Author Topic: 1975 CB750 F0 SS First build, first bike. (Read 8371 times)

Tazergnome · « **on:** May 01, 2012, 12:15:58 AM »

So I've been talking to some guys on this forum for a bit on this project, but I thought it was probably time to move out into my own thread.

So this is what I have to work with:

I remember the first time I saw this bike when I was about 17. I went to my local hole in the wall bike shop and looked around. I instantly fell in love with this bike. I couldn't explain it at the time but I couldn't find any other bike I liked more...well save maybe the 1978 Ducati Darmah in the show room...but for different reasons. I saw something amazing inside the steel of this bike. All of the scars and abuse I could see told a story. At the time I had no way of affording her. Mac wanted $800 and I just didn't have it. (Good thing too, because that's a bit high and if I did have it I would have done it.) About a year or two later I stop by again and she's still there. He want's $600 or so this time. I still didn't have it but that rekindled my desire for a bike... specifically, that bike. It was another few months before I stopped by with $200 in cash. He sold it to me for $450 with an extra engine case thrown in. After that life happened and I started a family. She ended up sitting for a few more months until I started reading "The Zen and Art of Motorcycle Maintenance". The book effected me in such a deep way because it said many things that I've thought but never known how to say, but it also made me absolutely sure that I needed to rebuild that bike. Not just rebuild, but understand her completely.

I know that this bike has been a drag racer before she was parked, but I do have a title for her.

Known mods:

RC Enginerring pipe, no baffle (need to make, find one)

Extended swing arm

Drag handle bars

Dyna CDI system

No lights except headlight

Chopped off tail and poorly welded on grab bar.

No front brakes...lighter means faster, right?

So here I am, stripping her down bit by bit and studying everything I see. This forum has been the single greatest resource I have had in learning about my bike.
Like I said before this bike has many scars and many problems, but I look forward to solving each problem and re-engineering anything I can. Rumor has it that this bike ran when Mac bought it many years ago, not well, but it did run.

Problems known so far:

Cracked crank case from chain ripping into it. [Solved?]
Solution: Aluminum tape and black gasket gunk...might have to swap cases, but if I can I want to make the patch work.

Plug 2 and 3 don't fire. Checked points, found something interesting under the points cover. Dyna CDI was installed. Checked coils. One was stock, and the other was off of some Kawasaki, but they were both 5ohm. Looked online and found that Dyna systems need 3 ohm coils. After market Dyna 3 ohm coils are $160...so I looked around a bit more and found that DOHC 750 coils are 3ohm. Ordered some from ebay, $30. [In progress]

When looking over the coils and CDI I found that the entire wiring harness is fried. The wires from the alternator to the rectifier are melted and only 2/3 are making contact. Many wires are chopped and spliced. Many wires are burnt and melted. Then I looked at the fuse box...all of the fuses are higher amperage than needed, some twice as much. I looked around Mac's shop and found a few wiring harnesses, but they were all damaged or brittle. Then I remembered the simplified wiring diagram posted on this site. Looked it over and decided to build my own. Doing this will let me move everything to a better place, possibly a Santee style box. [Advice]

Rear wheel is too far left...I have no idea on this one.

Support bars under gas tank are poorly welded back on. I might fabricate a bolt on system like the one seen on this forum, or I might just cut and weld new bars on. I've herd argument saying that they are needed for structural integrity and that the bolt on systems don't cut it. Either way I'm vary curious about what's been done with the cams and heads. [Discussion]

Before it's asked, I do have carbs. Off for rebuild right now. I find it odd that will all of the mods done to this bike the jets are still stock size.

Where can I get the best price for a rebuild kit?

fastbroshi · « **Reply #1 on:** May 01, 2012, 03:20:48 AM »

I guess you didn't pick the best candidate for a rebuild but it's not the worst either. That frame would've scared me off honestly but nothing a good welder can't fix.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #2 on:** May 01, 2012, 08:35:06 AM »

Well, you do have a bike.......

Hope you have a good job too. That should be quite a project. Good luck. If I can be of assistance shoot me a PM.

Tazergnome · « **Reply #3 on:** May 01, 2012, 08:43:25 AM »

That's the strange thing, I was attracted to this bike because of all of it's problems. While it will be harder to get running I feel it will also be more rewarding. This bike has such an amazing feel to it. It also presents such a challenge that by the end of it I can say I know how to fit just about everything on a CB750. To be honest I want to use this bike as reference for my mechanical ability. Since I've never worked as a mechanic professionally I need to have something that can prove that I can do good work.

Thanks Jerry, That's basically my wife and best friends reaction. But this project is starting to come together. Yesterday I bought a wiring harness for a jeep and gutted it for wire to build the wiring for my bike. I'll post pictures later.

Tazergnome · « **Reply #4 on:** May 01, 2012, 11:17:45 PM »

So I went to a salvage yard and ripped the wiring harness out of a 90's jeep to use the wire for building a new wiring harness. Cost about $20, some time, and some cigarettes.

Overall I think it was a great idea except most of the wires are just slightly smaller than those in my bike....part of me wants to just use them, and the other part is telling me that could be a bad idea. Could I maybe double the wires between each point? Would that cause more resistance or other problems? [Noob question]

I did have some cable of the right gauge so I started rewiring something simple, the start and kill switch. After studying what wires connected where I soon realized that the person who wired this before me had NO idea what they were doing. That should be a bit odd coming from a newbie, but this person had the kill switch crosswired with the ground and only one coil. The wire from the kill switch was wrapped in clear tape then electrical tape.

The splice points were held together with gum wrapped in tape. Oddly enough it would probably work for years to come...but I wanted none of that shenanigans on my bike.

Solder and heat shrink tubing.
I happened to find a great deal on heat shrink tubing, harbor freight was running a 50% off sale on it. 10 bags for $15

I'm looking hard at fabricating a seat pan to hold the electronics. Maybe drop the battery down a bit. The other possibility I see is since my rear wheel is extended I have some space in front of it for either a tool box or a electronics box.

steakCB550K · « **Reply #5 on:** May 02, 2012, 09:42:46 AM »

Good luck on the build, I am looking forward to how the wiring harness turns out. Very ambitious of you.

Tazergnome · « **Reply #6 on:** May 02, 2012, 03:16:09 PM »

I'm using this as my diagram. It makes since and looks easy.

Unlike this...

I'm really starting to like the idea of the seat pan, although it may conflict with the battery or oil tank. I'll come up with something.
I think I'm going to reserve the space in front of the rear wheel for a metal tool box. The long green kind that real tools used to come in. Should be able to make a slide in system for it. I'm also eyeing a tail from some other CB750 with a plastic box built into it. Plus ammo box side bags. I should have enough storage in the end.

captain awesome · « **Reply #7 on:** May 02, 2012, 07:01:16 PM »

Keep at it, and you'll get it back on the road. That swingarm still scares me though.

Tazergnome · « **Reply #8 on:** May 02, 2012, 07:38:56 PM »

Do you think it might cause stability issues? Or is it just the wheel being too far left? I was thinking about swapping wheels and seeing if it fixes that. The wheel looks off but the swing are looks straight to me.

It might be a minuet before I can work on it. I'm in with my wife tonight for my daughters birth.

But I think I'm going to work on some concept images tonight while I'm waiting.

captain awesome · « **Reply #9 on:** May 02, 2012, 07:49:12 PM »

Dunno. Only way to find out is to tear into it and take some measurements to see if it's square.

Tazergnome · « **Reply #10 on:** May 03, 2012, 04:43:11 AM »

Sounds like a plan. Will everything else being so buggered up it wouldn't be a shock. The chain did rip into the crank case, so if it was pushed hard enough to do that it might have offset the swing arm.

I has some free time ("sleep") last night and put together a concept for this bike.

MS Paint for the win.

From left to right:

I've herd that moving the break calipers to behind the forks helps shift the wight so the the bike handles better. I don't know, but I like the look of it. Might do more research before I go for it.

I love the tank on this goldwing by Kevin Rowland. I think I'll do something similar with the straps although I am hesitant to drill into the tank to mount them. Rare earth magnets maybe? It would be removable and very convenient.

I really like the polished raw metal look done my Crowe Customs and The Tarantulas. This bike is a masterfully done and is far from what I'm shooting for with it's clean construction and class, but I still see many things I would like to use on my "rat". I was thinking about doing a racing stripe down the middle in raw metal. The super sport tank has that nice ridge that just begs to add contrast to a paint scheme.

This bike built by Pat Jones of MotoHangar really captures some of the concept that I'm going for. It's beautiful in all of it's rusted glory. I loved the side cover and wrapped pipes used on this bike.

The center is my draft of the concept I'm going for. I still have some things to add and change, but I like the look so far.

Bottom left is a K&N filter with oil cooler. Great addition to any bike so I've heard.

This final bike I decided to include is by Marco Luk. I love everything about it save maybe the seat tail, but only maybe. I am tossing the idea of lowering my bike around, and I love the dream tank used. I will probably get tank pads for my tank. The solid wheels are something I would love to include on my bike eventually. Till then I might use covers on the wheels. But I don't know how good of an idea that would be.

Another thing included is the Firestone tires. If ANYONE knows where I can get these or something like them for less than $200 each I would be grateful. I am also thinking about going with enduro tires for a very rugged survival bike look.

captain awesome · « **Reply #11 on:** May 03, 2012, 06:44:43 AM »

Skip the Firestones and get something that won't handle like #$%* and cost a ton of money. I like the Dunlop k70 for a vintage tread, decent price, and good road feel.

Tazergnome · « **Reply #12 on:** May 03, 2012, 07:37:02 AM »

I really like the price and I like the tread more anyway. Is there something similar with a slightly more rugged tread?

captain awesome · « **Reply #13 on:** May 03, 2012, 07:46:07 AM »

I think the k70 is a pretty rugged looking tread. Are your wheels 19 up front 18 out back?

Tazergnome · « **Reply #14 on:** May 03, 2012, 08:14:50 AM »

"Should be" is the right phrase here. I think they are, they look stock enough. I've got a few wheels I'm going to try out in the rear to see if that wheel is just too far left...

It is, honestly it's about perfect for the look I'm going for. Unfortunately the look of my bike is all I have to go on for now. I know I eventually want to do something interesting, but I'm trying to keep myself from getting too ambitious at this point. Limited time/money/knowledge means if I try to get fancy I'll never ride. I know that I want to keep allot of the "patina" of this bike. So I don't plan to do the super clean and rebuilt look that allot of classy cafe bikes have.

captain awesome · « **Reply #15 on:** May 03, 2012, 08:33:20 AM »

You need a priority list.

1. get bike running
2. get bike running well
3. get moving under it's own power safely
4. make it fancy

Tazergnome · « **Reply #16 on:** May 03, 2012, 08:46:45 AM »

Sounds about right. I'm really debating wither to cut the bars and look at the cams. I know it's something I'm going to do before the bike gets too far. I think hearing her start should be my first priority right now. I ordered some dohc coils for the dyna system. Once I get the electrical work and the carb cleaning out of the way I can go from there. I was reading through the bio-hazard build and the bikes have almost identical problems. His was a bit worse I think, but it gives me hope. I'm thinking I might need to replace the bottom casing if it's too bad. I haven't heard any grinding in the kickover, so hopefully it may just be an annoying leak or no problem at all. I can hope for that, right?

captain awesome · « **Reply #17 on:** May 03, 2012, 09:47:44 AM »

Worse case scenario you find a new motor or use the good case half you have.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** May 03, 2012, 12:30:59 PM »

Get a welder to take a look at your case once you get that broken area clean. That same welder can install your frame kit too so don't cut up the frame and bugger it.

Look at the cams ?? SOHC = cam. The stock cam is one of THE best stock cams for the 750. Why do you want to look at it?

+1 get her running then fine tune so it runs as best as possible before moving forward.

As far as the rear wheel goes, do you have the 2 stock spacers installed? Doesn't look like it's straight/lined up correctly. Just don't know how that swing arm measures width wise to the stocker.

Tazergnome · « **Reply #19 on:** May 03, 2012, 02:19:12 PM »

Cap'n Awesome

I've got a k5 motor as a spare. So I've got options.

Jerry

I saw that done in the bio-hazard build.
Your right, you'll have to excuse me. Very tired at the moment. I'm in the delivery room with my wife. Few hours away from a daughter.

I'm curious what the PO might have done, the frame has been cut to access the cam...and they have done a few things to the bike, including "upgrading" the fuses......

I'll have to measure when I get the chance.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #20 on:** May 03, 2012, 06:29:41 PM »

Forget us and bikes! Early congrats on the daughter!! Just keep the bike to play with as your personal diversion. Your wife may not understand it though as they think raising kids is rocket science

Roach Carver · « **Reply #21 on:** May 03, 2012, 08:04:57 PM »

I wouldnt be too worried about the wire. The new repro harnesses also have smaller wire. Just tidy it up a bit. Like ive said.before. Get the wiring straight. At least get good power.to the.coils. Clean the.carbs be meticulous about it. Set the valves. Tighten the cam chain. Check timing. Fresh oil and filter and get it to run. If it wont do that theres no need to worry about paint or where to put the caliper. If you want to borrow a stock swingarm to compare let me know.

Roach Carver · « **Reply #22 on:** May 03, 2012, 08:08:21 PM »

Also, congrats!

Tazergnome · « **Reply #23 on:** May 04, 2012, 06:43:11 AM »

Quote from: Jerry Rxman Griffin on May 03, 2012, 06:29:41 PM

Forget us and bikes! Early congrats on the daughter!! Just keep the bike to play with as your personal diversion. Your wife may not understand it though as they think raising kids is rocket science

Oh, I already have. For now...

Quote from: Roach Carver on May 03, 2012, 08:08:21 PM

Also, congrats!

Thanks!

Quote from: Roach Carver on May 03, 2012, 08:04:57 PM

I wouldnt be too worried about the wire. The new repro harnesses also have smaller wire. Just tidy it up a bit. Like ive said.before. Get the wiring straight. At least get good power.to the.coils. Clean the.carbs be meticulous about it. Set the valves. Tighten the cam chain. Check timing. Fresh oil and filter and get it to run. If it wont do that theres no need to worry about paint or where to put the caliper. If you want to borrow a stock swingarm to compare let me know.

So it should be able to handle the same current?
I swear the 2-3 coil was wired into some random place on the harness. I'm starting to suspect that the PO wasn't the one who installed all the mods, he just did a $h!t job of maintaining the bike. I've got one from that K5 I dismantled, thanks though!

Roach Carver · « **Reply #24 on:** May 04, 2012, 06:48:12 AM »

I am not a wire expert, but i think I read somewhere that newer wire is better for some reason and is able to get by being a smaller diameter. Dont take my word for it though. Do some research or figure out how to test it. I dont think I would piggy back my wires though.

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Author Topic: 1975 CB750 F0 SS First build, first bike. (Read 8371 times)