my new/used Yamaha PW50 thread

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my67xr said:
what are the first 4 digits on the head tube ?
and are they the same as the numbers/letters stamped into the case on the underside of the engine ?
Click to expand...

I will let you know when the frame comes back since it's getting fixed/modded atm. The numbers on the motor are 4x4006424 :) thanks mate
 
yours is an '81 PW50H same as mine, 4X4000101 >
an '82 PW50J is 4X4200101 >
 
WOW i'm actually shocked at how old it is. wow. So that makes them 33 years old. Thinking that kids mostly ride these bikes and then they get passed around to family ect. It would have had so many kids learn how to ride it, so many crashes and stories and only god knows how many different owners lol. I wonder how much of it is original. That piston looked that old aha

It's so old aha Thats amazing. I thought it was around 83-89 but I wasn't sure about it. Thanks heaps for finding that out mate :) wow
 
went to tighten up the rear wheel etc, and found that the tyre did foul on the r/h side
so i had to modify it to suit, it now clear the swingarm by 5mm
i'll finish it on sometime today and repaint it (zinc etch primed in pic)









 
thanks,
i shouldn't have chosen then to actually do it i think.
cause i still have a bit to do to my Atomik before the weekend, and now i have to find another tyre for the front of the PW to raise it to match the rear
the new rear tyre is about 35mm taller than the old one, and has lifted the back up a bit
i was just going to swap the new modified clutch in, so it was ready to go for the weekend.
but thought Morgan will be pretty sandy and he could do with some extra grip as well

and the rain over the last few days hasn't really helped either.
 
The bigger tyres should go good.Do you still have the stand under it ? Mine was catching on all the lumps so I took it off for more clearance and it worked a bit.
 
yeah the stand is still there, Cj only weighs 24 kg
i might make a side stand for it at some stage, then take the centre one off, but it does make it easier for tuning etc
 
after writing that above, i thought stuff it i'm taking it out and doing the clutch

so i pulled the engine out again,
here it is with the side cover off




now undo the circlip and take the clutch flywheel off




next i slid the old clutch off, and refitted the modified one (heavier springs and filed back clutch pads




i refitted the flywheel and circlip, and then the side cover, so it is now all back together.
ready for a test ride after school tomorrow
 
today i thought i'd check the piston/bore with the way it was running.
it all looked ok, just a it rich so i gave it a clean up/out.

thought i might do a bit of porting/polishing while it was apart.
i opened up the top of the exhaust port and widened it about 2mm, this will help the gases escape easier
i also semi knife edged the transfer ports, and the intake port to help it flow better
and cut back the short returns a little as the ports enter the cylinder.
when i refit the cylinder i will use 2 base gaskets to lift the exhaust port and give it more flow
the standard PW50's piston sits 3.5mm up past the bottom of the exhaust port.













and i also cleaned up the head inside and out.
the flat silver i used when i sprayed it the first time stained easily, and was hard to clean.
so i rubbed it back and resprayed it with a silver base, and a couple of coats of clear engine enamel to seal it all.
and i repolished the combustion chamber as i didn't spend much time doing it the first time, and i had left a few scratches



 
so i just fired up the PW...

jeez what have i done ????? :confused-smiley-014
 
Yeah what did you do to it ? You beat me to porting a pw but i'm kinda glad that you did it first to iron out the kinks lol. I'm going to do it to mine if you don't have any problems with it :)
 
ok, so i fitted the big front tyre, it just fits
but i'll need to make the stand about 1" longer so the back wheel will lift off the ground.

now, the engine/starting it up.
i started it after getting it back in and set up, the thing revs pretty quick
it is definately louder too, so more exhaust must be getting out

the clutch mods,
hmm i must remember to try one thing at a time
high stall springs, and half the friction material work really well....... for a drag bike
it needs to be at about 4500 rpm to start moving now, instead of the standard 1600 rpm or so

Cj had a couple of rides on the driveway, he took a bit to get used to it.
i wish we had a big long area to try it out on here.
but i think i'll pull the engine out again and try it again with the standard springs and the half clutch pads.


i can blip rev it now to 3500 before the back wheel starts to spin
 






i had to cut the rear fender mounting bracket off and move it up about 25mm too, to give the tyre some more clearance






uni filter is now on, i need to make up a snorkel to raise it up a bit though, it rubs on the frame




and i also modded the brakes while it was apart,
i cut some diagonal slots into the brake shoes, so they bite a bit better when you use them
 
thats very similar to how my boys ktm nock off was set up when it showed up brand new, made it almost impossible to ride. ended up getting the local bike shop to add more washers in to the clutch set up which dropped its engage point by about 2000 rpm
 
wow that's awesome in a way. I'm pretty sure my clutch has had some work done to it all ready but still way less then yours ahaha That would be so fun to ride.

So the porting went well then ? Could it be because of the double base gaskets though ?

You should post up a video before you fix the clutch up again.
 
yeah definately do the porting
i made both the new base gaskets for it, i used some 1mm thick gasket paper, it was a bit fiddly to do but they turned out good.

 
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