need help - vibration on injected superior o-320

andre nunes · #1 02-09-2009, 09:39 AM

Need help. My RV9-A is equiped with a Injected (siver hawk) Superior 0-320 160hp and a wood propeller. Now I have 11hrs on it. The engine is performing great in cruise settings, but after the first flights I noticed a vibration in the 700 - 900 rpm range. The engine shakes in this rpm range and its very disconfortable. In this setting all EGT's indicates almost the same thing and when I lean the engine the vibration get's better, but doesn't disapear. My mechanic said it can be the propeller, but normally wood props doesn't have rpm restrictions and the dynamic balance is done for the cruise settings rpms - so it wouldn't solve the problem. Does anybody faced the same problem or know what can be happening? Thanks in advance for all coments.

breister · #2 02-09-2009, 10:05 AM

What is the compression ratio?

If it is over 8.5:1 that is pretty normal according to both my personal experience (I have an IO-320 with 10:1 pistons) and anecdotal evidence. Electronic ignition didn't seem to help that particular problem.

Just curious for thoughts from others - if you add injection to an O-320, doesn't it become an IO-320 by definition?

Jamie · #3 02-09-2009, 10:05 AM

So 700-900rpm should be close to idle on the ground. It's shaking on the ground, but smoothing out when you power up?

yakdriver · #4 02-09-2009, 10:19 AM

It is the wood prop. Wood props don't have the flywheel mass of a metal prop so get quite shakey at low RPM. My friend's RV6 did the same thing. He ended up putting a balancer behind the prop. This was in the early 90s and the balancer had some big ball bearings in some kind of viscous solution. It did work very well and had over 1000hrs on it when he sold the airplane.

andre nunes · #5 02-09-2009, 12:46 PM

My compression is 8.5:1. Slick mags. The engine shakes in the ground and in the air, when I reduce power to land. My idle is set to 600 rpm in order to easy the slow down for landing.

rv9av8tr · #6 02-09-2009, 01:40 PM

It sure sounds like prop balance, unless this is something new.

If it this is new / a change, then I'd be checking engine mounts.
Maybe something related to ignition timing??