Vintage Project - Yamaha DS7 - 250

[wheatonFJR]

We coulda had that all apart for ya at tech day!!

That's what he was afraid of.

[CollingsBob]

A 2 stroke is just a pump ..and in order to pump efficiently there can be no leaks. New seals all round, most of which van be purchased at any bearing supply, careful cleaning of mating surfaces and a thin coating of Hylomar on the 2 halves of the crankcase, new cylinder base gaskets, careful port matching should do the trick.

http://hylomar.com/hylomar-product-rang ... compounds/

[extrememarine]

Trying to keep all the parts and pieces semi organized as it comes apart...

We coulda had that all apart for ya at tech day!!

That's what he was afraid of.

[CollingsBob]

Match the profile of the top of the port to the piston skirt bottom as well as matching the intake & exhaust tracts..small changes will yield good results....and if those modest gains arent enough for you then I think any 350 engine from the R5 to the RD350 will fit into that frame. You might also consider changing the swing arm bearings for ones made out of bronze for greater cornering precision.

[extrememarine]

Thanks for the input, but right now, I'm not interested or funded to turn this into a vintage track bike. I have read plenty on the potential of these little 2 strokes should one want to go that direction AND have the open ended checkbook to fund it...

I just want to get it running and to be able to cruise around the neighborhood.

Match the profile of the top of the port to the piston skirt bottom as well as matching the intake & exhaust tracts..small changes will yield good results....and if those modest gains arent enough for you then I think any 350 engine from the R5 to the RD350 will fit into that frame. You might also consider changing the swing arm bearings for ones made out of bronze for greater cornering precision.

[philharmonic]

Match the profile of the top of the port to the piston skirt bottom as well as matching the intake & exhaust tracts..small changes will yield good results....and if those modest gains arent enough for you then I think any 350 engine from the R5 to the RD350 will fit into that frame. You might also consider changing the swing arm bearings for ones made out of bronze for greater cornering precision.

Can't you just put a set of pistons, cylinders, heads and carbs off an RD350 right on an RD250?

[Hppants]

I'm still subscribed - glad to read this thread is resurrected.

That motor has a special place in my heart. When I was a kid, everyone wanted the Mach 1 Kawasaki. But I wanted the RD350. Maybe just a smidge (and I mean a SMIDGE) slower, but the bike could do so much more than go straight.

[CollingsBob]

Match the profile of the top of the port to the piston skirt bottom as well as matching the intake & exhaust tracts..small changes will yield good results....and if those modest gains arent enough for you then I think any 350 engine from the R5 to the RD350 will fit into that frame. You might also consider changing the swing arm bearings for ones made out of bronze for greater cornering precision.

Can't you just put a set of pistons, cylinders, heads and carbs off an RD350 right on an RD250?

I dont think so...I seem to remember that the bore size in the crankcase is smaller, the crank is different with a shorter throw and the connecting rods are shorter.

[extrememarine]

I'm still subscribed - glad to read this thread is resurrected.

That motor has a special place in my heart. When I was a kid, everyone wanted the Mach 1 Kawasaki. But I wanted the RD350. Maybe just a smidge (and I mean a SMIDGE) slower, but the bike could do so much more than go straight.

The farmer's almanac forcast is calling for a pretty harsh winter. That means more project time in the garage. My goal is to chip away at it a luttle each evening, and update weekly here for those interested...

Sent from the Tapatalk app...

[Uncle Hud]

<clipped> I have read plenty on the potential of these little 2 strokes ...

My late 1970's RD400 was a screamer. Wouldn't think you'd need any engine work to make it track-worthy.

[bungie4]

Stumbled across this rd250..

https://m.imgur.com/gallery/NcQxlCt

[extrememarine]

Stumbled across this rd250..

https://m.imgur.com/gallery/NcQxlCt

Very nice and clean! I've seen some very cool looking cafe RD250s, but part of me just wants a near stock runner. After that, who knows...

Sent from the Tapatalk app...

[philharmonic]

Match the profile of the top of the port to the piston skirt bottom as well as matching the intake & exhaust tracts..small changes will yield good results....and if those modest gains arent enough for you then I think any 350 engine from the R5 to the RD350 will fit into that frame. You might also consider changing the swing arm bearings for ones made out of bronze for greater cornering precision.

Can't you just put a set of pistons, cylinders, heads and carbs off an RD350 right on an RD250?

I dont think so...I seem to remember that the bore size in the crankcase is smaller, the crank is different with a shorter throw and the connecting rods are shorter.

It doesn't prove it will work, but the rd250 and rd350 had the same 54mm stroke, the 250 was square 54 x 54 and the 350 was 64 x 54. I could see that the bore being bigger could preclude the jugs working.

[CollingsBob]

I started out with an R5...then after I blew the transmission I replaced the entire engine with one out of an RD350...then I replaced the front end so that I could replace the drum brake with a singke disk. Then I started port matching, putting extra ports into the pistons, drilling the reed valve stops in order to maximize reed valve lift. Expansion chambers led to an increase in main jet size to 220, at the same time the stock airbox was discarded in favour of K&N’s..Clipons and rearsets got added at the same time as a seat/tank/fairing from a TZ350. By now it was seriously fast, used a shitload of gas and needed pistons once a season. I had succeeded in turning a real nice, kinda fast bike into a stupid fast bike with a light switch for a throttle that was sooo single minded that it was no longer a lot of fun all the time. I sold it and bought a 750 Honda. Not as fast, way more reliable, cheaper on gas..and a fuckton quieter.
Now you know why I will never replace the mufflers on my FJR..

[raYzerman]

Trying to keep all the parts and pieces semi organized as it comes apart...

We coulda had that all apart for ya at tech day!!

That's what he was afraid of.

Grow a pair!! WE offered to help at Tech Day, but no, you have to do it your way. Just put in in a coupla boxes like I got and figure it out later. You'll remember... really! That RD motor should fit in one box, not two like I got this......... ya gonna come help me?

[extrememarine]

I think it was PhilJet that said it best..

"...still not taking my bike apart at tech day..."

With a little bit of progress, I hope to have this thing at the spring tech day so we can get it tuned and running...

[extrememarine]

Getting closer to similar status as Ray's bike in a box...

Everything from the steering head back has been disassembled. Front end is next after I get the parts bagged and boxed



Sent from the Tapatalk app...

[raYzerman]

OH my....... that looks way too organized

[wheatonFJR]

Looking good, cept mebbe that crack in your front tar...that you were replacing when the other stuff gets done.

I'm not sure, but from here it looks like the fork seals are installed upside down.

[extrememarine]

If Ray helps me put it back together, the fork seals will get flipped and end up right side up then.

I plan on running these tires - just going to add some gorilla tape to the inside to keep them together about 90...

Looking good, cept mebbe that crack in your front tar...that you were replacing when the other stuff gets done.

I'm not sure, but from here it looks like the fork seals are installed upside down.