XBR 500 MODS

[xbally]

I know there are various ways of getting more power from an XBR500 but which is the easiest way to go?Ive been checking through my back issues of classic Mechanics to find the article by Rod Gibson where he swapped 600 or 650 engine parts but I seem to have mislaid it.I know there are people on here who have successfully carried out these mods-can anyone help please?

[SteveC#222]

You can either fit the barrel and piston from an XL600 (R?) to the existing engine - you have to get the right model but there are several threads on the forum if you search for them.  The other way is fit a complete NX650 Dominator engine. Should keep you busy over the winter!

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

[Propellor]

I'm confused by the info on the primary gears, given in the article. He says the xbr500 has a lower primary ratio than the nx650 yet the tooth numbers he gives are clearly the opposite.

So which way around is it?

Cheers

[SteveC#222]

I haven't done the mod myself, but as I understand it you swap the Domi clutch basket/primary gear for the XBR ones.

[Propellor]

He says the xbr has a lower primary ratio than the nx, but I'd have said the other way around, based on his counting of the tooth numbers.

He complained of clutch slip. A higher reduction ratio will multiply torque more. So, not only will the assumed extra torque of the nx650 place a higher burden on the clutch, but the higher primary ratio of the xbr will multiply that effect.

[SteveC#222]

Could well be, Probably a good idea to fit heavy duty clutch springs anyway. Sticking the NX lump in doesn't really make it much faster but the extra cubes make it quicker.  The White Bro's mods with the 600c barrel piston, bigger carb, better cam and exhaust made it ( well a GB500 actually) quite a bit faster but it's a lot of money. Personally I like it as it is.

http://www.champsclock.com/gb500hu.htm

[Propellor]

........Sticking the NX lump in doesn't really make it much faster ..........

That was going to be my next question. The max power listed, as standard, isn't any higher than the xbr. From memory.

Cheers Steve.

[Moto63]

Hi Steve,  many thanks for posting the champs clock link, makes for very interesting reading. It will be interesting to compare the performance figures to the bike I have on the bench at the moment.(once it's finished)  It is under going a very similar engine rebuild but mine shud hopefully weigh a little less than a GB/XBR as I,ve removed quite a bit of stuff that I didn't req. I'll keep you posted of developments as I progress and once I figure it out i,ll post some pics.   Regards. Michael

[Propellor]

I was interested in the bit about the gearing vs max speed.

Anyone know of a dyno curve for that bike?

Michael, what gearing you planning on running? Keeping same wheel dia?

[Moto63]

Good evening propellor ,  yes I am stil going to run the same diameter wheels, both with ally rims, the front laced to a suzuki gn250hub the rear laced to a honda dominator hub both with stainless spokes and power coated hubs n rims. Regards the gearing, I have had an alloy rear sprocket made up to suit the dommi hub that is 2 teeth larger than the original XBR sprocket, i may be able to get one made up which is 1 tooth larger but I,m going to try the other set up first. The main problem being that the dommi hub will not allow me to have the original XBR set up as the hub/sprocket carrier diameter is to large to accept the same amount of teeth as the XBR , I must say tho that I do quite fancy lowering the gearing just as a difference to my XBR cafe racer which runs standard gearing. It really is a case of "suck it n see" . I will keep you and anyone else out there that's interested posted of any developments as I progress.   Cheers. Michael

[Propellor]

Good evening propellor ,  yes I am stil going to run the same diameter wheels, both with ally rims, the front laced to a suzuki gn250hub the rear laced to a honda dominator hub both with stainless spokes and power coated hubs n rims. Regards the gearing, I have had an alloy rear sprocket made up to suit the dommi hub that is 2 teeth larger than the original XBR sprocket, i may be able to get one made up which is 1 tooth larger but I,m going to try the other set up first. The main problem being that the dommi hub will not allow me to have the original XBR set up as the hub/sprocket carrier diameter is to large to accept the same amount of teeth as the XBR , I must say tho that I do quite fancy lowering the gearing just as a difference to my XBR cafe racer which runs standard gearing. It really is a case of "suck it n see" . I will keep you and anyone else out there that's interested posted of any developments as I progress.   Cheers. Michael

Gotcha. Sounds cool ee o.

Does that mean you will be pulling wheelies like the nice man in the article?

At least with the dommie primary gears being a lower ratio there's always a possibility to adjust back the gearing upstream? It would lower the torque into the clutch (and therefore the load on the gears) but also make the gearbox run at a faster speed. I assume that the centre distance between crankshaft and clutch is identical on each machine?

[Moto63]

Yes I,ll certainly be giving it a go, always was a sucker for a good wheelie especially before old age n vertigo set in (eee when I were a lad...blah blah blah)

[xbally]

Thank you posters , particularly Steve .I've had a look into this and must admit to being rather confused about what will work and what will not! I am not mechanically enough minded or competent to do the work myself but have a mate who is but he is not very familiar with the XBR / XL/ XR engines.I don't want to start this unless or until I'm sure I can get the right parts or engine and that it will be a relatively straightforward swap.I know that some of you on here loving nothing more than the challenge of seeing what will fit or can be adapted to fit but that is not me! Any further comments would be very much appreciated!

[JOOLZ]

There are so many mods for the XBR, you have to decide first what you want out of the bike, all out HP or something you can live with day to day. Like they say speed is just a question of money, how fast do you want to spend. If you need help with anything send me a message and I will see if I can help

[SteveC#222]

Bear in mind also that if you increase the power/speed significantly you will probably need to upgrade the brakes and suspension too!

If you just want to pep up the pickup rather than absolute performance then changing the gearing and fitting an XL600R CDI might do the trick at a moderate cost.