1980 CB400T Hawk, Advice needed for ADV build

Discussion in 'Some Assembly Required' started by Azazel, May 25, 2013.

  1. L.B.S.

    L.B.S. Long timer

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    You're in Vancouver? Huh! Small world 'n all that.

    A 1980 CB400T was my first street-only bike. By street-only I really mean my first non-dirt bike or dualsport bike, but that didn't stop me from going off road on it heh heh.

    I put over 120K on that one, rode it to Mexico and back, took my girl to Prom on it. Have so many fond memories of that bike.

    Then got a 1982 CB450T second hand for $900.00 (in 1985-ish) and raced it at Westwood. Which I'm hoping you are old enough to even know about or remember, lol. :D

    Funny, I didn't think the CM450 engines were different than the CB450T's, but I don't seem to see the little finned sump oil "cooler" sticking down on your bike? Curious.
    #21
  2. Azazel

    Azazel Adventurer

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    Hah, the bike is actually about ten years older than I am! The oil cooler is there, it's just got a giant gap in the middle where the fins were sheared off in the crash that totaled the donor bike for that engine (or so I was told). Part of the reason I'm swapping out the whole bottom end this winter.

    I love this bike, it handles everything I throw at it. From redlining the Coquihalla to crawling up FSR's that make guys on enduros give me crazy looks when they pass by! :D
    #22
  3. Azazel

    Azazel Adventurer

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    Tore down the on-frame 55k engine this weekend, and just in time. Now I know why it was eating oil all summer!

    [​IMG]

    My rebuild of assorted parts is now such a hilarious frankensteins monster:
    - Crankcase & Pistons off 22k engine, new gaskets & rings.
    - Cylinders & Cam head off 55k engine, check tolerances & hone.
    - Camshaft off 22k engine.

    What a mess.
    #23
  4. Azazel

    Azazel Adventurer

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    Sending this in to get checked out by a shop since I don't have the tools. Hopefully the undersides look better...

    [​IMG]

    ...Because my backup head is 100% gone to rusted town and it isn't coming back.

    [​IMG]
    #24
  5. Leaf

    Leaf Been here awhile

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    It'll buff out! :D

    Seriously, though, I'd scrub & derust them both good and lap the valves a little and see if they seal up. I'd give you good odds of having two usable heads there... Can't hardly tell from here, but it doesn't look like any of the valves are burned to me (though the one exhaust valve on the upper head looks a little odd, maybe, and maybe they are all pitted underneath...). Though there is a distinct possibility that I don't know what I am talking about... Did you keep your valve clearances in spec?
    #25
  6. L.B.S.

    L.B.S. Long timer

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    Mine was prone to a little over heating (the '80 400T) and started to smoke and burn oil around 80,000 km's I think it was. I rebuilt it, and discovered the pistons were scored and melty looking around the upper circumference, and the crowns were a black carbonized mess. The inlet valves were ok, but both my exhaust valves were burned and one had a big crack in it!

    It was fine for many more years and miles until I bought the 450T, and I ended up giving her to my best friend to start him off in motorcycling. :D
    #26
  7. Azazel

    Azazel Adventurer

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    Top right exhaust valve is just displaying a scratch through the carbon that I put there when probing how much buildup was everywhere. I'm taking it in for inspection, as it came off the 55,000km engine.

    The bottom head is worse than it looks, I shined a light up the carb ports and the stems are growing rust forests on them. The two right side injection valves look pristine, but everything else aside from the block itself may be unsalvagable.

    I suppose if the valves are pitted I'm pretty much resigned to playing Ebay Roulette on head assembly's, aren't I? They certainly don't sell the OEMs anywhere. :cry
    #27
  8. Leaf

    Leaf Been here awhile

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    Hmmm, maybe....

    I am getting ready to tear one of these motors down. If it is worth rebuilding, that's what I'll do, but if it's not worth messing with than I may end up with some extra valves I'd be looking to get rid of... No promises of any sort, but... You know...

    Edit: Really though, I am surprised by how bad something can look at first blush and then how nicely it'll clean up and go back together and run... My CB400T was bordering on being a parts bike when I got it (and it's still an ugly rusty piece of junk), but it runs pretty darn good for a 35 year old heap... I bet the rust will clean up ok. Maybe still burn a little oil through the valve seals if the rust has migrated up that far and leaves some places for the oil to work down into the combustion chamber, but still run ok... Maybe. As long as the valve seating surfaces aren't too far gone to be smoothed out to seal good. :D A little oil down there might help with valve life anyway. I hear stories of people with really old stuff mixing some 2-stroke oil into their gas to help keep the valve seats from wearing.

    Standard Disclaimer: I may not know what I am talking about, so, you know, take my opinions with a healthy grain of salt.
    #28
  9. WYO George

    WYO George Long timer

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    Nice project, I have a '78 CB400TII that I plan on doing somthing with. It was my first bike and I still have it despite a couple dozen others coming and going over time. I'm leaning towards building it as a scrabler type bike with some slightly increased suspensino travel / ride height and posibly some luggage of sorts. Right now it's sitting in three different crates waiting for re-assembly:D
    #29
  10. Azazel

    Azazel Adventurer

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    Thanks Leaf, that's very kind of you. I called a few shops and they basically acted like I was retarded for asking about a valve inspection on a head that's already off the engine, so I guess I'm going all-in on a bedroom rebuild here. :evil

    Gstanfield, I just picked up this old aluminum Krauser rack off Ebay for about $130. You'll have to fabricate the mounts out of flat steel, but they are perf for the frame:

    [​IMG]
    #30
  11. Leaf

    Leaf Been here awhile

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    Nice.

    When I was a kid, I remember dumping a box containing a torn apart XR200 engine (with one of the valves embedded into the top of the piston) into the arms of the Friendly Local Motorcycle Mechanic and saying "fix please!" The look on his face was Mastercard-priceless. :lol3

    But rebuilding motorcycle engines is fun! Don't be scared! Get the tools you don't have inexpensively off Horrible Fright, er Harbor Freight, and just doooo eeeet. :D

    And, pikshurs, please! :clap

    Maybe we could rebuild both our motors at the same time, share photos and grumblings, and have friendly competitions of oneupmanship over whose motor is more screwed... :rofl I have that CM400E motor that needs looked into... But I wanted to do a CB900 first... Ohh decisions... :cry
    #31
  12. WYO George

    WYO George Long timer

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    If you run into a snag on the engine let me know. I have a complete factory service manual for my '78 and while the two aren't 100% the same bike, they should be the same engines and I'll gladly look up info if you need it.

    George
    #32
  13. Azazel

    Azazel Adventurer

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    Thanks George! I've got both sitting beside me, so it's just between me and my shaky hands at this point.

    New tank! Off a CB450 this time, so I've gained an extra liter of fuel capacity over my previous one. Going to swap the handlebars out to prevent this one from getting punched in if the bike topples over.

    [​IMG]
    #33
  14. WYO George

    WYO George Long timer

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    Extra capacity is good!! I'll be cutting and welding my stock tank for some extra capacity. It has a dent right on one of the style lines so it's no waste to cut it up. I'm thinking I'll shoot for 4.5-5 gallons total. Maybe I'll get off my butt and start working on it in a couple weeks. You've inspired me to do a build thread!
    #34
  15. Azazel

    Azazel Adventurer

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    Recently I've been reviewing my goals and become concerned at the longevity of the frame I've chosen to work with here.
    (Picture grabbed from another build forum, not mine):

    [​IMG]

    Primarily my concerns are:
    - That the crankcase acts as the base portion of the frame, rather than bottom tubes.

    - The center downtube is a hollow cube of 1/4" steel halves, welded in the center, which flares out at the bottom where the crankcase bolts on.

    - The tail is made up of two thin leaves welded onto the arches of secondary loops.

    Overall I'm wondering at the longterm survival of this in rough terrain, especially with any meaningful fuel hanging off those funky tail supports. :hmmmmm


    In other news, cylinder head is in a friendly machine shop being looked at, should know if it's salvageable next week.
    #35
  16. Leaf

    Leaf Been here awhile

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    Mine has been fine over some really rough stuff, and with that sidecar bolted onto it yet. I don't think the engine-as-stressed-member is a weakness at all. I have broken the upper rear sidecar mount a couple of times, but the actual load-bearing part of the motorcycle frame has taken it all like a champ.

    I think your biggest hurdle to off-roading it is the short travel of the stock suspension, especially the rear. It likes to bottom out on really rough stuff and make my back sore. Perhaps without a sidecar on it, yours won't be so bad. But mine is a back breaker if you're not standing on the pegs. You may want to see if you can devise some way to put some longer travel shocks on it. Which may be somewhat difficult, seeing as how the CB400T's double-clevis shocks are of an uncommon configuration...

    The other thing that is a little annoying is that big ol fat exhaust collector / crossover chamber right under the engine. It likes to hang up on rocks. At some point, I have a CL360 exhaust that I want to try to fit on mine to try to get all that stuff up off the ground where it's hitting stuff, but that will require moving the electronics, and that is annoying. Not really feasible to just remove the collector either, imo, as I believe it's required for proper exhaust scavenging and you'll lose power from the already somewhat anemic engine without it. Though perhaps a crossover pipe of some sort would have the same effect. But then you've got something hanging down there to catch on rocks, again, just not quite as fat a something.

    Also, for really heavy off-road, you may want a larger front wheel. I am running an 18" rim, but with the tire on it it's the same diameter as the stock 19" w/tire. It will bounce up over the medium/small obstacles if you give it a little sass, but it doesn't like the big stuff at all. Maybe a dirt bike front wheel would be good if you are going to be really serious, but I don't get that serious on mine. Nothing worse than logging roads for me.

    It's also got a pretty tall 1st gear for off-road stuff. On mine, I went up a tooth on the front sprocket to gear the whole thing down a notch, but it's still a little too tall for doing really nutty stuff. And at 65 mph on the highway, it runs really high RPMs and burns more fuel.

    I dunno... Just my opinion, all that.
    #36
  17. CruisingRam

    CruisingRam Frankenbike builder

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    Engine as stressed member is one of the best designs of all. Don't sweat it.
    #37
  18. Leaf

    Leaf Been here awhile

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    Soooooo, at the risk of being a nag... How's the project coming? :lurk

    I'm too busy with my day job to work on my own projects, so I have to get my fix somewhere! :lol3
    #38
  19. Azazel

    Azazel Adventurer

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    Sorry guys, it's been a long cold month so I've spent it acquiring parts and getting stuff fixed. :clap

    Cylinders honed, new gaskets & NOS Pistons, valve head re-machined, newly painted in high-temp black and new valve seals:

    [​IMG]

    I just need to acquire piston rings, side cover gaskets, and a ton of assorted o-rings and I'll be ready to put it all back together next month!
    #39
  20. WYO George

    WYO George Long timer

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    I wouldn't worry about the frame as it's a lot stronger than you're imagining it to be:D

    Engine parts are looking good, keep up the build!
    #40