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Thread: Derbi Reactivation Project--The Return of the Wicked GPR

  1. #16
    apriliaforum expert ToraTora's Avatar
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    Unhappy Other People's Work

    Thanks for the info Matt. If I had a lath I'd probably give that a go. Without one though I don't trust my hand sanding ability to do it properly. :P

    I thought I was making great progress today. Finished up with a bunch of the cleaning last night and had planed to do the assembly today. Everything was going well, and got it the main cases buttoned up. The cranks spins nice and smooth, but the transmission doesn't want to spin well in fifth, and wont go into sixth. I hadn't taken the trany bits apart so I didn't expect this to be an issue. But really since there were signs that this engine had been opened previously should have given me pause to do a proper inspection.

    The Heat! This is pretty much the only kind of gun I have--I say pretty much because there's a glue gun around here somewhere too. :P



    The bearings dropped in.



    Checking the new gasket.





    The crank sitting in the new bearing before full insertion.





    Almost time to put it together.



    The sexy new Malossi drive shaft seal.



    The manual states to make sure the bolts are all clean. This is the before shot, and they aren't too bad, but I did some cleaning on them anyway. The torque setting on these bolts is 6NM, or about 53 inch pounds.



    All together, and waiting to come apart.


  2. #17
    apriliaforum expert mattology's Avatar
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    are you spinning both shafts when you try to switch gears and have it completely vertical?

    I slip fit the cranks by hand. No lathe, just V-blocks

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

  3. #18
    apriliaforum expert ToraTora's Avatar
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    Wink Phase Shift

    Yeah I took it apart, and cleaned it all out. Then made sure by the docs it was all together correctly. It's working now.

    Sadly due to my current circumstances I don't have access to the usual tool action. Notice I'm working on the kitchen table. :P


  4. #19
    apriliaforum expert ToraTora's Avatar
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    Talking A Peek at the Future

    Made a little progress today, but I'm waiting on some tools to return, and that's slowed me down a bit. So I decided to put some of the pieces together to see hows it's going to look. :P












  5. #20
    apriliaforum Junkie matt_booth's Avatar
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    So my doopler endurance 39mm wouldnt work with the xtreme kit damn..... 39mm to 40mm would it work or is it a marketing ploy i mean 1mm really ? Thats a gasket ahaha

    Considering going for this kit on my am6 id be interested in what itd be like to "deal with" on the road when yours is complete a write up on the kit would be greatly apreciated
    Last edited by matt_booth; 10-01-2015 at 03:03 AM.


    2014 cpi sm
    77cc airsal twin ring racing
    modified airbox
    21mm delorto phbg
    Yasuni r3
    V force 3 reeds by stage 6 <~ amazing
    Motoforce racing inlet manifold
    Rpm limiter spoiling the powerband

    Future work
    lightening flywheel
    top performance cdi ( if i can find what terminals do what)
    Maybe a 28mm carb



  6. #21
    apriliaforum expert scottydog's Avatar
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    Very nice looking, so clean and new! Tora so why was the 45mm stroke engine not so happy? I'll probably get back to work on mine, I have the jets now to get back to work on it.
    Currently

    Honda MBX, Dream 50, Solo 50, NSR, CBR 150
    Moriwaki 80, Derbi GPR50

    In works

    Honda NSR (SP)
    Honda RVF150R / NR150 custom

    Previously

    Kawasaki AR80
    Honda RS125

  7. #22
    apriliaforum expert ToraTora's Avatar
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    Wink Responsive Design

    Matt, the stock stroke on the AM6 employs the shorter dimension of making a not quite 50cc engine. The Derbi EBE/EBS/DB engines use the 40mm dimension. To make a "fifty" they actually have to come in just under 50cc, because of regulations. They can call it a 50, but the actual displacement has to be just under 50cc. Derbi put the longer dimension in the stroke, Minarelli put it in the bore. But the folks that make BBKs, and cranks know this so you don't have to worry about it.

    Scotty, I haven't yet opened up the stroker engine to find out. I just put together a leak down kit which I intend to employ on that engine once the MityVac returns (it was loaned out). Guess I need to make a soapy water solution for testing too. Once I do the leak down test I'll use that information for further study. I suspect there is an air leak in the cases that's causing a lean situation that contributes to an overly hot combustion chamber resulting in seizure. But that's just my current hypothesis. I need to do some testing, and inspecting to find out. This is also why I'm so interested in the EGT and lambda sensors. I really want to know what's going on with these engines so that I can avoid the future seizing action.

    Thanks for the nice words on the cleaning. It takes a huge amount of time to do it.

  8. #23
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    Question about your RPM pickup on the DB motors. Does it use a RPM gear like the AM6 or is it a signal pickup? Im trying to see if I should keep my stock guages or go rs4 stuff but I dont know how to get the input.
    2005 Rs50 Rs4/GPR clone

  9. #24
    apriliaforum expert ToraTora's Avatar
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    Wink What Time is it? (again)

    Hey D,

    Funny I just posted this in your thread. The older Derbi engines did employ a gear off of the crank. But in 2002 I think it was they went to an electric pickup tach. It simply has a wire that wraps around the plug lead. Some gauges have you plug into the trigger that connect to the coil. On page one of this thread I posted an image of the MyChron4. I'm seriously considering this as a dash replacement on this bike because it has the sensors I want, and with the GPS unit it can do speed as well. Plus it is a data logger. Lots of good info could be collected. Imagine being able to corollate (after your ride) the temps, RPM, and rates of your favorite roads. The only thing I think it's missing is some sort of barometer, and lambda sensor. But you could look up what the conditions were for that day, and maybe there's a lambda solution. Koso makes a lambda pickup that's specific for two strokes. But I'm still in the research phase for that unit. Matt's got the MyChron already, so we can pick his brain about it.

  10. #25
    apriliaforum expert ToraTora's Avatar
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    Wink Moichido--how to set a balanced GPR engine with a performance crank

    It's a strange feeling when you search for help on the web, and your posts on how to do things are the closest you find.

    Today, with the help of my friend Ed, we cracked an important Euro2 Derbi engine secret. There are two versions of of these engines. One that has a balancer, and one that doe not. The balanced engine has markings on the gears to indicate how to set things so that the balancer is properly aligned with the crank. All of the performance cranks I've ever seen for the Derbi engine are designed for the non-balanced engine.

    Now let me quickly state that when I say balanced in this context I'm not talking about machining the crank so that it is itself balanced. You could, and would probably benefit from doing that with either engine.

    Here's a stock GPR balanced crank from the clutch side.



    Here's the Airsal crank.



    And a stock Senda non-balanced engine crank



    By comparing these you'll notice that the balanced crank features a stepped design, while the non-balanced cranks feature a taper design. It may be a little difficult to see with these phone photos. My apologies.

    Here are the two different primary drive gears for these cranks. The one on the left is the stepped design (I believe it to be Derbi part #00H02610381), and features a notch on the top of the gear, and a woodruff key slot. Notice that the taper gear on the right (I believe it to be Derbi part #00H02601381) features neither of these items. Yes you will need to source one of the taper gears if you upgrade your crank on one of the balanced engines (which is why I included the part numbers).



    If you have a Senda with a non-balanced engine, and you upgrade your crank you'll not run into this issue. But if you have a GPR which features a balanced engine you will run into an issue when you go to set the alignment for the balancer, because there is no mark on the gear.

    Ordinarily what you would do is set the balancer to align with the case mark, the mark on the balancer gear like this:



    Then you would turn the crank so that the notch on the gear aligned with this mark, but now you cannot because there is no mark on the gear. What do you do?



    Well as it turns out it's pretty easy. Aligning to that mark would actually just set the crank to TDC (top dead center). So all you have to do is set the balancer to its mark, set the crank to TDC, and then set the clutch basket into place. Mystery solved.

    Last edited by ToraTora; 09-30-2015 at 01:51 PM.

  11. #26
    apriliaforum expert mattology's Avatar
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    Nice work on the balancer. depending on the weight of your reciprocating assembly, it's stroke, and it's operating rpm, as well as the angle it is mounted in the engine, you can experiment with phasing the balancer to see when it is the smoothest in the powerband.

    My guess is that it will always be smoothest to the factory setting, because vector summation, but you can be surprised at times.

    If you run a longer stroke and a larger bore piston which will obviously increase the mass, you can experiment with machining the balancer, and pressing in tungsten inserts which will make the balancer have a greater effect vs the first order vibrations of the larger recriprocating mass it is trying to damp.

    i would absolutely always run a balancer if given the opportunity. I'm building a 500cc single right now with a balancer for a road race bike. you know, some day, when i'm home for more than 16 hours at a time.


    leak testing


    buy yourself a bottle of Snoop and never look back
    Last edited by mattology; 09-30-2015 at 08:20 AM.

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

  12. #27
    apriliaforum Junkie freedomgli's Avatar
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    Quote Originally Posted by ToraTora View Post
    It's a strange feeling when you search for help on the web, and your posts on how to do things are the closest you find.
    I know the feeling! But seriously, thanks for all the project updates. The technical detail and photos are really insightful and gives us hobbyists inspiration to follow in your footsteps with our own projects.

  13. #28
    apriliaforum expert ToraTora's Avatar
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    Cool Torque, it's not just a fun movie.

    I've set the balancer wrong before, and it made the bike unridable. On my EBE075 engine I had to replace the shifter mechanism. This required removing the clutch basket. I was very new to these engines, and didn't yet have the proper docs. Paz was the test rider, and rode the bike for a whole day. When we got back to my place I took it for a spin. I couldn't believe how much it vibrated. I asked him about it. His response was he thought that was normal for the Derbi! Damn Aprilia riders!

    Anyway, after that I did some research, and started to get the balance right.

    That snoop stuff looks pretty cool. I'm probably just going to head down to the Dollar Store, and pick up some kid's bubbles for now. Later I'll try out the snoop. But I've got a slightly bigger issue to deal with for my leak testing. It turns out the MityVac I bought is unidirectional. It will only suck. I can use my bicycle pump as it's high volume low pressure, and can easily do the required 6psi, but I'll have to come up with a different connection to the leak plugs.

    The main reason Ed came over last night was because I was tearing up all the gear pullers. The pinion just didn't want to come off. I had tried heat, and a hammer to break up the static friction. But I was getting nowhere. Ed brought over some high end snapon action, and we proceeded to chew up his puller. The nice thing about the snapon puller is that it had a good surface for hammering. It doesn't take a lot of force with the hammer to switch the static to kinetic, but it took about 20 blows to accomplish it. Today I discovered why it was probably so difficult. The torque setting for the pinion is 8 to 10 Nm. Yeah almost nothing. The person that had previously worked on the engine probably torqued it to 30 or 40 Nm. The thing is it's not the nut that holds the pinion in place, it's the taper. The nut simply creates the correct amount of friction. Such a classic wrenching mistake.

    So lets help fix this situation with even more technical detail. Here are the Derbi Torque Specs!

    Derbi torque specs.pdf

    Click image for larger version. 

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  14. #29
    apriliaforum expert ToraTora's Avatar
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    Wink Getting Creative, and the Derbi Clutch Basket Assembly

    Need a Special Tool?
    Getting creative with solutions is part of the tuners tool kit. Lets say that you want to torque the clutch basket bolt. The setting is suppose to be between 35 and 45 Nm. That's a fair amount of force. But lets say that you don't have the custom tool to hold the clutch in place. Here's what you can do. The output shaft can be held with a 16mm six point socket. The transmission needs to be put in gear. The nut on the basket is a 19mm. If you turn the nut, and hold the output shaft the engine will spin. A good size screw driver placed in the forward engine mount such that it rests on the wrench holding the output shaft will keep the engine from spinning. Thus the nut can be brought to full torque all without any of the special tools.



    Setting up the Clutch
    When you place the clutch disc in the basket make sure the labels face outward.



    The next point of interest is this mark on the basket.



    When you place the face plate on the basket line up the Derbi logo with the mark on the basket.

    Last edited by ToraTora; 10-03-2015 at 11:25 AM. Reason: spelling

  15. #30
    apriliaforum Junkie matt_booth's Avatar
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    Cheers so alll these updates, yesterday due to me finally getting annyed eith my clutch slipping i decide to buy dome stiffer springs
    my clone am6 is slightly different oviously like it has 5 clutch springs
    so i had to buy 2 packs of 4 -_- if only i could of waited another day aha another interesting thing about the clone is that the exhaust mounting uses bolts instead of the springs but whats great is the bolt paterns the same as tge db050 ( my airsal has the bolt patern aswell)
    Back to tge point in hand damn....... 2 packs -_-
    Last edited by matt_booth; 10-01-2015 at 03:02 AM.


    2014 cpi sm
    77cc airsal twin ring racing
    modified airbox
    21mm delorto phbg
    Yasuni r3
    V force 3 reeds by stage 6 <~ amazing
    Motoforce racing inlet manifold
    Rpm limiter spoiling the powerband

    Future work
    lightening flywheel
    top performance cdi ( if i can find what terminals do what)
    Maybe a 28mm carb



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