Chassis Design

James DiTullio
October 18, 1999




Mounting an Engine



Puppet speaks:

Hello again...Now this may seem like a stupid topic, but I have the ability to make a project out of anything...Mounting an engine may seem like a simple task, drill a few holes, make a few plates, stick in a couple of bolts and your done... Well, Let me start off by telling you that I had a P/S bike ( from a reputable manufacturer ) in my shop for repairs. Now granted, this was a couple of years ago and things may have changed since then but as we were putting the engine in we noticed that there were 8 triangle plates with holes and 22 bolts with nuts and washers. We got two of the bolts started and preyed the engine up to align the rest of the bolts. When they were all in place but not tight I was able to move the engine 1/8 to 1/4 inch by prying on it. I was wondering how you aligned the bearing plate with the engine able to move like this and then we noticed that there was a little play in the bearing plate to...Sooo.....I guess it all works out....

I believe that the engine should be a part of the chassis in that it is a big chunk of fairly stiff aluminum, so why not use it to your advantage...?? When you put a bolt in a hole you need clearance to make it fit, This results in a little bit of play and no matter how tight you make the engine, when you dump the clutch it will move a little bit and put a slight bind on the output shaft and sometimes the crank. I thought that there must be a better way of doing things soooo.....

When I mount a motor, the first thing I do is drill and tap the cases using helicoils, then I put the frame in my jig and the motor on a jig I have made to hold it at the proper height and angle. I weld the lower left center mount to the frame and weld a plate ( 3/4 X 1 ) sticking out from the mount to hold the motor up. On the right side I make two saddle mounts from the motor to the frame on the lower center and the right front ( these never come off the motor ) and attach them to the frame with hose clamps, now when you put the motor in, it rest on these mounts and the rest of the holes will line up. Next, I make the tabs up for the other mounts and weld the nuts to the tabs. On the rear I use two aluminum plates that go from the front of the seat to the bottom frame rail and to the motor ( you will see the importance of this in a later article on frame stresses ) I then weld on the tabs, mark and drill the holes, then I counter bore the holes for flathead Allen bolts ( the ones with the tapered heads ) and bolt the plates in. The Suzuki and Kawasaki require a spacer so I make a stepped spacer and press it into the motor plate. The left front mount is made the same way. Now, when the motor is in and bolted up there is no play ( the nuts are welded on so there is no play and the flathead allens allow no movement ) and the motor becomes a part of the chassis. I make the outboard bearing plate the same way...If you've ever seen one of my chassis you will notice that all the nuts are welded on for everything. It makes it a lot easier to work on that way and prevents any misalignment....
later...

pup...




Back