75-76 Yamaha DT400 Build(s??)

Discussion in 'Old's Cool' started by TravisK, Nov 30, 2016.

  1. baloneyskin daddy

    baloneyskin daddy bikaholic

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    I looked at a parts fisch today and the orings I was referring to are listed as gaskets .Didn't check for availability though.If it was me I'd use O-rings. One goes under the doohickey that the reflector screws into and the other fits into the little stepped washer .They do quell a little of the vibration getting to the headlight.
    #21
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  2. TravisK

    TravisK Adventurer

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    Cheers! I like to keep up momentum whenever I can. I love doing this stuff and I'm lucky to be in a position where I can spend some time on it daily. I don't have any experiences or memories with these vintage bikes, but I always fall in love with the models I work on. It happened with my CT90 and it's happening with these DTs. The communities around these vintage bikes are just amazing.

    Interesting... I think I found #21 underneath #19 when I got the bike, so that's where it is now. It fits so nicely. I don't have #20 for either side. Hmmm...

    cmsnl.com wants 28 euro for #21 and 4.50 for #20. That seems a bit excessive to me.

    This is beginning to feel like one of those instances where I think I know more than the skilled engineers who designed the bike. Like you suggest, I think I'll find some o-rings of suitable dimensions to isolate the fork ears (top and bottom) and eliminate the up-down play, while I keep #21 under #19 to help isolate it from the lower triple. That should do a good job. Thanks for the help with this, the devil really is in the details and I usually bungle the details up real well. I appreciate it!

    [​IMG]
    #22
  3. TravisK

    TravisK Adventurer

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    I picked up both frames today from CMR Racing. These are the original 2 frames I had, remember. I also have 2 frames already in my garage, one of which is the rolling chassis.

    Both are now rock solid and back to stock. Yes, I know the shocks are mounted backwards but these frames will be stripped down again anyway.

    [​IMG]
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    For the frame on the left, they fabricated and mounted a kickstand bracket that looks brilliant. It's a perfect replica. They also made sure the frame is true.
    [​IMG]

    For the other frame, they brought back the right rear shock mount so the frame is true.
    [​IMG]

    They also machined new bosses for the passenger pegs.
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    For both frames, they fixed the kickstand ears. On all my DT frames, the kickstand ears are bent out so the kickstand hits the ground 100 miles away from the bike. At least 2/4 of my kickstands are fixed now!

    So now I'm thinking I'll vulture 2 of the shocks (from the left frame in the 1st picture, the good shocks) to complete my rolling chassis. All shocks will eventually be repainted and rebuilt so it wouldn't be a permanent thing anyway.
    #23
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  4. TravisK

    TravisK Adventurer

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    So I did exactly that, vultured the pair of (good looking) thermal flow shocks from the other frame. They won't be permanent but I want to mock this thing up and make sure all is well. So I also stole my good pair of rims, which has rubber that isn't actually rotting.

    [​IMG]

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    The kickstand works too, but it's got a little side-to-side play as the ears are bent (like I mentioned in my last post). But this one isn't too bad, the kickstand is out probably 0.5" farther than it should be on the ground. The return spring is rusty, even after I cleaned it up. I have 2 replacements, but it's a purely cosmetic issue right now so it can stay as-is. Truthfully I just hate removing and replacing return springs.

    [​IMG]


    So, the list of stuff to do gets more and more detailed and difficult. I can hook up the front and rear brakes, provided my cables are OK. I can refinish the switch housings for the handlebars. I have the airbox to refinish, and I may vulture a seat from another bike too. Who knows.

    I'm also pretty set on putting one of my 400 engines in this now. I am always changing my mind [​IMG]The other 400 engine I have matches the frame, so that one will be built up along side this one.

    I can probably have these two up and running for the summer. Then I can source a 250 engine for the other frame. The last frame has almost no parts with it, but I'm thinking of building it into an early RT1 clone if that's even possible.
    #24
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  5. Powderfinger

    Powderfinger Been here awhile

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    Earlier in your thread you mentioned Power Dynamo 12v ignitions. What is the story on that? Do you still use a battery? I was wondering if that setup would work/fit on my 78 IT400 project.
    #25
  6. TravisK

    TravisK Adventurer

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    Yep, you can use a 12v battery if you want. The kit replaces the old magneto and CDI, and comes with a regulator/rectifier and ignition coil. Lot's of good reviews of this modification, people saying it gives much more reliable spark and makes the bike easier to start. Not to mention the benefits of having 12v.

    Here is the wiring diagram for my kit on my bike.

    [​IMG]

    I'm not sure if they make a kit for the IT400, you'll have to look into that. I don't know anything about the IT series actually :hmmmmm
    #26
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  7. Powderfinger

    Powderfinger Been here awhile

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    Thanks, I will have to contact them and see if they think it would work. I think the end of the crank is the same on both bikes and the ignitions are similar.
    #27
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  8. spokester

    spokester Long timer

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    Fukkin Fantastic!
    #28
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  9. TravisK

    TravisK Adventurer

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    I remember reading one of the members on the Yamaha Enduro forum helped Powerdynamo develop the system for the DTs. You might have some luck asking over there as well.

    I was reading more about installing the system today, and apparently it requires rejetting on a lot of these big bore two strokes. That's how big of a change it makes to the spark :evil
    #29
  10. TravisK

    TravisK Adventurer

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    Cheers!

    Not too much to report today. I sprayed the foot pegs, brake lever and part of the brake lever assembly. They're hanging up to dry now.

    These are them before cleaning. The two perches are ready to be painted as well, but I can only do 6 things at a time in my ghetto "booth"
    [​IMG]
    #30
  11. baloneyskin daddy

    baloneyskin daddy bikaholic

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    Are the shocks on backwards?
    #31
  12. baloneyskin daddy

    baloneyskin daddy bikaholic

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    After looking into it I see they are on correctly,sorry. The picture of the bike in your trunk has them reversed.
    #32
  13. TravisK

    TravisK Adventurer

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    Yup, it's a common mistake and I keep having to look at a google image of the stock bike to make sure I'm in the right!
    #33
  14. spokester

    spokester Long timer

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    #34
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  15. TravisK

    TravisK Adventurer

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    Nice!! Thanks for sharing, I love reading stuff like that. That motor looks great. A few things threw me for a loop. Are you at all worried about the powder coating not holding up to the heat of the cylinder? My powder coater advised against me doing the heatshield for the CT90 exhaust, because it might be too hot there. Also, painting a piston??? I didn't know that was a thing!

    I hope my engines come out looking half as good as yours. My rough plan is to disassemble the second one (first one already done), remove bearings, get all the cases/cylinder etc vapour blasted, paint with Dupli-Color engine enamel, pop the new bearings in, get the cylinders resleeved (or nikasil or something), get the cranks rebuilt, then get them both back together. I'll likely start on this in February, hopefully having them both done up by the time spring rolls around.

    Right now, not much happening on the bike. The pegs and brake lever are dry, so I may get them on tomorrow, hopefully then I'll be able to verify the brake torsion arm is a good fit. The next (and one of the last things I can do) is the airbox, which is in quite a sorry state.
    #35
  16. TravisK

    TravisK Adventurer

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    So, spokester, you inspired me to do some engine work (something I've been dragging my feet on)

    I spent an hour scrubbing these crank case halves in soapy water, then put them in the oven at 275 F for about 30 mins.
    [​IMG]

    There are 7 bearings total in these two halves, four radial and three needle. The two radial transmission bearings fell out at the 30 minute mark by themselves. The two crank bearings took some persuasion with a hammer but did come out without any real fuss. One needle bearing came out with a punch and a few knocks.

    The remaining two needle bearings are blind and I don't have a way to get them out. This gives me an excuse to buy a blind bearing puller set :D

    The five cooperative bearings
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    One blind transmission bearing, still in its place
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    The other blind needle bearing, which is used in conjunction with the clutch. Apparently (info from Yamaha Enduro forum) this one is only use when the clutch is actuated so it's not too important.
    [​IMG]

    So 5/7 ain't bad. I'll order new bearings and a blind bearing puller set. Then I'll reheat the cases and hopefully get those two needle bearings out and all new bearings in. I'm sure the real event will involve more cursing.
    #36
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  17. TravisK

    TravisK Adventurer

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    Yesterday I started tearing down Engine #2 (a 400 as well). A previous owner had stripped the threads on the rotor where the flywheel puller screws in, so that was a major pain to pull. Luckily its getting replaced by the PowerDynamo rotor so I didn't have to be gentle.

    When I got the engine, the piston was good and stuck. Early on, I sprayed PB Blaster in there but didn't try anything else, as this engine wasn't high up on my priority list. By the time the flywheel was pulled, the piston was free, so that was easy.

    Engine #1 is on the 3rd oversize, if memory is serving me correctly. Engine #2 looks like it may actually be standard! The piston is in great shape, but I forgot to take pics of the side. Oops. The piston from engine #1 was badly scored. This one looks almost new

    [​IMG]

    Not my finest camera work, yea. But the cylinder looks half decent. I'll take a bore gauge to it soon and see exactly what the situation is. Maybe I can get away with a hone and some new rings???? A guy can dream...
    [​IMG]

    Now comes the ugliness. The bottom end is not in good shape. A rusty paste covers the crank. The crank isn't free to rotate all the way around either, because the connecting rod gets stuck. I was planning on doing a bottom end rebuild anyway, this just cemented the plan. Engine #1 was in much better condition than this one in the bottom end.
    [​IMG]

    Under the right side cover was full of a white paste. There was also some white chalky powder that came out. I'm guessing whatever this powder was worked its way into the oil and has created this paste. It looks not unlike vomit
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    [​IMG]

    And that's where we are at today. No doubt I'll strip this whole bugger down to the nuts and bolts. The inside of that bottom end is gross.
    #37
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  18. JCool

    JCool Long timer

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    Water and aluminum oxide.
    #38
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  19. TravisK

    TravisK Adventurer

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    Makes sense to me. There was some corroded aluminum back near the rear engine mount. What a nasty goop that forms, though...

    Continuing to strip down Engine #2

    Everything removed from the right side
    [​IMG]

    It seems the support where the tach worm gear sits has been welded. I assume the original casting broke and this was the solution. I'm not sure the implications of this, if I should trust someone else's aluminum welding or not.
    [​IMG]

    Cases split. These ones came apart real easy. I used my Tusk crankcase splitter for the second time, no complaints.
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    Right side crankcase half
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    I used the crankcase splitter to push out the crank from the left side crankcase half. These crank bearings are totally shot. Takes quite a bit to make them rotate. I wonder why....
    [​IMG]

    The crank is in a poor state. There was some fabric down near the big end. I suspect perhaps someone shoved a rag in there while working on the top end and forgot, or a piece got snagged.
    [​IMG]

    The two pieces of metal sticking out, which prevent the connecting rod from rotating fully. I'm not even sure what these pieces are, perhaps pressed in there and never meant to be removed. They aren't on any parts fiche
    [​IMG]

    When I get back from vacation I'll take the cranks, cylinders and pistons from both engines to a shop and see what's what. My ideal situation would be get both cranks rebuilt, and get both cylinders resleeved back to stock bore with Wiseco pistons. But, this crank is in bad shape and I'm not sure it's prognosis.
    #39
  20. ericm

    ericm Long timer

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    Those pieces of metal are sheet metal caps over balance holes in the crank wheels. I've never seen them come loose but I've yet to take apart an engine as rusty as that. A crank builder may be able to press them back in.

    I prefer stock Yamaha pistons to Wisecos. Yamaha pistons have a higher silicon content than forged Wisecos so they don't expand as much when they get hot and can withstand more heat before deforming. I ran Wisecos in one of my street RZ350s and they did ok. The track RZs got Yamaha pistons. But on a big air cooled single the piston leads a very hot life and I'd want the more heat resistant stock parts. Also the Wisecos require greater clearance so they're noisy on startup. There's no need to put in a stock size sleeve if you have a good piston for the current bore and the bore is in good shape.

    Also for your use I recommend keeping the Yamaha oil injection. Yamaha engineers knew what they were doing. Unless you're racing the oil pump works better than premix. Use good synthetic oil. I like Redline Allsport- it works and makes the exhaust smell good too.

    I beleive there's a DT shop manual in one of the Intertec collected manual books.
    #40
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