prop shaft rattle

[tedemerick]

I lhave a 1991 tiara open with 454 gas engines. When at slow speed I am getting a slight rattling noise that I think is coming from the shaft on the starboard engine. I am wondering whether there are bearings in the struts that might cause this. I had the shafts measured for straightness and they were ok.

[anthem]

Sounds like the cutlass bearing is bad.

[Chris Burkard]

If it truly is coming from the prop shaft, then it can only be the cutlass bearing, shaft seal assembly or the shaft coupler. I'm assuming you checked the props? I have seen loose props make a rattling noise. I know you said the shaft was checked for straightness, but have you had the props balanced recently? My suggestion is every 5 years if you don't hit anything.

The other drive train issue that can cause a rattle like sound is the transmissions or motor and transmission mounts. These issues can actually travel down the shaft and make it appear the noise is coming from the shafts or props.

If you do figure it out, post it so others can learn from your experience.

[tedemerick]

thanks for your input. I think this is my problem.

[tedemerick]

thanks for your input. I think this is the problem.

[Uhehner]

As Chris said, look at a loose prop. I have seen where the key was preventing the prop from fully seating on the shaft. And how about a rough idle causing the gears to rattle. Capt. George

[sawdustdad]

Before you go too far, make sure it isn't your gear rattling. Velvet Drives, at very slow idle, will develop a rattle if the springs in the damper plate are worn or broken. It's no big deal from what I've been told. If you bump the throttle up to 1000 rpm and it goes away, that's likely the issue.

[Chris Burkard]

As Sawdust mentioned, Velvet drive transmissions are know for rattling as they age. Start at the props and work your way to the engine.

[jmk]

This can be totally normal for a Hurth 630 (ZF63) family gear. It is typical and not something to fret over. It comes from the fact that rotation speeds are not constant but fluctuate due to cylinder firings 4 times per revolution. This causes rattle that disappears at higher RPM. If you have one bad spark plug then the rattle can be worse, so check all your plugs. But keep in mind that it seems to show up on the Stbd side for Hurth gears because they are reversing gears and the port is actually not running identically to the stbd, but through a different gear train. Lots discussed on this elsewhere. A tight cutlass bearing can cause the shaft to deccelerate more between ignition events, leading to more rattle as well.

[Lured Away]

Odd, I have a 1988 31 and just started having the same problem starboard engine. It is a non rhythmic rattle/knock. My mechanic said exactly what sawdust dad said. When bump up slightly goes away.

Mechanic said don't worry about, but what do others say?