Topic: My first complete build 72 CB750 - completed for now...

[algophobe]

I've been working on this one for a while, probably since 2013. My first major build so everything is a learning experience. I got this hideous beast from Victorville, CA about 60 miles from where I live for $600. Came with a cigarette lighter mod. More pics to come.

[Marco83]

Keep them coming

Sent from my MIX using Tapatalk

[algophobe]

the tear down begins. and a pic of the aforementioned cigarette lighter

[algophobe]

we were in transition at the time to moving to a new house, so the first priority was to get the engine and frame on new wheels to make it easier to transport to the new house. the front hoop was slightly bent so I got my hands on a used one in good condition. re-lace both wheels and remount temporarily.

[Marco83]

cafe racer build?

[algophobe]

now in the new home, I was able to really dig into the engine and dismantle it. when I got to separating the engine case, I found this suspicious cement on the well of the front spocket... scrapped it off and found out what they were hiding.

oh and yes café build

the pic is laid on it side, but you can appreciate the inside of the crank case the sizeable crack they were hiding. not know what to look for when buying a used bike. this escaped me. doubt that I would have seen it even if I knew what to look for, since it was hidden behind the sprocket cover.

[algophobe]

I opted to find a matching bottom case from ebay. and soda blasted it and repaint it with VHT spray can. thinking back I should have gone the extra step and have it media blasted and power coated, but I read so much horror stories about retained media in oil channels.

[calj737]

I hope you bought/used the entire set of matching cases. The “halves”are not interchangeable as they are align bored.

[algophobe]

I hope you bought/used the entire set of matching cases. The “halves”are not interchangeable as they are align bored.

you're talking about the boring for the crank case bolt? I believe I inadvertently did as the halves don't align right.  I bought them separately on ebay from the same seller. I have to cop to that lack of knowledge. here are the test fitting and build of the lower end. new bushings, new chain guide and seal of course.

I built a wooden stand as I hadn't acquired the welding skills yet.

[MauiK3]

Unmatched engine cases will not work, the crankshaft bearings won't match.
I'm not sure why any seller would even sell one half unless it's for an art project.

[algophobe]

Unmatched engine cases will not work, the crankshaft bearings won't match.
I'm not sure why any seller would even sell one half unless it's for an art project.

Even if you use new bearings based on the codes stamped and test press-fit with filament gauges and the clearance is correct? Granted the stamp code is only on the bottom half the crankcase.

[Davez134]

Unmatched engine cases will not work, the crankshaft bearings won't match.
I'm not sure why any seller would even sell one half unless it's for an art project.

Even if you use new bearings based on the codes stamped and test press-fit with filament gauges and the clearance is correct? Granted the stamp code is only on the bottom half the crankcase.

Yes, even with new bearings it will not be right. The cases were bored as a set at the factory, so there is no way to correctly use 2 mismatched cases. Not when talking in .001" measurements. Look in classifieds here or post a wanted ad for matched cases and do it right.  You can also have your existing bottom case repaired.

[algophobe]

I'm pretty certain I used both of the newer halves of the case, but not 100%. Its been about 2 yrs since all this went down. I'm surprise there aren't any markings to indicate the top and bottom halves are indeed pairs. at least not to my knowledge. It when you've put everything together that you start questioning and doubting if you forgot something. damn it!

just a side note, the plastigages I used were 0.001-0.003"

[HondaMan]

The guys are right: you can't mix cases...easily...to do so, you MUST have the crank holes align-bored, and this usually results (best case scenario) with using the Black (thickest) bearing shells, followed by turning down the crankshaft journals to get the clearance needed. Often, they are far enough different that this won't work, but I have seen it done, once. Only once...successfully.

It is much cheaper to fix the cracked case, and it usually works OK. just make sure the case mating face is flat above the new weld, or else have it welded up and have a machine shop touch it back flat to match the sealing surface. This is much more commonly done than you might think!

[algophobe]

Thanks for the advice gents. I don't doubt you're right. Issue is I'm not sure whether I did it or not. Worst case scenario what would be the result? Premature uneven wear of the crank shaft and engine failure? I'm assuming that it would run fine initially if started up. The reason why I ask is that I'm currently pretty far in the build. There are a few issues that I work around, and if I have to pull the engine and start from scratch I'm wondering whether I need to redo the frame as well. One being the rear hoop coming close to the rear tire which I compensated with longer rear shocks. Most likely would have to lengthen the front fork tube slider to prevent the bike from being too squirrely. And second issue is whether to just redo the frame and add a frame kit to allow for upper in maintenance without having to remove the engine in the future. Here's a pic of her current status.

[Terry in Australia]

Looking good mate, notwithstanding the mismatched cases. It looks like you're pretty set in your ways and want to run it as is, and to be honest I'm interested in seeing how it'll go too, so just remember that if the engine does lock up at warp speed, your clutch lever is your friend. Cheers, Terry.

[MauiK3]

Yamiya right now has a K2 case for $266 plus shipping. Mismatched cases will likely result in crank shaft failure. Good cranks are hard to find.

[algophobe]

you all don't know how i'm dancing for joy with my 2 yo daughter right now as i did a little detective work and found out 100% that I used the correct matching pair. this was a lesson in good photo documentation during a build, especially it its your first. I dug thru the old photos and found a pic of the engine when I first took it out of the frame. if it pleases the court, i'ld like to present the first pic as exhibit 1. if you look closely the last 4 digits are 5863. exhibit 2 is the pic of the cracked lower case (as show in previous pic) which was replaced. exhibit 3 is the pic of the engine case painted with vin#... 5526 ergo, both bottom and top half of crank cases were used and purchased as a matching pair, albeit on separate ebay purchases. case closed! booya!

in all honesty, I would have kept going with the build, finish and running for a few blocks just to have the satisfaction of hearing her roar, then go back to building the engine from scratch again.

[algophobe]

Seriously guys, you're inputs are invaluable, especially for a first timer like me.

So to continue the show and tell, new pistons and rings were used, and port polished, and cylinder installed. the guides and old chain was actually in pretty good condition. new studs. I must say Dean of Hackaweek and his videos were what gave me the confidence to go thru the engine build. I found it better to put the cylinders on this way even with me doing it alone. not sure how you all do it. I bought the piston ring compressors that were useless, and instead used large hose clamps. then had a local guy replace the valve guides and new valves and lapping. I use the stuff from cb750supply or vintagecb750. not sure how you all feel about their product. covers were all cleaned and polished. new clutch plates of course. the started checked out ok as well as dynamo. I ran her using the starter on a car battery and the oil pressure checks out on the top end as well as with the aftermarket oil gauge tapped on the right side galley plug.

I tried Dean's technique with the drano cleaning but ended up creating pits in the valve cover.. even when polished it looked like something for a steam punk look or rat bike. so had it power coated which filled the pits smooth.

Not sure how you all feel about using sealant on gaskets. some guys are religious about using them dry?

[Terry in Australia]

Looking good mate. I had a look at a couple of that Hackaweek dude's vids on youtube, and was less than impressed. Drilling holes in oil galleries for oil pressure gauges when you can just buy an adapter is dumb, and using caustic soda to "etch" aluminum? What the fcuk for? As you discovered, caustic is the last chemical you should use.

Seriously, those vids should have a warning, telling prospective first time bike builders that the vid is being made by a noob who doesn't have any experience himself, and any advice therein should be treated with suspicion. I'm glad you came thru relatively unscathed.

[calj737]

Drano for cleaning aluminum? WTF! I’ve only heard positive things about his videos on here, but that would make me very alarmed-

[algophobe]

frame moded, all extraneous tabs shaved off as well as rear mounts for rear foot peg, planning to use short 4:1 pipes so I won't need the hangers. hanger braces for eventual mounting of oil tanks from Cognito Moto and rear hoop and pans created with my newly acquired MIG skill... which requires some "fine tuning". swing arm gets new copper bushing. and the whole thing went to powder coating.

[algophobe]

the rear seat and cowl was purchased from Dime City made by Bedlam, which dictated the length of the rear hoop, which caused issues with the gas tank mount clearance. I devise a new mounting system for the gas tank by welding a new tab and with the use of grommets and spacers mounting to the original battery box mounting holes worked out well.

[algophobe]

cleaning up the tank was quite the struggle, there was quite a bit of rust, which I tried electrolysis, which works ok, but flash rust rebuilded quickly during the drying process, after a few cycles a sizeable hole had to be patched by the local pros and smallers ones were patched with POR15 which helped coat the tank as well. I initially tried Red Kote but it was rubbish.

the front fork was redone combining two sets of forks. the original fork was raked out with long tubes which developed a slight bend over the years of abuse, therefore was swapped out for original length tubes. lower portion power coated, new seals and Progressive springs installed with contrasting Joker Machine caps.

the bike had after market triples that were in decent condition when I bought it, so I kept it, but it didn't have stoppers, therefore tank dents are noted. so I fashions new stoppers from old sockets and tapped it into the lower triple.

[algophobe]

Wheels temporarily mounted, I purchased these Progressive rear shocks from Dime City.  I had to figure a way to drop the engine in by myself, help sometimes is in short supply. For about $40 in raw material, I welded together this rig to drop the engine in. It bolts to your run of the mill motorcycle lift and is secured using ratchet tie down. surprisingly worked the first try.