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DT360a scrapper bike

21 Jul 2020 21:42 21 Jul 2020 21:45 by akara1.
akara1
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DT360a scrapper bike #1
Hello all!
many years ago I owned a dt360 a that was ported with an mx pipe and I had a blast on it for a few short weeks before it was stolen, ever since then I've wanted to own another Yamaha Enduro and recently I came across this bike at a scrapper and picked it up for a hundred bucks. I set myself a budget of around a 1000$ to restore it and at least to get it back up and running and riding again. I know that if I looked long enough I could have purchased a running reasonable shaped bike for around $1,500 but instead of doing that I decided to save this bike from being reclaimed back into the Earth and make it my own and have fun learning in the process. the bike is extremely rough and missing some few things, the engine is seized and won't shift

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21 Jul 2020 22:44
Mothersbaugh
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DT360a scrapper bike #2
Two things: Welcome; you belong here.
And: If you think that one's bad, you need to look up the thread called, The Good, The Bad, and The Ugly! You're starting with, maybe not a queen, but certainly a princess, there! :Buds
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22 Jul 2020 03:18
Snglsmkr
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DT360a scrapper bike #3
Welcome! This is a good place to hang out when your fixin up a rider.
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22 Jul 2020 21:34
akara1
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DT360a scrapper bike #4
thank you all for the warm welcome. I spent today tearing into the bike and trying to assess what it needs and what I can repair.
first thing on the list with to try to unseize the engine
for my plan of attack first I unbolted The jug from the crankcase to see if the crankshaft itself was free.


I was able to get the jug unbolted and was able to get the crankshaft to move. it was at that point I bolted The jug back on got a two-by-four and started beating on the top of the Piston with a sledgehammer.
eventually after around 30 minutes I was able to extract the Piston from the bore enough to reach the wrist pin where I could disconnect it.

imagine my surprise after removing the Piston from the bore I found after a light hone and removing the stuck rings and giving the ringlands a good cleaning that the piston and bore seem to be in good condition with no scratches

this bike is coated in a thick layer of what I can only describe is oxidization iron oxide rust and mud mixed with 2-stroke oil. I tried washing it with my gas powered pressure washer and it didn't put a dent in any of the mud on the engine can only diligent work with a steel wire wheel would cut through the mud.I managed to get it stripped down to the bare frame with only a few casualties such as snapping bolts off for the instrument bracket,the exhaust, and the oil tank.

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22 Jul 2020 22:00
apex
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DT360a scrapper bike #5
Sounds about right :side:

Good progress!!

Allrighty Then

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23 Jul 2020 20:06
akara1
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DT360a scrapper bike #6
cut up my stock muffler today based on inspiration from user Meis here on the forum
not exactly sure how anyone else does this as i couldnt find much info on it so i just went for it.
I had some dimensions from a book for the RT2 MX as well as MX360 expansion chamber dimensions.
Got an idea from these that the rear baffle cone should be around 6-7 degrees.
I made a cone up from 20ga sheet that was 91mm by 24mm and 275mm long, which is a 7deg cone.


I took this cone and held it up to the end up the factory muffler where I thought I should place it, and I sectioned the stock muffler with a sawzall where I would need to weld the cone to the belly. I also made the cone out of 2 peices to make it fit the angle, and also its much easier to form two smaller cones by hand than a long single one. After I cut open the belly of the stock muffler I found it to be a double wall construction with fiberglass packing and perforated steel inner layer. Heres a photo looking up towards the header.

As well as this in the back it has a baffle "plate" instead of a cone.

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23 Jul 2020 20:15
akara1
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DT360a scrapper bike #7
Once i realized there was a baffle plate and packing and a tube in the back taking up a bunch of room I decided to remove all that to make room for the new baffle cone I was going to shove in there. I sectioned it once again towards the back as well as I drilled out 1 spot weld that holds in the baffle plate and removed the plate, I cut out the inner layer and cut down the baffle tube with a sawzawll from the rear section and removed all the fiberglass.



Once this was done I Hammer in the baffle cone into the rear section and trim it even with the existing cut I made. I weld the edge together so that the final chamber will be air tight.



With the rear section done and ready I pull some of the packing out of the edge from the front header side section I cut, and pinch the layers together so that it makes a smooth transition to join where the new cone is before I weld it back together


Then once this is done I weld it back together! all done!


Once I hit the welds with a flap disc and hit it with some paint It will be very hard to tell its been modified!
For anyone interested in more detail about the dimensions of the pipe, I made a little image here that compares the RT2MX, MX360, stock muffler, and my own creation, along with what RPM each should be tuned for based on my own calculations, I havent been able to try the pipe just yet!

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23 Jul 2020 20:19
RT360Fan
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DT360a scrapper bike #8
Very nice work

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23 Jul 2020 20:28
mdscott
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DT360a scrapper bike #9
I knew the 74 DT’s Exhaust were choked, now why my Dt360 runs better with Meis’s sleeper pipe.
Nice project you got there. Good thing the piston and bore are good, that will keep you on budget.

Thanks Mark
Roseville, Ca.

'06 GL1800
'98 KDX220
'75 Norton
'73 CB500K
'01 Honda CT110
'87 PW50
'64 McClane Edger
'02 Honda XR80R

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28 Jul 2020 22:36
akara1
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DT360a scrapper bike #10
Got my frame back from blaster this weekend and put some work into the bike,
Painted the frame and triple clamps and swingarm with black epoxy
I kept a spot on 2 of the engine mount tabs bare for grounding as well as masking the threads for the coil so it grounds.

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Purchased these chrome signals 30 bucks for a set of 4, was able to make them fit the bike nicely.
I put some work into straightning the fender, as it was caved in when I first got the bike, but I didnt bother too much with the little dents and dings it has, because its a dirt bike and the fender is covered in factory spot weld marks anyways. I painted the fender and the headlight brackets Alabaster silver which I think is a honda color. My bike did not come with the original thermoflows and I did not feel like fitting them, I used to have some and was not impressed! I am going to try these chinese shocks at 60 bucks a pair cant be worse than what I had, I have used them on another DT and they worked decently, 13.5" long.

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Next thing on the list for me was to fix up the engine cases, they were in quite rough shape with gouges and the sprocket cover was exploded, sadly I did not have the missing peices for it either, but I was able to repair the sprocket cover with some aluminum brazing and some 1/8" flat stock that I formed with some heat. It's not quite the same shape as original but I'm glad I was able to repair it to my satisfaction.

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I then turned my attention to the clutch and magneto covers, as well as the cylinder and head, all had lots of corrosion and needed lots of sanding to get rid of the white dust and pits.

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I was able to get them polished up decently, I just worked on them until I felt i was happy with them, not a mirror polish. I put a clear coat over all the polished stuff, I am going to hope it doesnt look too bad when it wears off.

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Then it came time for me to deal with the seized up bottom end that was covered in oil and wouldnt shift, and had a rusty crank.
I was able to source a cheap used crankshaft from ebay for around 100 bucks, it was straight and the rod has no pitting and is very smooth and tight like new, but the only thing was the threads on the primary side were a little messed up from whoever removed it.
I split the cases and removed the old crank rather easily with some tapping. I warmed the cases and installed some new Japan 6306 C3 main bearings, nice and buttery smooth, they dropped right in after I pulled them out of the freezer.

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While I was in there I cleaned out all the grime and clutch material that had built up in the old transmission and tried to figure out why it wouldnt shift. When I pulled the cases apart I noticed this roller fell out.

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Mysterious I thought at the time, I was not thinking about the shifting issue and I assumed that the roller was from a bad roller bearing in the transmission.
After some closer inspection I found the pin missing from the shift selecter drum, and the retaining tab meant to hold it in place broken!

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Without the pin in place the shifter mechanism was unable to advance the drum past 2nd gear. Perhaps the reason this bike was parked? I refit the pin to its home and put a NOS plate to hold it down.
And with that sorted It was time for the cases to go back together.
I fitted the crankshaft to right side case first, against the advice of the service manual (!)

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I am working on this bike with only some basic tools, I dont have a crank puller, though in hindsight I should have made one or purchased one. My method was the same as the bearing installation, This time I froze the crankshaft overnight as it has some thermal mass to it. As well I also spent some time gently warming up both cases.
The crank slipped easily into the right side, I went to go install the left side case on, and the shift fork rod fell out of place, causing the forks to fall from their channels in the shift drum, which delayed me just long enough for the bearing in the left case to grab the crank while not being installed all the way. This had me quite frantic, as my case sealer was drying! I was able to pull the case togother gently with its own bolts by turning them all in series a half turn at a time, I gently warmed up the bearing race with propane (not too much to discolor anything), and everyhing finally popped into place with no warps or cracks, the crank turns nice and smooth with no binding. Quite a bad idea to do it this way and I learned my lesson against installing it on the wrong case half and not using the proper tools.

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Finally cases together, smooth nice condition crankshaft, nice clean decently shifting transmission!
I also figured out where the oil leak on this thing was coming from, At some point in this bikes life it had a replacement left side crankcase fitted to it, probably from another chain exploding incident. The case on it now has no engine number punched into it. As well as this, I found that it was missing the blind plug that goes where the shift fork rod goes in the case! I was very confused by this for a few minutes.

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In the spirit of honesty here I will tell you all about my adventure with the primary gear nut.
When I bought the crankshaft I knew the threads on the crank were not perfect, but honestly they looked OK
After getting the cases together I tried for about 30 minutes to get the primary gear nut to thread onto the crank, but no matter what I tried It would go wrong or get stuck. The problem was that somene had hammered on it and this didnt visibly damage the threads but it increased the diameter of them, making it like 18.5mm. As well as this the end of the shaft has a keyway notched into it to drive the oil pump and this make the end of the crankshaft itself like a 2 flute tap of its own! very hard to get it to cooperate with anything but perfect threads. So i bought an M18x1.0 RH thread die and managed to fix up the threads. I ordered a brand new primary gear nut from yamaha as well. Once I did these two things all was well with the threads, but the Nut yamaha sent me was too tall and fouled on the clutch cover! So the crank wouldnt turn. I put the nut on the bend grinder and finally got everything installed and working OK.

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After I got the Primary gear torqued down I fitted a Yamaha Banshee clutch kit I got from ebay for 20 bucks. The frictions fit nicely, I soaked them in motorcycle oil before final assembly. I also filed down alll the ridges on the clutch basket.

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Finally with all that done I threw the top end on the engine, and put the engine in the bike, I just couldnt help myself

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And thats it for now!
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