, I think I know what I'm going to do.

The engine I'll build first (657 cc at first, 740cc when I get the piston situation figured out). The wheels and CBR swingarm will be fit to the OEM nighthawk frame and I'll finish up the bike from there. At least to where it runs and stops.

Then, I'll take an 80 cb650C frame a friend of mine is willing to give up for free and build a jig picking up the critical points off that. Once the Jig is built, I can look at building my trellis frame on whatever timeline I decide. frame will be built in steel as I don't want to go through the hassle of heat treating aluminum after the welding is finished (if you don't heat treat after welding, you can end up with brittle weld joints). Steel is also easier to control warping and moving when welding. I may look at doing it in chromoly, but I've never worked in that before. I mostly use 1018 and 6063, so there will be a bit of a learning curve with chromoly tube.

No need to rush to build the trellis frame in order to get the bike rolling again (and not just sitting around in pieces taking up space) as well as things like modifying the VFR fuel tank and other needed metal work to pull it all together.

[tourmax]

So my bud called and he’s got a couple parts he wants me to take away. No charge, just get it out of his hair:

80 cb650c frame and swingarm
82 cb650sc frame and swingarm
Cb650 lower cases, crank, rods and transmission
“650 OHC” rocker covers
63 hp cam
Mac 4 into 1 and megaphone
Pulser cover
Battery boxes and assort bits, pieces and fastners

Only catch is it’s nearly a 5 hr round trip. At 2 bucks a liter, thays more than a couple bucks in fuel…

[MauiK3]

Seems like it may be worth it.

[tourmax]

oooo....sexy:



Different engine package, same frame idea....

[tourmax]

1985 cb650sc (nighthawk) oil cooler:





Bolts right up. No muss, no fuss.

On my bike, I had to make one small change. Because of the 4 into 1 crossing in front on the engine, I had to trim two of the lower fins on the filter housing. Took like 60 seconds with the dremel.

[tourmax]

So I’m thinking about the frame again. As mentioned, one of the “scrap” frames os from an 82 nighthawk, the same as the one I have on the lift.

What I’m thinking is to cut the headstock out of the original frame and use that to build the trellis frame from. Biggest plus to that is I keep the oem headstock which has the vin stamped in it.

I’ll use the second frame to build the frame jig from and should I just botch the trellis build, I can use that frame to at least put the bike back together and deal with the wrong vin at a later date (if needed).

Sure, having the original headstock in a new frame technically is a reconstructed vehicle and there would probably be ins issues should I ever have to make a claim, but I won’t tell if no one else does…

[Gurp]

I sure won't. In the classic car industry they straight swap vin plates more often than you would think.
Hell for a lot of 40s 50s and 60s American cars they sell the rosette rivets to do it. Of course they sell them for "Restoration" purposes.
Classic Harleys are the same way. Lots of "restamps" running around.

[tourmax]

got my eye on a set of cb900c pistons. 64.5mm. Would work out to around 740cc's. 64.5mm is one of the "big bore" kits for the cb750 sohc.

So, cb750 liners in a 650 block and rework the piston crowns to work with the cb650 combustion chambers and valve reliefs.

We'll see how it works out if I get the pistons and give 'er a go....

[SOHC4 Cafe Racer Fan]

got my eye on a set of cb900c pistons. 64.5mm. Would work out to around 740cc's. 64.5mm is one of the "big bore" kits for the cb750 sohc.

So, cb750 liners in a 650 block and rework the piston crowns to work with the cb650 combustion chambers and valve reliefs.

We'll see how it works out if I get the pistons and give 'er a go....

I have the Dynoman 62mm pistons (674cc kit). What kind of compression will your 64.5 mm pistons produce?

[tourmax]

Alrighty. I'm sitting here thinking about the bike and have come to the realization that this is going to have to be a full build. I'm kind of piecemeal-ing it right now, which means you end up spending more than you wanted to when you're done.

So I think this will be the order of things:

1. Frame build. I don't see a lot of sense in fitting parts and pieces to the CB650 frame when I'm eventually planning to ditch the frame for a trellis frame. Adding to the decision is the CBr600 arm is wider than the OEM 650 frame pivots.  So instead of shaving down the swingarm, I'm just going to space out the pivot plates a feww mm, which will also help with wrapping the frame tubes around the carbs and engine. I'll also rework the vfr750 fuel tank to fit the frame and engine combo. I'm thinking I might have to split the tank in half and add a few inches in order to look right on the perimeter trellis frame. The tank needs to be reworked to fit right with the side covers anyways, not to mention it's the wrong color. The frame/bodywork is going to take a while, I'm giving myself 6-12 months to get that done.

2. Electronics. Pretty self explanatory. Wiring, Ignitech spark controller, coil on plugs, switches, lights, gauges, etc.

3. Engine. The engine will take a back seat to the frame. I've been looking at building it as a 657 (62 mm pistons) and a 740 (64.5mm pistons). I was planning to throw the 657 together while I built the 740, but now that just seems like wasted cash. So I'll run the stock 626 for a while and build the 740 cc. The 626 smoked a fair bit when it last ran (had new rings, but they didn't seat for some reason) and I don't expect 20 years outside is going to have helped it any either. But. the engine can do for a while or at least it can provide a "buck" to make the frame fit the engine. Then a 740 will just drop in where the 626 was. It also allows me lots of time to rework the intake and exhaust ports (for the downdraft carbs), unshroud the valves, do a little work on the combustion chambers and fit the 900 pistons with the 750 liners/valve clearances, Comb Comb compression ratio etc.

I've got most of what I need here already. I'm still waiting for the swingarm to show up and then there will be the bulk steel to build the frame (1.5" 1/8 wall 1018 tube, ERW), but just about all the other little bits and pieces I already have. Except the time that is.....LOL!

[tourmax]

got my eye on a set of cb900c pistons. 64.5mm. Would work out to around 740cc's. 64.5mm is one of the "big bore" kits for the cb750 sohc.

So, cb750 liners in a 650 block and rework the piston crowns to work with the cb650 combustion chambers and valve reliefs.

We'll see how it works out if I get the pistons and give 'er a go....

I have the Dynoman 62mm pistons (674cc kit). What kind of compression will your 64.5 mm pistons produce?

Not sure off the top of my head. I'll have to do the calculation and measuring later down the road to get a better idea.

Here's a comparison of the 900 pistons to the SOHC 750 pistons:



that's from "satanic mechanic" web site.

As you can see, more dome, higher CRH (deck height). That's not so much a problem as adapting SOHC 750 pistons (if not the 750 F Models) to a SOHC 650 results in a lower  compression, both from the bore increase and putting mostly flat top pistons into the 650 "hemi-style" chamber.

I'll have to look at a couple options to get the 900 pistons in there. One option is to shave the piston height down and rework the valve cut outs, another is to see about adding a spacer to the base gasket and what may happen in the end is a combination of the cut the piston and add a spacer. The 3.5mm increase in the bore may also allow me to rework the head chambers to provide a stronger squish band, but I need to get it all in front of me before I can say either way what needs to be done.

Edit: opps. 64.5 mm makes it a 729, not 740cc. 65.5 mm makes it 752 though....which is the limit of the 750 liners in a the 650 block.

[Kelly E]

This build is very cool. It's beyond my skill set, I'm a better rider than fabricator. I bought a 1980 CB 650 new this month 44 years ago. It looks like it will be a great bike to ride.

[tourmax]

Well, took the plunge and ordered up some used cb900c pistons. 64.5mm bore, with a 55.8mm stroke that works out to 729.3 cc’s. 

64.5 mm is too big for the 650 liners (66mm od) so I’ll bore out the block and slip in a set of cb750 liners (sohc). They’ll take the 64.5 mm pistons (same size as the 836 kits iirc) with just an overbore.

The sohc 750 pistons need to be reworked before they play nice with the cb650 parts and the 900 pistons have an even higher ch, so machine work is a given. On the plus side, the 900 pistons have lots of room to make a decent dome to go with the 650 hemi chamber. Even better than the cbx1000 pistons I think:





Probably make spacer to take up a mm or so at the base gaskets (less shaving needed on piston top) and I’ll likely end up making my own head gaskets from copper rather than having sone one off/expensive gasket made.

Should be interesting.

[tourmax]

So, after doing some more measurements and layouts, I'm definitely going the have to split and widen the VFR750 tank.

The outer frame rails need to pass out and around the head so it work out to roughly 19-20 inches wide. The VFR tank is only around 17 inches wide at it's widest point.

If I set the tank on the bike at it's original width, it's going to look weird sitting inside the frame tubes.

I'll probably split it right down the middle and cut the filler cap out in it's own piece (or the tank would be wider on one side compared to the other) and make a sheet metal piece to join it all back up again. Spitting the tank isn't all bad, it's got a couple dents I'd like to work out and there's no access with it all in one piece. I could fill them, but I'd rather do the metal work so only a thin skim is needed instead of 1/8-1/4 deep.

I also had to drill out the fuel cap key slot. I've never had a key for it and the tumblers are (were) corroded to the point where picking the lock wasn't an option. On the plus side, the interior of the tank is pretty clean. There's a little skim of surface rusting, but it pretty much removes with a brush of the fingertip.

[tourmax]

Ebay tachometer showed up today.

A little bit of screwdriver work:



Et voila!

Guts to build my digital tach with a needle sweep that takes inputs from the digital ignition.

[tourmax]

Postman brought me a present today:



Clamp is in the chain guard because it got a little deformed in shipping. It’s already starting to go back to original shape.

Let the perimeter/trellis frame work begin!

[tourmax]

Holy Bocce Balls!!!!

Ordered the steel today for the trellis frame.

It's 5 bucks a foot!!!!!!!

Been a little while since I've ordered any amount of steel, but that's just cray! Steel has been climbing fast for awhile, but it looks like the recent inflation crap has supercharged it!

Well. at least Ive got enough scrap lying around to make the plates, tabs, gussets, etc.

I went with pipe instead of tube, because tube is another significant up charge. Tube is just pipe that's been processed further, so I'm not worried about strength. It's all just flat steel rolled and welded anyways, tube is just forced through a set of mandrels to make it dimensional consistent and flatten the weld seam on the inside. The only issue is pipe is a little bigger in diameter than tube. Still the same amount of steel and wall thickness, it's just not "squeezed to tight tolerances. Not a big deal on something like a frame.

Now, I have to figure out building a tube bender or see if a decent one can be store bought at a price that doesn't mean I'll have to give up half my wedding tackle for it...

[tourmax]

Well, raw materials are now in house:



Now I just have to decide between a full custom trellis perimeter frame or do a Moto Martin "copy".....

[Gurp]

How many feet did you end up ordering?
Think you'll have to order more as the project progresses?

[tourmax]

How many feet did you end up ordering?
Think you'll have to order more as the project progresses?

4 eight foot sections plus the mechanical tubing for the headstock.

Should be enough, but more is just 5 mins down the road from me.....

[tourmax]

Tearing the bike down to the bare frame made me realize I had pulled the antidive units off the rd500 forks, but hadn’t built a block off plate yet. Pulling the forks off without the plate would mean a big, oily mess in the garage floor. So, a bit of tine on the lathe/mill and:





For right now, they fit and perform the intended function. Later on, I’ll remove them and do up the finishing work so they look nice.