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Wayward 2003 GPR

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al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Mon May 23, 2022 7:21 am

So it's been 2 weeks, and progress continues. All be it slowly.

First off, lets take care of that water pump. Wasn't surprised to see the corrosion. But take a look at that drive gear. It looks like something rapidly dis-assembled itself and made it to the gears. Luckily the oil pump gear is in better shape. We won't be using the oil pump, so that gear is going to live the rest of it's life pumping water.

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Click the image to zoom in. You can see the damage to the gears on the lower gear.
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Also cleaned up the clutch linkage, and replaced it's seal. Note, that the clutch lever, and shift lever use the same oil seal. It' a 12-20-5 seal.
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On another note, I ordered a 40mm Malossi piston pin to see of that would work with the Airsal piston. Hurray, it works! The Airsal kits piston uses the same roller bearing, but we ordered a more one just incase.
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Lastly, does anyone recognize the logo on the bottom end? I feel confident it's not a stock bottom end, but would love to know who manufactured it. This is the logo on the connecting rod.
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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Tue May 31, 2022 1:16 pm

Lots of progress, just not a lot of photos to show it. Most of thsi long weekend was spent sanding, and priming - sanding, and priming - sanding, and priming. But if you put in the effort now, the end result can be spectacular.

As I sanded down through the paint layers, I found that the tank, and front fairing were at one point candy apple red. Anyone ever remember a red candy flaked GPR?

And don't worry I didn't sand down the side plastics. They are being set aside for someone who needs a set to complete a restoration. The are not perfect, but the decals are in fairly good shape.

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Had to do some repair work to the hinge holes. They were "fixed" with zip ties when I got it.

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VT78racer
Posts: 6
Joined: Tue Oct 22, 2019 6:27 pm
Location: Kentucky
Replica: 2003 Derbi GPR race bike - CR80 transplant
2000 Derbi GPR race/street
1999 Derbi GPR street
x 2

Re: Wayward 2003 GPR

Post by VT78racer » Thu Jun 02, 2022 8:12 am

It's probably a 2003 Malossi replica paint scheme. Mine has bright red with flake in it. If you find the paint code let me know!
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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Jun 13, 2022 6:06 am

Cases are getting ready to be joined - very exciting! Heated the right side bearing with a heat gun, and froze the crank overnight. It's pretty humid at this time of year. So before putting the crank in the freezer I gave it a good spray down with WE-40. And did it again once I got it into place. Just to help disperse any water once the frost melted.

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The new Malossi intake on the left, and the stock on the right. Quite a substantial difference between the two. I plan on using the stuffer, but would love any thoughts from others.

Also got the front brake rebuilt. Could not find a rebuild kit anymore in the states. Eventually found it from Racing Planet

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And pro tip, when rebuilding your brakes, don't use vice grips to remove the pistons. And if you do, don't shove them back into the caliper.

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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Tue Jun 21, 2022 6:32 am

WOOT! Engine joined and everything is spinning freely. Baked the left side for about an hour at 150* Carefully joined, and started slowly working the bolts tighter. About 1/4 turn at a time moving around and around. Still had to give a "tap" to the bearing to fully seat it, and allow the crank to spin freely. I used a deep socket that was as large as the inner bearing race. With the other side of the crank resting on some wood. One moderate strike with the hammer, and all was good.

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This is a pic without a base casket. And the piston is almost at the top of the cylinder. With the gasket it just about leaves enough room for the head. I'll get all the gaskets in, and the dead torqued down and get a reading on the squish. But I suspect I'll need to take a little off the head. Not to bit a deal ,just up the compression a little. That can be compensated by higher test fuel.

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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Jun 27, 2022 10:42 am

Lots done over the weekend. Assembled the engine, and did a pressure test. First off another nod to ToraTora, when assembling I coated the paper gaskets with engine building lube. Super sticky stuff that keeps the gasket from ripping if, or when, you need to open things up again.

With everything buttoned up, I could finally check the squish. Simple process is to use a bit of solder, couple of inches worth. Bent it gently so you can stick it down the spark plug hole and point it towards the side of the cylinder. Craig the engine over, and you will feel the piston as it touches the solder. Keep cranking, and the piston will smash the solder against the head. Now you have a good idea of how close the piston is getting to the head.

Our target was between 0.85, and 0.75 millimeters. We can go back later and change out the base casket to make subtle changes is the final squish. The setup we are going to start with are:

0.85 mm squish at the piston edge
0.95 mm squish at the inner edge of the squish band
0.65 mm base gasket

It's a rather thick base gasket. But has the benefit of raising the cylinder putting the bottom of the ports, at the top edge of the cylinder at BDC.

With that settled, it was on to pressure testing. A simple process, using some rubber compression plugs. I only took the pressure it to 5lb but everything looks good. If you do this, you will see the pressure dropping if you only look at the gage. So grab some bubble soap and start smearing it around the gaskets. If you have a leak, you will se large bubbles forming. You can confirm that the leak is in the rubber plug shaft by smearing that as well.

One other thing to note. With the Airsal Extreme kit, the exhaust studs go into the side exhaust ports. So use some high temperature coper gasket compound to help seal the threads.

With the engine in a good state, it was on to keys and locks. The bike came with one key that fit the ignition lock, and the fake tanks lock. But didn't fit the pilot seat. So it was off to find out if the lock could be re keyed. Or if I would need to find a 3 lock set. Turns out it's not that hard to re key one of our locks. This link will do a better job than me of describing the process. (https://electricmotorcycleforum.com/boa ... pic=9330.0)


My lathe is a small hobby tipe. So cross cutting can sometimes push the cross slide backwards. So I use a clamp to keep that from happening.

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Nicely cut down, and polished up

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And don't forget to cut the gasket to match the cylinder

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All ready to be buttoned up
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You can see how the stud hole goes into the exhaust side port

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All buttoned up with a little bit of pressure

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And some bubbles through the center shaft of the rubber plug.

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It's simple to make on of these. Just grab 2 rubber plugs from your hardware store. Find a car cylinder pressure tester at a swap meet, or yard sale. And order a blood pressure cuff. The gage goes to 300 mmHg (millimeter of mercury). That's about 5.8 PSI. You don't want to go over 7PSI as you may blow out a seal. Not as big a deal in a single cylinder engine. But on multi cylinders you risk blowing out the center seal. And that means you get the opportunity to rebuild the engine again.

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And lastly some pick of the lock, and it's re-key

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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Fri Aug 19, 2022 7:24 am

Don't worry, it's not a stalled project. Just took a little time to enjoy the summer. Here is a sneak peek at the body work.

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User avatar
al_pritchard
Posts: 46
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 7
x 60

Re: Wayward 2003 GPR

Post by al_pritchard » Tue Sep 13, 2022 6:24 am

Got the fiberglass fairings from Air-Tech yesterday. I'll get some better pics as I get them prepped for paint. But wanted to share a little with the group.

I'm going to preserve the original side fairings - If someone is in need of them let me know
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I also got the front, and rear mud guards
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Im happy with the quality of the parts. Not exactly cheep, but you get what you pay for. I have ordered from them in the past, and the quality is top notch. They can also do carbon, but that gets a little pricy for my project. The bike to the left is a Bridgestone built up for AHRMA 200GP. It al so has an Air-Tech fairing, and tank
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Question - Does anyone have a picture of the front mudguard securing plate?
I'm assuming it's a flat plate with threaded holes, that sits on the inside of the fork mount.
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User avatar
jkv357
Posts: 224
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 425
x 116

Re: Wayward 2003 GPR

Post by jkv357 » Tue Sep 13, 2022 7:30 am

al_pritchard wrote:
Tue Sep 13, 2022 6:24 am
(SNIP)
Question - Does anyone have a picture of the front mudguard securing plate?
I'm assuming it's a flat plate with threaded holes, that sits on the inside of the fork mount.
I'll try to get a pic for you, but yes, it's a flat plate with 2 threaded holes.
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User avatar
jkv357
Posts: 224
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 425
x 116

Re: Wayward 2003 GPR

Post by jkv357 » Sun Sep 18, 2022 7:40 pm

This is what the bracket looks like -

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