81 KZ550 to GPZ Conversion insight needed

Well...My plan was to sell this and replace with a GPZ but I came across most of the parts at an amazing price. So far I have both front and rear wheels with rotors, rebuilt front forks, entire front brake assembly and the rear brake and caliper.

Has anyone else here done this conversion? Seems pretty straight forward except for the rear brake master cylinder mounting. Anyone have any pictures they can share? Thanks in advance.

Look up Harm and then admire his 550 conversion to a ELR clone



He is a past Bike of the Month Honoree

Dave

For simplicity, you'd probably keep the rear drum brake, unless you want to do some welding/fabbing for the master. You'll also need the spacer/carrier for the rear caliper, and probably different torque link for the carrier, which may need a mount welded on the swingarm.

If you do swap to a rear caliper, you probably want to source a newer master, like this:
www.kzrider.com/forum/5-chassis/531950-a...l=component&type=raw


(It looks like you have the front figured out, if you have 81 Kz550D1 parts)
For reference, for others who may be interested: For the front, you will need Gpz fork sliders. The standard model sliders have the caliper mounts farther away from the axle in order to handle the larger disk on the standard model. The two gpz disks are smaller, and thinner. If you have 7-spoke gpz wheels, then you can only use disks from the 81 Kz550D1 gpz. The later ones had different mounting bolt patterns.

The easiest thing to do for the motor is drop in some Gpz cams. Kz550D, Kz550H use the same cams, and the Zx550 cams should drop in as well. Most people suggest using the standard cam timing instead of the Zx550 cam timing.

If you want an actual gpz motor, you will need higher comp pistons and supposedly some porting on the head, but I'm not sure on that.

The carbs are pretty easy... just a bump in the mains by about two sizes.

loudhvx wrote: For simplicity, you'd probably keep the rear drum brake, unless you want to do some welding/fabbing for the master. You'll also need the spacer/carrier for the rear caliper, and probably different torque link for the carrier, which may need a mount welded on the swingarm.

If you do swap to a rear caliper, you probably want to source a newer master, like this:
www.kzrider.com/forum/5-chassis/531950-a...l=component&type=raw


(It looks like you have the front figured out, if you have 81 Kz550D1 parts)
For reference, for others who may be interested: For the front, you will need Gpz fork sliders. The standard model sliders have the caliper mounts farther away from the axle in order to handle the larger disk on the standard model. The two gpz disks are smaller, and thinner. If you have 7-spoke gpz wheels, then you can only use disks from the 81 Kz550D1 gpz. The later ones had different mounting bolt patterns.

The easiest thing to do for the motor is drop in some Gpz cams. Kz550D, Kz550H use the same cams, and the Zx550 cams should drop in as well. Most people suggest using the standard cam timing instead of the Zx550 cam timing.

If you want an actual gpz motor, you will need higher comp pistons and supposedly some porting on the head, but I'm not sure on that.

The carbs are pretty easy... just a bump in the mains by about two sizes.

Thank you for that. I am pretty sure I have the front totally taken care of. I have the 7 spoke gpz wheel with the discs on it, the forks from that bike along with the entire brake setup from the same bike. Should just be a drop in.

I am going to do the rear disc setup as I have the GPZ rear wheel with disc from that bike. I am also going this route because I need the drum mag wheel for my KZ650.

Is the 81 GPZ swing arm a direct bolt on? I believe I have the correct rear master and caliper on the way. Welding that tab is no real big deal to mount the master.

Wildman1024 wrote: ...
Is the 81 GPZ swing arm a direct bolt on? I believe I have the correct rear master and caliper on the way. Welding that tab is no real big deal to mount the master.

I think most 550 swingarms should swap. But there is a small chance that the early ones may have used grease fittings for the swingarm bearings. I can't rule out that the bearings could be different then. The gpz did not have a grease fitting. You may want to check your swingarm... or check part numbers for the swingarm bearings on Partzilla.

I had very little success getting an 81 gpz550 (D1) rear master that was not pitted. If you are going to fab a mount, I would just go ahead and convert it fully to a Ninza 250 master, as described in that link I posted. That way you can fab it so it won't need spacers etc, and you will be able to get rebuild kits in the future (rebuild kits never existed for the 81 gpz master that I could find). The Ninja master (ha) feels perfect for the 550. It's the same diameter piston etc.

You may need a brake lever since the drum brake pedal wll likely have different mechanical connections than the gpz pedal. The gpz pedal might be a different length since the gpz used footpegs that were set further back. I'm not even sure if the pivot point is in the same place on the two frames, but I think they are.

Another minor thing is the sprockets are different between the two bikes, so you may need a slightly different length chain unless there is enough room on the adjuster, or you can swap sprockets. The gpz is 38/16. 40/17 may give virtually the same ratio. (The internal gears are all the same.)

I'd just find an 81 GPz550 D1 frame and go from there. I bough one for £1 a while ago from ebay. Fames generally are the bits you can't even give away on these. I've scrapped several.

I've had about 10 of these 550's in my time including z550, but the triple disc brakes and footpeg triangles really make these. Also less obvoius refinements: Showa teflon coated forks as standard plus IIRC slightly revised frame geometry. I did an unfinished kz/ GPz clone just like you are thinking but gave up on the idea.

chopping the rear brake mounting and going for custom rearsets with a rear disc would be a better option imo.

I agree. If you're going to fabbing parts for the rear brake pedal, might as well go full bore. The standard KZ pegs are pretty lower and forward of the Gpz pegs. And the gpz has a likage activated shifter, whereas the Kz has a simple shifter.

loudhvx wrote: I agree. If you're going to fabbing parts for the rear brake pedal, might as well go full bore. The standard KZ pegs are pretty lower and forward of the Gpz pegs. And the gpz has a likage activated shifter, whereas the Kz has a simple shifter.

I have never ridden the gpz but I am pretty comfortable with the standard KZ pegs.

I guess if I can find a frame I might go that route and just transfer everything over. If not I think it will just be OK using the GPZ swing arm and tacking on a bracket for the rear master. That's not to hard.

OK...Made some progress last night. Got the rear end apart, new swing arm on, wheel on and shocks etc. Just gotta finish the brake caliper install and get a master cylinder hooked up.

If anyone is interested in this bike I will be re posting it for sale again. I have come across another project I would like a little more than this and there is only so many bike I can have.

No eBay APP ID and/or Cert ID defined in Kunena configurationNot sure if the z500 frame mounts are different, but something like this maybe?

You'll probably get more if you sell it stock,and you'll save yourself a lot work . The front on this one that I have has been converted.

mjg15 wrote: You'll probably get more if you sell it stock,and you'll save yourself a lot work . The front on this one that I have has been converted.

Nice bike. Where in NY are you? I have the back of the bike all converted except for the tab for the master. The front is an easy fork swap