Author Topic: 1972 CB750 Resto-mod build (Read 19006 times)

Davez134 · « **on:** June 11, 2013, 07:29:04 AM »

Hello everyone. I've been a member here for about a year now. I haven't posted very much, as Ive been spending most of my time researching and reading posts by others to complete my bike. This was my first build and I am very thankful for all the help and advice from everyone here!

A little background about the bike...I wasn't looking for anything in particular, and I have never really paid any attention to the CB750 before. I saw this one for sale on Craigslist and thought it would be a cool project and make a reliable daily rider to work. It wasn't running, had been sitting for a few years, but the engine wasn't seized so I bought it and trailered it home. After putting in a new battery, cleaning the carbs, and cleaning out tank it started up. I rode it daily for about 8 months and then got the itch to tear it down and rebuild everything, re-using all the parts I could and upgrading a few things to my taste here and there. I wanted to start this post to document what I did and give some advice on what worked good for me, so that maybe I could help someone else out who is on the fence about tearing down for the first time.

I attached a picture of the bike on the trailer, complete with mismatched rims, flat black rattle can paint, straight lead pipe for handle bar and other half-assed bits including a bunch of spliced wiring. I am still uploading all my pictures to my computer and will post my progress when they are done.

Bankerdanny · « **Reply #1 on:** June 11, 2013, 11:28:53 AM »

That front rim looks like a Lester, they can be quite valuable so be careful with it.

Davez134 · « **Reply #2 on:** June 11, 2013, 12:50:12 PM »

Everything I did to the bike at first was just to get it running and rideable. The carburetor slides were stuck from sitting for so long so I soaked them overnight in some sea foam and once I was able to move them, I disassembled them and cleaned everything. I bought 4 rebuild kits and reassembled them. Next, as I was trying to figure out the wiring and why my turn signals weren't working, I noticed that the wiring harness had been hacked up with cut and spliced wires everywhere and no real way to keep track of anything. I bought a new complete wiring harness at a very reasonable price. Then I moved on to the brakes, rebuilding caliper, master cylinder and replacing rubber hoses with stainless ones. This got it running and I rode it this way up until December, when I started tearing down for resto-mod. Things I learned:
1. Good quality carb rebuild kits are not that expensive and to me made a huge difference over trying to clean and reuse what I had.
2. Electrical/wiring is not my forte and I did not want to be chasing down wiring issues later. New harness was way to go here.
3. If replacing brake hoses with braided lines, make sure the fittings are oriented same way as factory ones and get plenty of new washers.
4. Bleeding brake lines with a Mighty-Vac pump is the way to go!

Davez134 · « **Reply #3 on:** June 11, 2013, 01:04:08 PM »

Started tearing down on New Year's Eve. The project was actually my wife's suggestion! Things I learned here:
1. Download shop manual from this site! Also get Haynes manual, each has their their place and it was nice for me to have both.
2. Take lots of pictures before and during disassembly
3. Be super organized. I laid everything out in the orientation that it came off the bike and labeled it.

The method I used to remove engine was laying it on its side and lifting frame off. I tilted it over onto a wooden dolly that I made to the points cover didnt get smashed and lifted right off.

Davez134 · « **Reply #4 on:** June 11, 2013, 02:23:05 PM »

Next I printed out the Honda manual, followed it exactly and got to work on the motor. It had a few leaks around cylinder head, and I suspected I may have to replace a few valve guides. I removed and cleaned pistons and saw by number stamped into them that they were Wiseco's 836cc pistons. Then I took my cylinder head to a reputable shop here in town. They re-cut valve seats, replaced valve guides, lapped valves and cleaned up head. They also measured my bores and pistons and said I could just hone them and be good to go.

New rings installed

honed with Flex Hone

Things I learned here:

1. Get new rings, pin clips etc.. everything manual says to replace. Why reuse old ones if you have already done this much work. Also getting a correct cross-hatch hone is important for oil on cylinder walls.
2. I got good quality gaskets from Cycle-X. Their kit was the most complete I could find and I have not leaked a drop in the 2000 miles I have put on bike since rebuild.
3. Pay attention to torque specs for everything.

I was nervous about this as I have never rebuilt a motor before, but if you take your time, follow the steps in the manual and send out parts you dont have the tools to repair (like my cylinder head) its not that hard at all. It was actually way easer than I thought it would be!

Davez134 · « **Reply #5 on:** June 11, 2013, 04:08:11 PM »

I used a engine stand from harbor freight, got some 90 degree angle brackets so I could make it work with this engine and mounted it so I could strip off old paint and repaint. What I found that worked best for me was aircraft stripper. I brushed it on a little section at a time, let it sit for a little while then started scrubbing with red 3M pad. After I thought an area was clean, I did it again. I spent 3 straight days prepping it for paint. As far as paint, I used the VHT high temp primer and VHT wrinkle black out of the spray can. Followed directions exactly and it came out great. I think the prep was key. On cylinder head I used VHT "cast aluminum" color. I sprayed jugs and head separately prior to assembly.

Davez134 · « **Reply #6 on:** June 11, 2013, 04:17:41 PM »

I only had one little setback while assembling the engine. The bolts that hold down the cam towers stripped out the threads and would not hold torque spec, so I had to take the cam out again. I have heard of heli-coils to fix this before, but I came across another product that looked more sturdy called Time-serts. more expensive, but worth it in my personal opinion. Upon looking closer, some holes already had heli coils in them, so I removed and replaced all with the Timeserts.

stripped

repaired with timesert insert

Davez134 · « **Reply #7 on:** June 11, 2013, 04:28:48 PM »

Wheels were taken apart for powder coating. Getting the bearing out was a pita without the removal tool but I managed, knowing I was going to replace them anyway. I followed advice on people here for removing the bearing retainers, then just hammered out bearings using a punch inserted through opposite side. there is an internal spacer that sits against bearing and you need a pretty fine edge to grab that bearing. I soaked with PB blaster and used a little heat as well to help.

I took the wheels, frame, brake caliper and rotor, headlight ears, gauges and all little brackets to powder coat.

wheels before

after

lwahples · « **Reply #8 on:** June 11, 2013, 05:11:38 PM »

Nice work,rims look sweet!

Davez134 · « **Reply #9 on:** June 11, 2013, 05:41:28 PM »

Quote from: lwahples on June 11, 2013, 05:11:38 PM

Nice work,rims look sweet!

Thanks! I'm really happy with how it turned out. I'll be posting more pics soon.

Davez134 · « **Reply #10 on:** June 11, 2013, 06:48:53 PM »

After getting parts back from powder coating, I started reassembling bike. I laid engine on side again and slid frame over it, being very careful not to scratch anything. Took my time and it worked out great. then with the help of a friend righted it and lifted back onto stand.

I wanted to lower the stance so I put on shorter shocks in the rear and lowered the front about an inch and a half.

Now the bike was almost vertical on the side stand, so I cut about 1 1/2 inches off that as well and welded a triangle support for added strength.

Davez134 · « **Reply #11 on:** June 11, 2013, 06:58:41 PM »

That seat had to go, so I took it to an upholstery shop with a picture of what I wanted and they nailed it!

I got a MAC 4-1 megaphone exhaust, replaced exhaust crush gaskets, found some emblems and had my friend (professional painter) handle tank and side covers. I did complete tune up on motor per shop manual. Got a nice set of angled feeler gauges for valve and points adjustment and 4 vacuum gauges for carb synch. I noticed engine was running good, had equal compression in all cylinders, but #3 plug was sooty black, all others nice golden brown. From searching this forum, I narrowed it down to faulty spark plug cap. measured resistance and it was almost 11k ohms. Replaced all 4 and she runs great, starts right up and pulls hard all the way. had to mess with jet sizing and needle clip position but got it dialed in by using search tool on this forum! For what its worth, carb casting number is 657B, I have 120 main jets, 40 pilot jets and clip 4th groove from top of needle.

Davez134 · « **Reply #12 on:** June 11, 2013, 07:05:23 PM »

Last thing i had to do was fenders. I wish I would have done this before powder coat so I could have made it one piece by welding to frame. Guy I bought it from had chopped off rear fender mounts, so I had to find a fender and make some new mounts. I found an ok condition fender, cut a little off with dremel tool and made some mounts.

Then I found a brake light I liked and sent all out for powder coat

Blitzburgh207 · « **Reply #13 on:** June 11, 2013, 07:10:36 PM »

Nice. Good work on the bobbed fender/brackets/lights as well. Good looking bike.

Davez134 · « **Reply #14 on:** June 11, 2013, 07:29:12 PM »

I had the front fender, but was dented and no brackets. I rode it for a little while without but learned that those brackets are part of the integrity of the forks so I located some and painted/repaired fender.

Bike is now complete with front and rear fenders. Everything works as it should and it runs like brand new! I couldn't be happier with results and I learned so much from you all. Thanks!!

Davez134 · « **Reply #15 on:** June 11, 2013, 07:29:45 PM »

Quote from: Blitzburgh207 on June 11, 2013, 07:10:36 PM

Nice. Good work on the bobbed fender/brackets/lights as well. Good looking bike.

Thanks! I thought about how to pull it off for quite a while haha.

Davez134 · « **Reply #16 on:** June 11, 2013, 11:31:28 PM »

Quote from: Bankerdanny on June 11, 2013, 11:28:53 AM

That front rim looks like a Lester, they can be quite valuable so be careful with it.

That's one reason I went with spokes. Much cheaper than trying to find a Lester to match for the rear within budget! It's in great shape!

brandEn · « **Reply #17 on:** June 11, 2013, 11:43:12 PM »

Great looking bike!

Retro Rocket · « **Reply #18 on:** June 12, 2013, 02:02:07 AM »

Watch that pipe on right handers Dave, it'll hit the road pretty easily....

Davez134 · « **Reply #19 on:** June 12, 2013, 08:39:35 AM »

Quote from: Retro Rocket on June 12, 2013, 02:02:07 AM

Watch that pipe on right handers Dave, it'll hit the road pretty easily....

Yeah already found that out in a ride through Red Rock Canyon haha! I'm looking for something now with a little more "up turn" after collector

immortal · « **Reply #20 on:** June 12, 2013, 09:49:06 AM »

Wow, what a great project...Awesome!

volthause · « **Reply #21 on:** June 12, 2013, 10:54:51 AM »

Nice build! Looks great.

Davez134 · « **Reply #22 on:** June 12, 2013, 04:53:46 PM »

Thanks for the kind words guys! I love riding it, except Ill have to drive my car more often for a little bit. Ran some errands today and temp outside is 106! Bike runs fine in the heat...rider not so much.

Davez134 · « **Reply #23 on:** June 14, 2013, 10:02:52 AM »

So, for my latest project update I got a little away from the resto and more toward the mod. I just installed the basic Pamco ignition earlier this week. I didn't get the coils because as part of my resto I put in NOS Honda coils as well as new plug caps. The installation was very easy. I ran the wires to stock location near oil tank using factory type male connectors (didn't want to cut or splice any wires) covered with shrink tubing. Ran the switched power wire under tank and connected to black/ white wire near coils, again using factory type male connector and a single male into double female that I found at local electronics store. Came out really clean. Probably overkill but didn't want to chase down any wiring problems from bad connections and it can easily be changed back to points in future with no modifications.

I really like it so far. I know from reading posts on this forum (read a lot before I switched) that heat was a concern. It has been 105 degrees plus this entire week and the unit has been great. As expected, no noticable performance difference, but real consistent idle and in my opinion a little faster/easier start. Part of the fun of having older vehicles is the maintenance. While I liked adjusting points, I think I'm going to like not doing it more.

pamcopete · « **Reply #24 on:** June 14, 2013, 06:40:39 PM »

Really a cool looking bike, Davez134. I'm glad you chose PAMCO. The wiring you chose is the way I wired my '74K-4.

Not sure where the rumor about heat started, but probably from someone who is not familiar with modern electronics. Back in the day, like the '60's or '70's, heat was a factor in electronic design, especially a product designed to work in an automobile engine compartment or even right in the engine itself, but the PAMCO uses modern components that will withstand the heat of operating in the engine.

The IGBT transistor that actually triggers the coil is a purpose built part from International Rectifier that was originally designed to work in plug on coil systems. It has an operating temperature rating of 175C which is equivalent to 347F. The only other active component, the Hall effect sensor, has an operating temperature range of 150C or 302F. Neither part is operated anywhere near their maximum current capability. The transistor is mounted on what is essentially a very large heat sink.

The original PAMCO electronics were designed for the Yamaha XS650 and they were mounted in the points housing on the cylinder head, the hottest place on the engine, and they have been working there for thousands of bikes since 2008. Not a single heat related failure has occurred in that time.

Ride. Enjoy. Life is simple.

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Author Topic: 1972 CB750 Resto-mod build (Read 19006 times)