Noisy alternator belt

[Jrskygod]

Ok I need help!!

RV10 with PP alternator. I pulled the prop to replace the front seal. I decided not to replace the alternator belt while the prop was off because it had been changed about 50 hours before. Re-installed everything ran up the engine all was well. Test flew the plane and while taxing back to hanger belt started making noise at lower RPM's but not at idle. Checked alignment and that was not the problem, tried belt dressing, that didn't help. Bummer!!! Pulled prop back off cleaned belt dressing off of everything, checked the alternator pully and flywheel for any signs of problems and found none, put a new belt on and the prop. Ran up the engine and the darned belt started making noise at lower RPM's but not at idle again. Anybody have this problem before or have some good ideas because I'm tapped out and bummed.

[Raymo]

I highly doubt your belt is making the noise. Maybe someone else can listen for where it is coming from while you run up the engine?

[Jrskygod]

I'm about 90% certain it's the belt. It sounds like a belt slipping. I have set the belt tension with a torque wrench and verified it after running. The odd thing is it only makes noise above idle and below about 1200 RPM.

[Larco]

IF it is the belt it must be way to loose and slipping under a load. you should not be able to spin the alt pulley using a wrench inside the belt while holding the prop still. Larry

[jjconstant]

Actually, there is a spec somewhere that gives two methods of correctly tensioning the belt. One has to do with deflecting the belt (pushing on it to deflect it a measured amount) and the other method is to put a torque wrench on the pulley nut and hold the prop. There is an acceptable range of torque where it is supposed to slip. I don't recall what those numbers are.

[Raymo]

Pull the breaker for the alternator. If the noise quits, I was wrong

If it doesn't, look for something chafing in that area.

[Jrskygod]

I tightened the belt to 11#' which is the correct amount of torque for a new belt so I know the belt is tight and not slipping.

[Jrskygod]

After tightening the belt to spec the squeel still present. We began a systematic analysys. What we have determined is that it is not the alternator belt at all. We removed the belt from the alternator and tied it off clear of the flywheel and what is actually occuring is that the squeeling noise is only present when we taxi the plane. Just running up the engine does not produce the squeel. It only manifests itself after you accelerate the plane and pull off some power as when you are coasting. There must be forward movement of the plane at just above idle rpm for the squeel to be present. If you bring the engine speed above 900 RPM or so the squeel goes away. If you lower the engine speed to 550 or so idle the squeel goes away. We have moved the prop governor control at full range while the squeel is present with no change, so I dont believe it has anything to do with the governor. We eliminated wheels and brakes from the equation as I have laid on the wing while taxing and the noise is definatly coming from the engine and not from the gear. At this point I am totally out of ideas. All I did was pull the prop and replace the leaking crank seal. The noise was never present before the prop was pulled. One thought I had was that maybe it was coming from the injector body when the butterfly was just cracked open a bit, but why will it only make noise when the plan is moving and why did it not make noise before? To say I'm stumped and at a loss is an understatement. Hopefully someone out there has had this problem before.

[Jrskygod]

Its been a month now and the noise investigation continues. The front wheel has been pulled to absolutly eliminate that as a culpret. All is well in that area. Next someone suggested perhaps the pressure relief valve in the prop governer might cause a similar noise so the governer has been sent to the shop for IRAN as well as the prop which was due also for time. Someone mentioned AD 2015-02-07 and its corresponding SL1343B. This AD which became effective in March 15' lists a series of Aerobatic engines however our engine is is an IO-540D4A5 which was purchased new from Van's in July of 2005 and is not part of the AD. What the AD refers to is the possibility that a setscrew that holds the governer drive gear shaft in place may become loose. The AD refers you to Lycoming SL 1343B which covers all wide deck 320, 360, 540, 580 and 720 series engines with a front mounted governer. Ours is in this series. Basically the Sl gives instructions at the next overhaul to replace a clip that holds the shaft with a setscrew or if the engine already has a setscrew to secure it per the instructions provided so that it cannot come loose. We decided to just check and see if the shaft might be loose or something. We removed the access plug and inserted a magnet to capture the shaft and it moved. Whoa - its not supposed to move! it would rotate and move fore and aft over an 1/8". Ok called Lycoming. Their reply "Yep engine needs to be removed and cases split to tighten the loose setscrew; and - oh by the way - were not paying anything, even tho it was our engine assembler that screwed up. Sorry!!! Bye."

So now I gotta pay for an engine tear down on a 500hr IO540 just to tighten a setscrew. Bummer.

So word to the wise. Next time you have your prop off, if you have one of these wide deck engines with a front mounted governer pad you aught to pull that plug and check to see if the shaft is loose. Bad things will probably happen if that setecrew falls completly out and that shaft is free to move around. Just say'n. I was just lucky with this one.

I'm also pretty sure that the squealing noise we were chasing was not caused by this setscrew problem, so dont wait to hear a funny noise. I'm quite certain the noise is coming from the governer itself and I will report back here when the problem is solved.

[BillL]

Bummer on the shaft - and ahhh . . . getting the shaft. What a lousy design.

To the noise - hard (impossible actually) to identify a sound in a txt, but is it possible it is a vacuum sound - like due to intake air leaking through a crack or vibrating at a gasket?