Derbi—The Red Power

[toratora]

Most of the recent effort has been put towards the PMPR, the Malossi bike, and the Cobra, but the Silver bike hasn’t been forgotten. There was a small window of time to check out the head on it. Since the head on the PMRP failed it was logical to surmise that the one on the Silver bike could be suffering from the same problem. This was based on the two bikes behaving in a very similar fashion, and the compression tests showed them both to be at around 75psi. Well all that information was fine, but it turns out that the Silver bike must have another issue causing its circumstances.




Prepping the head for removal.


With the head off it was clear to see that it looks brand new. No damage like found on the PMPR head, and the o-rings were in perfect order as well. There is some slight scoring on the cylinder wall, but not really enough to keep it from turning over. Still they really should have put the o-rings on the cylinder like other kits such as the Airsal, Derbi, and Metrakit top ends.

[toratora]

I located the BRK 43mm stroke kit today. If I can figure out the spacing I can get this to work—which I would really like to do because with this kit I think the Malossi bike could become a very fun bike to ride. It would also have the added benefit of having figured out how to ensure a future for the EBE075 engines.

I have some spacer plates, but none of them really match up well to the cases. Really the best thing to do would be to find one of those laser cutting places, and have some custom spacers made.

I do need the correct wrist pin bearing though. I thought it was a 12x15x15, but that is incorrect. Once I have the correct size I’m going to swap out the studs and try to figure out the proper thickness of the spacer by combining the ones that I have, and checking the squish. That should get me to a close enough spacer thickness.

Airsal use to have a kit that came with a spacer. I have a friend that has one of those kits. I’m pretty sure the spacer for that kit would be the same for this one, so hopefully he can come up with the info. In the mean time I’ll keep messing around with what I have now.

[toratora]

I’m really starting to feel like I might pull this off!! Project 075 has been a very long time coming, and now I can actually see the light at the end of the tunnel.


Today’s challenge was getting some solder with which to check the squish. With Radio Shack gone there’s just no place that carries the proper tools around here anymore. I did find some 0.1" diameter non-rosin core at the local auto supply, which works for now.

I also pulled out the head nuts from the Euro3 engine. With these I could remove the studs. But it wasn’t easy. Even with copious amounts of penetrating fluid these studs were stuck. I had to use a three nut lock to remove them.


The stock M7 studs measure about 110.5mm, and the ones I bought from Maxi come in at 115.5. Clearly they are too short, and I can probably go with 120mm or maybe even 125mm studs.


To make this work requires the proper spacer set up. I don’t really have the proper spacer, but I have three from which I can experiment. One is a steal unit that is just about 5mm thick. The next is an aluminum Parmakit spacer that is about 4mm thick—this is probably what I'm going to employ. And I also have a ~1.5mm spacer that I got from Maxiscoot. I figured if I could test the squish I could figure out which spacer to employ.


I tried the combination of the 4mm and 1.5mm and that was too much. Then I tried the 4mm with two thin gaskets, and that’s actually very close. That came out to a squish of 0.18mm, which is not enough. By adding a coper gasket it got to 0.42mm. This is very close to the 0.65mm target zone, although I might go for more like 0.7-0.75mm for better over rev. This engine should have very decent torque considering it has a longer stroke, and the bore will go from 47mm to 50mm.


Another issue I ran into is that the little end bearing isn’t a 15mm, it’s a 16mm. So I’m going to have to source the proper bearing for it as well. Lots of little things to order, but it is getting closer and closer!

[toratora]

Today a bunch of stuff from Treats came in so I was able to make some pretty decent progress with Project 075.


Some of the parts are for the Cobra, and for Ed’s fleet, but most of this was for Project 075. Longer 125mm Polini cylinder studs, a 12x16x16 Malossi little end bearing, some M7 washers and nuts for securing the top end, and a gasket kit. While wrenching on the Cobra I noticed that the chain has seen better days. Treats just got in these Doppler 420 chains, and so far most of the Doppler parts I’ve bought have been pretty decent so I figured I’d try one of their chains on the Cobra, but maybe it’s going to end up on Project 075!


Removing the old studs was quite an ordeal. Not only did I have to employ the penetrating fluid, double wrench, and the triple nut lock, I also had to bring out the heat gun. Eventually though they came out, and I was able to move forward.


It is interesting to compare the various cylinder studs. The Polinis are 125mm, the stock ones are 110.5mm, the Maxiscoots are 115.5, and the Metrakit ProRace cylinder studs are 125mm. I used permanent thread lock with the new studs, and bagged up the stock studs in case I may need to employ them in the future.


The Polini studs went in swimmingly. Then I put things together as I had previously with a bit better torque. The squish measured at 0.40mm, which is too little.


Then I employed the gasket kit, removing the thin Parmakit gasket, and replaced it with the new thicker gasket.


With the gasket change, and the o-rings in place the new squish came in at 0.63mm, which is very close to the target—something between 0.65mm and 0.80mm. With a slight gasket swap, and some sealant I’m confident that the proper squish is obtainable.

Next up is modding the spacer and gaskets so that they don’t impede the flow of the charge into the transfers. I’m also going to have to open up the cylinder’s transfers a bit to line up with the cases since the 075 has much wider transfers than the 050 for which the cylinder was designed. But now I’m getting ahead of myself!!

[toratora]

I was chatting with Sean about this project when I suddenly realized that I hadn’t checked the port timing. In addition to the squish the port timing is another rather important variable. So it was time to charge up the bore scope.


As it turns out the timing is off by quite a bit. Previously when I tried to solve this problem I ran into this issue, and it’s what stopped me. Given enough time I had forgotten about it!


Here we can see that with the piston located to bottom dead center (BDC) the exhaust port is actually quite close to the proper amount, but the transfer ports are all much lower than the piston lip.


I was finding the blue light from the bore scope’s LEDs was having issues with getting a proper photo. I tried placing a flash light in the exhaust port, and turned off the bore scope’s light. The photos do have a better look to them. And the conclusion is that with this set up the port timing is severely compromised.


I think I might be able to ameliorate some of this issue with piston ramps, but I need to do some more research before I go forward with this idea.

[kaldis12]

I would raise the cylinder to match the transfers, and machine down from the head or the cylinder top to achieve the desired squish.

[toratora]

I would raise the cylinder to match the transfers, and machine down from the head or the cylinder top to achieve the desired squish.

If I had access to a machine shop then that would be an option. But I really only have access to what I can find in my kitchen, and last time I looked there wasn’t a lathe in there!

[kaldis12]

Oh I see, that kinda sucks maan. Anyway wish you good luck with that kit. (Not like with the Stage6 )

[toratora]

I dug out some more gaskets making a sandwich of copper, paper, spacer, paper, and copper. This created a squish of 0.91mm. More than the target range I was going for, but should be decent enough. The third photo is of the stock base gasket with the spacer illustrating where I’ll need to modify the spacer, gaskets, and the cylinder for optimal flow to the transfers.

I also did a bunch of visual art photos with the bore scope. With some changes to the camera setting I’m now getting much better photos. The ultra blue lighting is cool and all, but makes is much more challenging to tell what’s going on.

[toratora]

I had intended on taking the Silver bike’s engine, and fitting a top end in good working order. But having looked at the engine from the race bike I picked up last year I think I’m going to go with it.


It seems to have had a little bit of work done on the cylinder, and should be able to go together quickly enough. I might need to service the water pump on it though...