What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

The Mystery Sound...

bjdecker

Well Known Member
Ambassador
Greetings Hive Mind -- I'd like your help to identify the source of a sound and determine if its going to cost me $$$ or worse...

The hardware/configuration:
200 hour TTAE RV-7 with Lycoming YIO-360-A1B6,
Dual Lightspeed Plasma III ignitions,
Skytech PM/LS 149 starter,
EarthX ETX680 battery,
Cole Hersee/Littelfuse 24115 Master Relay,
Cole Hersee/Littelfuse 24021 Starter Relay - wiring as per OP-30, OP-31
Starter "jumper" removed - Starter Solenoid powered via separate 18ga wire from "I" post on Starter Relay.

The scenario:
OAT was about 40°F and I followed the normal pre-ignition sequence. I turned key to engage starter and heard a sound similar to a cat being crushed by the garage door -- a high pitched "squeeeeeeeeeee" followed by the engine firing on the first blade (< 180° of rotation).

The sound stopped the instant I released the key, so I suspect the noise is coming from the starter motor, starter solenoid, or perhaps the starter relay.

All the connections are tight, corrosion free, etc.

I did replace the starter solenoid at ~40 hours with the Borg Warner BWD S5613 and it's been trouble free since...

Anyone else experience this?
 
I'm just guessing but the first thing that came to mind was the belt slipped for a second. Check belt tightness and even consider loosening and check the alternator for free rotation by hand.
 
I'm just guessing but the first thing that came to mind was the belt slipped for a second. Check belt tightness and even consider loosening and check the alternator for free rotation by hand.

Thanks! The belt is tight (per HET installation guidance), and the sound definitely follows the starter and not the alternator -- which is off during start (my procedure - MASTER ON, ALT OFF, STARTER ENGAGED, ENGINE RUN, ALT ON...)
 
Well then, if the sound is definitely following the starter then that's the obvious place to start. Perhaps a bearing has spun inside. Regarding your start sequence you could still get a slipped belt despite the alternator being off. Before spending the money for a starter I would take a few minutes loosen the belt and make sure the alternator pulley spins freely. If the alternator pulley spins freely, then seriously consider the starter.
 
Starter squeal.

In the front of the starter housing is a bushing that the Bendix shaft pivots on. You might try lubricating that with some 50 Wt engine oil. On both sides of the bushing.
 
My wife's Decathlon makes the same sound; for some reason the starter relay makes a screeching sound while under load if the battery is low on charge. Fly a bit and make a stop after the battery is fully charged and the harmonic from the relay is gone on the next start.
 
My wife's Decathlon makes the same sound; for some reason the starter relay makes a screeching sound while under load if the battery is low on charge. Fly a bit and make a stop after the battery is fully charged and the harmonic from the relay is gone on the next start.

Interesting - I'll have a look (err...Listen) at the Starter Relay. FWIW, start volts are ~13.5Vdc at the battery...
 
Lycoming recommends silicone spray on the snout bushing and the bendix shaft. Less likely to attract dirt.
 
My wife is curious to know how you know a sound similar to a cat being crushed by the garage door.
Caution: she is a border line crazy cat lady :)
 
My wife is curious to know how you know a sound similar to a cat being crushed by the garage door.
Caution: she is a border line crazy cat lady :)

Uhm, I was guessing about the auditory emissions of a feline trapped under a sufficient mass...Nothing to see here, move along...
 
More Noise...

For the Sky-Tec LS/PM starter, see Note 6. Not exactly what post #8 says.

https://skytec.aero/wp-content/uploads/2019/11/LS-and-PM-Drawing-Install-Instructions.pdf

i-tLdMZfk-M.jpg

Thanks for this Carl, good thing to add to the CI checklist.

Ambient temperature definitely has an effect on the sound -- today's test run and flight @ 75°F didn't result in the usual loud squealing [not cat] sound.

It seems to be emanating from the firewall, right side, between the pedals. The only devices here are the Master Relay, Starter Relay and Battery.

I am trying to think of a way to isolate the noise further without risking bodily injury to friends/acquaintances...Run a tube from each/at a time into the cabin and listen during cranking?? Any others??
 
Last edited:
Quote: "My wife is curious to know how you know a sound similar to a cat being crushed by the garage door.
Caution: she is a border line crazy cat lady"

Uhm, I was guessing about the auditory emissions of a feline trapped under a sufficient mass...Nothing to see here, move along...

You guys are killing me. I just about spit my IPA across the kitchen. 🤣🤣
 
T
It seems to be emanating from the firewall, right side, between the pedals. The only devices here are the Master Relay, Starter Relay and Battery.

Sounds can behave in weird ways, so you may think that's where it's coming from, but it's being reflected there and originating somewhere else. E.g., in a newly-purchased classic car, I thought a rattle was coming from the right-hand dash area, my buddy as passenger thought it was coming from the *left-hand* dash area, and my spouse finally pointed to the driver's sun visor and said "it's coming from there". And she was correct. But you should have seen my buddy and I messing around under the dash, in the glovebox, around the instrument panel, etc., while driving to try to find it.

Anyway, just a thought...it might sound like it's coming from there, but not be.
 
Same cat

I have the same lash up on my RV-8 and I have been fighting the same cat noise problem. I rebuilt the starter(https://www.youtube.com/watch?v=IS1QVtCLoVw&ab_channel=MikeLauer). Nice to know the starter guts are a off the shelf automotive starter. However, still have the same problem - slow turning starter when it's cold outside and that cat is still screaming when the starter is engaged. Next steps are whether the master relay and starter relay are giving interrupted current to the starter motor. I did check the Concorde battery which was a shock - its rated at only as 225 amps cold cranking power. That won't start my lawn mower...
Any thoughts?
 
Guidance from Prestolite

Keep Your Direct Drive Engine Starter Clean To Avoid Trouble

Many starters manufactured by Prestolite and Electro Systems are in use with Lycoming engines. From time to time these starters used on our direct drive engines are returned to the factory reported as malfunctioning, but investigation here revealed the problem to be dirt. The location of the starting motor on many aircraft engines subjects the Bendix Drive of the starter to contamination from dust, dirt, and moisture because the drive housing is open and the engine constantly circulates air around the starting motor.

Typical indications of a dirty Bendix Drive are:

1. Sluggish operation—operator has to make several attempts before the starting motor will crank the engine.

2. Noisy operation—a grinding noise when the starter is energized.

3. Failure to engage.

Whenever any of the above complaints are received, the starting motor should be removed immediately and the Bendix Drive cleaned and lubricated. Oil should never be used because oil in that location collects dust and dirt, becoming gummy and causing the Bendix Drive to stick.

In most cases it will be necessary to partially disassemble the starting motor in order to service the Bendix Drive. The latter should be removed from the motor shaft to insure thorough cleaning and lubricating. Clean the area in front of the Bendix Drive pinion before removing the drive from the shaft.

Do not use carburetor cleaner or any solvents that could damage the rubber block inside the Bendix Drive. Use only clean petroleum base cleaners such as kerosene or varsol.

Thoroughly clean the Bendix Drive to remove all dirt and contamination from the screwshaft threads and control nut. If the drive is exceptionally dirty, the drive pinion cup can be removed to insure a thorough cleaning job. Do not attempt to remove the control nut.

After the Bendix Drive has been thoroughly cleaned and blown dry with compressed air, lubricate the screwshaft threads and ratchet with a silicone spray. Lubricate the motor shaft with the same silicone lubricant before installing the drive assembly on the shaft.

The subject of Textron Lycoming Service Instruction No. 1278 is starter drive lubrication.

---------------------------------
Not to engage in a debate of who's right or wrong, this just supports what I was taught in A&P training in 1976
 
Last edited:
Same cat different starter

The SkyTec starters are of the gear reduction type so not direct drive. There is a planetary gear reduction between the starter pinion and the bendix so you have to remove the starter from the nose piece and then you can disassemble the gear box. Three planetary gears that need to be cleaned and greased and put it all back together...
These starters are called PMGR starters which are ubiquitous in Ford products.
 
The SkyTec starters are of the gear reduction type so not direct drive. There is a planetary gear reduction between the starter pinion and the bendix so you have to remove the starter from the nose piece and then you can disassemble the gear box. Three planetary gears that need to be cleaned and greased and put it all back together...
These starters are called PMGR starters which are ubiquitous in Ford products.

True, they are different. However, the front end of all Lycoming starters is exposed, so the concept of using a dirt non-attracting lubricant is valid.
The risk of the drive being slowed by contaminant captured by oil is the eventual loss of ring gear teeth due to partial engagement.

The downside of silicone spray is the need for frequent reapplication, i.e. every oil change.
 
Mystery sound

I had the same screech on a couple startups and couldnt figure. Then my alternator started playing up. Took plane power alternator off placed pulley in a vice and found the rear bearing was us. When i opened up found the sound was the bearing slipping in the housing . Check your alternstor. Mine had done only about 200 hours.
 
Back
Top