after 175hrs - it starts to vibrate in cruise? = Help...

[JCN247DE]

ok, i've read the threads on prop balancing, etc. But this one has me a bit baffled (and not the kind you rivet and swear at..)

I have 175hrs on the Aerosport O-360, 9.2-1's, LSE, Slick Mag, Hartzell BA72" CS prop set-up in my -7A. On a long cross country a few weeks ago at 9,500, 2400rpm, 100ROP I notice a slight rythmic vibration that varies with rpm.

That's funny! Never been there before. Not bad but I can just notice it in the CDI needle shake and on my PDA screen shaking a bit. Ok, land at home base. Check the spinner screws = tight, check prop blades with twisting = ok, Check engine mount bolts = ok.... what gives? the plane was painted 80 hrs ago and the shake just shows up?

can a new prop suddenly go out of balance or track at 175hrs?

Jeff - slightly vibrating in OH

[DanH]

<<I notice a slight rythmic vibration that varies with rpm.>>

"Varies with RPM" and "rythmic" are two good clues. Need more info about the rythmic part. Did you time it, ie, can you determine the frequency of the beat and state the RPM at which you took the measurement?

Dan Horton

[Captain Avgas]

Originally Posted by JCN247DE

I have 175hrs on the Aerosport O-360, 9.2-1's, LSE, Slick Mag, Hartzell BA72" CS prop set-up in my -7A. On a long cross country a few weeks ago at 9,500, 2400rpm, 100ROP I notice a slight rythmic vibration that varies with rpm.

It is my understanding that the Hartzell 72" BA CS prop is not recommended with high compression pistons.

[Stephen Lindberg]

Have you checked the torque on the prop bolts? Because the vibration deveoped after a period of smooth operation, I'm thinking that something that was previously tight has loosened. Also, how about the engine mount to fuselage bolt torque? Prop tracking? Easy places to start. Good luck, keep us posted.

[brianwallis]

1. Remove the spinner
2. Inspect the prop and see if you see any red dye anywhere or excessive amounts of grease anywhere... to indicate a cracked hub and or lack of servicing or metal parts that are vibrating against each other.
3. Service the prop with the right grease if it takes it... sorry... away from my desk right now to look up the prop...
4. Remember to remove the zerk fittings before you service it. (ask your local mech to do it for you please.. the whole prop lube if you can)
5. Inspect your rear bulkhead of the spinner... engine mounts and firewall for cracks.
6. Inspect the leading edges of your prop blades for dings...
7. check prop bolts....
GOOD LUCK!!
Brian

[gmcjetpilot]

May be the engine has sagged a little over the 175 hours. Now that it's sagging, cables, hoses, wires, airbox and engine baffles may now be rubbing and transmitting more vibration to the cowl, engine mount and firewall? It does not take much to transmit annoying little vibrations to the cockpit.

Here is my "Lord Corp" engine isolator advertisement, they are superior to other brands.

[JCN247DE]

Thanks for responding with the suggestions. Ready for this? Interesting.

The prop was greased during my annual. During the process of re-installing the spinner, I used a mix of 1/2" and 5/8" long SS screws to reattach the spinner (got mixed at the work bench.)

The vibration was coming from the unbalance of the screw weights around the spinner back plate.

Lesson learned. Bag the hardward after removing and lable it before you mix things up.

also, the 72" hartzell can be used with the piston / carb set-up if you stay out of the restricted RPM for continuous operation.

Jeff

[Captain Avgas]

Originally Posted by JCN247DE

also, the 72" hartzell can be used with the piston / carb set-up if you stay out of the restricted RPM for continuous operation.

Jeff

I'm inclined to think you just made that up. Please refer us to any documentation from Hartzell that provides testing and recommended RPM restrictions for their 72" CS BA prop on an 0360 with 9.2:1 high compression pistons.

[gmcjetpilot]

Originally Posted by Captain Avgas

I'm inclined to think you just made that up. Please refer us to any documentation from Hartzell that provides testing and recommended RPM restrictions for their 72" CS BA prop on an 0360 with 9.2:1 high compression pistons.

The whole topic of what Hartzell and RPM restrictions or RPM/MP restrictions, what kind of ignition, compression of crank (with dampeners) is complicated to follow.

BA prop on the Superior 360 has NO restrictions, because of the dampened crank.

When you add anything, compression or ele-ignition than that changes. The BA prop has been tested on the un-dampened crank 360. Here is the restrictions for the BA, F7496 blade, 180hp, undamp crank, mag or LSE plasma or unison laser

- No MAP above 22" w/ rpm below 2350 rpm.

- 2600 rpm or less after take off as soon as practical

- 72" min



They have also tested FADEC limits and they are a little different. Hartzell has not tested any high compression pistons. So you are a little in the dark when it comes to high compression pistons.

Hartzell has done an amazing job supporting experimentals, RV's in particular and testing non-stock ignitions, but they can't test every compression ratio. They have tested only the 8.5 to 1 compression. What effect does that have? Call Hartzell.

If you want a custom prop survey Hartzell charges about $25,000 to $50,000!

[Captain Avgas]

Originally Posted by gmcjetpilot

When you add anything, compression or ele-ignition than that changes.

George you're doing it again.....getting your "then" and "than" confused.

Repeat after me : If I know more than everybody else then I have a duty to impart my knowledge to them.