Vibration of Max Prop in gear on lowest revs - suggestions for causes?

[hoped4]

We recently relaunched after having the cutlass bearing replaced. I also greased the 3 blade folding Max Prop (which doesn’t involve dismantling the prop ). Having gone to run the engine a couple of times, when in gear at lowest revs (800rpm), there is a significant loud vibration noise -nose more than vibration. As soon as I move the throttle a bit even just to 900rpm, the noise disappears. This happens both going from 800 upwards but also when I reduce revs from say 1200 etc downwards to idle at 800rpm . It could be one of the blades not positioning itself at lower revs but would this be the case when reducing the revs as well?
Any suggestions as to causes?

 

[sailorman]

engine revs too low, increase the idle spd , i get the same issue when under 1k rpm with my 2 blader

 

[Norman_E]

As above, but if 800 revs is the normal recommended idle speed for the engine it may be that the engine mounts are a bit too soft and that the engine has a harmonic vibration at that speed.

 

[Solwaycruiser]

"It could be one of the blades not positioning itself at lower revs but would this be the case when reducing the revs as well?"
Maxprops are feathering and work by mechanical gearing therefore can't be the above suggestion which might have been the answer with folding props that rely on centrifugal force to open. AFAIK!

 

[michael_w]

Not enough engine revs. Because the new cutless bearing is tighter than the old, the engine is idling slower.

 

[pagoda]

Not enough engine revs. Because the new cutless bearing is tighter than the old, the engine is idling slower.

It's not impossible the rev counter is reading low. I had some doubts about ours. I bought a fairly inexpensive hand held optical RPM gauge and found idle was about 125RPM lower than recommended. Easily sorted. Engine now feels better than before.

 

[sailorman]

It's not impossible the rev counter is reading low. I had some doubts about ours. I bought a fairly inexpensive hand held optical RPM gauge and found idle was about 125RPM lower than recommended. Easily sorted. Engine now feels better than before.

Thats the answer

 

[hoped4]

Thanks , I'll check the revs. Hopefully, that's the answer.

 

[wilkinsonsails]

How old is the prop .? We had a problem with wear in the gearing on one Max prop, age around 16yrs.
We sent it back to Darglow for a test, who explained the vibration at the lower revs was the rattle point .Lots of grease helped, but eventually the solution was a new prop.

 

[hoped4]

The prop is just 8 years old so hopefully not nearly time to replace it yet.