Topic: 1972 CB500 "An Inherited Basket Case"

[fantino]

Okay, cool! Thanks for the extra info.

Granted a key is still needed for the steering and seat lock and I see it as more of a convenience rather than security feature anyways, but does it not somewhat defeat the point of having a keyless ignition system if it can be easily bypassed? ^_^

[calj737]

Depends upon where you install the m-unit doesn't it? You can easily bypass the stock ignition with a simple wire jumper at the fuse panel. Does that make these bikes inherently easy to steal? I guess so... at least with the m-unit, there's also a built in alarm 

[fantino]

Haha, true. I guess without an immobilizer type ignition system that requires an RFID handshake these bikes are inherently pretty easy to steal. But that  would require the ignition system and key system to share the same computer and it's not as if those systems are terribly secure these days either, even less so on something that two or three guys can lift into a truck ~_~

[SOHC4 Cafe Racer Fan]

Yes, once a lithium battery discharges to a certain threshold voltage it will not recover.

[fantino]

According to Google Translate, the Japanese means "Horsepower". Nice touch. No regrets picking this up, it's really beautifully made. I didn't realize the baffle end cap was a machined piece with all those reliefs, looks pretty trick.

I also placed a big order with Dynoman, in addition to picking up a set of 550 jugs to overbore. Save for the cams and internal coatings, I should have just about everything I need for the motor at this point, save for a few odds and ends.

My pockets are feeling pretty light at the moment 

[Camrector]

Nice. I haven't seen one with that end cap. Looks sick.

[fantino]

Still just making little bits of incremental progress here and there. I have two broken down 15 year old BMWs that need my time and money at the moment   

Pistons, MLS headgasket and viton base gasket showed up from Dynoman. They're so pretty:



These will eventually get sent out for coating, but I will wait for dry fit with the cam as Cal advised. The 126-20 *shouldn't* interfere, but I'd rather be safe than sorry.

550 jugs showed up this week, I'll clean them up a bit this week and hopefully get them off to be flattened and bored for the new pistons. I work next to a big diesel marine shop that does good work. Apparently they can work on cranks up to 10' in length :O

Speaking of cranks, lightened crank is on it's way back from APE right now.

I finally finished repairing a past blunder with the oil line conversion on the head. New inserts are installed in both sides, flattened, fins clearanced and ready for an M10 banjo fitting. I'm going to send the head out to have the combustion chambers and exhaust ports coated with TBC at Swaintech this week. Once those come back, the next step is to get them to Mike to have the intake valves oversized and valve seats recut.

I picked up some fittings for the clutch conversion. Was originally going to run a hard line through the hole in the cover next to the clutch mechanism and up through the original clutch cable hole with a fitting to connect to a soft-line. I bent up a few iterations, but nothing has really looked quite right. The offsets are too close to make a single bend and a big sweep of hard line on the outside of the clutch cover doesn't look any tidier than just running a flexible line over the clutch cover, so i will probably just go with a single flexible line.

Double checked my calcs on the clutch conversion, I should be able to comfortably generate ~300-600 lbs of linear force and sufficient travel with a 1/2" or 3/8" master cylinder. I have yet to confirm this, but stock clutch basket takes ~200lbs to compress, with HD clutch springs should take ~400lbs.

[fantino]

A pretty sweet package came in the mail today. Clocks in around 16 lbs, which is a healthy 20-25% reduction from stock crank weight. Great work from APE. Sounds like I'll get my balanced rods back from Mike pretty soon here too. I also decided to add a little something special to the crank a bit later on, I'll probably make the purchase after I get the cam + top end sorted out with Mike.

Head is boxed up to go to Swaintech for coating, just waiting for my OS intake valves to show up so I can send everything off.

In other news, I finally found my aesthetic inspiration for the bike, something I haven't really seen on an SOHC4 yet and from a source I never would have expected. Gonna keep the finer details to myself for a bit, but let's just say I'm 100% back on board with an all composite tank, seat + full-fairing. I will probably look into making the tank + seat myself since I have the know-how and resources. I would also like to custom tailor the laminate which is not really a (feasible) option with most composite tank suppliers. The fairing I will likely purchase as I don't want to invest the time or money into tooling.

[SOHC4 Cafe Racer Fan]

The idea of a composite tank sounds interesting.  Artracing made a carbon fiber fuel tank (check out his replica Bimota build).  Make sure that your resin can withstand use with ethanol based fuels.  There are many horror stories of fiberglass tanks failing when using modern gasoline.

You have a hell of a collection of performance parts.  Looking forward to seeing it come together.

[calj737]

Caswell Tank Liner. And thats all I've got to say about that...

[fantino]

I've been following the Bimota build, really impressive stuff.

I'm a composites engineer by education and trade, and while certainly not an expert at fab work, I do have quite a bit of experience and plenty of resources available. I think this leaves me in a fairly unique situation to really get what I want out of this part of the project.

In regards to modern gas, it's definitely a challenge, but some of the issues I see:

• Laminating resin: most tanks are made with a general purpose laminating epoxy -or- even worse, polyester. This is simply a matter of economics, it's a labor intensive process to build a tank and they don't sell for that much. Using higher end materials really eat into profits and often require additional considerations.
• Service Temp/Postcure: our tanks are on top of hot engines and live at elevated temperatures. When epoxy cures at room temperature, it reaches a state called vitrification where the polymer structure is unable to form any additional crosslinks. This will give the resin a specific glass transition temp (it is actually a range, as epoxy is not crystalline). As the laminate gets warm and reaches the glass transition range, it will see significantly reduced mechanical and chemical properties.
  
  If you raise the temperature above the Tg and bake the part for a few hours, it will allow additional crossklinking, effectively raising the service temperature of your laminate and allowing it to resist solvents and maintain strength at a higher temp. There is obviously a limit to this as eventually maximum cross-linking will occur and at a high enough temperature, you will start degrading the polymer chains.

For now, I plan on using MAX GRE for my laminating resin. It is a Novolac (phenol formaldehyde) based epoxy formulation specifically for resistance to fuel, same as the Caswell coating, but at a better volume price and tailored to laminating. This way my entire tank will be made of what most folks only coat the tank with. Eliminates the chance of a coating disbonding.

I will probably make a sample and submerge it in gas for a month or two to see how it does. If I'm not satisfied, my next course of action is to try a fluoroelastomer coating (viton) on both halves of the tank, joined with a caulk of the same material. This is the same material used in most modern day fuel systems for gaskets and sealants and is *extremely* resistant to modern fuels. It's just a little pricey and I have to get it through work, the few suppliers of these products don't do sales to individuals.

If all else fails, I work next to a marina that sells E-free gas

I also plan to use a combination of carbon and kevlar for the laminate. The kevlar will provide both abrasion resistance and toughness (less brittle/crack prone) in case the bike ends up on its side.

[Tews19]

Did I miss the explanation on the exhaust tip?

[fantino]

I haven't seen any other MGP exhausts with that tip yet. He must be trying something new, I guess.

[Camrector]

Did you weigh your crank before and after APE chopped it? Mine started at 24lbs and came back at 18.5lbs

[fantino]

~20.5 to 16.4.

Is your weight including the charging rotor?

[Camrector]

No rotor was off. Maybe my digital home scale that I used was a little off too.
I wouldn't think that there would be a 3 to 3.5 lb difference in crank weight.
Mine was a 76 cb550 motor. Maybe they beefed up the cranks a little on 550s?

[fantino]

No rotor was off. Maybe my digital home scale that I used was a little off too.
I wouldn't think that there would be a 3 to 3.5 lb difference in crank weight.
Mine was a 76 cb550 motor. Maybe they beefed up the cranks a little on 550s?

Perhaps so. The rotor for my new charging system is a scant 225g, so my final crank assembly will be pretty trim

Updates since my last post:

• +1MM Intake Valves showed up
• Head is at SwainTech to have the chambers, exhaust ports, valve faces and exhaust valve radii coated with thermal barrier coating
• Electrex RPK-1550 alternator system on order. Significant weight reduction in the overall system, + improved output and balance
• Picked up a fluoroelastomer coating for my gas tank liner. This stuff is *the business*, but it don't come cheap.

Did some design work on the tank. Still needs some tweaking, but here's a little peek





My inspiration came from an unlikely (for me) source: Harley Davidson. I was acquainted with the XR750TT and fell in love! Such an awesome story and gorgeous bike. I've tweaked a few things here and there, plan on using a more flush mount filler cap and had to make the shape and lines work for the CB frame, but overall I'm pretty pleased with my interpretation. I will pick up the fairing from Airtech in the future.

[Edit] a picture of the XR750TT for reference:


Next steps for the tank (+seat) project are as follows:

• Slice up the model and make a cardboard skeleton to mock up on the bike, checking for clearances + fitment
• Design tooling off part surfaces. I do this for a living, so this shouldn't be too much of a challenge. I'm going to make the mold directly out of 1/4" cross-sectioned slices of MDF finished by hand and avoid making a master + splash mold
• Build a 1-2 layer FG test part
• Build final part
• Trim final part
• Coat tank halves
• Caulk + bond tank halves
• Paint
• Install hardware

That's it for now. Need to let the bike fund recover a little bit, then sending the cam + rockers off to be taken care of, along with the head, by Mike.

[calj737]

Ill be interested in your experience with the Electrex. I've had an eye on it for some time.

The only possible objection I see to that beautiful body work is the Lock-to-Lock distance. The tank has culverts, but not really sufficient voids for clip-ons under street riding conditions. Road race makes sweeping turns, not 90* bends. Might want to factor that in if you plant to plan any street use. (Just an observation)

[fantino]

Ill be interested in your experience with the Electrex. I've had an eye on it for some time.

The only possible objection I see to that beautiful body work is the Lock-to-Lock distance. The tank has culverts, but not really sufficient voids for clip-ons under street riding conditions. Road race makes sweeping turns, not 90* bends. Might want to factor that in if you plant to plan any street use. (Just an observation)

Yeah, absolutely. I had the same thought in mind about the bar clearances, I made a few adjustments near the front to try and make some extra room, but the model is still very much "in work", I haven't finished up the tunnel clearances + mounting either. I'm going to start with a quick CAD mock up of the forks and bars to go along with the frame to test the clearances, tweak and scallop (if I must) and then a physical check with the cardboard prototype to make sure I won't be slapping my tank silly on the street.

[calj737]

What plan for exhausts do you have? Are you attempting to recreate the XR from a CB? That should be interesting given the "extra" cylinders 

[fantino]

Haha, that would an interesting challenge. But no, I'm sticking with my MGP 4-1. My inspiration from the XR doesn't extend much past the body work as I don't care to run a drum brake up front or switch to iron heads   

[SOHC4 Cafe Racer Fan]

Very nice rendering of the bodywork.  Looking forward to seeing it come together.

[fantino]

Just a quick update, I wanted to show off some fancy new piece of kit

The Electrex alternator kit came in today. it'll be awhile before I'm able to test the output, it will be interesting to see it's capacity compared to the original system. It is a permanent magnet based system, so it will generate power without a battery which is pretty awesome. You can see the new pieces next to the old. The kit also comes with an Electrex regulator/rectifier built specifically for their race alternator systems and a wiring harness with good quality connectors.



The original alternator system (including cover) weighed in at around 8.5lbs, 1200g/2.75lbs being the rotor attached to the crank.

The Electrex alternator weighs in at a total of 1.9lbs! The rotor is about 285g/.6lbs, which brings my entire rotating crank weight Just under 17lbs total. The rotor is also very small and nicely machined (it is an aluminum core with the crank taper fit into a steel shell), so what little weight it does add to the crank is very balanced and close to the center of rotation.

Cal, you were correct about the clearances from the forks, to maintain ~60* of motion lock to lock, I'll need to pocket a bit of material out of the front (I've already moved the tank as far back as it can go) -or- sacrifice some range of motion. I suspect I may do a bit of both, take 5* off the total range of motion and remove what needs to be removed to add enough clearance. I know some road going sport bikes have as little as 45* of rotation in the forks, but I'd rather not have to do a 100 point turn to get the bike in and out of the garage 

If I can get through all my (paid) work this week, I will try to finish up the last few details on the tank design so I can slice it up and make a mock-up hopefully this weekend.

[calj737]

Damn sexy stuff! Doesn't their kit also use their ignition coils and a CDI box? Or is that a different version?

[fantino]

That is the STK-1550 you are thinking of.

The STK is a complete CDI ignition system with an integrated (lower capacity) stator to run battery free, with the intention of dropping the entire stock alternator setup. The stator setup in that system doesn't have enough output to power other electrical systems on the bike, so it wouldn't work for me but would be amazing on a dedicated track bike. It also looks to be a pretty decent value considering it includes the stator setup + a full CDI ignition system and coils.

I picked up the RPK-1550 which is a bolt on replacement to replace the existing alternator setup with a (much) lighter, higher output, permanent magnet alternator. It was actually a bit more expensive than the STK kit, but will suit my needs better.