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Wayward 2003 GPR

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User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Thu Mar 10, 2022 6:36 am

Talk about not having any room. Its' a tight space between the controls, and the fairing. I ended up using the rear brake reservoir - and order a replacement for the rear. I made the bracket out of a small scrap of aluminum.

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User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Mar 14, 2022 6:38 am

Dreadful weather over the weekend - snow! And morning rain in Daytona delaying a lot of the Daytona 200 racing. Gave me some time to kick around in the shop.

Because the handlebars are a bit longer than the original, I didn't want to use a long bar end. So I turned down a little aluminum, and made my own. I'm rather happy with the way they turned out. The grips should extend to the end of the throttle, or just past. So the end of the bar will have a black band, then the aluminum end.

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One of the challenges of buying a bike in a box, is that inevitably some bits are not in the box. I ordered a tank cover spring from eBay. And then needed to make a retaining rod. So back to the lathe with a scrap piece of stainless rod. And pesto, a shiny new part.

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Still on the hunt for a replacement front wheel. Getting the broken bolt out s not the only issue. Someone also powder coated over some oxidation. On the inner wheel where the tire bead sits. Might explain the "slow leak" in the front the PO told me about.
1 x

User avatar
jkv357
Posts: 218
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 414
x 115

Re: Wayward 2003 GPR

Post by jkv357 » Mon Mar 14, 2022 7:18 am

al_pritchard wrote:
Mon Mar 14, 2022 6:38 am
(SNIP)
Still on the hunt for a replacement front wheel. Getting the broken bolt out s not the only issue. Someone also powder coated over some oxidation. On the inner wheel where the tire bead sits. Might explain the "slow leak" in the front the PO told me about.
If you hit a dead end, let me know.

I've repaired many corroded and damaged wheels, and most likely can fix it. It would get completely stripped, media blasted, chemically treated, masked, and powder coated as close to original as possible.

http://www.apexcustomcoating.com/media-blasting/

I have a custom machine shop nextdoor that most likely could get the bolt out if you can't.

I've coated mine, and can say the quality of the factory wheel isn't great - but we can get it back to looking better-than-new.

http://www.apexcustomcoating.com/rims-wheels/

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Jay
www.apexcustomcoating.com
1 x

User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Mar 28, 2022 7:35 am

Now it's on to the engine. It's stamped SENDAH, so if I understand correctly it's the equivalent of an EBE050?

From the look of things someone has ben in here before. So extra attention will be used to double check everything. And judging by the look of the clutch basket, and clutch screws. The last person in here did not bother with using the correct screws. 2 almost striped screw heads, and one was finger tight. (shaking my dam head)

Note the marks on the clutch basket
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I am so glad I got them out. Used an impact screwdriver - I love that tool
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And they didn't bother to bend over the retaining washer
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On the positive side, the clutch looks almost brand new. But they did manage to get one clutch plate in backwards
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User avatar
Jaxx
Posts: 51
Joined: Wed Jun 19, 2019 1:41 am
x 38
x 16

Re: Wayward 2003 GPR

Post by Jaxx » Wed Mar 30, 2022 11:18 am

Yeah, those clutch bolts can be a little tricky to unscrew with just an ordinary screwdriver, I use 1/4" ratchet and new, undamaged philips bit and it works fine.
0 x

User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Apr 11, 2022 6:26 am

People do the craziest things. For instance, hooking the rear brake peddle switch directly to the brake light. So when you pull the brake lever the brake light comes on, but then you also press the brake peddle it turned off. Genius! Now that we have the wiring worked out, it's on the the engine.

First off, would love to hear some recommendations for a big boar kit, pipe, and carb.

Saturday was "make a tool" time. Could not find a case splitter anywhere. But I did manage to find the flywheel tool at Treats

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One thing when splitting the case. Use the proper tool! Someone before me didn't. I'll bet they used a generic 3 arm splitter and tried to split it from the cover hols. It didn't work. Should be fine, just not going to be a pretty engine.

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Case came apart with no drama.

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I'll pause for a moment, and tell you that I was a little worried before splitting the case. When I drained the oil I noticed some flakes in the oil. I couldn't get the magnet to pick them us, and suspected that they were aluminum. When I got the case split, this is what I found all over the inside of the engine.

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Turns out it was the liberal application of Yamabond. PSA, use a gasket set! If you must use something like Yamabond, use it sparingly.

It looks like the crank is almost new. All the measurements are well within specifications. Certainly not what I would expect from a bottom end that has seen over 3k miles. Anyone recognize it? Part number on the side is: 30129512.

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User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Mon Apr 18, 2022 1:52 pm

Stumbled across this last week on Treats. It's a Airsal Xtreme 80cc big boar kit, well most of a kit. It's missing it's gaskets, exhaust studs, and water inlet. And the best part, it's not the correct head - I seem to remember ToraTora having this issue in another thread. No matter, all the parts are easily obtainable and on the way.

This kit uses the stock 40mm stroke. So no engine case modifications are needed.


The old piston and rings weight is a scant 58.5 grams. The new big bore piston and rings comes in at 88.1 grams. And is technically 49.94mm with a bore of 50mm you get a nice 0.06mm not to tight, but not to loose.

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Mildly aggressive porting :laughing: I'l get some measurements at some point this week to share with the group.

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Someone was kind enough to do some polishing on the exhaust port. 26.14mm wide with a bridge. The two little ports on top to the left and right also exit to the exhaust, you can kind of see the shadow where they enter the port. Interestingly the also exit further down the exhaust port, and the studs penetrate into the passageways. So then we install them, I need to remember to seal them or we will have a leak.

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If you look closely you can see the half moon there the head doesn't line up with the cylinder. Almost looks accidental as the cast in holes line up with the cylinder. The good news is the cylinder fits on the engine case.

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And lastly they also drilled a couple of holes on the exhaust side of the piston. You may have read in some of the other build threads. This helps to cool the exhaust bridge.

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Couple of questions for the group. I need carb and exhaust recommendations ,or thoughts.
2 x

User avatar
jkv357
Posts: 218
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 414
x 115

Re: Wayward 2003 GPR

Post by jkv357 » Tue Apr 19, 2022 6:20 am

I have the factory 75cc Derbi engine, and it came with an Arrow pipe and 24mm Mikuni Flatslide - which was WAY off when I got it. Rejetted and finally got it to run well, but I still think 24mm is too big. Your ports are bigger, but I'd still stick to 22mm or so (unless someone has specific experience that says otherwise). A smaller carb is going to give you better throttle response in the low and medium RPM range, with just a slight drop in max power. Needing to wind it up all the way, all the time, is a pain.

I don't recall the other carbs that people like - but it's not the Mikuni.

Treats should know, or someone here will chime in.


Jay
2 x

User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Wed May 04, 2022 1:32 pm

Global supply chains suck!

In the mean time, a little preview of things to come. The local powder coater came through with a beautiful job. Taking some styling inspiration from current MotoGP and Moto3. The bike will be a mat black, with a large Derbi logo, and have a pink front wheel. Blending the Aprilia MotoGP bike, with Ana Carrasco's Moto3 bike.

Don't panic, I'm not planning on painting over the original side fairing. Going to get some new ones from Air Tech.

Mat black for the rear wheel, and a pink with a hint of sparkle for the front
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Another pro tip, lightly sand the edges of the powder coat. So that it doesn't extend over the uncoated surface. Then you bold up the disk, It can put pressure not eh powder coating and cause it to flake off otherwise.
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Also brand new NG disks front and back
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ToraTora had a tip in one of his threads about using a unlock nut on the tightner to keep the bold from vibrating out. I used a small section of fuel line to get a similar effect. It does beg the question of how you would safety wire these?

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More when all the parts arrive!
2 x

User avatar
al_pritchard
Posts: 28
Joined: Sun Jan 09, 2022 2:15 pm
Location: Atlantic Highlands, NJ
Replica: 2003 Derbi GPR 50cc
x 6
x 44

Re: Wayward 2003 GPR

Post by al_pritchard » Mon May 09, 2022 7:37 am

PARTS!

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And perfect timing because the weather was awful this weekend. So I spent some time with the engine.

For starters, the new head arrived. This time with the proper spacing to fit the cylinder studs.
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A quick step over to the lathe, and a hand full of sandpaper scraps later. The chamber is all polished up.
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Then it was on to some porting work. The gasket set that comes with the Airsal is a bit ambitious. You cant actually take that much material out of the Derbi case. And the aluminum is not very thick there. But what you can do is round the edges, and put in a shadow channel.

It's so helpful to have a good tool when doing this. I am lucky that my wife has a jewelry studio. So I get to borrow her rotors tool.

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And some work on the cylinder. Didn't do to much, just match it up to the gasket, and work off some of the casting market.

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It looks so nice sitting all together.
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Look at that, another striped screw

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Stay tuned for more adventures.
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