Mystery Noise from Stinson 108-3 w/ Franklin 6A 350

[fav321]

Hi guys, I was wondering if anyone had any insights on the following problem I am having.

I own a Stinson 108-3 on floats with the Franklin 6A 350 CIR 1999 425 TT.

I am getting a fairly loud squeak noise starting at 2000 RPM. From idle to 2000 RPM there is no sound.

Things I have done to identify the noise include:

- isolated alternator by removing belt (noise still there)
- removed alternator drive and covered hole with a plate (noise still there)
- removed vacuum pump and drive and covered hole with a plate (noise still there)
- removed magnetos and had 500 hour inspections (no problems found)
- governor was removed and tested (no problems found)
- tack cable was replaced (noise still there).

All engine temperatures and oil pressure are normal.

Has anyone else with the Franklin Engine had similar problems? Let me know, I'm getting a little nervous and not sure what to try next.

Thanks

[J31]

Check for rotating items that could be rubbing on something like the baffles or cowling. For example the engine may twist enough for the spinner back plate to rub on the cowing.

Is is a squeak, or a constant squeal?

Look for mice.....sorry just kidding.

[fav321]

Thanks for your reply.I have gone over all cowlings and attachments very throughly, found no indication of chaffing or wear.

[Meecka]

Have you checked the oil screen yet?

[fav321]

Yes,also cut open remote oil filter both clean.

[GyvAir]

Reaching a bit here, but have you checked the engine mount and isolators for security? Had an improperly installed mount to firewall bolt on a C150 make an intermittent squeak one time. Stack up was missing a washer or two, leaving it thread bound just short of proper torque.

[robertw]

Hi there,

this might sound a bit elementary, but how do you know that the mystery noise is actually something coming from the engine? Is it possible that the vibration frequency that the engine produces at 2000 RPM is causing something in the interior or structure of your Stinson to rub together and produce the squeak? Interior panels rubbing? Gear sitting in the back seats? Acrylic window squeaks? It's good to rule these types of things out before spending time and energy on the more expensive items.

[Jungle Jim]

Check the tach cable. I had a similar sound with my 165 hp Franklin.

Jim

[fav321]

Thanks Jim, I replaced it with a new one, noise still there.