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1982 YZ250J *pic heavy*

Started by Nkreig, May 05, 2019, 02:17:28 PM

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Its good to see the site back up and running.  Big thanks to Mark!!   Last year I picked up a 1982 YZ250J off of my neighbor.  Over the winter I tore it down to see what I was working with.  This was the first year for quite a few advancements in the YZ line, some good and some not so good thoughts.  The mono shock, water cooling and power valve were the biggest additions.  With a little bit of research I found some solutions to some of the design flaws of this bike.  The owner prior to my neighbor already addressed the biggest design flaw, the radiator placement.  For some odd reason the radiator was placed behind the number plate mounted to the triple tree.  The engineers then routed the coolant through the steering stem and inside the frame.  When the seals aged and started to leak the coolant would destroy the bearings.  A popular mod is to bypass the steering head pathway and route hoses around the stem.  Another issue is the suspension, the rear is way to soft for anyone over #180.  RaceTech has some great offerings for the vintage motocross bikes so that is who I called to start gathering goodies to bring the suspension up to modern standards.  I picked up new front and rear springs for my weight,  gold valve emulators (front and rear), new bushings and seals for the front, a new seal head for the rear and all the accompanying accessories.  Next up was the engine.  I replaced all of the seals and gaskets.  Upon pulling the clutch side cover off I found there was a huge crack repaired with JB weld.  Something to note about repairing a bike with JB weld while everything is still assembled,  it does not dry in the presence of oil!!  So I had to clean everything inside the tranny and clutch side.  New side case and fresh oil then buttoned it all back up.  While I was in there I replaced the coolant pump impeller with a fresh one as well.  So as it sets today,  Everything is reassembled and cleaned but when I checked the compression i'm only at 135ish psi.  I'll get to that in the next post!  A post is no good without pictures, so here's some of the progress.....

This is when I first got it home.  Not a bad looking start.


Here are some more pics of the suspension and coolant rerouting....


Here is the cylinder I just picked up for it off of Ebay.  It does have some porting done to it but to what extent I don't know.  I am hoping and experienced eye can chime in and tell me what I have.  It has boyesen ports added but I have never personally seen them done as two small holes.  I was always under the impression you want them to be about a 1/2 inch in size but, again, I am not very experienced with porting myself.  Please feel free to chime in.

Banshee Hp

You could connect those dots. They probably didn't small enough carbide burrs to go in those holes. I start these with a .250" hole and 3/16 burr and end up 3/8.

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It been a minute so I thought I would post some updates.  The top end from Ebay now has the boost ports opened up and smoothed out.  Everything is reassembled with the exception of the head. When I pulled the old top end off the head had some damage to the dome.  I have another on the way in excellent condition.  At some point Im going to bead blast the old top end and send it off to have it refreshed and some legit port work done.   I'm having Jemco build a new pipe since the old one looks like it was used as a hammer.  Anyway, here are some fresh pics...