Vibration M-7-235C, IO-540

[Millemr]

I have a M-7-235C, Lycoming IO-540 W1A5. Have owned it for four years and put 200 hours on it. After buying the airplane I quickly noticed it has a vibration from 2225-2325 RPMs. I immediately had the prop dynamic balanced which produced zero change. Aside from this the engine has always been rock solid. I’ve accepted that it’s just a harmonic issue with this particular plane and have always refrained from operating in that range. However, recently I’ve had a couple of flights where the engine appeared to run rough and I’m again revisiting the vibration issue. The last flight where it appeared rough, I brought the prop back to 2100 and it smoothed right out. I’ve checked compressions, injectors and spark plugs-all appear good. I’m currently in the process of getting an Insight G3 graphic engine monitor installed to better see what’s going on with the engine. Has anyone else noticed a vibration like this in their airplanes?

[gbarrier]

possible valve problem.

[Millemr]

The valve issue has been mentioned. That could be the source of the recent engine issue, but still wondering about the persistent vibration from 2225-2325 RPMs. With that one the vibration is even visible on the fuel, oil temp and oil pressure needles. In fact, I usually just bring the prop back until the vibration is no longer present in the engine gauge cluster needles and that’s right at 2200 RPMs-which is my cruise power setting on the prop.

[TxAgfisher]

Have you looked at the engine mount/bushings?

[VA Maule]

Try getting a different shop to rebalance the prop @ the RPM that the vibration seams the worst. Some are much better or worse than others.

Probably a longshot but since the vibration came with the plane look closely at the prop ,are both tips tracking straight, is there any rotational slack with the blades to the hub ( where their could be a slight variation in pitch between the blades causing a cavation of the slip stream [ acting similar to a stall buffet being felt like a vibration] )

[gbarrier]

Did the airplane sit for a period of time before you bought it. Counterweights may be frozen.

[AndrewK]

Couple more things to check if none of the above corrects the issue:

Check for signs of engine rubbing cowl and transferring vibration to airframe.
Ensure bottom cowl screws are snug and holes are not elongated.

[montana maule]

I had a Franklin engine do the same thing. After the crank shaft broke in flight the problem became obvious.

[maules.com]

Ouch

[Millemr]

Thanks for the info guys! I don’t believe the cowl is rubbing, but I’m going to look closely at that and the mounts. Then I think it’s going to have to get another prop balance.

I gather no one else is seeing a vibration of this sort where you can see the vibration in the fuel quantity needles from 2225-2325 RPMs? But it’s smooth outside that range?

[TimB]

After 20 years of overhauling just the Maule 540 engines I have found that Lycoming puts most of them together with 4 connecting rods pretty close in weight and 2 of them way out of balance some times more than 15 grams. Just pulled one apart an IO-540 W1A5 and two of the rods more than 17 grams out from the rest. Yes, I send them out for a better set with a total of 5 grams between any one rod.
And the Lycoming pistons are found up to 7 grams out of balance in a set also.
This may help find your out of balance issue.

[Millemr]

Thank you for the info Tim. Funny enough, that is exactly my engine. IO-540 W1A5. Wonder if there is a connection there? How many hours were on that engine you mentioned and why did it need overhauled?

[TimB]

Metal in the oil filter, Cam shaft and lifter body, about half of them are cams and the other are prop strikes. all of them had 2 rods way out of balance from the rest.

[UP-M5]

timB, you said you send the rods out for a better set. who do you send them to? can you grind/polish enough off the heavy ones to match them all up? is there a way to balance the pistons?
i ask because i will be tearing down a -W1A5D in the near future for OH.

[pilot]

Kurt, you can balance rods some, but 17g is a big difference. Seems like an amount that large could be balanced out by having the big ends resized.