M38A1 Engine Chirping Noise

[chris99]

Hey guys! Long time listener - first time posting. Newly rebuilt F134 engine (stock, 24 volt, with fording plumbing in normal position), of which I did all the work minus decking the block, so I worry every second I did something wrong.

During the 15 minute break in of the engine (doing the rebuild engine break in as spec'ed in the TM) I'm getting a weird chirping chittering noise. It really sounds like it is from the generator side. It sounds exactly like a fan grazing against radiator fins! But my fan has perfect clearance all around and there is no damage to the rad that I see. Stethoscope to the WP, Rad hoses, generator, and anywhere else didn't amplify the sound. Increasing rpm either drowns out the noise or makes it go away. I hope it's just an old fan belt, but I never heard a belt make a noise like that.

Just wondering if anyone has heard anything similar, my searches came up unfruitful. I had to pull the rad to fix a leak on the timing cover so wanted to ask while I'm still in the process of hanging parts. Link is below. I've seen YouTube links here before so I hope it's okay with the mods, let me know.

Thanks all!

https://youtube.com/shorts/q0ZfmN_QgGc? ... wB7wMA76ao

[RonD2]

Hi Chris, and welcome to the forum 1st post.

No harm to run the engine for a few minutes without belts to see if the chirping disappears?
Then install one belt at a time to see if one or the other is the culprit?
Or cut to the chase and install new belts?

Maybe experiment with belt tension loose and tight to see if it affects the sound?

With good belts all I can think of is water pump or generator noise.

Good luck! Let us know what you find.

[wesk]

If you have an extra generator pulley just disconnect the generator from the belts. With the extra pulley on a steel rod or pipe free to spin use it to maintain belt tension without the generator. No noise = fic generator. Same chirp means eliminate water pump and reconnect generator and do the same test with the water pump.

[chris99]

Thanks for the advice guys! I obviously broke something else chasing the oil leak so I'm down for parts again. I will post an update when I have her running though and can check everything.