information about gpz 550 frame mod

[rob3216]

Hi
i am looking for help, i own a 1982 gpz550 unitrack. i have another fuel tank that has the fuel gauge mounted to it, my fuel gauge is on the speedo cluster, and i want to swap tanks over but there is a size difference, has anyone done this themselves before, and if they did what did they have to do, and i am planing to fit gpx 750 front forks and rear tyre to it was well as i want a bigger diameter tyre as i think the bike revs to high at high speed, and i am hoping that by going a larger tyre it will drop the revs down

[BrettZZR]

Can't help on the other stuff, but if all you want is to mess with ratios then rather play with sprocket size.

(-8

[Gosling1]

forget the tank swap mate - you are trying to fit an 1100 tank to a 550 it just doesn't work, the 1100 tank is far too big. The GPX front fork swap is a bit of a woftam on a small bike like the 550, it will steer heaps slower with a fat front tyre. BrettZZR is on the money about gearing - you sort that out with different sprocket sizes not tyres. To drop the revs, go to a bigger front sprocket as the first option.

Best thing you can do with the 550 is leave it stock. Don't change wheel sizes or diameters, just get some good fork springs and a better rear shock. These will make a world of difference for the better. Fit some Pirelli Demon tyres, these are plenty sticky enough to drag footpegs.

[h.b.bear]

Other than all that and you decide you want to sell it send us a pm

[dutchy]

I thought he was talking about the fuel tank on the later model 550's that had the gauge on it???

[rob3216]

Hi
thank you for the information i was looking at swapping the tank as well as swapping the wheels and front forks, to a set that i have off a gpx750 as the wheels are a bigger diameter

[Gosling1]

.....I thought he was talking about the fuel tank on the later model 550's that had the gauge on it???......

that might work but you would also need the later dash with the fuel guage/LCD display.

........ i was looking at swapping the tank as well as swapping the wheels and front forks, to a set that i have off a gpx750 as the wheels are a bigger diameter.......

a bigger diameter ? Don't you mean wider ? GPz550 rims are 19/18 as far as I recall - GPx 750 rims are 16/18 ??

Mate you really do not want a 16" front wheel. These are so old-school is not funny. Very difficult to find decent tyres to suit the 16" front these days - almost impossible really. These will make your bike steer really weird, as the front is a pretty wide size. This does not mean its better - its worse. The steering will be really slow because the rest of your geometry won't change. Besides, you will have to change disc brakes and caliper etc as well - it will be a massive pain in the arse for no gain.

Just get some good tyres for your stock rims, upgrade the stock suspension and leave it at that. GPx rims are a road to pain.

[rob3216]

Hi
Thank you all for your help, I was given a gpx 750 less the motor seat fuel tank etc, and i thought it may be easy to swap my gpz550 front forks to the gpx ones as hey are larger diameter, as well as swap the gpz rear wheel to the one that came off the gpx as yes it is wider and a bigger diameter, as i find at 100km a hour at the moment i think the bike is revving far to high, so i just thought by fitting the larger diameter gpx wheel it could be a easy fix to the prob.
I also bought a spare motor and with it came a fuel tank that had the fuel gauge on it and yes i was hoping that i could swap the tank over i got the speedo cluster as well with it, the motor i bought is a gpz550 motor so i asumed the tank was off a gpz550 as well but yes i see it is a bit longer.
My bike is a 1982 gpz550, i do know its a old bike but i do like it and i am just trying to spruce it up a little as well as drop the revs at higher speeds as i do want to travel on it a bit, and as well as if the lager dia back wheel does drop the revs of the motor a wider tyre may make the bike handle a bit better.
Thank you all again for your input

[bonester]

In have a GT550- same engine. No choice in wheels or gearing as mine is shaft drive. Great little bikes though. Go well and handle and brake better than they should. Things to watch are rusty fuel tanks and holed carb diaphragms.

[Gosling1]

.... Things to watch are rusty fuel tanks and holed carb diaphragms.......

yep, holes in the diaphragms are a pain in the arse.

Rob - having all those spares is great - especially the motor stuff. But changing wheels/forks etc is a lot of work. Nothing will bolt straight up, you would need to modify the GPx steering head to suit the GPz550 dimensions and then you could just bolt the entire GPx front end onto the 550. The rear end would need a lot more work because the GPx wheel/tyre combo is going to be wider than the GPz550 - and you could run into issues with clearance with the skinny 550 swingarm. Wider tyres do not mean that the bike is going to handle better - bikes just don't work like that. Putting the wider tyres on the 550, will make it steer much slower and it will feel like a pig to ride. The stock size rims & tyres are far better for handling - believe me - some of us have been doing this shit now for 30 years and know what works and what doesn't.

I reckon you would be far better off just finding an old GPx 750 motor and fitting that to the GPx rolling chassis you already have.

As far as the revs being too high - just change your gearing mate, its easy as. New chain & sprockets, either go up 1 or 2 tooth at the front, or drop a few teeth on the rear. This will sort out the revs at cruising speed instantly. The diameter of the tyre only makes a small difference on bikes, for street bikes its far better to fix your high revs with a gearing change, not tyres.

[bonester]

H1 and H2 ZXR750 engines would fit the GPX too I would imagine

[rob3216]

hi
thank you all for your information i will change the sprocket size and not the wheel, looked like a good idea at the time(lol), i will let every know know how i go.
Regards
robert

[Gosling1]

Look forward to some updates on the bike Rob - pics are always good as well

I have some really good memories of the GPz550 - a good mate of mine bought one of these new back in the day, he went on to buy a 750 Turbo eventually. But for about 12 months he had the 550 and I rode it a few times.......one of the best memories was a strop back up home from the coast, with a guy on an RD350LC which was in really good nick, it had chambers fitted and was tuned well......we came up the Clyde from Batemans Bay flat-strap all the way to Braidwood, he barely made it to the first garage after using a full tank from Batemans really good ride, we had a ball.

With some simple suspension upgrades and good tyres - a 550 can be a very very good little motorcycle.....

[rob3216]

i will pull the bike out of the garage on the weekend and get some pics and upload them
it is a great bike to ride, i have had a ball on it