CB400T Shitbox Build - Daily Driver
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CB400T Shitbox Build - Daily Driver

This is a discussion on CB400T Shitbox Build - Daily Driver within the Project Builds forums, part of the Caferacer.net Forums category; Hello All, I'm a new guy to this forum as well as motorcycles. Let's kick this off with some background --- My history with engines ...

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Thread: CB400T Shitbox Build - Daily Driver

  1. #1
    Senior Member jakejensen's Avatar
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    CB400T Shitbox Build - Daily Driver

    Hello All,

    I'm a new guy to this forum as well as motorcycles. Let's kick this off with some background ---

    My history with engines and wrenching etc. is in big block V8's, trucks, and Camaros. Not exactly bikes. I've rebuilt two ford engines out of trucks; one a 460 V8 (pictures attached), bored over and upgrades throughout, and the other a straight 6 which was a real turd. I have also rebuilt 2 small block Chevy v8s (the old 350), one of which was a shop motor the other was in a 1971 Z28 camaro. I have had the experience of removal, tear down, bagging & tagging, sending parts to a machine shop, fitting, checking clearances (plastigauge), then re-assembly. So far none of those projects have melted down. So far.....

    I did all of the builds in my family workshop, which was a structural steel shop, where I had about 7 years of experience in fabrication and metalwork. I built the engine test stand, fabbed up a flat bed truck bed for the project, generally modified everything on the old truck we were messing around with.

    So I basically have no idea what I'm doing, when it comes to bikes.

    I recently moved from Michigan to Germany. I needed a bike to cruise around town on and also was in dire need of a project. First I found a workspace, which is literally a bomb shelter, and now found a bike (80,000 kilometers on the bike). I will be getting a TIG welder and some other tooling to do the (limited) fabrication on the frame. I bought the 1981 CB400T, from a guy who used it as a daily driver for 10 years in the city. It was used, maintained-ish, and now is going to be hauled over in order to be a less ugly (much more safe) daily driver for me.

    Issues with the bike: It's a cb400.... so there's that. Hasn't been in any accidents, rust free, overall still in serviceable condition. Safety wise.... Here's my initial reaction after tearing the forks out.

    Brakes; two discs in the front drum in the rear. It's got two solid front brake rotors, both of which are still service capable. From what I read on the internet (.....) it seems like the front rotors are safer and more effective in wet conditions when they are slotted and drilled. Is that true? Am I okay to stick with the stock ones or do I need to get upgraded rotors? The previous owner had braided steel brake lines put on it, which are in good condition. The master cylinder is in good condition, aside from cosmetically looking like shit. The brake calipers are in good condition and work well.

    Engine; It has an obvious piston knock (skirt slap). It's unclear yet why, as I haven't pulled the cylinders off. It runs alright, dogs hard in the higher gears which could be a result of the carbs being dirty (haven't looked yet) or the oil rings are toast. It starts up fine, dies on idle if the throttle isn't revved a little bit, until it gets warmed up. I was going to test the choke but I couldn't because the cable is completely fucked up. IF they cyclinder is toast, I found a new one on this site (https://www.davidsilverspares.co.uk/...A/part_175587/) which also sells stock spec pistons as well. I'm not opposed to rebuilding the top end for fun, but I'm afraid if the cylinder is toast that the heads will need to be rebuilt as well. I've still got to inspect those when I pull it apart.

    Drivetrain; The chain is toast. I will replace that. The sprockets look okay, but from what I read it's likely a safe bet to just replace them with the chain. The transmission and clutch work without flaw, it holds every gear all the way through, without dropping out or jumping, and shifts smoothly. I really don't want to tear into the bottom end of the engine, if I can avoid it. But, I have the manual so if the concensus is that safety requires a total rebuild of the crankshaft and transmission, I'll go through the whole fuckin thing I guess.

    Frame; This thing is in very good condition - but fuck is it ugly. I haven't decided if it's worth the effort to rebuild the rear frame, just for cosmetics. I am kicking around the idea of just cutting off the frame behind the shock mounts, and then putting a hoop around the back to support the new seat. The only thing I wonder is if it will make it un-safe to build new mounts for the shocks, also the idea of getting the geometry right is intimidating. I have seen CB400t builds with a mono conversion but that seems like a huge waste of time to me, for a putt around bike.

    Lastly, This is a budget build for me. I want to re-use as much of the original parts as possible, making safe to drive but still have some fun modding it up with custom fab work for fun. I like the cafe racer look and style, so I want to follow that overall design. I bought the book THE BUILD by Robert Hoekman Jr. as an intro the the aesthetic and process for building a cafe racer that doesn't suck. So now I'm appealing to you all for details. Follow along in this thread for updates.

    Thanks in advance for your candid responses!Name:  cb4001.jpeg
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  2. #2
    Senior Member woodsman's Avatar
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    Looks well cared for. The 400's are a bullet proof little bike.

    Too me, if you want something different and period correct then a late '70's early '80's superbike replica would be the right style of customization. If the bike on the cover of Hoekman's book is an indication of what there recommending I'd take what you read with a grain of salt. Honda Twins forum is a good site for info on the old twins.

    How about a Freddie Spencer tribute but assembled from a 400.
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  3. #3
    Senior Member jakejensen's Avatar
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    Quote Originally Posted by woodsman View Post
    Too me, if you want something different and period correct then a late '70's early '80's superbike replica would be the right style of customization. If the bike on the cover of Hoekman's book is an indication of what there recommending I'd take what you read with a grain of salt. Honda Twins forum is a good site for info on the old twins.

    How about a Freddie Spencer tribute but assembled from a 400.
    Thanks for the post. Thoughts on the Hoekman book noted.... some of the bikes in that book seem a little..... artsy.

    That 400 4 look is awesome. I love the look of the four downpipes at the front of the engine. That bike looks high performance for sure!

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  5. #4
    Senior Member woodsman's Avatar
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    It's a 750, a tribute to Freddie Spencer's AMA superbike of the era. You could have the same look and a fun bike to ride. Your's has superbike bars now, rework the suspension, good rubber, maybe a sprocket change if it's a commuter. The seat recut and covered in a Corbin gunfighter style. If you can TIG weld you can build the tight fitting up swept exhaust with parts from these guys. Motorcycle Components-Cone Exhaust Stuff

    Cutting frames is not a good idea, despite all those doing it
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  6. #5
    jcw
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    A fork brace from tarozzi, racetech fork valve emulators and springs set to your weight, set of Ikon rear shocks, braided steel lines and a good brake master cylinder if possible, bars to suit your riding height, best tires that FIT the rim. Those would be the performance mods I'd look at.

    I wouldn't worry too much about the frame. It is what it is unless you want to brace it for performance reasons, which doesn't really jive with a budget build.
    The rear subframe will kinda just depend on what tail section/seat you want to fit. IMO, the rear seat hoop has been done to death and usually done wrong.
    I'm looking through google and it looks like you can do what you say and cut and shape the rear portion of the subframe just behind the shock mounts to blend into the seat. But remember to recreate the crossmember back there to regain structural rigidity. Shouldn't be a problem if you are a decent welder.

    Personally, I'd get the performance mods done first, then get it running and figure out what compromises you can make to the riding position that make sense. Jumping straight to low clip on handlebars, and rearsets and high seat immediately puts you in an uncomfortable position that you may not want.
    Do you want to be comfortable on long rides, or look cool on your way to Starbicks?
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    jcw
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    A twin is a perfect bike to test your fab and welding skills on a custom exhaust! It's not as easy as it looks, but it can be done. I would do that last, but I would definitely do it. Unless there is a readily available aftermarket one.

  8. #7
    Senior Member Teazer's Avatar
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    CB400 SuperDream. That's the only 400 twin that looked good. Sounds like it's baiscally sound. I'd replace the chain and sprockets, check tires and replace if required, check all the cables and give it a good service. And check the compression. Sounds like crap in the carbs - probably just a little varnish from years of unleaded with alcohol in it. . Might be time to drain the tank and check the fuel tap for garbage and clean teh crabs. You might get away with a can of Seafoam or the local carb cleaner.

    Check the front disk pads and if they're worn, get some better than OEM ones. Old bikes with disks were notorious for their lack of wet weather braking. Modern disks and pads are much better. See if EBC or SBS offer replacement disks if the braking is not up to par.

    As for Cafe Racers, I'd forget everything in that book and all the art bikes on line. It looks like fresh paint on the bodywork, but a change to say Freddie replica colors might look good.
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  9. #8
    jcw
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    Quote Originally Posted by Teazer View Post
    CB400 SuperDream. That's the only 400 twin that looked good.
    +1....

  10. #9
    Senior Member 540nova's Avatar
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    Quote Originally Posted by jcw View Post
    A twin is a perfect bike to test your fab and welding skills on a custom exhaust! It's not as easy as it looks, but it can be done. I would do that last, but I would definitely do it. Unless there is a readily available aftermarket one.
    I offer custom stainless steel exhausts for the CB350 twin.
    Www.MerlinCycleworks.com

    Sent from my SM-G955U using Tapatalk
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  11. #10
    Senior Member jakejensen's Avatar
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    Great stuff!

    Quote Originally Posted by woodsman View Post
    It's a 750, a tribute to Freddie Spencer's AMA superbike of the era. You could have the same look and a fun bike to ride. Your's has superbike bars now, rework the suspension, good rubber, maybe a sprocket change if it's a commuter. The seat recut and covered in a Corbin gunfighter style. If you can TIG weld you can build the tight fitting up swept exhaust with parts from these guys. Motorcycle Components-Cone Exhaust Stuff

    Cutting frames is not a good idea, despite all those doing it
    Woodsman, (and everybody!) Thanks so much for the feedback, helps me a ton. This whole discussion about focusing on upgraded suspension and brakes is timely. I uncovered this little gem today while cleaning and inspecting the forks. Is the welded stem a safety concern? Definitely looks HOMEMADE.

    I replaced the seals on both forks today, but it sounds like I might be better off putting more of my budget into just buying new suspension and updated brakes. Living in Berlin, it rains a shit ton, particularly ALL YEAR.

    The brake calipers are in good shape, boots are not worn out, and the rotors are also in good shape. I pulled them all off to paint and re-seal the metal.

    Welding a new exhaust is intriguing and sounds fun. Only thing I wonder about is emissions or safety regs? I know on trucks (remember that's my only point of reference) you can't fuck around too much with the exhaust because the DMV will shut you down. How does that work with bikes?

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