420 cc four stroke engine

**Tim shupert** · 04-21-2015, 01:58 PM

I want to use the 420cc 4 stroke on a small airboat.
What type of engine mounts are need to keep the vibration down to a minimum?

I plan on running direct drive also.

Any ideas?

**dr.peck76** · 04-21-2015, 06:19 PM

What was your engine used for previoulsy? rubber isolators are great but need to be able to handle the thrust forces from the prop on a direct drive. as well as any reaction forces.

**Papee** · 04-21-2015, 07:46 PM

Everything I have built from 8hp Briggs, VW, and my 084s where always solid mounted. I have never had any vibration issues at all unless the prop was unbalanced. Still then there was not much vibration and only at certain rpms.

**lahti** · 04-21-2015, 08:10 PM

Hi; For what it's worth I have used squares of 1/4 to 1/2 inch thick conveyor belt as vibration mounts successfully. Just cut suitably sized squares and drill a hole in the middle. You need 2 per mounting point. Order is mount-belt square-motor-belt square-thick washer-double nut. If you want the bolts can be welded to the mount or a stop can be welded in front of the motor base to the mount to absorb the thrust. I've never needed the extra support--but? Mike

**Tim shupert** · 04-22-2015, 01:26 PM

its a brand new engine and i am building from scratch. I though i would try a set of berry issolator mounts that are suppose to have good dampening effects.
Any thoughts?

**Papee** · 04-22-2015, 10:28 PM

Mounts are good but a sturdy engine stand is most important. For forty years or so we mounted the smaller engines on a post type mount made from pipe and flat plate. There were two sizes of pipe used so one fit inside the other allowing the motor to swivel. The shroud was attached to all this so turning the engine would steer the boat.

**dr.peck76** · 04-22-2015, 10:37 PM

Hey Papee, I've seen pictures of those and I had I guy ask me build him one like that. After I Quoted him he wasn't that interested. How did they handle compared to the ones you build now?

**Papee** · 04-22-2015, 11:03 PM

They were just little pusher motors. For the most part they never got on plane. I did have a lightweight Sears boat with a 8hp set up on a swivel mount that did plane though. It really wasn't bad for a Jon boat. It did plane but didn't really go fast enough to slide so it was pretty safe. People were amazed to see a small 8 hp plane like that. Then again I was 100 lbs + lighter back then.

No external gas tank just the small tank on the motor. I'd love to find a small boat like that again to show it can be done. It was a Briggs 8 hp with a 36x17 prop on it. The prop was made by Culver Props, they were bought out by someone in Texas I believe.