Chit ya normally don't see, Diff disected.

[warp9.9]

Paul, You really have too much time on your hands .

Really appreciate the effort you put into pulling that diff apart. I was curious how the pinion was secured in the housing and now we all know. I wonder why Triumph never installed a taller 5 gear to lower the top end rpms. The engine has the torque to do it. Would cutting a new 5th gear set with a taller ratio be an option?

I doubt that could be done. Lets say you want to keep the same Diametral Pitch (probably a modal pitch because its metric)[Diametral or modal pitch is a ratio of number of teeth per inch or per 25.4mm of the pitch diameter or modal diameter of the gear. Now look at each gear take the fifth input shaft gear it would have to get larger not so bad when it comes to not disturbing the drive dogs on it but the engine case will not allow for much growth of the gear maybe a tooth or so I would have to put one back together to actually measure but from the pictures I have there does not seem to be a lot of room for growth. Anyway the bad gear 5th out put has the drive dogs for locking first gear to the splined output shaft. the dogs already are weakened from machining the gear teeth in it. this gear would have to get smaller most likely eliminating the dog teeth. So now you have to see if you can redesign the first gear dog drive slots meanwhile you cannot mess or change the inside diameter's of those gears. Not really going to happen without a new engine case design making room.

 

[warp9.9]

Great work Paul...would it not be easier to change the output gear/shaft ratio in the box...plenty of space in there.

Now since these are helical gears you can do a little more even though you can not change the center to center distance of the two shafts. Fortunate that the angle of helix does change the difference between the real pitch diameter verses the normal pitch diameter as calculated in spur gearing. this could allow adding a tooth on the output shaft helical gear and removing one from the helical gear on the torsional damper shaft. Provided you can do this without disturbing or redesigning the torsional spring drive mechanisms. Still a better shot here but it take some calculations. The reason this stuff gets to be pricey is since most gearing is generated verses using a involute cutter. Making the cutter for something of a limited run is about expensive as making a die to make one razor blade verses a few million hits before you need to sharpen or perform maintenance on the die. Still the tow helical gears look like the best option. Id you weren't just trying to change the engine rpm at highway speeds, I would recommend raising the engine rpm but clearly this is not for max speed.

 

[TURBO200R4]

13 DRIVE 37 DRIVEN = 2.85 ratio
14 drive 35 driven = 2.50 ratio enough to make a difference
would the 14 tooth have to be that much bigger?

 

[scot in exile]

A sixth gear would have been nice but honestly I rarely ever think about it.

 

[Paul Bryant]

So do we need someone who can cast a new housing or a bloody good toolmaker? Seriously, I had a mated who worked with CX500 bevels to us in a JZR car (Guzzi powered). He had some pretty fancy machining done by a toolmaker in Melbourne .... I don't know who though. Unfortunately, said JZR put him into a tree, so I cant ask him. I really think that this needs further investigation. Great start Paul .... some of you brain surgeons out there .... how do we do this?

LR, yes this is possible, but at what expense ?
Us blokes will spend a kazillion $ playing with our toys, like the guy that made this swingarm.
I heard around 10 grand to buy one !
CNC Machined from a solid block of alloy.
So yes it is a start.

 

[Paul Bryant]

13 DRIVE 37 DRIVEN = 2.85 ratio
14 drive 35 driven = 2.50 ratio enough to make a difference
would the 14 tooth have to be that much bigger?

This thought could be worth investigating some.
As you say just how much bigger would a 14 tooth pinion be ?
I think the next question would be, would the 2.50 ratio be enough to achieve a reasonable drop in RPM at cruising speeds (which is what this is all about)
C'mon you Maths Guys out there do some Math for us and tell us exactly what the RPM drop would be at 60MPH.
I could do this myself, but I like to share

 

[Paul Bryant]

Great work Paul...would it not be easier to change the output gear/shaft ratio in the box...plenty of space in there.

That's another option, Warp and I have spoken (briefly) about this before, his comments below.

 

[1olbull]

Paul,
Ditto on the gratitude for doing this research!
My thinking is my stock engine now pulling 160 RWHP will not pull red line in 5th gear and actually tops out a few mph higher in 4th gear.
The 1st & 2nd ratios can/should be raised some, but the rest are good IMHO.
Changes in the tranny ratios perhaps?

 

[TURBO200R4]

i think that the idea is to get an rpm drop at about 75 to 80 so instead of 3000 it might drop to about 2500 i would guess that the 2.50 diff would accomplish that.
will wait for the math guys.

 

[R-III-R Turbo]

13 DRIVE 37 DRIVEN = 2.85 ratio
14 drive 35 driven = 2.50 ratio enough to make a difference
would the 14 tooth have to be that much bigger?

I think the next question would be, would the 2.50 ratio be enough to achieve a reasonable drop in RPM at cruising speeds (which is what this is all about)
C'mon you Maths Guys out there do some Math for us and tell us exactly what the RPM drop would be at 60MPH.
I could do this myself, but I like to share

with 80mph being round 3000rpm, changing to the 2.50 ratio would drop revs to 2631rpm @ 80mph


done some quick maths & interestingly the final drive ratio appears to kind of take the tranny gearing (when in 5th) out of the equation. think 5th is around 1:1 ratio anyway

take a Metzeler 240/50 R16 rear tyre. 16" is 406mm, plus the 50 aspect ratio on a 240 section means 120mm tyre depth to rim. 406+120+120 = 646mm overall rear wheel diameter.
circumference C = 2 TT R, so in this case C = 2(22/7)323 in mm
=2030mm
=203cm

1 mile is 1,609.34m or 160,934cm

so the rear wheel must rotate (assuming no slip) 792.78 times per 1 mile
since we are talking about 80mph as the example then the rear must rotate 63,422 times in 1 hour so that's 63,422 RPH @ rear wheel
or 1057 RPM @ rear wheel

now - final drive ratio based on 13/37 is 2.85, so engine is running 3000 RPM, divide that by the 2.85 ratio gives 1052 RPM @ rear wheel

5 RPM difference in results going about it in 2 different ways

change the 2.85 to 2.50 and that should work back to 2631 engine RPM @ 80mph