DRP: Derbi Reactivation Project

[toratora]

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.

[toratora]

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.

[toratora]

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.

[toratora]

When I assemble an engine I like to use grease to lube up all the bits. The piston, wrist pin, little end bearing, gaskets, o-rings. Pretty much everything get a bit of grease. Shops sell engine building grease for this purpose. It helps with the sealing, and protects the parts during assembly, and first startup.

Prepping for assembly. Polished up exhaust port.



Trimming the base gasket.



Bridge cooling holes in the piston (the drill slipped on the middle whole opps!).



Okay time to put on the top. This is a method I learned from the Moped cats. First you put the clip into one side of the piston (the side you wont be sliding the wrist pin into initially. Then slip the piston into the cylinder.



Then partially slide in the wrist pin to the edge of the first side of the piston leaving room for the crank, and little end bearing (you can do this step pin in before putting the piston into the cylinder).



Next rotate the crank to TDC, and carefully slid the cylinder onto the studs to the point where the wrist pin lines up with the little end of the crank with the wrist pin bearing already in it.



This next step is crucial! Once the cylinder is sitting there with the pin through the bearing waiting for the other clip to be inserted take a clean rag, and cover up the area below the piston. If you drop a clip into the crank case you might have to split the cases to get it out. It's much easier to cover it up with a rag.



Then insert the second clip.



After that the cylinder can be lowered down to the base gasket. I then like to check to make sure the piston isn't above the bottom of the ports when at BDC (bottom dead center).



Then place in the o-rings.



Then place on the head (it has it's own o-ring that you need to put on first--here the grease helps keep it in place when you flip the head into position).



Add the washers and nuts, and tighten to around 10-12 Nm using a cross pattern slowly from one stud to the next. Do this repeatedly until all the nuts are at the proper torque. It's important to not tighten one down all the way, and then go to the next. You could damage something that way, and you probably wont get a good seal.

[toratora]

I have to say I was excited to get to this step. I had already built a leak down test kit, but it wasn't going to work because the MityVac that I bought (sometime ago now) only does vacuum. They make a MityVac that can do both, but I didn't get that one. So I had to make a mod. I removed the brass fitting and employed a new valve stem that I had bought for another project, but didn't use because I could only get one of them.



I also made a stop at the Dollar Store today to get some bubbles. They only have the humungous version--32oz! I probably wont be needing any Snoop for quite a while. My roommate had never seen bubbles before so we had a grand time making them all over the kitchen--it's going to real easy to wash the floor next time.

I then hooked up the bicycle pump, only to find the system didn't hold pressure at all. It turns out that the exhaust studs on the Airsal Xtreme actually go into the passages. This was good to find out so that when I install the exhaust I'll employ sealant on the studs. So I popped in some studs temporarily, and tried it again. This time there was pressure, but as you can see this helped prove the validity of the Bubbles solution as an effective tool.



I also found a small leakage where I apparently didn't trip the case gasket well enough for the intake manifold to make a proper seal. Previously I would have missed this issue which would make tuning a pain in the ass, and likely as not cause a lean issue at some point--which could contribute to frying the engine. I really feel like I'm upping my game.



Don't worry Scotty, I'm going the be trying this out on the 45mm stroked engine soon.

[toratora]

Right, lots of posting today. You'd think that I've made great progress, and will soon be putting the engine into the bike. Well you'd be wrong. First I discovered that the RCS that I got was for 1" bars. Yup Harley action. Oh well. I'm not quite ready to install them, so the replacement will probably be here before I'm ready for it.

Next I thought the tranny was messed up again. The engine was doing that only turn so much, and then stopping thing again. I was almost convinced that it was the transfer gear. But I was wrong. I put my ear on the head, and I could hear the knocking. It was ever so slight, and not even enough unless the head was bolted down. If the head is just sitting there the o-rings lift it enough that there is no contact. Wow.

When I got this kit it was sort of a bastard. The box made claim that it was for a Euro3. But clearly the cylinder is for the Euro2. So I bought it. The cylinder works fine on the engine. Everything lines up. But the head is drilled with different dimensions. This didn't matter though, because I have a bunch of Airsal heads. :roll eyes:



Or so I thought. It turns out the 45mm Xtreme heads extend deeper into the cylinder than the 40mm stroked Xtreme heads. Here check them out.





And as you can see here there just isn't enough room for that much insertion.



So I could deck the head to the point that it didn't insert as much, but then the profile would be changed, which would dramatically effect the squish. I could use a bunch of base gaskets, until there was enough room, but that would kind of mess-up the transfer ports as the piston would be below where it should be for these port designs. This is one of those things that proves you should have your own personal lath hanging around.

[toratora]

Yeah things rarely go as planed! I guess I'm kind of use to that these days. :/

I went over to Treats today. Benji is going to get the proper head for it for me from Airsal. Yeah Benji!!! In the mean time I'm going to try two different things. Base gaskets, and look at the 45mm stroked engine. Benji hooked me up with a very attractive offer on the 45mm stroked kit. Lets hope #4 is a winner!

GLI, JP did some machining on a head for me on the Cagiva when I got the 150cc kit for it. He made a ring just like you are talking about--I'm sure he could do the same thing for this head, but since Benji can get me the proper one I might as well wait for it. I have a bunch of base gaskets laying around so I might as well give that a shot. If it doesn't look viable I can wait for the proper one to show up. In the mean time I'll build up the stroked engine.

By the way Benji has an Xtreme kit in stock for the Euro3 engine (it's got all the proper stuff, I checked). It's the 40mm stroke version so it will work with most any stock lengthen crank. If you have a Euro3 engine I'm pretty sure he'd give you a good deal on it. Either contact him directly, or let me know, and I'll help you.

[toratora]

I gathered up a bunch of base gaskets, and tried them out. I've left my solder at a friend's place so I can't yet do a squish test. That will have to wait. But the piston is sitting at about the right place at BDC so there is hope!

The only concern would be if it was more likely to develop an air leak at the base gasket. I've run into that issue previously. Case in point. I pulled out the 45mm stroke engine, and got the leak down test kit in play. The only place it is leaking is at the base gasket. It's doing this on both sides. This is with a Metrakit top end made for a 43mm stroke that I adjusted to work (it didn't work) with a 45mm stroke crank. This was one of those, well what do I have around experiments.

The good news though is that it's not leaking at the cases. So maybe the issues is something that I can address without splitting the cases. It will require further investigation.

[toratora]

First a quick look at the 40mm kit. With all the gaskets I'm getting a small leak at the back of the base gasket. I'm hoping that I'll be able to work on that, and fix it.

Okay now for the 45mm kit. It was difficult to photograph this because to get enough light on the subject the camera would strobe. But you can see oil in the bottom of the crank case. I suspect that this is trany oil. So yeah I'm probably going to have to split the cases to find out more. Ouch!

[toratora]

Hey Tom, yes if it is the main seals--you can change them out by removing the clutch cover, the clutch, pinion gear, and on the other side the stator/flywheel. But in this case if it was a bad main seal letting in the oil it would be on the clutch side. However, my current hypothesis is that on the 45mm stroke engine the gasket has failed, and that's what is allowing oil into the crank case. I suspect this because we had to remove some material to allow for the crank. We may have removed too much. Let me see if I can find a photo...okay it's in this photo, but hard to see. Anyway, I'll check the main seal on the clutch side before I split the cases on this engine.

For the 40mm stroked engine I was able to do a squish test. It was way too close. So I added more gaskets. I can get enough squish if I use multiple metal gaskets, but then I get leaks. Based on all the leaky action I've been finding I wonder how I ever built anything that ran previously. I am so glad that Matt posted about the leak down test kit. Plus, now I get to play with bubbles.