The Mega Paso Engine

(Updated: June 26, 2008 - Scroll toward the bottom for the most recent update)

[The 916 engine from a 1999 ST4.]

May 23, 2008
This is the engine that I intend to try to stuff into a 1988 Ducati Paso 750 frame. The engine is a 916cc desmoquattro from a 1999 Ducati ST4. The swingarm bosses on the cases are different than the original Pantah engine's and the ST4's mounting lugs are wider, so both of these items need to be addressed to be installed into the Paso's frame. The Pantah was also air/oil cooled whereas the desmoquattro is liquid-cooled. I think I know how I'll address this, but that is much later in the project to worry about, now.

To make this conversion a little easier, I have the wiring harness, ECU, and throttle-bodies from the same ST4 that this engine came from. So, not only will the Mega Paso have a desmoquattro engine in it, but it will be fuel injected, also!

June 26, 2008
I'm knee-deep into this engine installation, and I now know why this is not a swap that happens on a regular occurance. Several mounting points on the engine cases are too wide and need to be cut down. I didn't want to have to tear the engine apart to have the cases machined, so I had to improvise.

Once I took the measurements from the Paso engine in the original Paso Project, I marked the 916 engine. The differences were 0-7 mm, so I had to trim several of them down. At first I took a hacksaw and/or a Dremel with a cutting wheel to them. At times, the Dremel would bind and shatter the cutting wheel, though.

[Engine mounting lug when I first started to cut it down with a hacksaw.]

Then I filed it with a really coarse file and then a more fine file. To get it finished nice and true, I had to make a finishing tool. I took an old engine bolt and slid one of the Paso's original engine spacers onto it. Between the head of the bolt and the spacer, I used double-sided tape. I had some extra sanding disks for my disk sander and cut circles out of it. I made them with the outer diameter a the same as the spacer, and cut a hole in the center for the engine bolt shaft. Ijust peeled the paper off the back of the sandpaper, slide it over the bolt shaft, and stuck it onto the spacer. This is what it looks like.

[Tool made of an engine bolt, spacer, and sandpaper for finishing the mounting lug modifications.]

To use this, I slid the bolt through the engine case, attached a drill to the other end, and used the drill to "machine" the engine mounting lug nice and smooth.

[Using the homemade tool on the mounting lug.]

If there was a high spot, using this tool would show it. If it seemed too high for the 120-grit sandpaper to cut through it in a short period of time, I used the fine file on the high spot to make it more level. If the lug looked fairly true in its cut, I'd just spin the sandpaper until I was hitting all of the lug and making it nice and smooth and true. Here's what two of the lugs looked like after I finished them.

[A mounting lug after smoothing it out with the homemade tool.]

[Another example of the work done with the tool.]

I only removed a little material at a time when I was getting close to the final dimensions. I also was trial fitting the frame over the engine to see how close I was getting. The end result was that I probably won't need any shims to mount the engine. The Pantah engine uses two fairly large spacers on the right side, and if I have to use a shim, it will be 0.5-1.0 mm in thickness, so it looks like I got it nice and close. The bad thing is......I still can't get the frame to lower completely into place.

The stock Pantah engine has the lower engine bolt exposed in the middle section. I didn't think anything about this until I couldn't get the frame to slide the last 5-7 mm so I could slide the engine bolts into place. It took a minute to figure out where it was hitting. You guessed it....I was hitting the shrouded section of the lower engine mount. It was hitting the loser rear suspension link mount on the frame. Here is a comparison of engines.

This is the original Pantah engine in the assembled Paso.
[Rear lower Pantah engine bolt showing the unshrouded section of the engine castings.]

I'll have to get a better picture, but this shows the shrouded section of the lower mounting bolt channel.
[The shrouded section of the lower engine mount that is hitting the frame.]

You might be able to see where the frame and engine case are touching in this picture.
[The 916 engine hitting the frame.]

Not only is this a problem, but it looks like I'm going to have to trim the front of the frame and have Scott at Metal Visions reweld the frame for clearance of the horizontal head. It should be a fairly easy job for him, and this frame mod should not affect any structural aspect of the frame. I removed the horizontal timing belt cover for a little more clearance while lowering the frame onto the engine.

[The horizontal head hitting the frame.]

[Another view of the horizontal head hitting the frame.]

So, it looks like I still need to modify the engine a little and cut and reshape the lower right frame-rail for horizontal head clearance. I'll try to do both of these things soon.

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