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Other 2 strokes / Re: Mending small crankshafts
« Last post by robrd on September 17, 2022, 05:14:59 PM »
Have you seen some of the crank rebuilds on you tube done in back street sheds, their tools include hammers only, lump and sledge, but, They seem to run OK!
Aircooled RD Tech Help 250cc and Above / Re: RD400C transmission oil disappeared?
« Last post by robrd on September 17, 2022, 05:09:47 PM »
Try putting a catch tank, (bottle), on your gearbox breather pipe and take it for a run. Like said before, after just twenty miles loosing that much oil you would be lucky if your motor run if it was leaking into the crank and would surely oil your plug up. After a ride, check the catch tank and if it's empty it's a mystery.
Aircooled RD Tech Help 250cc and Above / Re: RD400C transmission oil disappeared?
« Last post by bitzz on September 17, 2022, 04:52:00 PM »
The pistons go up AND down. Half the time the crankcase has positive pressure, half the time it has negative pressure.
If the thing sucked back 1.5L of oil in 20 miles the plugs will show and the thing would smoke like a bear.
A leak down test is in your future.
Other 2 strokes / Mending small crankshafts
« Last post by martin1957 on September 17, 2022, 04:05:29 PM »
I had a small 2T tiller and filled it with straight petrol by mistake. Ran it at full throttle continuously and after 15 minutes it stopped dead. Seized. Its a 26cc vertically split engine. Piston port, Ball bearing mains, caged roller big and small ends.
After a bit of fiddling I worked out it was the bottom end. Pulled it apart and it was the big end caged roller broken up. Everything else was fine.
Using a big pin punch, club hammer, and big vice I drifted the end pin out. I read the numbers off it and got another for £2 on ebay.
I dropped it onto the old end pin that was only discoloured, not damaged.
I hammered the two halves back together, until they were the original distance apart.
To true it up I kept putting it in the crankcases and trying to spin it. Some taps to turn the crank webs a bit and more trial and error until it span freely when both the vertical crankcases were put together.
It took a bit of hammering but it now works perfectly.
Some nay sayers will say you need special equipment etc, but with nothing to lose I tried this and it works fine.
I would be interested to see images of a worn one as in normal use, nothing touches it except oil. Corrosion due to water could get it as well....
Aircooled RD Tech Help 250cc and Above / RD400C transmission oil disappeared?
« Last post by Eugene Haymes on September 17, 2022, 03:51:07 PM »
I just finished having my bike partially repainted (frame, engine cases) and some new parts (no engine work done). I added 10W30 oil to the transmission to the proper level. On my first ride of 20 miles, I started hearing a hissing sound in 6th gear. When I got home, it would not downshift below 5th. There was no oil in the transmission that I could measure. I put oil in it today and it is not leaking onto the ground. Where did the oil go? Can it be sucked from the engine through the crank center seals? I would think that the crankcase would have a positive pressure. I am broken hearted. 
Aircooled RD Tech Help 200cc and Below / Re: yamaha labyrinth seal, for 100cc 125 cc twins
« Last post by GTDWH on September 17, 2022, 10:58:36 AM »
Hi all, yes I do have one, if any one is interested I could take some photo's showing the dimensions. It came a few years ago with an RD125, 1975 I think, along with a couple of other crank parts. Being as there are no parts touching the labrynth I wouldn't have thought there is much wear if any?
under normal circumstances they work just fine, it's over time they wear, given how some bikes are thrashed and ridden very hard, they do wear and are needed from time to time.
I just got a rebuilt crank back, which didn't need one, so I still have 2 new labs, but have 2 more cranks to get rebuilt.
over all they have stood the test of time, in the past when I was in the trade, most were needed after an engine failure, or very high mileage.
Biggest problem now for anyone needing 1, is they are very rare and hard to find.
When you do find 1 the price tends to be very high, 1 on ebay now for around £200

Aircooled RD Tech Help 250cc and Above / 1975 RD350 aAir Filter Question
« Last post by chilly56 on September 17, 2022, 03:33:50 AM »
I have two UNI filters on my RD, don't like the way they're crammed in the frame. Want to do the Y-boot with single filter mod. Any suggestions on what size filter fits the boot and in the frame ?? Appreciate some advise...thanks!
OK, as per  @pidjones recommendations,
-Threw out Clymers(trash)
-I reset the handlebar clutch adjuster all the way in.
-Loosened engine side clutch locknut
-Turned screw and backed off an 1/8 or so(like factory standard)
-Started up bike and still wouldn't move but it kind of tried(improvement!)
-Started turning out handlebar screws(tightening) and got more movement
-fiddled with engine side setting and handlebar adjuster in relationship to each other.

Seems like engine side needs to have a lot of play for maximum movement for the wormdrive
Whereas the clutch handlebar lever needs to be tighter so the cable is most responsive.

On another note that may be of interest, I never touched this engine-side adjuster since I got the bike and with the lower and upper adjusters sort of sync'ed for best performance the throttle response has been so much better. I am wondering if the old cable(and new) just didn't get the plates engaged correctly. When the clutch pull arm can be actuated with the best leverage(handlebar) and distance(worm drive) the shifting and engine surging/gugging has stopped.. So I am guessing it was partially engaged the whole damn time? I was tearing up the neighborhood shifting nicely and no throttle weirdness which I assumed was a carb issue

Thanks so much again! Rebuild adventures continue

Another set of meaurements would be good, to compare with the ones we have.

Does anyone have close-up photos of a worn labyrinth seal?
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