6 Speed Vision

[The Prophet of Doom]

Issue 21 of the Rov Newsletter mentions Greg Stephenson's vision  bored out to 640cc with 90mm Ferrari Dino pistons and a 6
spd. transmission out of an RD 400 inside the cases and to top it off it's got a dry clutch on it.

OK so I'm pulling my engine to do some cam work and thought - where could I get myself a 6 spd setup that will fit the vision.  RD400s are just about non existent now.  Any done this before?  Are these fairly standard or all different? Any ideas?

[fret not]

This sounds like the fellow is not afraid of work.  I imagine the RD transmission doesn't just happen to fit the XZ cases without some fiddling, but maybe it could happen. ;)  My first thought is of the ratios relative to overall gearing.  Since the XZ has a fixed ratio for the rear drive the internal transmission ratios would need to have an over drive ratio for at least the top gear, if not the top two.  At least a higher ratio than the standard XZ transmission, otherwise there is precious little advantage since the XZ pulls well over a fairly wide power range.

A six speed transmission is attractive at first consideration, but unless it offers overall higher gearing it would just be 'bling' to have more gears.  This is where chain drive shines as it allows selecting final drive ratios.  Hmmmmmmm . . . . . .  8)

[dingleberry]

I would think a 6 speed gear cluster from a dirt bike might be easier to procure but not having much experience with gearboxes I can't comment about fitment. But it does get a bit mathematical I believe to have the gears optimizing the engines power/torque characteristics. The only advantage would be for racing perhaps to get closer ratio gearing. I agree with Fretnut about chain drive being a far more practical and easier mod.

[motoracer8]

 RD400's are chain driven, I wonder what was used for the main shaft?  Maybe it was converted to chain drive.

[The Prophet of Doom]

It's not just bling, but totally practical.  I've got the Euro gearing on mine - so better at highway speeds than US versions, but a bit slower off the mark.  The advantage with a 6 speed box is that you can have both and that's something you won't get by fiddling around with a rear sprocket.

[Ken Williams]

It may be a lot of work.  At best it could just drop in.  Vision and RD400 engines are from the same era.  RD 250, 350 and 400 transmissions are interchangeable.  The 400 is closer ratio when compared to the 250/350.  This is a RD400 transmission in a RD250 lower engine case. 

[fret not]

Those horizontally split cases are soooo much easier to work with than the vertically split cases like the XZ.  They all work, it's just that some are less difficult.

[The Prophet of Doom]

Comparing fiches it's pretty clear that although they share the same basic design they don't share a single part.   
This would not be a drop in that's for sure. 

[fret not]

It's time for someone with a RD to open it up and measure some parts with a micrometer or at least a dial caliper so we can compare them to the XZ parts.  I have a couple dial calipers and a couple XZ motors, one is apart now.

[Ken Williams]

Here are a few caliper measured dimensions for the RD:

Input shaft left side bearing OD:  30 mm
Input shaft right side bearing OD:  52 mm
Output shaft left side bearing OD:  62 mm
Output shaft right side bearing OD:  33 mm
Input to output shaft centerlines:  58 mm
Case side to side:  114 mm

[fret not]

Thanks, Ken, that's a good place to start.  I have a XZ apart so I can get some measurements for comparison in the next day or so.

Regarding the measurement for "case side to side", is that inside to inside? or overall outside to outside?

[The Prophet of Doom]

As far as I can gather from parts lists (350 - I couldn't find a 400 fiche - but I think they are similar) , the XZ has a fine spline, but the RD the same as the clutch spline which is coarse and square.
Good if you were going to run a sprocket, but perhaps a deal breaker if keeping the shaft

[Ken Williams]

The case side to side dimension is between the inside walls.  As I recall, The 350 and 400 have different sprocket splines, one coarse and one fine.  I think the 350 was fine.  Caveat:  details recalled from previous decades may not be accurate. 

[fret not]

 " details recalled from previous decades may not be accurate.  "

HAH!  You too?

[The Prophet of Doom]

Perhaps there are several sizes of course (square cut) spline - I've looked at a dozen 350 and 400 transmissions on ebay and none have the fine spline that the XZ does - this might not apply to them all of course - variations between years are done just to annoy.

[fret not]

Upon some semblance of scrutiny I see the transplanting of a RD transmission will be significantly more involved than a weekend project.  To begin with the transmission shaft centers are not quite the same, they miss by about 2 mm, and the bearing sizes are significantly larger in the XZ.  It is a difficult operation to measure the inside distance in the XZ cases as they are inside (flash: I just thought of a way to make the measurement, so, more later on that)

Needless to say, I doubt anyone here will expend the energy or funds to accomplish the transplantation of an RD transmission in the XZ cases.  Just at first view it would require significant welding up and machining of 'new' homes for the bearings on the countershaft. 

My caliper that reads in mm is a vernier type, so not sufficient accuracy for measuring transmission shafts.  It is very nice for down to about .2mm but machine gears and bearings need significantly closer accuracy.  I have a dial caliper that reads in thousandths of an inch which is pretty close, and I can convert to mm with a calculator if needed.

[Ken Williams]

It appears the idea of a RD transmission for the Vision has been put to rest for all but the most determined. 

I could not find evidence supporting my earlier assertion that RD250/350 and 400 have differing drive splines.  The picture I posted is a RD250 or RD350.  I also looked at 2 additional engines that are not disassembled.  This includes the race engine on which I remember replacing the RD250 transmission shafts with those from a RD400.  I would have to split the cases and count gear teeth to verify.  Anyway, these transmissions all have identical countershaft splines, 13 external teeth cut into a 25mm shaft. 

[fret not]

"Here are a few caliper measured dimensions for the RD:"
                                                                             
                                                   RD                     XZ
Input shaft left side bearing OD:  30 mm              42mm
Input shaft right side bearing OD:  52 mm            62mm
Output shaft left side bearing OD:  62 mm            72mm
Output shaft right side bearing OD:  33 mm          47mm
Input to output shaft centerlines:  58 mm             60mm
Case side to side:  114 mm                                 104mm

The transmission shafts each have a 20 and 25 mm end the bearings fit onto (each shaft has a big end and a small end, as indicated by the bearing sizes)

Fitting an RD transmission is not beyond human capabilities but also it is not a task lightly taken on as at least one shaft would have to be moved closer to the other by 2mm.  This is serious modification and fabrication = $$$$

Maybe the reputed XZ had the cases chopped off and attached the case and transmission from an RD. It might be easier than moving a transmission shaft. ::) :o :police: ;)

[dingleberry]

It's not just bling, but totally practical.  I've got the Euro gearing on mine - so better at highway speeds than US versions, but a bit slower off the mark.  The advantage with a 6 speed box is that you can have both and that's something you won't get by fiddling around with a rear sprocket.

This might solve that problem but would create a few new challenges.
http://www.ebay.com/itm/AMR500-Supercharger-BSA-Norton-Triumph-Honda-Yamaha-Harley-Quad-ATV-Snowmobile-/360449473866?forcev4exp=true&item=360449473866&vxp=mtr

Nice price... I spotted a kit for my Speed Triple and it was about 4000 GBP :o :o

[vl5150]

Interesting thread for me.  In addition to my Vision, I have a '74 RD350 and a '77 RD400.  I thought the Vision was small and light until I hopped on the 2 strokes, lol.  The Vision is now my "Harley" cruiser.