new here

[guest1988]

Hello everyone as the titles say i'm new here and joining because I have just finished my latest project and soon it will be time to finaly start on my xbr650 .yes I put he 650 engine in and had a few problem gearing it so you folks look like you know what your on about so any help(please) would be great . My interests are model engineering finished a 2 inch scale steam traction engine see picture . Now the.workshop clear Iwant to get the bike this year

[deleted to save space]

[SteveC#222]

Welcome to the forum.

Have you read Dr Rod's article on the 650 convertion from one of the bike mags years ago?  He used a NX650 Dominator engine and to get the gearing right he simply swapped the NX clutch basket and primary gear with the XBR ones - they are supposed to be a straight sawp - and he said the gearing was spot on.

If you want a copy of the article PM me your email off forum and I'll send it to you.

Should be an interesting project!

[002]

Same Crank Cases and set up so shouldnt be a problem !

If you wanted to go the whole nine yards...swap various gear box parts and keep the same gear change pattern as the lever is reversed !

Jethro

[guest1988]

Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental cock up. The bike has been stored for about 4 years but am keen to get started .

[Propellor]

Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental ******* up. The bike has been stored for about 4 years but am keen to get started .

Hi

From memory looking at my brothers xbr the main problem with attempting to raise the gearing (lower the ratio!) of the final drive is that you need to either put more teeth on the front or less on the back. The front is already pretty tight with regard to the clearance to castings I think?  And for memory to remove teeth on rear you risk the linksgfouling the sprocket nuts?

Give us the teeth numbers and also the teeth numbers of the primary for both versions and let's see if we can work out the problem? Are the Gearbox ratios normal xbr?

What road speed coincides with max power rpm?
Cheers.

[guest1988]

Thanks for the reply propeller had a look at the sprockets and the gear box sprocket has 16 teeth wont take anything bigger rear sprocket is 34 teeth .think the top speed 70 or so mph as I remember its 4 years since I last had it on the road and pops wheelys easy in 1st gear .

[Propellor]

Rod Gibson link. (Thanks to steve222!)

http://www.dolecek.de/xbrat/bikeclassik.htm

Just trying to find xbr gear ratios now

[Propellor]

Thanks for the reply propeller had a look at the sprockets and the gear box sprocket has 16 teeth wont take anything bigger rear sprocket is 34 teeth .think the top speed 70 or so mph as I remember its 4 years since I last had it on the road and pops wheelys easy in 1st gear .

If you're as far out as you're suggesting then the dommi gearbox ratios must also be different to xbr, as well as primary and secondary ratios.

[Propellor]

I can tell you that what you have lost in the primary you appear to have gained back in the secondary!

You are running a very high secondary gearing by what I can fathom. Probably at the limit.

[Propellor]

Thanks to moto 63 for e mailing me the xbr gear ratios.

Xbr top is 0.875 (top is a speed increasing ratio)

On tinternet it says dommi top gear is 0.84

Getting late so not best time to work over details, but at first glance your overall top gear gearing is about normal!

Go over again everything you know you have in there for certain and I'll check over figures tomorrow. You sure you got out of third gear? Lol.

Edit: you're not running anything weird tyre or wheel sizes?

[Propellor]

Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental ******* up. The bike has been stored for about 4 years but am keen to get started .

Just been re reading your posts and it looks like you have the xbr gear set and xbr primary set? So, basically, you have an xbr! As far as ratios go. But your final drive ratio is higher than stock xbr (as far as I can tell). So you appear to have an over geared xbr. This makes your opening post confusing?

Have I got that right?

Are you saying that it is too low geared because the effective engine rpm range has come down? Is it stock dommi tuning?

[Moto63]

Wheelies easy in first gear. WOO OO. Can I av one please. 

[SteveC#222]

Stock gearing for the XBR is 15 front and 36 back.

If you know the actual gear ratios there is a calculator to estimate speed/revs

http://www.gearingcommander.com/

If it will only do 70 and wheelies easily it sounds like the gearing is way off.  B&C sprockets can make almost any size to order from blanks if you need an unusual size. It should pull roughly the same speed as a standard XBR but will be quicker getting there.

[Propellor]

Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm

There's the problem. The difference is 1.17.

So we need to take the overall gearing found in the xbr and multiply it by 1.17. 

Assuming same tyre size.

I have all ratios now for xbr and I have ratios for dommi from a tinternet site. But it would be better if anyone can provide dommi gear ratios from a manual.

Then we can work.out the best way to get Wart up to a reasonable speed!

[SteveC#222]

Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm

There's the problem. The difference is 1.17.

So we need to take the overall gearing found in the xbr and multiply it by 1.17. 

Assuming same tyre size.

I have all ratios now for xbr and I have ratios for dommi from a tinternet site. But it would be better if anyone can provide dommi gear ratios from a manual.

Then we can work.out the best way to get Wart up to a reasonable speed!

Seek and ye shall find ( on page 6)

http://www.eikholt.net/hpalt/download/NX650%20A%20Section%201%20Service%20manual%20.pdf