So it's been a while since i posted about the RD 350 "project" Looking a the post i last did it has been 3 years already. I should feel well rested after hibernating that long. In reality i got up to speed with several other projects and drove the RD around town and to work. Had lots of enjoyable times. But there's other projects lurking around looking for time on the workbench. And i've taken an interest in Flat-tracking.
So it was time to fix up some carburetor issues and addressing the broken of fin's of the left hand cylinder. Those eaten away fins bugged me ever since i dove in this project 7 years ago. Via facebook marketplace i managed to buy a pair of user RD350 cylinders with heads. I don't exactly remember why they were up for sale, but they came with a pair of unbranded pistons and the notification that they should be bored and honed to size. Also the seller stated that their machine shop suggested a larger size of pistons.
I've always wanted to fit the YZ85 membranes which i kept on stock, but needed extra room in the cylinder to fit. So this june i bit the bullet and pulled the head of this lovely bike.
Which got my engineering bits all tingly and you can clearly see excitement.
Here's the job laid out before us. At this point in time i thought this was a 2 weekend job. Weekend 1 pulling the cylinders off, fitting the membranes during the week, sending the barrels for boring and honing and fitting it a weekend later.
After cleaning the head, cylinder assembly and engine blok, i removed the carburettors, exhausts, gastank. And janked the Cylinders off, At first glance it looked okay. I was running 0.11mm and 0.09mm of play, the roundness of the cylinders was less than 0.04mm. Which in my opinion are reasonable values. Also no fretting or scuffing to be found. But the right-hand cylinder was bored 0.25mm larger than the left hand one. The bike didn't really seem to mind, except it always was running rough at idle.
With this found, looked on to other things as the unequal bore would be addressed with the new pair of cylinders. I to took it up to see if the right and left cylinder would match, on key features like port timing and compression ratio.
Out came the degree wheel, luckily i could use one piston from my own cylinder set pull the rings and time the left and right cylinder. They both matched up really nice (130° / 185°) with an 0.4mm bottom gasket.
Then i used a piece of PMMA (plexiglass) to measure both cylinder head volumes by filling the (rather exactly) with motor oil. Both are 16.8cc, with piston dome retracted at 1.2mm squish and the sparkplug taken out of the equation. which boils down to 1:12 compression ratio not to wild.
This means all light's were green to make fit this pair of beauty's. I had to find a way to fit those rediculously large YZ membranes. So out came the files, die grinder and pocket light.
Midway in the process, filing / milling and scraping away material in order to make larger things fit small holes.
One down and one to go,in the end i made a templet out of a gasket. Which helped me to rough it in.
After which there's a lot of trail and error fitting and fettling. In the end i got it to fit. After which i continued to use my trusty old wetting stone to flatten the sealing surfaces and my tap to clean the threads. Just after two weeks i felt confident enough to send the cylinders with new pistons out to get a fresh bore and hone.
After couple of days they lined up my cylinder and took a few cuts and i got a call from the workshop....
They were unable to get my bore clean! I had to invest in another set of pistons. so they can bore out a bit more. How ever it was "Vacation season" so i had to scramble to source new pistons in order to save these cylinders. Lucky i was able to buy a set of Wössner pistons in the right size up. so back to the machine shop they went.
The wössner pistons are coated with that friction reducing stuff, but also machined really nice. look at the difference in porting size, that should help performance.
The work still wasn't done, i had to take off the "lip" as this is only suited for the LC or Banshee cylinder porting. The Machine shop did a top-job during my holiday, making the cylinders straight and to size. I Did some additional deburring of ports as they felt sharp and i wasn't wanting the rings to snag.
I made a set of new paper bottom-gaskets and annealed the copper head gaskets. I tried to reuse the exhaust gaskets but i destroyed one while removing. Still everything assembled with ease!
I ordered a set of exhaust gaskets and Carburettor parts. I've switched to 5DP7 needles and different 169P0 emulsion tubes.
All assembled again in autumn, but looking pretty as ever.
Under the seat a word from the "sponsors"
Here i am raging with excitement ready to kick it over. The bike fired up the first kick, which is a really good sign always. She sounded angry and fierce. I went out for a short drive the next day. And got a few heat cycles in. How ever after i couple of runs i kept the throttle open at high RPM's and i could feel it lean out. so i ordered bigger main jets.
Fitting the 240 mains made it run fine, i can now put the bike in 6th gear. Strangle it to 55km/h and open the throttle (WOT) she'll accelerate without hesitation or spluttering right up until 170 km/h. For me this is an succes!
Unfortunately, it's winter storage time again. And I'm struggling with the number of bikes v.s. number of project on hand. The family needs a larger house, i'm wanting to go harder at this flat-track thing. So i'm thinking of selling this one, i'll need the cash and room... this'll end up in a couple of sleepless nights...
