new here

[SteveC#222]

Hmmm.... I've used a different gear calculator http://woodsware.aciwebs.com/gears/gears.asp

I put in the ratios for a stock XBR @ 7500 max revs which gives a top speed of 110mph which is about what was claimed by Honda

Using the NX650 gear ratios, with the XBR primary gearing ( clutch basket and primary gear swapped) and Wart's current final drive 16/34 this gives a theoretical top speed of 104 mph @6000rpm.

Does this sound about right? 

If that is right, then it suggests the overall gearing is about right  but why is it only going to 70mph ( XBR's will do 70@5000rpm in top) .

[Propellor]

Hmmm.... I've used a different gear calculator http://woodsware.aciwebs.com/gears/gears.asp

I put in the ratios for a stock XBR @ 7500 max revs which gives a top speed of 110mph which is about what was claimed by Honda

Using the NX650 gear ratios, with the XBR primary gearing ( clutch basket and primary gear swapped) and Wart's current final drive 16/34 this gives a theoretical top speed of 104 mph @6000rpm.

Does this sound about right? 

If that is right, then it suggests the overall gearing is about right  but why is it only going to 70mph ( XBR's will do 70@5000rpm in top) .

Cheers Steve.

The table above is obviously for the dommi. Trouble is that the teeth numbers given by rod Gibson don't give the ratio listed above. Who is right? Can I trust rod gibson's info for the xbr primary? Do you have any data? Mick (moto63) has e mailed me a page from his official manual showing stock xbr gear box teeth numbers, so I have those. Just need the primary ratio from a reputable database, in case the rod Gibson data has been misprinted or something.

I can do the calcs, no great shakes, but I need the data to be accurate to start with and we possibly have anomalies creeping in?

[guest1988]

Cant thank you guys enough taking so much time to help me out .gearing is the one thing that I just cant get  my head round have no problems rebuilding the engine and on going repairs and making steam engines from scratch. The engine has had a lot (the 650) spent on it reboure  piston rings cam tensioner and guides and cam little end bearing piston pin bearings  as I said the bike has been unused for 4 year and is a real mess but worth doing I have both the xbr500 and the 650 Honda workshop manuals .  beginning to dout my work so am going to start checking a few things am sure its ok but wont hurt to check

[guest1988]

Will post gearing info from Honda manual

[Propellor]

Cant thank you guys enough taking so much time to help me out .gearing is the one thing that I just cant get  my head round have no problems rebuilding the engine and on going repairs and making steam engines from scratch. The engine has had a lot (the 650) spent on it reboure  piston rings cam tensioner and guides and cam little end bearing piston pin bearings  as I said the bike has been unused for 4 year and is a real mess but worth doing I have both the xbr500 and the 650 Honda workshop manuals .  beginning to dout my work so am going to start checking a few things am sure its ok but wont hurt to check

No problem mate.

A) we're here to help out

B) I actually enjoy doing this stuff  I need a life, I know.

 Nothing would please me more than to know that, between us all, we've come up against a hurdle (yours in this case) and found a solution to clear it. The alternative is to nip down your local dealer and buy a brand new bike...... Nah!

[guest1988]

XBR 500 PRIMARYREDUCTION 2.482 (72/29)
GEAR RATIO1 2.384 (31/13
                   2 1.555 (28/18
                   3  1.200 (24/20
                   4   1.000 (23/23
                   5   0.875 (21/24
  FINAL REDUCTION 2.400 (36/15)   G.11:2.7571

 ANY HELP

[Propellor]

XBR 500 PRIMARYREDUCTION 2.482 (72/29)
GEAR RATIO1 2.384 (31/13
                   2 1.555 (28/18
                   3  1.200 (24/20
                   4   1.000 (23/23
                   5   0.875 (21/24
  FINAL REDUCTION 2.400 (36/15)   G.11:2.7571

 ANY HELP

Yeah big help ta. Rod Gibson had 31/72 teeth, giving 2.32 ratio. To be honest that is a slight anomaly. From your description of symptoms we're looking for something huge!

[SteveC#222]

The chart is based on

1/ the use of XBR500 primary gearing ie you have swapped the clutchbasket/primary gear from the Dommi for the XBR ones.

2/ the use of Dommi gearbox ratios

3/ a final drive reduction based on 16t front and 34t rear sprocket ( I think thats what you said it was running)

4/ 6000rpm red line ( i'm not sure if this is correct)

I did a seperate chart based on bog standard XBR to check how it came out and it appears to be pretty much spot on so in theory the chart shows what you should expect your bike to do if the above information is correct.

Is it reving out fully?

I didn't bother doing a bog standard Dommi chart as it is quite a bit different.

[Propellor]

The chart is based on

1/ the use of XBR500 primary gearing ie you have swapped the clutchbasket/primary gear from the Dommi for the XBR ones.

2/ the use of Dommi gearbox ratios

3/ a final drive reduction based on 16t front and 34t rear sprocket ( I think thats what you said it was running)

4/ 6000rpm red line ( i'm not sure if this is correct)

I did a seperate chart based on bog standard XBR to check how it came out and it appears to be pretty much spot on so in theory the chart shows what you should expect your bike to do if the above information is correct.

Is it reving out fully?

I didn't bother doing a bog standard Dommi chart as it is quite a bit different.

Ah. Sorry. This whole thing will probably get confusing I guess. My interpretation of what he has is the xbr primary (whatever that is) and the xbr gear cluster. With a special final drive set up.

[Propellor]

Putting down the basics:

Std xbr setup.
Primary 2.482
Top gear 0.875
Secondary (36/15) 2.4

2.482x0.875x2.4=5.21

7000/5.21 =1343 rear wheel rpm

Wart set up.
Primary 2.482
Top gear 0.875
Secondary (34/16) 2.125

2.482x0.875x2.125=4.61

6000/4.61=1303 rear wheel rpm.

(Please feel free to correct any mistakes!)

What that rear wheel rpm equates to, we can calculate later, but it's obvious there shouldn't be much difference in top speed. This doesn't stack up against what wart tells us, but they appear to be the facts?

It looks like the dommi primary set would help raise the gearing a bit more, bringing it somewhere like a stock xbr overall ratio.

Bit of a mystery chaps. Steve has reached a similar conclusion. It's over to you wart.....

[SteveC#222]

Just re calculated with XBR ratios + 16/34 final drive @6000rpm which comes out with a top speed of 99mph - so something is still wrong somewhere 

[SteveC#222]

Just a random thought having re read your original posts - you say it revs out right into the red to the point it has bent the needle - Are you sure it's really revving out fully? The reason I ask is that when XBR tachos go wrong they read double the actual revs! ( wasted spark system so 2 sparks/impulses per rev but there is a special gremin that lives in the rev counter that only counts every other one until it gets a headache and starts counting both!)

At tickover it's not so obvious - it shows about 2000rpm but as soon as you rev it, the needle shoots around like a race bike! at 60/70mph it's bouncing off the stop!

Just wondering if you have a knackered tacho showing mega revs and a clutch slipping with the extra torque of the 650 engine? as I said just a thought - ignore me if I'm stating the bleedin' obvious - but I've found it's usually the silly little things that cause a lot of the headaches.

[guest1988]

stevec#222 funny you say that as I remember the taco went into the red waved about for week  packed up altogether soon after clutch did slip may be it was slipping more than I realised . so I'll start pulling the bike to pieces ready for. sand blasting and powder coat frame and check engine clutch primary drive gear sure its right I'll check so should I keep gearing as is for now. Thanks everyone for the time given .

[JOOLZ]

Welcome to the group, I like XBR's  and engineering Are you running the standard 90 section rear tire, I use an 80 and it changes the gearing quite a bit, take the height of the tire into consideration when calculating the gearing

[SteveC#222]

stevec#222 funny you say that as I remember the taco went into the red waved about for week  packed up altogether soon after clutch did slip may be it was slipping more than I realised . so I'll start pulling the bike to pieces ready for. sand blasting and powder coat frame and check engine clutch primary drive gear sure its right I'll check so should I keep gearing as is for now. Thanks everyone for the time given .

Re - reading Dr Rod's article he had problems with clutch slip and had to fit HD springs and 650 clutch plates so this could well be at least part of your problem.

Also found out that the NX red lines at 7250rpm - 6000 rpm is peak torque - so re calculated gearing with your 16/34 and it gives a theoretical top speed of 119mph!!!  ... I doubt the engine is going to be powerful enough to pull anything like that so you may find you eventually need to go back to something like XBR gearing of 15/36.

Keep us posted!