Topic: 1972 CB500 "An Inherited Basket Case"

[fantino]

Hope y'all like lots of pictures

My head, cams + rods came back from Mr. Rieck this week. Excellent, meticulous work from Mike, as always. I couldn't be happier!

Fancy new Megacycle 126-20 cam and hardwelded rockers. Picked up an OEM slotted sprocket from Mike too.



Grinding on the head + rockers to make clearance for the cam



TBC coated combustion + exhaust chambers + valves (Intake enlarged 1mm)



Balanced + shot peened rods


And all of my top end parts together at last! Cylinders are back from getting bored out and decked as well.


Next steps on the motor are:

• Test fit motor, check piston clearances, double check bearing clearances
• Disassemble motor
• Send pistons + bearing shells off to be TBC and/or dry film lubricant coated
• Replace engine cover + valve cover fasteners with SS torx button heads (bearing cap bolts are SS 12pt ARP, case bolts are SS mini-flange TEKbolt

After a few too many drinks one night... I ended up picking up an 03' R6 front end for a very good price, as well as seals/bearings/fork oil to freshen everything up




I've been lukewarm to the idea of a front-end swap, but in examining my overarching goals for the bike, the R6 swap won me over for the following reasons:

• Right side up forks look period correct at a first glance but with modern cartridge insides
• R6 assembly weighs 5lbs less than stock fork assembly
• Bigger fork tubes + axle are more rigid
• Adjustable and re-valvable
• 4 pot caliper and floating disc weigh appreciably less than single stock disc + caliper, much less a dual disc setup, with vastly improved performance

I never said I was particularly original, so much thanks to FunJimmy and Franky for putting in the work to make this swap a breeze. I turned the hub, spacers and adapters more or less per Franky's drawings over the break:




At first I thought I did a terrible job machining the adapters, but it turns out they're fine and the CBR disc I picked up just had a ton of lateral runout (~.060"). $200 later (about as much as the rest of this swap cost me...) and a brand new disc is on the way. Apparently the EBC disc is ~300g lighter than the stock CBR unit. The hub with adapters weighs <100g more than the stock hub. The overall reduction in unsprung weight vs a dual disk setup is pretty significant, I'll report on final numbers for comparison soon.

Remaining tasks for the front end swap:

• Install steering stem bearings, new fork seals + oil
• Strip black paint off lowers, bead blast, clear coat
• Paint hub center silver
• Re-lace and true rim
• Mill caliper mounting flange for sufficient clearance

Didn't get too far on the tank this last month, but I did print a plug for the center so I can join the two halves together.



Next steps:

• Bond tank halves together
• Coat tank in epoxy/glass microsphere fairing compound, sand smooth
• Paint Plug
• Polish, Seal + Apply Mold Release
• Make splitter plates for mold sections

Lastly, I picked up a CBR600 F2 swingarm for $30. It's a pretty close fit to the frame, so toying with a swingarm conversion as well. It will need shortened 2", shock mounts added and will need the bushings adapted for the stock swingarm bolt. I'd rather not drill out the frame. I can do the machining and prep-work/jigging for welding, but will find a certified welder to re-weld the cross brace and shock mounts as I'm not comfortable enough with my welding skills for structural work. Know thy limits!



That's all for now!

[calj737]

When you deck the jugs and mill the head, you also need to shorten the locating dowels, so be sure to check that.

What material is that swing arm? It looks to be steel? And it looks thin walled. If so, I'd suggest you make a plug to join the arms where you cut it so when you re-weld it, you're adding strength back to that area. Unknown metals behave differently to welding/work hardening from the heat. (As you undoubtedly know).

Tank plug looks ultra sexy 

[SOHC4 Cafe Racer Fan]

When you deck the jugs and mill the head, you also need to shorten the locating dowels, so be sure to check that.

What material is that swing arm? It looks to be steel? And it looks thin walled. If so, I'd suggest you make a plug to join the arms where you cut it so when you re-weld it, you're adding strength back to that area. Unknown metals behave differently to welding/work hardening from the heat. (As you undoubtedly know).

Tank plug looks ultra sexy 

Echoing Cal, I am curious as to how you are going to section the swingarm, to preserve structural strength. 

And yes, that tank plug looks awesome!!

[fantino]

It is steel, yes. As far as I can tell, it is just carbon steel and not chromoly or anything too fancy.

It might not be readily apparent from the photograph, but the cross brace is simply welded on top/to the side of the tube section of either arm. The tube cross section on either arm is continuous from end to end.

My plan is to carefully cut out the existing cross brace keeping the arm sections fully intact. I'll Grind down the excess brace/weld material on both arms, and trim the cross brace down to match the inside taper of the arms as needed to fit 2" up from the current location. I will be jigging up the arm before cutting so everything stays constrained.

I will also be grinding off the monoshock mounts and other brackets.

On the axle side of the swingarm, the slots need extended 2" and the ends lopped off to match. I plan to weld a cap onto the ends to maintain rigidity since the slot will now be open to the back of the arm.

[calj737]

Might be a whole lot easier to cut out the cross brace and replace it with new, rectangular tubing of the correct dimensions. As for shortening the overall length, why not cut the arms mid-run and take the section out there? Then you can leave the axle end/slots as is?

[fantino]

Might be a whole lot easier to cut out the cross brace and replace it with new, rectangular tubing of the correct dimensions. As for shortening the overall length, why not cut the arms mid-run and take the section out there? Then you can leave the axle end/slots as is?

I'm less comfortable cutting out a section out from either leg and welding it back together. jigging and proper re-alignment of the pieces seems tricky. I also don't like the idea of running a weld right through the middle of the beam over a fairly long, unsupported span with a point load (shock mount) nearby.

Setup to extend the slots on a mill is easy, welding an end cap on to shore up the tube ends is also pretty easy and seems like a more structurally conservative approach.

Not a bad idea to just weld in a new rectangular cross brace, but I like the large section of the existing cross brace as well as the large fillets on the inside edges spreading out the load. If I can just trim it and slide it back, I'd be pleased.

[calj737]

'm less comfortable cutting out a section out from either leg and welding it back together. jigging and proper re-alignment of the pieces seems tricky. I also don't like the idea of running a weld right through the middle of the beam over a fairly long, unsupported span with a point load (shock mount) nearby.

That's not an unusual thought about welding. Funny thing is, the weld is likely to be stronger than the surrounding metal by leaps and bounds. If the tubing is thin, I would use a slug (think smaller OD tube slid inside at the seam) and weld the two halves together and to the slug. That will increase the strength even more, insure alignment, and move the tire flare forward. But your way will work too. Mine is 6 cuts, and 4 welds.

Re-welding the existing brace would give me pause actually. You don't know its metallurgy and re-welding it may actually diminish the strength of the metal adjacent. Not that the cross brace sees direct stress, but as a matter of consideration.

As for welding closed the swing arm ends, instead consider making a square aluminum plug with a pressed fit. Would be very cool and allow a bit of customization. 

[fantino]

That's not an unusual thought about welding. Funny thing is, the weld is likely to be stronger than the surrounding metal by leaps and bounds. If the tubing is thin, I would use a slug (think smaller OD tube slid inside at the seam) and weld the two halves together and to the slug. That will increase the strength even more, insure alignment, and move the tire flare forward. But your way will work too. Mine is 6 cuts, and 4 welds.

I'm a plastics guy, but I remember just enough from strength of materials to know you're entirely right about weld strength (though I presume the added strength over the base material comes at the cost of ductility which explains why brittle failure occurs in the HAZ).

Something about being on two wheels makes me irrationally paranoid about defects/inclusions and crack propagation in parts that keep said wheels on the ground  But you're probably correct, it would be easier to cut and weld with a plug.

I totally spaced regarding the ends, they get filled up with adjustment blocks for the axle. The stock CBR blocks will work, but they're kinda ugly and will need sleeved for the correct axle diameter. So it may be a good opportunity to make something a little nicer looking.

[Camrector]

Looking great my friend. You won't be disappointed with the R6 front end. I rebuilt mine with all racetech internals (gold valves, springs etc etc). I highly recommend the rebuild. Piece of mind alone.
I went chromoly on my swing arm ( again piece of mind) from denis at cmr

[SOHC4 Cafe Racer Fan]

I went chromoly on my swing arm ( again piece of mind) from denis at cmr

Oh you did, did you?  Copycat!   You'll be pleased.

[Camrector]

Oh yeah Don. It has almost the exact same engine as this one too lol. Gsxr front end though. I'll start the build thread here soon.

[fantino]

Thanks Cam! Was thinking about the gold valve. May happen sooner or later, but I'm probably picking up some Gazi shocks first so I can start preliminary frame and body work fitups. I'm tired of all this stuff laying on the ground!

I'm meeting with Richard at Wasco Frames in Tacoma this week to talk about modifying the CBR arm or building a new box arm. If the cost isn't multiple times more to build new vs modifying, I'll strongly consider it. Time will tell

I just placed a big order for all the supplies I'll be needing to finish the tank plug and build the mold with enough leftover for the seat. Pro-tip: there are some really good deals on fiberglass fabrics on eBay. I just scooped up 16 yards of 6.8oz plain weave in 60" width for $3.45/yd (for reference, $6-9/yd is average for lower qty purchases). That's a TON of fabric for $55 (and free shipping to boot).

[fantino]

I took a trip down to the frame builders in Tacoma to see what they thought about shortening the swing-arm.

Cal, they agreed with you about cutting and re-welding the arms, at least as the most cost effective option. I will be able to retain the stock CBR chain adjuster this way too, if I want. As for the brace, we went over a few options, ended up deciding to saw an ellipse out of the existing brace and weld in a new piece to match the contour. This will give enough clearance to fit the 18" wheel with the shortened arm. Will also be changing the shock mounts to run eye to eye instead of eye to clevis shocks. I should have the "new" arm back in a few weeks.

I'll take care of welding on small brackets and such for the chain guard and rear brake when I get to that, as well as any machining to accommodate the difference in axle/pivot bolt diameters. Eventually I'll powder coat the arm to match the frame. It shouldn't look any more out of place on the bike than a Dresda arm would by the time I'm finished.

The cush drive rubber in my rear wheel is showing some radial slop. Since these rubber parts appear to be NLA, I tracked down a couple NOS ones on eBay. I'll use those to make a silicone mold and I'll cast a new set out of 90A polyurethane and give everything a good coat of poly grease before I re-install.

I re-rebuilt my front wheel onto the modified hub this weekend too and got everything back into true; .015" lateral and .020" radial runout, which is good enough. It will need re-trued after it's been run for a few miles anyways, they tend to settle out a bit under load. The new rotor arrived and bolted up reads around .0025" max runout, so I'm happy with that.

What's left to finish up the front end is:

• Mill caliper down for sufficient clearance
• Strip and refinish fork lowers
• Install new steering stem bearings
• Install new fork seals and oil
• Bearing hood for underneath top triple
• Rebuild calipers, new brake pads

My epoxy shipment was slowed down due to snow on the West Coast (this place SHUTS DOWN when it snows), but hopefully that will come in this week so I can start working on the tank and seat again.

[SOHC4 Cafe Racer Fan]

What did your frame builders charge you to mod the swingarm, if I may ask.  I have one of those laying about, and a buddy who is mid-build with a 550 project.  It might be worth his while to send it to your guy.

[fantino]

They didn't quote a firm price as the arm needs a little straightening as well. Low-end estimate was $500 including the fab work for the shock brackets if all goes smoothly. We'll re-evaluate if they dig into it and the cost goes up significantly from there.

Still cheaper than a new custom swingarm and in their opinion was cheaper than building a brace for the stock arm (plus this would have added a bunch of extra weight compared to the CBR arm.

[fantino]

Took a break from any work on the bike as I caught the plague (flu) and got busy with work.

Work Completed:

-Milled the caliper 3mm for clearance with the spokes

-Picked up new main and big end bearings. They all measured out OK but a couple sets were showing wear through to the coppery layer. Figured I wouldn't regret replacing them all. Greens all around, everything plastigaged out at .0015 except for the main bearing #1 and #5 at .002. This is consistent with the case markings and measured crank journals. It's within spec and other main bearings aren't readily available, so I'm fine with this.

-Forgot about the case bores being a little tight for the 550 block, so I opened them up with a 60 grit cylinder hone. Only needed to remove about .5mm to make em fit.

-Fit the rings to the block, .010" on the compression rings all around. The wiper rings all have a gap of .015-.016" without any filing. I double checked the cylinder bores and they all spec out at the correct clearance to the pistons skirts as specified on the sheet that came with the pistons (.003"). The spec sheet specified a .011" wiper ring gap, so I figured they would be a bit tighter starting out. The Honda manual gives the std ring gap as .005-013" with a servicable limit of .027" so I guess I shouldn't be worried? Spec sheet says a few thou loose is better than too tight.

-Started dry fitting the motor to check clearances. Luckily DaveBarbier is working on the same thing right now so a lot of the questions I would have had are already being answered in his build thread The pistons are sitting about .010 below deck and squish is measuring out around .055 with a .020" viton base gasket and .040" MLS torqued down. This is a little higher than I would like so I will switch to a .010" base and .036" head gasket to bring it down to ~.041". I was targeting .038" but would rather err a little conservative the first time around. I can always deck the block a few thou later on.



-Picked up a new rocker cover, as my old one had a crack in it. Took quite a while before another 78' cover with the improved rocker shaft design showed up. This is good too because I'll have a spare cover to modify for degreeing in the cam to check valve clearances.

-I decided on a minor redesign on the tank. Partly to make it easier to manufacture (the way the bottom half nests into the upper half) and it was just a little too big for my liking so I scaled it down 5% (doesn't sound like much, but it has quite a bit of visual impact). I didn't want to put a ton of work into something that won't be just right. I'm working on printing out new sections for the plug which will take a while, but the new surfaces will require significantly less hand work to be made into a functional mold.

-Discovered that the rear axle on the CBR swingarm and the stock swingarm are in fact the same diameter! This simplifies the conversion quite a bit as I'll only need to modify the spacers to center the wheel correctly and make some bushings for the pivot bolt. No big deal. Other than the welding which I am no expert at, this is an easy-peasy conversion.

Up next:

-Gotta degree in the cam and check clearances to the valves. Not expecting any surprises but I'd rather be safe and know what I'm working with. I'm going to just remove the base gasket to check this. I figure if I have enough clearance at .035" squish I'll be good for my slightly more conservative clearances I'll actually be running.

-Once I've confirmed clearance I'll be sending the pistons to SwainTech for TBC coating on the domes and then sending the pistons, various shafts and bearing shells off to MicroBlue for WS2 dry-film lubricant coating.

[Camrector]

All the Yes! Gooding great work.

[calj737]

All the Yes! Gooding great work.

Whatever the fcuk that means?

[540nova]

All the Yes! Gooding great work.

Much liking saying you!


Sent from my iPhone using Tapatalk

[SOHC4 Cafe Racer Fan]

All the Yes! Gooding great work.

I've heard of butt-dialing. Maybe this was a butt-post.

[Camrector]

^ Good looking

[SOHC4 Cafe Racer Fan]

Fantino,

Are you traveling down to Portland for The ONE Show?

[fantino]

Unfortunately not, I'll be going North that weekend instead. Shame though, looks like a super cool show!

[754]

I have a swingarm like yours, I plan on shortening. I will cut the pivot tube out of the front. Then clean off the weld to reuse the tube if possible. Then i will relocate a hole in the swingarm to put the tube in, then weld it in . Probably have to taper down the rectangle tubing at front, to look proper.  Then add shock mounts to rear for twin shocks.
 I would think 500 should cover most of it, in your case..my only cost will be the tig welding, and my time..

[fantino]

754 that's a clever way of doing it, I hadn't thought to just move the pivot forward. I imagine you've got to be a little more clever about fixturing while welding to keep everything aligned?

In other news, the bike fund took a little bit of a hit this weekend as I ended up picking up a truck!

It's a 72 Jeep J4600. Looks like a big project in the photos, but it has a freshly rebuilt AMC 360 with all the bolt on performance bits, refinished interior and wiring, good bones and all the rust repair and most of the body work already complete. Just needs a little more body work, some paint and a day putting all the trim back on. These J trucks are getting harder to find and I picked it up for less than the cost of the motor rebuild.





I'll finally have a good vehicle to haul all my other projects around with!