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Horrible Sound from my 261
#1367307 Wed Jul 01 2020 02:42 PM
Joined: May 2001
Posts: 1,451
W
Shop Shark
My 261 has been giving me a sound for a while. I thought it was from the water pump which was going to be changed to Dave's repositioning adapter and new pump so I didn't worry. I decided to check that theory yesterday. I removed the fan belt and the sound persisted. Yikes!

The noise starts at about 1300 RPM and is gone at about 1700 RPM but maybe it's so high pitched only the dog can hear it. The sound is louder when placing a stethoscope end on the crankcase vent tube than the valve cover. More yikes!

Click for a video. What are your best bets for the source? Any other checks I can make?

Noise Starts at 1300 RPM [sandeace.com]
.


1948 3/4-Ton 5-Window Flatbed Chevrolet

28 Years of Daily Driving. Now with a '61 261, 848 head, Rochester Monojet carb, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
Re: Horrible Sound from my 261
Wally / Montana #1367311 Wed Jul 01 2020 02:57 PM
Joined: Jan 2013
Posts: 1,648
S
Shop Shark
Wally,
More than likely you need another harmonic balancer, I had one do the exact thing last year

Last edited by sstock; Wed Jul 01 2020 02:59 PM.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: Horrible Sound from my 261
Wally / Montana #1367325 Wed Jul 01 2020 04:48 PM
Joined: Nov 2019
Posts: 360
O
Shop Shark
Man oh man. Hard to tell from the video as it sounds more external than internal. Sounds like something has come loose and rubbing.


"If you can't fix it with duct tape it's an electrical problem"
1949 5 Window 3100
Veteran of the USAF
Re: Horrible Sound from my 261
Wally / Montana #1367334 Wed Jul 01 2020 05:11 PM
Joined: Feb 2004
Posts: 20,562
H
Boltergeist
Check the free play on the clutch pedal. It sounds like you've got a throwout bearing that's running all the time and it's in the process of failing. You should have a minimum of 3/4-1" of free movement of the pedal before you start feeling the clutch begin to release. Do you have the proper pedal return spring on the clutch?
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Horrible Sound from my 261
Wally / Montana #1367388 Thu Jul 02 2020 12:52 AM
Joined: May 2001
Posts: 1,451
W
Shop Shark
I think the sound comes from the front of the engine. I crawled under the truck while Mrs. Wally gave it some gas (wheels very well blocked!) and the sound was not coming from the throwout bearing.

How does this type of harmonic balancer go bad? It's been on the 261 since 2004. When I increase the RPMs, it doesn't wobble, vibrate, etc. It stays spot on.

Can you replace a harmonic balancer while the engine is in the truck?

Thanks for your help!!

Here's a video with perhaps better sound.

Another Video w/Sound. [sandeace.com]
.

Last edited by Wally / Montana; Thu Jul 02 2020 12:54 AM.

1948 3/4-Ton 5-Window Flatbed Chevrolet

28 Years of Daily Driving. Now with a '61 261, 848 head, Rochester Monojet carb, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
Re: Horrible Sound from my 261
Wally / Montana #1367408 Thu Jul 02 2020 03:23 AM
Joined: Jan 2016
Posts: 564
S
Shop Shark
Water pump bearing. ?

Re: Horrible Sound from my 261
showkey #1367419 Thu Jul 02 2020 04:08 AM
Joined: Mar 2004
Posts: 4,544
M
Shop Shark
Originally Posted by showkey
Water pump bearing. ?

He said he removed the belt which took the water pump out of the picture and it still made noise.

Mike B smile

Re: Horrible Sound from my 261
sstock #1367423 Thu Jul 02 2020 05:08 AM
Joined: Sep 2011
Posts: 710
B
Shop Shark
Originally Posted by sstock
Wally,
More than likely you need another harmonic balancer, I had one do the exact thing last year


I'll 2nd the balancer. The rivets that attach the pulley to the back of the hub get loose & will eventually crank the pulley. The rubber will still look good which can fool you.


BC
1960 Chevy C10 driver 235 T5 3.73 dana 44
1949 GMC 250 project in waiting
1960 C60 pasture art
G.M dealer tech since 1980 & counting
Re: Horrible Sound from my 261
Wally / Montana #1367463 Thu Jul 02 2020 03:20 PM
Joined: Feb 2004
Posts: 20,562
H
Boltergeist
The engine will run with the balancer removed, also. I'm hearing a squeal from a tight main bearing that is about to lock up for some reason. Don't run it much more before you dig into things and find the source of the noise.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Horrible Sound from my 261
Wally / Montana #1367467 Thu Jul 02 2020 03:40 PM
Joined: Jun 2004
Posts: 8,200
W
Master Gabster
I realize you say it sounds like its coming from the front of the engine, but that sounds like when the shield in front of the flywheel is rubbing the crank.

George


They say money can't buy happiness. It can buy old Chevy trucks though. Same thing.

1956 Chevy 1/2-Ton Pickup

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