- Mar 11, 2012
- Gold Coast, East Coast of Australia
I see where you're coming from Wizz but the setout of the mounts on a bed mounting isn't dependent on the existing bolt pattern on the engine. The rubber mounts cannot be directly bolted to the bolt holes of the engine in any case so the engine is first bolted to a plate or a pair of flat bars. If a plate is used the plate can be a large square if that is what is wanted, and the rubber mounts spaced well apart at the four corners of the square. However, the twisting moment from the torque of a small engine like this, in practice, is usually quite a bit less than the moment produced by the thrust since the thrustline is raised by the re-drive.Duncan, I would add a mount to the 4 you are ordering. With the short front to back spacing of the mounting holes compared to the height of the thrust line the engine will be trying to lean forward due to the thrust. A fifth mount from the top of the engine straight back to the firewall would stabilize this movement.
So in this case I would bolt a pair of 10mm flat bars fore-and-aft to the existing engine mounting bolt pattern and then the rubber mounts would be positioned in front of, and behind, the existing pattern. That gives a rubber mount footprint of about 8-10 inches laterally and about 12 inches longitudinally and previously I've found that works well for that range of horsepower.
Addition of a fifth mount tends to harden the whole arrangement up so much that unpleasant vibration gets transmitted back to the airframe.
If it proved necessary you could always add another mount up high but I would not use a Universal mount for that, I would suggest a vulcanised mount (see pic) used in shear rather than tension or compression and they are readily available over here.
All that said, there's nothing wrong with having a spare mount or two since the postage for the first one costs more than the rest of the order, and extra items add just a little to the postage cost.