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RD350 Project Mustakrakish

Started by bostontrackrat, May 22, 2020, 12:26:31 AM

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bostontrackrat

#105
So some interesting developments today.

First, the RD400 race bike shown above:  Turns out, it's not an RD400.   Upon closer inspection, it's an RD350, with RD400 wheels, swingarm, and gas tank.  This works for me.  The RD350 motor allows me to have full parts interchangeability with my street bike, and the boxes of parts I've already collected. (and I've heard the 350 likes to rev better at the track anyway).  The RD400 wheels and longer swingarm will provide more stability in corners, and the tank with its knee cutouts is easier to grip on when leaning off the bike.

Second:  I had a Eureka moment while inspecting the street bike's engine today.  I still couldnt figure out why it had stopped spinning in the bike.  Re-reading here I took quocle603's suggestion and pulled the cylinders back off to check to see if the retaining clips were still in each side of the pistons (they were).  While doing this I happened to notice this on the side of the engine.





Whatever idiot assembled this engine (yours, truly) didnt torque down the nut on the end of the crank!  Incredible.

There's a suspect circular mark at the corresponding spot on the side cover.



I think I've solved the mystery of the seized engine.

The last couple threads on the end of the crank are a little smushed now, and it's really hard to try to get the nut back on, so I'll have to go find a tap to clean it up.   In the mean time, a question for you guys.   The large washer behind the nut, that retains the primary drive gear and woodruff key is shaped.  1: is it supposed to be or is this damaged?  2: should the concave or convex side face in towards the gear?





Thanks in advance!

85RZwade

Rather than buy a die to clean up those threads, consider a thread file. A far more versatile tool to have :twocents:
I post waayyy too much

pidjones

Quote from: 85RZwade on July 20, 2021, 12:23:03 AM
Rather than buy a die to clean up those threads, consider a thread file. A far more versatile tool to have :twocents:
I agree. That would be a one-time use die, but a thread file proper pitched would see many uses. Have to admit though, I'd hit it with a needle file. Should only have some soft embedded aluminum fouling the threads.
"Love 'em all.... Let GOD sort 'em out!"

bostontrackrat

Thanks guys.  I had originally thought of just filing it, but was afraid of screwing it up.  But I'll give it a shot.  I'll stop by Harbor Freight and grab some needle files and I'll go extra slow and steady on it.

rodneya

Thats a type of lock washer. I always install it with the bulge facing out and some blue locktite on the nut.

bostontrackrat

Thanks guys!

The file worked well on the crank, but the threads in the nut are messed up as well, and I cant get to them with the file.  I've tried just running it on and off a few times, but it still gets really tight when it's on, so I wont be able to get an accurate torque spec when I tighten it down.   Does anyone have an extra one in their stash they could part with?   I'm also going to rummage through my parts bin later today.

SoCal250

Rodney is correct on the washer. It's a belleville type, the concave side faces the gear.

FYI, the nut is still available new from Yamaha for about $3.
Yamaha 90170-16425-00 NUT
75 Yamaha RD125B   75 Yamaha RD125B (project)
75 Yamaha RD250B   75 Yamaha RD200B (project)
73 Yamaha RD350     77 Yamaha RD400D   79 Yamaha RD400F  
91 Yamaha TZR250R  89 Yamaha FZR400   05 Yamaha FZ6   
05 Yamaha XT225TC  82 Honda MB5  02 Aprilia RS250 Cup (sold)

bostontrackrat

Thanks!!  I ordered it up from Partzilla, should be here mid next week.  In the meantime, I just got a pile of jets in from Economy Cycle, so I can start tuning the race bike.   That's one's gonna need a name too.

85RZwade

I post waayyy too much

bostontrackrat

Quick update:  Got the replacement nut for the crank, and got it installed, went on nice and easy.  I timed the engine, got it back into the frame, and setup/adjusted the clutch.  I'll take pictures tomorrow.

Question:  While timing the ignition I discovered that TDC has a bit more of "notch" to it than I remembered previously.  I know there is supposed to be a bit of a "no mans land" at that point, but it seems more pronounced than I expected.  It also seems more subtle at TDC on Cylinder 2 than on 1.   Otherwise everything seems to turn smoothly and quietly.  Cause for concern or is this normal behavior?

m in sc

i hear ya. well, you can put a dial gauge in it, and measure angle from 1mm btdc and 11 after tdc on both cyls and see if the angle is the same. IF its not, it may show a worn rod or wristpin bearing. (on the 'longer duration' one)

:twocents: