Ducati 2-Stroke Service Info

The engine assembly page has a lot of stuff I learned about these engines and how to put them together; I hope this will help fill in the blanks. Because if Ducati ever had any 2-stroke service information, I couldn't find it. I wish I would have taken more pictures, but I never do. I had to start with a basket case, so everything was halfass apart and I only had the parts book to guide me through the assembly. Here's what I had after I got the cases washed up. Then I disassembled the clutch basket and removed that assembly, and removed the seals and bearings. I left the kickstarter idler gears (left top photo) and clutch actuator shaft (coming down just to the upper left of the idler gears) in place as they seemed fine. My crank had a bunged-up thread on one end where the someone tried to force a left-hand thread to come off like a right hander. By some miracle Eurotrash Jumbalaya had a crank for $50, that was a steal! (They also have pistons and gaskets for these, but see my caveats below before buying gaskets from them.) Also notice the chunk of case missing, bottom left on the upper left edge. This chunk is busted off on every Duc 2-stroke case I have ever seen. It's right over the chain and I have to believe that the chain does it when it loosens or breaks (I have the chunk, so I know it's not "just like that").

Anyway, here are some assembly notes:

#1 job is to get a parts book for your engine. There are real differences between the 48 and 100 engines. Getting a Brio book is really important if you have a basket case, but not so much if you're being careful and cataloging everything. Looking up the part numbers will not get you any results.

Luckily, some of the engine parts can be found. Ducati used the basic 2-stroke engine in mopeds, small motorcycles, and even things like water pumps.

If you are disassembling this motor, ask yourself why. If the bottom end looks/feels ok and the gears shift clean it up and be done. If you take it apart there is a good chance that it will never go back together. That said, taking it apart is pretty straightforward. However, there are some things you should watch for. TAKE LOTS OF PICTURES DURING THIS PROCESS. USE BAGGIES FOR EACH ASSEMBLY AND WRITE THE CONTENTS ON THEM USING A SHARPIE.

Take off all the shrouding. Loosen the head and remove the barrel - carefully, tapping the fins from the side with a rubber hammer if necessary. Remove piston clip and pin and remove piston. Release the clutch assembly springs and remove all parts. There are two clutch push rods that will fall out of the center hole and they have a ball bearing in between.

Using an impact wrench spin off the clutch nut and the crank nut (left side). While you're at it use the impact to spin off the sprocket nut on the right side, but leave it hand tight. Remove the clutch basket. use a small puller to get off the crank gear, it's a tight fit. Make some tool to remove the goofy round nut holding the points cover on, it's a pin wrench, really. Remove the right side crank nut -THIS NUT IS LEFT HAND THREAD - CLOCKWISE TO REMOVE! Remove the stator plate (two screws), taking pictures of where the screws go and orientation (there are a LOT of screw holes in the stator housing for different stators - only two are the right ones!). Carefully pull the wires out through the right half.

Remove the snap ring holding the kickstarter stop on the left half, and pull off the stop, (keeping in mind that it has a spring on it, under considerable tension, careful) and remove the stop and spring. You will have to find a way to get out the pivoting part on the shift arm that rides in a groove in the mainshaft and shifts the gears. I think it involves removal of a split pin in part of the shift arm, mine was off somehow already, and that's how I got it back on.

Use an impact driver to loosen the case screws; be aware that some come from the opposite side. Remove the screws. Start working the case apart trying to keep the shafts in the RIGHT half. No prying on the gasket surfaces. Smack the crank with a rubber hammer on the LEFT side and tap on the shift mechanism on the trans mainshaft, LEFT side. You can tap on the kickstarter shaft on the right side. When it starts to come apart start pulling the left half away from the right, looking for the loose barrel roller bearings that will fall out of the mainshaft bearing (all over the floor probably.. these are hard to find and probably still good, so don't lose any). Everything should be still in the right half when you separate the case halves. That's how you're going to put it back together when the time comes, so make note of EVERYTHING. Take pictures. The only thing that has to be in the left half during assembly is the kickstarter shaft, because the friction spring in that assembly fits over a pin in the left half, and it has to be installed without it slipping off.

If you're lucky and had been tapping on the left side of the crank, it will come out of the left side bearing and be sitting in the case. Start by removing the crank. The trans mainshaft is the one to watch out for. Remove the sprocket nut and sprocket, spacer, washer, etc. taking note of assembly. Now you're going to pull the shaft out of the bearing, but wait - when you do, there is a spring/single ball bearing pair on each side of the shaft that is held in ONLY BY THE INNER BEARING SURFACE. So when you pull the shaft out the springs will shoot out wherever, and the tiny bearings will fall wherever. You've been warned. Now you can lift the clutch/secondary gear cluster shaft revealing MORE loose roller barrel bearings, different size than the ones on the other side of the case. Don't lose any. Bag everything. Remove the snap ring on the kickstart shaft and the shaft.

That's it! Clean everything.

If you're familiar with what has to happen to replace bearings in a motorcycle case such as this, great. If not, find a good Vespa site that explains the process. Then have someone else rebuild your engine. This is not the engine to learn this on. Basically you have to lever out the seals and find a way to drive the bearings out evenly. Use a large socket that is a bit smaller than the outer bearing race. Then the new bearings go in the freezer and the cases in the oven, or use a torch, and if you're lucky you can carefully and evenly drive them in. If you're unlucky, you will have to repeat the process and hopefully you didn't screw anything up. Don't try this unless you are really confident in your mechanical abilities.

You have to source the seals and bearings from generic sources. This is easy - seals marked SMIM2035/7 have a 20mm ID (shaft) 35mm OD (bore) and are 7mm thick. Search for "seal 20 x 35 x 7". Be sure to get single lip seals, the double lip ones pop up sometimes but it's not what it had.

Bearings often don't have easy to decode markings like this, but you should have a Brio parts book. They list the generic size: RIV 1A 20 x 47 x 14 UNI 4203. Some of these numbers are important, but mostly you would search the web for "bearing 20 x 47 x 14" (even Ebay or Amazon can be great places to find these). Again, that's a 20mm ID (shaft) 47mm OD (bore) and a thickness of 14mm.

If there is any chance that your bearings are ok just run solvent through them, turning them around until they run smooth. I would not even remove the trans shaft from the right side output bearing if this were the case. Replace only the ones you know are bad if possible. This is NOT going to be a daily driver, it's a fragile ancient machine.

Gaskets can be obtained from Eurotrash Jumbalaya, but the barrel gasket they list for Ducati 2-stroke is not the right one. It looks like it in the picture but is all wrong (I did find one on Ebay). The case gaskets that they have are shrunken from time and need to be soaked in water to expand them. If I had it to do over I would just use case glue like Threebond 1194 and make sure I had the cases sealed - the original gasket is super thin shrunken paper and is not impressive. EJ has the clutch side gasket and that is a good one.

The kickstarter mechanism is fragile on these. The thrust washers take a lot of abuse and usually are slightly coned from the engaged shaft slamming into them. Flatten or replace them and get new o-rings. They are Buna o-rings 13mm x 1.6mm (2); I have quite a few left over. They are a bitch to get into the case when on the shaft without shearing part of them off, but it can be done. More on this later.

Install the crank bearing flush, then the output shaft bearing AND shaft assembled. Installing that output shaft in the right case half is tough, because you have to have the bearing on the shaft while you do it. If Ducati had a better way, I don't know what it is. The bearing holds in two small springs each with a ball bearing pushing in on the center shift rod/cruciform to provide detents for the gears. So when you push or pull on the shift rod the spring & bearing on each side move to the next groove and stop at that gear. The only other way to do it would be to install the bearing first, which you would normally do... but then you would have to somehow hold the little springs (which are under that biggest gear) flush with the shaft while pushing it all into the bearing (which is in the case under the whole mess with NO clearance). Believe me when I say it was hard enough to hold the springs in (holding the shaft in my hand) and get the bearing pushed over them. And if you accidentally pull the bearing off the springs they will shoot out and the bearings will fall somewhere (oh, the horror) and you will maybe find one of each after looking for a day. So don't do that. Stick the whole shaft & bearing assembly in the freezer for hours, and get the case really hot in the oven. Don't settle for cool and warm. Get the oven mitts on. If you do this right you should be able to tap the assembly right in; it might just push in. I had a tough one and had to use the sprocket and nut to help pull it in. Not too far; just enough so the gear almost rubs against the case. I don't know the spec but this is about where it's supposed to be, for end to end clearance inside the case when assembled.

Throughout this assembly do not be tempted to install any seals prematurely. You might have to apply heat at some point and that could possibly wreck a seal. The only seal that you HAVE to install before the cases go together is the left crank bearing seal. It's installed backwards, INSIDE the case with the bearing on the outside, so it's lubricated by the trans oil instead of the mixture. Nice.

So the only thing that gets installed in the left case half is the kickstarter shaft. Make sure all the parts look good and replace snap rings. New Buna o-rings 13mm x 1.6mm in the two grooves, one on each side of the gear. Grease the o-rings well and install the shaft in the left half. It's here where you will see how hard it is to get the left o-ring past the edge of the case without shearing off some rubber. Maybe something could be tightened around the o-ring to flatten it a little before install. Anyway, that's the easy one. After you get it in make sure the tension spring (on the gear) is around the pin coming out of the case and tighten a hose clamp around the shaft outside the case so it can't move off that pin. The o-ring on the right side will be a pain in the ass to get in when you're busy trying to keep track of several other things when you mate the cases, but you won't have to worry about the shaft falling in and coming off that pin.