Advice on an RD 250 build

[sprouty115]

Just a quick update: We showed the bike to my son on Christmas day and he was definitely very happy about it. But I also discussed in detail the work that would be required, both to get it back on the road and to kep it running. He definitely took the conversation seriously and we agreed to discuss it further after he had some time to think about it.

In the meantime we both decided the bike was worth getting road worthy so we dug a little deeper into the engine to see exactly what was going on. So after all the presents were opened we snuck back out to the shed and here is what we found:

• We pulled the clutch-side case and primary drive gear and then and measured the crank run-out. It showed .007 TIR. OK, so the crank needs to be re-built.
• Then we yanked the engine (took about an hour) and brought it into the basement to be able to work on it on a proper bench with better light and with some heat.
• The first thing I noticed was that the screws and bolts indicate that the bike has been worked on. Most of the phillips heads are pretty beat up and others have been replaced with hex-head bolts.
• Next, we pulled the heads and cyclinders and I showed him where the scoring was. They'll get cleaned and sent out soon too.

At that point we were sort of running out of time so we figured we'd call it quits. Then an odd thing happened - as I was moving the engine around I tipped it up slightly onto the clutch-side and out of somewhere rolled a single stainless ball bearing about .25" in diameter? The cases weren't split yet so this sort of surprised me.

Anyway now I'm into it and looking for a way to keep my son updated so he can follow along (the idea of us doing the work together won't really work for now). I may start a build thread or post it to a blog or maybe just keep this thread going? (thoughts anyone?).

[bykpimp]

I believe that ball bearing goes on the end of the clutch push rod shaft.

[sprouty115]

Excellent, thanks.

[markjenn]

Originally Posted by sp115

I may start a build thread or post it to a blog or maybe just keep this thread going? (thoughts anyone?).

I'd suggest you just post here. You already have a following.

I like your approach. Do the minimum to get it mechanically sound and running and don't worry about the cosmetics. Way too many folks start by tearing the bike down to the last nut/bolt and money on paint and polish. Most lost interest and the project becomes a basket case. Get it running and on the road.

- Mark

[sprouty115]

Originally Posted by markjenn

I'd suggest you just post here. You already have a following...
- Mark

Actually that's a good point, and I also could use the help the deeper it gets. I'll send him a link and have him join in.



OK, I've got the case split and here is what I've found so far...




Crankshaft - This thing is definitely whacked. The primary side actually has .010" TIR; the stator-side has .027"; the web/counter-balancer(s) show visible wobble (left/right). Heck there are even some jaw marks where someone clamped the crank in a vice! I've already sent an email to Lyn Garland at Vintage Specialties and he gave me pricing for a rebuild (around $600). But I think I'll email him back and see what his concern level is about the condition of the crank. I do have a local option for a used crank and stator for $120, which should be in better condition than what I have.


(vice marks in web - also note how the bearing wasn't positioned/rotated correctly by the person that did the last tear-down, the raised dot is supposed to mate with machined notches that are in the front where the cases meet)




(points cam with deep pits)




Pistons - they both show signs of scuffing but there is no damage to be concerned about. They also measure 2.116" (53.76mm). I believe this is the stock size, even though one of them has #5 next to the arrow on the piston crown. The cylinder bores also show some slight scuffing and measure 2.128" (50.05mm). I plan on doing the top end too and Lyn Garland recommended Bore Tech in Ohio, so I sent an email off to them for some info and pricing.

(piston top - cleaned up a bit with a wire brush)


(piston side)




Obviously I wasn't expecting this from a bike that is supposed to have only 6K miles on it, especially since the rest of the bike is so clean. Oh, well...next up cleaning the cases and more inspection.

[lrutt]

pistons actually look fairly normal for those miles, what does the cylinder look like.

That price for a rebuilt crank is pretty good. Just make sure the tack weld it up after pressing together so it will stay put. for all that work, I'd get the crank rebuilt vs used. At least you'll know EXACTLY what you have. Stator should be easy to source.

You could always buy a used motor/bike and have all the spare parts you need. Chances are you'd only need a top end job then. Just a thought.

Don't scrimp on that bottom end though, and make sure you have a reputable shop do the bore job. Personally I'd stick with stock pistons and go with the recommended clearances vs Wiseco forged with larger clearances. Wisecos will rattle more and unless you plan on racing, the stockers will work just fine. Do a good job of testing your autoluber just to make sure it's working, then properly bleed it when you get it back together. Run synthetic 2 stroke oil.

I just got my little Suzy T250 going last year. Didn't need near as much as yours but sure is a fun little ride. Will cruise at 60mph all day long as it's not even on the pipe yet at that speed.

Good luck.

[sprouty115]

Cylinder bores look about the same.
Looked around for an engine, in fact I'm still looking. Frustrating doesn't begin to describe the process.
As for the crank, even if I get another one I'll have it rebuilt. Bore Tech was recommended for the cylinders by Lyn Garland who gets high praise over on the 2-Stroke World site. Still waiting to hear back from them.
Thanks for the suggestions on the pistons and autoluber (currently disconnected).

[markjenn]

As I recall, there are some RD specialist engine rebuilders scattered around that do good work. You might consider just throwing the engine in an ice chest and shipping it to them. They know exactly what to look for and the tricks to getting a reliable engine.

- Mark

[sprouty115]

That would be the sensible thing to do, but I've already bit the bullet (and truthfully I'm really enjoying it).


Top end by Soapy Loofah, on Flickr

[sprouty115]

Crank - Got that sent off today to Vintage Specialties. Lyn gave me the heads up that it fits in a medium size flat-rate USPS box and ships for $11.75.

Also figured out how the crank got bent on the stator side - take a look at the back of the rotor and the giant chisel marks.




BTW, the back rotor (the piece with the all the marks) is loose and can rotate pretty easily. I assume it's not supposed to be able to do that?

Compare this with the image above.



Cylinders - spoke to Bill at Bore Tech about the getting them bored and honed. $65/cyl, seems pretty reasonable? He suggested adding .50mm to the bore size (I measure 50.05mm) and ordering the appropriate pistons. That would put me at 2nd-over. He also suggested ordering the pistons and sending them to him along with the jugs. Doesn't seem to be as much out there for the 250 as there is for the 350, but there are some available from HVC Cycle.

Other fun stuff - cleaned up the heads.


Started making a list as all the gaskets, seals and screws will need to be ordered and I don't want to forget anything.
https://docs.google.com/spreadsheet/...kNxa3l6QWVxeFE

[Vince]

It was a common mod to put the 350 topend onto 250s,that makes them considerable faster.Enjoying this thread,my first road bike was an RD 250 a very long time ago

[Shocktower]

Originally Posted by bykpimp

I believe that ball bearing goes on the end of the clutch push rod shaft.

Muffler bearing Yes clutch push rod

[RodT]

Check out Scott Clough Racing for the crank and cylinder rebuilds. He is the best around and I have used him several times and his work is excellent.


http://home.earthlink.net/~scloughn/index.html

[sprouty115]

Yeah the upgrade to a 350 would be nice, but I think I should leave that as a future option.

As for Scott Clough, I appreciate the link and I'll bookmark it, but I committed to Vintage Specialties.

[anonny]

Id recommend Wossner pistons if they make them got your year/ model

http://wossneronline.com/forged_pist...Path=50_71_111

Awesome forged pistons!