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02 Sep 2019
Your admin has not been on the site much as of late as my main computer apparently seized up :( I have had limited access, but will be back soon. Thanks. Mako
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TOPIC: Testing Transmission

Testing Transmission 08 Sep 2019 10:33 #1

  • Traderyoda
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When rebuilding an engine (complete tear down) how can you test to verify the transmission is working properly before sealing the case?

I closed the cases on my DT-1B rebuild and when I spun up the tranny I couldn't get into 5th. The case was freshly closed so I just popped it apart to see what was going on. I haven't gone hunting for the problem yet, but before I close things back up this time I want to be sure all's well before sealing the cases.

When assembling, I installed the crank in the left case with a puller (no crank shims on this motor) and the tranny in the right case, apply the goop (Yamahabond 4), and pulled the cases closed. Everything went together smoothly. I did not install the crank or other seals. The tranny rotates smoothly without any alarming noises, but I did not pull apart the tranny. I did the dumb thing and assumed the tranny was good because I didn't see any obvious issues. The motor was not in a running bike and I didn't spin up the tranny before dismantling to see how it worked (another mistake).

I'm sure I'll find the problem, but I wondered what I can do to test things BEFORCE closing things up... again!

Thx

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Testing Transmission 09 Sep 2019 11:37 #2

  • Traderyoda
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I found the problem... a spot of corrosion and a rough spot on the drum that was hanging up the fork. Polishing everything back up on the drum and inside the fork and all is well again. Still would like to know any tricks regarding ensuring things are well before sealing the cases.

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Testing Transmission 09 Sep 2019 14:20 #3

  • MarkT
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Bench shifting a trans is always "clunky". You'll need to spin the shafts.

On the 125/175 you can install the trans in the right case and test it pretty good... if I'm really concerned about something I'll install the trans in the cases without the crank or any sealer... for that matter on the smaller bikes the right side crank bearing is a slip fit so you can usually leave the crank in the left side case and take cases apart and put back together to test and check before sealing.

Been a while since I did a DT1 so I don't remember if something similar can be done. Almost certainly installing the trans in the cases without sealer or the crank installed can be done.
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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

Testing Transmission 09 Sep 2019 19:45 #4

  • Pedalcrazy
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On my DT400 I reassembled the complete assembly and wondered the same thing....Bought it not running so didn't know. Before putting the two halves together I rotated the assembly with one hand....tricky since the other case isn't holding everything together...and turned the shift drum with the other. You only have to rotate the assembly enough to see that one shift change happens. Find first gear with the shift drum. Put the shifter detent in to help get the drum exactly where it should be for each gear. Once in first gear I counted the revolution of the chain sprocket with a rotation of the crank. Next, turn the shift drum thru neutral to second gear...rotating the trans assembly again carefully to allow the forks to move the gears. Count the chain sprocket revolution again with one revolution of the crank. Continue this until you reach 5th gear and make sure your sprocket spins faster with each gear change/crank revolution. Happily I found mine worked flawlessly and confirmed when took it for the first ride. Hope that helps.

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Last Edit: by Pedalcrazy.

Testing Transmission 10 Sep 2019 05:48 #5

  • Traderyoda
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Thanks folks - great help. I figured that I wasn't the first to deal with this.

It became obvious to me that the best way to assemble the case was to pull the crank into the left case and install the transmission in the right. That's what I did when I first put it together and all went well - just wish I hadn't taken anything for granted. The transmission has almost no wear so I assumed... always bites me when I do that.

Since I didn't want to pull the crank I tried to avoid joining the cases to test things and just marked where the detent would be and slowly walked through the gears, count the revs on the output shaft as Pedalcrazy says. On this engine, the transmission shafts are very tight fits in the bearings on both sides. So when you put the cases together, without the crank, it's a pain to get it back apart. As MarkT mentioned, this hand spinning business is not ideal, but at least you can see the gears doing their thing and gain a decent amount of confidence that everything's working.

For anyone reading this, take the time to completely disassemble the drum. The tolerances inside are very tight and the slightest imperfection can hang things up. Don't put it in until it's butter smooth and lube with lots of tranny oil.

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