Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: xbally on September 07, 2014, 02:47:11 PM
-
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?
-
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 (http://www.dolecek.de/xbrat/bikeclassik.htm)
-
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
-
I haven't done the mod myself, but as I understand it you swap the Domi clutch basket/primary gear for the XBR ones.
-
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.
-
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 (http://www.champsclock.com/gb500hu.htm)
-
........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.
-
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
-
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?
-
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
-
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?
-
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)
-
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!
-
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
-
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.
-
Thanks guys. I am not after a huge performance boost. A modest increase in low to midrange torque is all I want . I am lucky enough to have other bikes so I can use them to go faster. I just feel that a little bit of extra pep would make life on the XBR slightly more interesting. I totally get the well made points about the brakes and suspension upgrades to match as I'm going through the same considerations with my MG!The XL600R CDI and change of gearing sound exactly the right place to start.If anyone can specify exactly what I need to get then i'll start there.Many thanks.
-
Best mod, and best performance for your pound is to fit the XL600R barrel and piston. Please remember if you use the XL600R cdi you will not be able to use the electric start
-
Thanks. I don't think I could live without the electric foot after all the years on Jap bikes. I used to have an Enfield Bullet 500 with an unreliable sprag clutch and that was a nightmare!
-
You,d be ok without the lecci start Martin , I,ve removed mine, mainly to save weight and it kicks over and sparks into life every time, no problem and that's with a high comp piston. Plus there,s something ever so "RETRO" about kicking it over. Cheers. Michael
-
Hmmmmmmmm!Not so sure about that Michael!Has anyone else removed the electric foot and how did you find it?Maybe I'm just an old wimp?
-
You,d be ok without the lecci start Martin , I,ve removed mine, mainly to save weight.........
Mad idea if you ask me. :D
Edit: ;D
-
Hmmmmmmmm!Not so sure about that Michael!Has anyone else removed the electric foot and how did you find it?Maybe I'm just an old wimp?
With the auto decompressor the XBR is very easy to kick over for a 500cc single BUT it is very handy to have the button when it does the XBR thing of stalling at tickover at traffic lights when you are at the head of the cue and the lights go green!
Out of curiosity how high do you rev it? with a big thumper it's tempting to change up at 4-5000revs but if you let it rev out a bit further in the 3rd/4th to 6000 + you'll find it has a nice little power kick near the top end of the revs.
Personally - while I have every respect for those who enjoy tweeking - I like the XBR as it is - a nice compromise of power/speed/reliability/rideability. Unless you really know what you are doing you can spend a lot of time and money and just end up with a lot of ball ache! .....been there, done that, had the empty bank account and ended up going back to standard set up!
-
Bloody hell where's the bulldog spirit in you all. "Mad idea" mmmm, We did,nt win a war by pushin lecci start buttons. LOL
Seriously tho, once I,d got used to the way I had to go about starting it (full choke when cold, then zero choke and one real swift kick when warm) she sparks into life virtually every time with the odd exception and then it,s 2nd or 3rd kick. Regards revving it, yes I do, quite a lot. Nice n steady for first few miles till I get out of town so to speak then I rev it very high, the bike was built to be ridden fast on twisty B roads and it has,nt disappointed so far, it absolutely flies up to around 90mph and goes up to 100 mph no problem but I,m quite happy at around the 80/90mph mark nowadays. (Must be an age thing) . It,s been bored out to approx 560cc and fitted with a high comp piston as well as a complete rebuild and a new mikuni carb and K n N filter ( no air box) it shud hopefully be gracing the thumper club stand again this oct at the Stafford show if you,re down there come and have a look, it,s a nice little bike. Cheers. Michael
-
I say do what you can afford, dont go ott for a road bike make the mods suit your riding style. I came across a company called CW cycle works or cycle wizard, who modify the head into a clover leaf pattern by welding it up between the valves and re machining and bore and stroke the NX out to 750cc and even a little bigger, they use the XBR gearbox with the NX650 2nd gear and the XBR clutch supposed to be really powerful and fairly reliable too
-
Bloody hell where's the bulldog spirit in you all. "Mad idea" mmmm, We did,nt win a war by pushin lecci start buttons. LOL
Seriously tho, once I,d got used to the way I had to go about starting it (full choke when cold, then zero choke and one real swift kick when warm) she sparks into life virtually every time with the odd exception and then it,s 2nd or 3rd kick. Regards revving it, yes I do, quite a lot. Nice n steady for first few miles till I get out of town so to speak then I rev it very high, the bike was built to be ridden fast on twisty B roads and it has,nt disappointed so far, it absolutely flies up to around 90mph and goes up to 100 mph no problem but I,m quite happy at around the 80/90mph mark nowadays. (Must be an age thing) . It,s been bored out to approx 560cc and fitted with a high comp piston as well as a complete rebuild and a new mikuni carb and K n N filter ( no air box) it shud hopefully be gracing the thumper club stand again this oct at the Stafford show if you,re down there come and have a look, it,s a nice little bike. Cheers. Michael
Michael, sorry if I confused things a bit there, my comment about revving it out wasn't really aimed at you as I know you have a quick XBR, It was really a question more for Xbally who started the thread as a lot of folks don't realise the XBR likes to rev out rather than just thump ( though it'll do that too). :-[
-
Absolutely no offence taken Steve , nice to know my bikes reputation precedes itself. I wish I kud take all the credit for the bike but I had the engine professionally rebuilt by a local chap who has an excellent reputation for doing these engines, mainly in classic motorcross circles and as I said before it certainly does,nt disappoint . On the point that joolz makes in do what your riding style req,s I totally agree, but I was used to riding very , very quick but wanted (needed) to calm myself down so built the XBR cafe racer,, I bought a new one back in 1986 and had very fond memory's of the bike so bit the bullit and bought one off fleabay and I just love the end result, so much so that I bought anther and now have that on the workshop bench and my triumph 1050 speed triple is going up for sale next week. Regards Michael
-
Steve-i take your point.I'm not someone who has come from a Brtit bike background and i do know that most Japs ,even big singles,need to be revved hard to get the most out of them. I always let my bike warm up before increasing the revs.Mine pulls quite strongly through the gears but doesn't seem to want to go much faster than an indicated 85 mph.I'm not after any more than 100 mph as my sports bike riding days have satisfied my lust for speed.My bike is a high mileage one (well over 60K recorded)and although its not been stripped it runs well enough for its mileage.There is a little cam chain rattle but i should think the top end must have lost efficiency after that number of miles assuming the engine has never been apart.I'm certainly not in the market for spending £s for a small performance gain but i would like the top end inspected for wear and at the same time if i could at least restore what performance may once have been there and /or increase capacity to 600 or 650 ccs all well and good.Thanks again to all posters.
-
Bloody hell where's the bulldog spirit in you all. "Mad idea" mmmm, We did,nt win a war by pushin lecci start buttons. LOL
..........
2. At least.
-
I say do what you can afford, dont go ott for a road bike make the mods suit your riding style. I came across a company called CW cycle works or cycle wizard, who modify the head into a clover leaf pattern by welding it up between the valves and re machining and bore and stroke the NX out to 750cc and even a little bigger, they use the XBR gearbox with the NX650 2nd gear and the XBR clutch supposed to be really powerful and fairly reliable too
Hi Joolz
is that cw work in the pics you posted of your xbr head?
-
No The head work on mine was done by XR's Only. Here is a picture of the CW heads on the left and a standard head an the right
[deleted to save space]
-
Isn't that a bit of lovely work Joolz.
Have you fitted it yet? Result? Compression must be high..?
Looks great. NZ yer?
-
Thats not my head, mine is a big fin head thats ported and flowed, but has a standard combustion chamber. I put that picture up just to show the difference on the CW heads
-
Thats not my head, mine is a big fin head thats ported and flowed, but has a standard combustion chamber. I put that picture up just to show the difference on the CW heads
Would you be able to post another pic of your head?
It's taken a while but I've finally tracked a fellow down that can do the work I'm wanting. Won't be modifying the chamber either. After a lengthy conversation with him, I don't think the mod will produce that much of a difference in HP for the cost.
A bit more cash to play with a decent stainless exhaust I think is best.
-
Here are a couple of pics of my head
[deleted to save space]
-
and another
[deleted to save space]