75-76 Yamaha DT400 Build(s??)

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

  1. TravisK

    TravisK Adventurer

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    Interesting, thanks for your input! As I hope I mentioned, I'm still rather new to this so I'm learning as I go.

    Part of the reason I was leaning towards Wiseco was availability, the Yamaha pistons are becoming hard to get and costly, as well as the rings. Luckily, the one from Engine 2 looks pretty good. Maybe I can keep using that. The piston from Engine 1 is trashed, heavily scored along the side.

    The reason I am going to use a block off plate is simply so I can get it running first. I have two oil injection rebuild kits, so I will rebuild both oil pumps and then install them. That way I can verify the oil pumps are working, after I'm already sure the rest of the engine and bike is good to go. I believe the service manual has the volume of oil that should be pushed by the pump at certain throttle positions, so I can verify that way.

    Right now, I am using the Yamaha factory service manual which I have been pretty happy with. I'll look into the Intertec one, thanks!
    #41
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  2. krampus von der fan

    krampus von der fan This one time at bant camp.....

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    Where did you source the ign/alternator? I have a DT400 that has weak spark and I can only get it running by pushing it.
    #42
  3. TravisK

    TravisK Adventurer

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    I got mine from PowerDynamo, this is the kit https://www.powerdynamo-shop.com/shop/show_product.php?cPath=4_41&products_id=285

    When you make an account, the discount should kick in and its 240 euro. Shipping is real quick, I had both within the week and I'm in Canada. Make sure to get the DC kit, they also make one for the trials bike that was AC.

    Like I (think I) said above, I read that people needed to rejet to richen the mixture after installing this
    #43
  4. krampus von der fan

    krampus von der fan This one time at bant camp.....

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    Thanks, got one coming. Now maybe I can start riding this pos again.
    #44
  5. ericm

    ericm Long timer

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    The Yamaha manual is good. I didn't think you had one hence the Intertec recommendation.
    The oil pumps are pretty reliable. I think that "oil pump" problems are often due to not keeping up on the oil level
    in the tank, having the pump cable misadjusted, or pinching the oil line while installing or replacing it. The pump being metered by both throttle position and rpm means that oil consumption can vary quite a bit. The first time I took a street RZ to the track it used most of a tank of oil with a single tank of gas. In normal street riding it'd go 3-4 tanks of gas. I've personally done the pinched oil line thing, it's an easy mistake to make. (this was an RZ500 which has longer more involved oil lines from pump to carbs than RZ350s or DTs).

    You should not need to change jetting with an ignition change if the timing is the same. The PowerDynamo looks like a significant improvement over the weak points ignition. While they mention an "advance unit" there's no description of the advance curve. The stock points have fixed timing. It's common for two strokes with variable timing to have a curve that's retarded at idle (to make starting easier), advances in the mid range running rpm and retards again at high rpms. If that's true and you set the timing to stock values you could have significantly advanced timing for much of the rpm range. That could cause detonation under some circumstances. Rich jetting is a way to reduce detonation (due to lower temps via cooling from the excess fuel). But if that's the case it'd be better to fix the timing.
    #45
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  6. ericm

    ericm Long timer

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    #46
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  7. TravisK

    TravisK Adventurer

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    Thanks for all of this info, and sorry for my late response. I just got back to business here. I have a ton to learn about CDI (and points for that matter). I appreciate you taking the time to help me out!!

    I will be using the oil pump, I don't intend on using premix forever. I just need to be sure I can rebuild it properly! So like I said, at first I might be on premix but for sure I will shift to oil pump.

    When the time comes to hopefully kick this engine over (hopefully April/May?) then I will probably come crying here for more input! Thanks again mate

    So, another update:

    With my CT90 at the show, I can get back to the Yamaha's. When I left it last, I had one pretty well done rolling chassis.

    I haven't sent the engine parts out yet, but I hopefully will this week.

    Today, I pulled off 2 more rotten tires from the last two DT wheels I have. Now, I have 3 sets of wheels. One which has rubber and is on the bike, and 2 sets that need a lot of cleaning before they get new rubber.

    I continued with the first thermal flow shock rebuild. I have 7 or 8 shocks that could be rebuilt, so this is #1 and I'm learning while I go.

    Before cleaning:
    [​IMG]

    After cleaning, with some toothbrush action but mostly ultrasonic:
    [​IMG]

    Hopefully in the next few days I'll get the shock body repainted and I can start reassembling the whole thing. Then repeat. And repeat. And repeat.
    #47
  8. TravisK

    TravisK Adventurer

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    Thermal flow shocks, by all accounts an aggressively mediocre rear shock for the time period. But with the lower-end modern replacements upwards of 500$ for a pair, I think I'll do what I can to get these thermal flows back in order until I can afford to upgrade.

    I currently own 4 pairs of thermal flows, all in different condition. I will probably go through all 8 to replace the seals and shock fluid.

    So you know what I'm talking about, I got this pair of shocks off of ebay for $40 Canadian. The left one is after my first rebuild, the one on the right was the "before" condition
    [​IMG]

    First thing is a good cleaning, I used blue scotchbrite and simple green. Then the tear down. I used zip ties to compress the spring, then its possible to remove the spring retainer from the top. Having another set of hands really helps.
    [​IMG]

    With the spring off:
    [​IMG]

    I simply disassembled carefully, and took note of where everything was. I used an adjustable pin spanner (for changing grinder disks I think) to unscrew the cap that holds the internals
    [​IMG]

    More detailed cleaning, I used my ultrasonic cleaner with more simple green
    [​IMG]

    To remove the seal from the cap, I used the same method I use for bearings. I used a sleeve anchor (3/8" maybe? Or 1/2"? I can't recall), passed through the top. Then I tightened the nut to expand the sleeve anchor to really grab the inside of the seal. Then, I used a punch to drive out the sleeve anchor with the attached seals.
    Here is the seal out (still stuck to the sleeve):
    [​IMG]

    Original seals are tricky to find. They were something like 23 mm OD, 12 mm ID and by my measure, something like 13 mm tall. Unfortunately, I worked off of incorrect info from the web and thought they were 15 mm tall. So, I ordered a pile of 23x12x7 and 23x12x8 from AVX Seals (https://www.avxseals.com/).

    So, here is me finding out the original seal is closer to 13 mm tall (the seal was slightly damaged leading to the 12.19mm)
    [​IMG]

    My "7mm" seals measure around 6.9mm. So I decided to stack two of them to achieve something around 13.7-ish mm
    [​IMG]

    So we are slightly over, by my measure about 0.6 mm. Not great, but hopefully it works. Unfortunately, AVX Seals only sell 7 or 8mm tall with this ID/OD combo.

    With the new double seals:
    [​IMG]
    [​IMG]

    Then I cleaned and painted the shock housing and spring (re-chroming the spring would be too much $$ for these shocks). I used Quick-Glo to polish the shaft. It had a couple of rough spots, but the polish helped to bring it into pretty good condition. I applied a light coat of grease. But, I think I'll have to keep an eye on the shaft to make sure it doesn't start rusting again.

    And there we go, the finished product. Now, I think I will give the same treatment to my other 7 shocks.
    [​IMG]
    [​IMG]

    All that's left is to fill with shock fluid (175 cc I believe) and put it on the bike and hope shock fluid doesn't spray everywhere on the first bump.
    #48
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  9. TravisK

    TravisK Adventurer

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    So the sitrep right now, I stripped and painted Frame #2, and began assembly. I'd like to get both frames to the same point, so I can go forward on them together

    Frame #2 in its current state is shown below. I never really planned out the colours on these two bikes, it just sort of happened based on the spray paint I have on the shelf. I do like the semi-gloss black of the frame here. For some reason, it came out glossier than the full gloss gray of the other frame (this is Krylon rust preventative enamel). I do worry I am going to end up with too much black, but we'll see where we end up. I do like how the black and silver play off of each other. I also painted the swingarm for Frame #2 black as well, but I don't have pics of that now.
    [​IMG]
    [​IMG]

    A reminder of the state of Frame #1 (it's been a while since I've worked on it, besides the new levers)
    [​IMG]
    [​IMG]

    So, to get Frame #2 on par with Frame #1, I need to mount the swingarm. I also need some shocks, which I began dealing with in the previous posts.

    For now, I need wheels. So today, I took a go at the rear tires. Good news, I can now have the rear wheel bearings (3 of them) removed in just a few minutes. I've had a lot of luck with the sleeve anchor technique.

    I have 3 sets of DT tires. The good set is mounted on Frame #1. The other 2 sets are in worse condition.

    One of my spare rear wheels has an issue which I previously identified (I'm not sure if I wrote about it here). On these bikes, the sprocket is attached to the clutch hub, and that assembly is connected to the rear wheel with a snap ring. I guess a previous owner lost the snap ring, so they decided to build up the metal around it by welding in some fashion. The metal which my screwdriver is pointing to is now welded on, and fixed to the hub. The sprocket is free beneath it, but there is no way to get the sprocket off or a new one on without machining down that hatchet job. Unfortunately, for now this hub is buggered
    [​IMG]
    [​IMG]

    That unfortunate find leaves me with only one rear tire available for Frame #2. Unfortunately (lots of unfortunatelies today) the rim isn't in great shape. Outwardly, it is OK and will no doubt polish up pretty good. But under the rubber is another story. The below two pictures are after I took a wire wheel to it. Some spots are far worse than others.

    [​IMG]
    [​IMG]



    I don't like that condition, so this rim will likely not be long lived on the bike. However, I need a rear wheel now so this one will do in a pinch. Now I have to make it acceptable. I used a rust converter to try to stem the bleeding. It is a jelly of phosphoric acid I believe.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    With most of the rust converted, I used Tremclad to try to seal it up.
    [​IMG]
    [​IMG]

    Lipstick on a pig doesn't even cover me here, but it'll do for now (maybe?!). I have some new rim tape to go on after the paint dries, then I'll take my first whack at mounting rubber. Then, polishing and cleaning the outside of the rim, spokes and hub, then on the bike it goes.

    Below are some pictures which show the rest of that rear wheel. It'll clean up OK, I think
    [​IMG]
    [​IMG]
    [​IMG]

    The dampers are solid rubber, and all of them are still in real good condition. I am pleased with that. It's the small victories, today...
    [​IMG]
    #49
  10. travis789

    travis789 Been here awhile

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    how is your progress on this? I'm thinking of buying one this weekend! Sorry I didn't see it before
    #50
  11. TravisK

    TravisK Adventurer

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    Oh nice! Let me know if you go through with it. I can't comment on how they ride, none of mine are running yet. Soon.... soon.... maybe...

    I have definitely been slacking on the progress updates. The last week or two was a freakin roller coaster in the garage. The weather started turning nice here so I started throwing all of my attention at getting frame #1 up and running, frame #2 has been put on the back burner.

    I got the cranks rebuilt, and cylinders bored out and new Wiseco pistons for both engines. Frame #1 is now at 86.00mm and frame #2 is at 85.5mm. Stock bore is 85.00.

    I put the crankcase halves together for frame #1, realized almost immediately I forgot the two locating dowels. Toyed for a minute with just pretending it didn't happen, then I got brave and split them again and put the dowels in. Ok... back together. Then I sheared the kickstarter return spring by being an idiot and trying to install the kickstarter backwards. Unfortunately that spring is inside the cases... so I split them again. I vultured the kickstarter return spring from bike #2 so I could get bike #1 back on the road faster.

    I am dumb:
    [​IMG]

    Luckily I own both a crankcase splitter and crank puller (both are Tusk)
    [​IMG]

    That was the last time I had to open the cases for bike #1. I got the rest of the engine together without incident, new seals, bearings, gaskets etc. I used the gasket kit from gasket king, as well as threebond 1211 and permatex RTV in some spots.

    All together, except for the PowerDynamo alternator:
    [​IMG]

    I created a pressure testing kit, to test and make sure the engine is air tight (necessary for two strokes, because they work on pressure differences).

    Motionpro makes a 2 stroke pressure test kit, but it would have cost me about 600$ Canadian. Too much for me to justify. So I went about making my own, following along the general direction of others online.

    This is used, I believe, for testing natural gas lines. I got it on amazon for 10 bucks.
    [​IMG]

    Here is the basic layout of how it will go in the intake. That gray pipe is just about a perfect fit for the rubber intake manifold, found at my local Home Depot. I brought the manifold with me and kept trying stuff until I found one that fit. It is what is known as PLUMB-EEZE poly insert plug, and it is the 1 1/2 or 1 1/4 inch size, I can't remember off the top of my head. I drilled a hole in the top and epoxied in one side of the male-male 3/4 MPT adapter. I then installed the gauge assembly with teflon tape.
    [​IMG]

    For the exhaust port (~43mm diameter), a perfect fitting freeze or expansion plug found at my local Canadian Tire:
    [​IMG]

    I removed the reeds for this test, but I'm not sure it's necessary.

    The testing was kind of cool, while also being a pain in the ass. I pumped it up with a manual bike pump, never going past 7 psi. It fell about 1 psi every 3 seconds to start, leaking like a sieve. I sprayed the outside with Spray Nine, though you're supposed to use water and dish soap. Basically whatever will make bubbles. I saw immediately huge bubbles forming around the intake manifold and cylinder head as well as my apparatus. I fixed the teflon tape, I used permatex RTV on the intake manifold, and I used threebond 1211 on the cylinder head gasket.

    The engine passed by my standards. It lost about 1psi per minute, but the only leak was on my testing apparatus where it sat in the intake boot. Cylinder base & head, crankcase, decompression valve and spark plug all had no leaks which I could find. No doubt if I fixed that leak on my test equipment it would have held pressure much much better than 1psi per minute loss.

    So, in theory, the engine should be good to go. In theory.....

    To start working on the chassis, I cleaned off an instrument cluster and got it mounted. Low miles!
    [​IMG]
    [​IMG]

    Right now, the paint is drying on the seat pan and hinges, as well as the tool tray, brake light bracket and front engine mount plate. Once those are dry, they will get thrown on the bike, as well as the engine, and it should start looking more like a motorcycle.
    #51
  12. TravisK

    TravisK Adventurer

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    A while back I got a seat cover for this bike from Sirius Consolidated. I tried putting it on and realized I am far from an upholsterer. Put a screwdriver through it at one point because I'm too hamfisted for this ****. This seat doesn't use staples, it uses metal clips on the bottom of the pan. It's not a one man job. With the help of my buddy, we got it put together and on the bike. It's got a few ripples at the back, which my pictures don't really show too well, but all in all it turned out good.

    "Good enough," has been the theme regarding aesthetics for this bike. This bike is going to be used for its intended purpose, and I don't want to fall into the same trap I did with the Trail 90 - spend too much time and money on making it look good, and then be too afraid to ding it up!

    I was happy to get the tank on it, and see it look more like a bike. When I got this specific frame, it was stripped and sitting beside someones shed for what looked like a long time. You couldn't buy a more incomplete bike if you tried, it was just the rusty frame itself. So seeing it come together with my spare parts has been really rewarding.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    So the status, Bike #1 (above) is coming along well, the engine is in the frame, the carb is being cleaned now. The misc parts like tool tray, airbox, battery box/oil tank etc are prepared to go on the bike. So are the tail lights. I don't think I own any indicators for this bike, I'll have to get some I think. Then it's on to wiring harness and electrical!

    Bike #2 is on the backburner, but with the experience I got from Bike 1 I think I can have it up and running sometime this summer.
    #52
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  13. TravisK

    TravisK Adventurer

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    I haven't been doing too much work on the bikes lately, but today I pulled the clutch cover on the DT to see why it won't go in to gear. I pulled out the clutch and shift linkage so it was just the bare shift drum head. It seems like the shift drum is fairly stuck. It's got a few degrees of free play but then it's rock solid on either end. Rotating the transmission via the rear wheel doesn't help it fall in to place either, still rock solid on either side. It's firmly stuck in some gear

    I would swear up and down that while I put the cases together, the shift drum was working correctly. Maybe I missed a shim or it popped out in the final part of the case mating

    It would appear I'm not much of a natural born engine builder, as I've cocked up the transmission on the CT90 and now the DT. [​IMG]

    Now I have to pull the engine and split the cases (again). This time I'm gonna be sure to measure and tolerance every single goddamn thing against the manual. Nothing gets by me this time [​IMG]
    #53
  14. TravisK

    TravisK Adventurer

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    Almost 2 years later upload_2019-3-18_9-48-24.gif upload_2019-3-18_9-48-24.gif upload_2019-3-18_9-48-24.gif upload_2019-3-18_9-48-24.gif :(:(:(:(:(:(


    The bike has been sitting, waiting, while I've been distracted elsewhere

    [​IMG]


    We finally rebuilt the motor. Last week we did the bottom end, taking it slow and making sure we didn't screw up

    [​IMG]


    Yesterday, we finished assembling the motor. We performed the pressure test, and it went really well. We lost ~0.3 PSI over about half an hour

    [​IMG]


    Next up is the timing, and reassembling the carburetor. Then we should be pretty close to popping it in the bike and getting it running with the race wiring. After that, electrics to get it all road legal. We are pushing hard to get it on the road by the start of the season.
    #54
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  15. specdog

    specdog Perpetual search for roads unused.

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    Glad to see you're back at it. Here's hoping things go smoothly.
    #55
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  16. TravisK

    TravisK Adventurer

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    Spent today moving forward. We put in the airbox boot, a new unifilter in the stock airbox, we installed the alternator (Powerdynamo/VAPE 12v system) and race wiring. The exhaust is on, but I'm missing 2 springs holding it in place. The exhaust is made by Circle F. We put on a new tach and clutch cable, we cleaned up the throttle cable as good as we could and installed it. We hooked up the fuel line with an inline fuel filter. As soon as we figure out the exhaust spring situation, and find a proper dipstick (the one that came with the engine is wrong), I think we will be good to try and start it.



    The front end needs work, the tire needs to be replaced, the fork tubes need to be filled with oil, new speedo and front brake cables have to go on, and I think new brake shoes and wheel bearings if its called for.



    [​IMG]

    [​IMG]
    #56
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  17. TravisK

    TravisK Adventurer

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    Well, it runs! We filled it up with 32:1 premix and 10w40 in the trans. It took some time for us to adjust the throttle cable properly too. The length is a little off, and the adjusters are all rusted. This cable is split in the middle, one end going to the carb and the other to the oil pump (that isn't there right now), so a generic cable won't work long term. I think I'll need a new one eventually


    Then the killswitch disintegrated between runs, so we had to wire up the ignition as the killswitch. I guess its a good thing it didn't happen when the bike was running.............. safety first, kids!


    We assume its lean, especially with the Uni filter and aftermarket exhaust, so I've ordered a few different jets and we will try to dial it in now.


    Attached Files:

    #57
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  18. TravisK

    TravisK Adventurer

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    Just a quick update, we had some issues with the clutch pack thickness with the new EBC friction and steel plates. The clutch was contacting the inside of the side cover. The people on the Enduro forums helped us figure out the new steel plates were a bit thicker than the originals. So we swapped in the original steel plates with the new EBC friction plates and all is well. This is detailed here, in case anyone online is having similar issues and looking for a solution.

    So as of now, we are ready to start dialing in the mixture. We are pretty far rich I think, the bike is almost constantly four stroking. So hopefully sometime soon we can spend a day toying with the jetting to get it running right.
    #58
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  19. Jmarkwolf

    Jmarkwolf Adventurer

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    Very interesting.

    I owned two of the DT400B/C's in the 70's. Put 13,000 miles on each of them. They were my primary vehicle through college and beyond. They never needed anything but scheduled maintenance the whole time I owned them. Always started first or second kick, and ran smooth as a top always. Loved those bikes, probably still my all time favorites.
    #59