"86 and 87 sle should be a flat reed engine, the flat reed engine came into play in 86, you can tell if it has a steel rear swingarm on a variant step thru, it is a flat reed, if its alloy, its piston port or pyramid
the 81 sle was pyramid reed, derbi rd’s were pyramid reed, derbi diablos are piston port, derbi lagunas are also piston port, the derbi ds50 scooter is flat reed'
quote by well known derbi conoseiour
Piston port engines cylinder inducted stroke: 43mm bore: 38mm displacement: 48.7cc compression 8.5:1 direction of rotation: counter clockwise facing magneto
Pyramid reed engines Pyramid 3-reed valve, Crankcase mounted stroke: 43mm bore: 38mm displacement: 48.6cc compression 8.5:1 direction of rotation: counter clockwise facing magneto.
Flat reed engines Crankcase 2-reed valve induction with triple transfer port distribution stroke: 40mm bore: 39.87mm displacement: 49cc compression: 10:1 direction of rotation: clockwise facing magneto. Max engine RPM: 6500
makin a water cooled derbi
A lot of people have asked me about this issue, and here I will try to clear any doubts about turning a moped liquid cooled. In this situation I will use a derbi variant with an old version of the (pro race for an aerox. Horizontal)
The first thing you are going to want to do is adapt the cylinder shaft/screws, For witch there is two ways of doing so. - First is the safest but hardest way to do so. Remove the shaft/screws and fill in the holes with aluminum bar/ screw or basically fill in the holes with aluminum. And shave it flush grind etc.. You get the idea. Now it’s as if it didn’t have shaft/screw holes.
Then you place the cylinder centered and mark the new holes. So that afterwards you can preferably using a stationary drill because you could run into problems if they are not straight. drill new ones. In this picture you can see the two screw/shafts from the right moved and the left ones unmoved.
-the second way is the easiest way but not as reliable. It consists of grinding the screw/shafts from the inside and the holes of the cylinder from the inside as well, keep trying until the cylinder gets all the way down. It won’t go in smoothly since it will be a little bit forced to fit. But I have done it like this and I have never had any problems. With a dremel these things are really easy to do.
(this is the chunk piece/part that has to be ground in the inside area of the shaft/screws)
(Here you can see where the cylinder has to be ground. It does not have to reach the top of the cylinder, because the gaskets will not sit right and coolant will leak)
If you are going to make your moped liquid cooled it’s almost necessary to match the ports so that you can make good use of the cylinder. To do this once you have adapted the screw/shafts you will have to mark up to where the cylinder transfers are. The way I did it was using a gasket. I used a metal gasket at the base of the cylinder then you cut it to the shape of the transfers ( kind of making a template). Here on the left of the picture you can se the gasket template already cut to the transfers on the left and center.
Then you place the gasket on the bottom end And mark/ traces what needs to be ground away. In this picture you can see the template and the marker tracings of what needs grinding on the left and on the right already done .
and now to grind away.
we run into a problem. The holes that appear when grinding there are two ways of fixing these. -one of them is to weld/ fill them in with aluminum -throw some kind of jb weld or other material from the outside and then grind away from the inside to make it smooth.
Now that we have the transfers matched the only thing left is to adjust the height of the piston. Since the derbi variant works with minarelli. For others I would have to study it. (I believe he is talking about the crank arm/ piston arm whatever it is called. Is compatible from derbi variant with some minarelli ones. ) to do this you mount everything but the head. And you look up to where the piston reaches if it comes out to much from the cilynder just add thick base gaskets until it fits well. If the piston does not reach to the top of the cylinder (which is what will happen) you will have to use a longer *piston arm , always use an arm that is bigger then what you think you will need because if you end up short you will have to buy another one. And change everything. In my case with this build the length of my piston arm was 78mm I only needed 4mm to reach to the top but I put one of 85mm. you need to find one with exactly all of the same measurements the one that I used and worked fine was this one.
Afterwards you can adjust the height by adding more base gaskets . The best bearings to use with this setup are these
There the bottom ones
Once this is done you have the cylinder mounted
All you are missing is the radiator system.
These are self explanatory. Top one talks about thermosifon hot water goes up cold water comes down no pump needed. Bottom one with a pump.