flybyme

I'm trying to mount a 4 stroke engine onto a venus 2, using a different mount (vibration dampening) than what came with the model. The engine mount to firewall holes will be different than the template that came with the instruction booklet. My question is, how do I know just where to drill the holes for the vibra-mount. The horizontal line that intersects the vertical line on line on the firewall, I know represents some reference point, but does it mean that the center of the backplate of the engine should be at the point of intersection of the two lines? kinda makes sense to me, but is this true, and can I get some feedback?









flyin' is like breathing........everybody should do it.

MinnFlyer

My Feedback: (4)

Basically, yes.

If you are mounting the engine upright or inverted, the vertical line on the firewall should be centered between the two mounts and the horizontal line should line up with the tops of the mounting rails ( "TOP" meaning the side of the rail that the engine will be bolted to).

If you're mounting the engine horizontally, switch the previous instructions.

Campgems

I use those mounts a lot. They are great for protecting the engine, they absorbe a lot of force in a hard landing the would otherwise go to the crank. Assuming that your are using the DuBro mounts here is how is set them up.

The first task it to mount the engine to the mounts. Then you can take the measurements to find the distance between the sides of the mount for finally locating the holes in the firewall. Also, please note that there is an up and down on the mounts, one edge of the beam is at 90 degrees to the back and the other is something quite noticably not 90 degrees. Work on the straight side.

The way I do it is to first locate the engine on the mount. With the four strokes, the rear carb becomes a problem. Also watch your throttle linkage. Usually a 4 stroke linkage kit is not needed.

I start first by finding that maximum back set on the mount. This is usually where the carb interfers with the mounting screw. Yes, you need the screw in the mount to determine this position. Once you have the location established, put a pencil mark on the center line of the front lug screw, on the mount. I then use a wide tip sharppie pen and color the entire top of the mounts. I use a machinest square and using the pencil mark, add 1/8" to the front of the mount and scribe a line across the mount beam. Now use a piece of cerial box cardboard and put it between the engine and the mount and find where the whole in the lug meets the scribe line. Mark that point with the scribe, usually the best is to scribe around the inside of the mount and then find the center of that with the engine off the mount. A sceond way is to carefully measure from the machined flat to the center line of the hole and the add 1/64 or 1/32 to give some clearance between the side of the mount and the crank case.

Once you have the first hole located, you can transfer it to the other mount side. Remember there will be a left and right side as it is very unlikely that the holes will be centered along the beams. Now, I drop two socket head cap screws into the motor that tightly fit the holes in the motor beams. Put a nut on each and snug them up. Now measure with your calipers outside to outside of the screw heads. Now measure one screw head and subtract this measurement from the outside to outside previous measurement. The rusult is the distance between the screws. Measuring from your first scribe line, transfer the distance between screws as a second scribe line. These are your center to center marks fore and aft. Transfer your distance between the insdide of the mount and the center of the front screw and apply that to the back screw and scribe that line. Just repeate the measurements onto the other mount beam. Make sure you now very carefully center punch the intersection of the two scribe marks for each hole. A trick here is to use a tap with a tapered point. These are very hard and very sharp, so they make an execlent center punch. With a fine point like this, you can actually feel the scribe line with the point and when you locate one line move until you fee the interscetioin. Very lightly tap the center punch, then look where the mark is at. if it is not exactly on the intersection, place the center punch back in your divot and lean the punch away from where the mark should be, and lightly tap the punch again. You can actually move the divit over the intersection. Once you have the divot where you want it, then you can tap the center punch firmly to make a larger divot.

Once all four are marked, the setup your drill press and use a vise. Level the top of the mount with the top of the vise. Now spot the center punch marks with a small drill, 1/8 works well, but the size isn't important as all you are doing is using a drill small enough the the tip fits into the divot and will not walk whe you start the hole. Spot both holes then change to your tap drill and drill the holes. While the beam is still in the vise, I then put the tap in the drill chuck and tap the hole by turning the drive pully on the drill press. This keeps the tap nice and straight in the drilled hole. Same drill on the other mount.

Now, mount the engine on the mount. I put screws in all four holes but don't tighten them. Then use a clamp and clamp one side to a flat plate, board or what you have handy. Pull the other side tight to the plate and clamp it down. Then tighten the screws. This prevents setting the mounts up in a parallelgram arangement. Once the engine is tight to the mounts, use the rubber centers and the socket head cap screw supplied and clamp every thing together on the two mounting lugs under the engine. This gives you a measurement point for finding the center to center across the engine. Same drill, measure outside to outside of the heads then subtract the size of one head. that gives you your spread, Now do the same up and down. You now have the height and you have the measurement for center to center of the four holes through the firewall. Center the hole pattern on the thrush line. The firewall mounting holes are centered on the top of the mount beam, so the interscetion of a line from the top right to the bottom left, and a line top left to the botton right it the center of the crank shaft.

I guess I should take some photos of the setup and post them. After I get my wing finished.

Don

Campgems

My last post was long. So, if you are using a Magnum, or OS 53, 70, or 91 and the dubro mounts, let me know and I'll take some measurements for you

Don