My 2002 Derbi GP1 Scooter Project

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Tyler VR
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My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Sun Jul 23, 2017 2:17 am

I bought this Derbi Gp1 that had a blown engine, I drove up to Seattle to pick it up. I've always wanted one but they rarely come up for sale, but it's kind of a gamble since it needs work. It's the first non Honda scooter I've owned and my first water cooled engine also. The previous owner claimed it did 55mph with a 70cc BBK before it popped. I've all ready got a new top end on order, hope that's all I need to get it running.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Sun Jul 23, 2017 4:08 am

I noticed some shards of metal in the case from the blown top end. I decided to flush it with brake cleaner and premix then suck it out, repeated that a dozen times.
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Re: My 2002 Derbi GP1 Scooter Project

Post by Wheelman-111 » Tue Jul 25, 2017 1:58 pm

Greetings:

Nice find!

Did you wonder why the liquid-cooled aftermarket cylinder kit grenaded at 3400 KM?
Cleaning the shards is an excellent idea, but it won't help much if the bearing rollers are already notched.
Consider splitting the cases, measure the crank thoroughly and replace the bearings. You'll sleep better.
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
Still Seeking Red PCX-150
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox, Carb and Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 99KPH

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Tue Jul 25, 2017 2:44 pm

The exact reason why it blew is unknown, looking at the old piston I'm guessing it was running lean and got too hot. This derbi also has a aftermarket exhaust pipe and little bigger carb. I'm thinking the previous owner took off the stock airbox and installed a high flow filter without re jetting. I'm avoiding splitting the cases, if I had to this project would probably go on the back burner until winter.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Tue Jul 25, 2017 2:53 pm

Got the new top end kit, it's a cheap one off ebay. I think the old top end is a brand called airsal, it's a aluminum jug and the new one is cast iron.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Wheelman-111 » Tue Jul 25, 2017 4:55 pm

Greetings:

I think you may be right about "got too hot"! Yikes!

I don't see the o-ring grooves in the new cylinder or the head. Is the O-ring just compressed by the flat surfaces, or are there ring channels I can't make out in the pics?

The outside top of the new head appears to be a better design. Hope it rocks!
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
Still Seeking Red PCX-150
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox, Carb and Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 99KPH

:coolcruise:

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Thu Jul 27, 2017 4:24 pm

Wheelman-111 wrote:Greetings:

I think you may be right about "got too hot"! Yikes!

I don't see the o-ring grooves in the new cylinder or the head. Is the O-ring just compressed by the flat surfaces, or are there ring channels I can't make out in the pics?

The outside top of the new head appears to be a better design. Hope it rocks!
Yeah there is a o-ring groove on the head but the ring doesn't appear to seat in the groove well, hope it seals good.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Thu Jul 27, 2017 4:27 pm

I had to buy this water outlet pipe since this top end kit it different than the last.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Thu Jul 27, 2017 4:45 pm

I went to install the new top and was torquing the head bolts when a head stud snapped. I was lucky enough to get a easy out to bite and got the remaining threads extracted from the engine block. I'm going to try again tomorrow with just some m6 all thread.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Sun Jul 30, 2017 1:14 am

It runs, just doing some heat cycles to break it in.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Tue Aug 01, 2017 4:22 pm

I keep blowing fuses just seconds after the ignition is turned on. The engine still runs, but I haven't rode it yet, so I've just been heat cycling it. I figured out the problem was the voltage rectifier/regulator; blew a lot of fuses trying to figure it out.

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Re: My 2002 Derbi GP1 Scooter Project

Post by Wheelman-111 » Thu Aug 03, 2017 12:57 pm

Greetings:

Did the fuses blow BEFORE you started the engine, or only after it was running? In the former case, it sounds more like a grounded, short-circuited wire. In the latter, did a new regulator solve the fuses blowing? That's a LOT of fuses... Like, 21?
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
Still Seeking Red PCX-150
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox, Carb and Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 99KPH

:coolcruise:

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Tyler VR
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Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Fri Aug 04, 2017 4:41 pm

Wheelman-111 wrote:Greetings:

Did the fuses blow BEFORE you started the engine, or only after it was running? In the former case, it sounds more like a grounded, short-circuited wire. In the latter, did a new regulator solve the fuses blowing? That's a LOT of fuses... Like, 21?
The fuse would pop 4 seconds after turning the key on without doing anything else, everything seemed to work for that 4 seconds. The engine started with the kick start even with a bad fuse, no lights or anything else worked. I went around and cleaned all the wiring contacts and light bulb sockets had corrosion I cleaned up, but none of that helped with the fuse problem.

A brand new rectifier solved the problem, $60 fix. At least I found a US seller, otherwise it would had been a 3 weeks wait from Europe. https://scooterpartsco.com/

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Re: My 2002 Derbi GP1 Scooter Project

Post by Wheelman-111 » Fri Aug 04, 2017 6:28 pm

Greetings:

Good thinking on pointing straight to the problem. Usually we end up throwing the wrong parts at it until the problem stops... with the right one. $60 doesn't sound too bad. Are these rectifers made in Italy, Japan or elsewhere?
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
Still Seeking Red PCX-150
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox, Carb and Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 99KPH

:coolcruise:

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Tyler VR
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Location: Portland, OR

Re: My 2002 Derbi GP1 Scooter Project

Post by Tyler VR » Sat Aug 05, 2017 3:19 pm

Wheelman-111 wrote:Greetings:

Good thinking on pointing straight to the problem. Usually we end up throwing the wrong parts at it until the problem stops... with the right one. $60 doesn't sound too bad. Are these rectifers made in Italy, Japan or elsewhere?
Probably made somewhere in Europe, I think it was a common vespa or piaggio part used on a few different models.

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