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Re: Horrible Sound from my 261
Wally / Montana #1367874 Sun Jul 05 2020 08:52 PM
Joined: Jan 2020
Posts: 499
D
Shop Shark
Oh how I dislike hearing one of these dependable old engine's having growing pains. In the past I have had harmonic balancer problems. Think of a toy top trying to spin with a weight on one side, now think about a large weight on the end of the crank shaft. This can cause all kind's of vibration sounds through the MAIN part of engine. Everyone is telling you problems that has happened to them or are aware. If Hotrod Lincoln is correct (he has never been wrong for me), you could have a serious problem with a main bearing. I would go with the simplest first then proceed to the next. Yup a throw out bearing or a piece of metal inside your flywheel pan can be nasty. Ask Hotrod Lincoln about the possible crank bearing issue. It is always best in possible serious internal situations to drop the oil pan. If metallic fleck's are present you have a solvable problem. Good luck. Let us know, that is how we learn. Doc.

Last edited by Doc.Hall; Mon Jul 06 2020 12:50 PM. Reason: misspelling

Currently making 1954 3100 better than new
Re: Horrible Sound from my 261
Wally / Montana #1367888 Sun Jul 05 2020 10:05 PM
Joined: May 2001
Posts: 1,534
W
Shop Shark
I removed the flywheel shield. The sound (which starts at 1300 RPM and fades away at 1700 RPM with or w/o fan belt) doesn't come from back there.

I used a stethoscope along the block and head and it gets louder up front. The distributor doesn't given much sound (except some zapping noise). The fuel pump doesn't give much extra stethoscope sound either but I replaced it today anyway with no effect. Just hoping and praying.

My clutch pedal has about 3/4" free travel and then the spring is pretty strong, the way I like it.

The balancer is the next thing to consider or pull. I probably should change it anyway because I think the too large pulley diameter is the one that Dave does not suggest for his water pump adapter plate.

My two standby old-timer mechanics have firmly retired. There might be 1 or 2 others in town that I would trust to at least help with the diagnosis.

Doc, I also think these engines are sooo dependable but my 261 is at least the 3rd engine in my '48! The radiator frame was cut once and welded. Then it was cut and not rewelded. So I didn't leave that kind of engine removal history when I removed the 235 and dropped in the 261.

I'll keep in touch but I will be out of state for the next 3 weeks or so but please keep giving suggestions anyway. Thanks for your help!!

Last edited by Wally / Montana; Sun Jul 05 2020 10:09 PM.

1948 3/4-Ton 5-Window Flatbed Chevrolet [sandeace.com]

28 Years of Daily Driving but now on hiatus. With a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 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 #1367902 Sun Jul 05 2020 11:45 PM
Joined: Oct 2019
Posts: 57
'
Wrench Fetcher
I'm just a new guy here. I am bringing a '37 back from 50 years of sitting in a barn and I'm no expert but I'm learning as I go.
I had a high pitch screech up front and a few drops of oil in the generator oil caps solved the problem.
It sounded a lot like your noise. I can't see in the video if you have a second belt running your generator.
Maybe I just got lucky.

Re: Horrible Sound from my 261
Wally / Montana #1367908 Mon Jul 06 2020 12:54 AM
Joined: May 2001
Posts: 1,534
W
Shop Shark
Sound persists after removing the single fan belt. Thanks, though!!


1948 3/4-Ton 5-Window Flatbed Chevrolet [sandeace.com]

28 Years of Daily Driving but now on hiatus. With a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 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 #1372440 Fri Aug 07 2020 02:37 PM
Joined: Jan 2013
Posts: 1,662
S
Shop Shark
Any updates Wally?


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 #1372498 Fri Aug 07 2020 10:37 PM
Joined: May 2001
Posts: 1,534
W
Shop Shark
I just got back, Steve, and reunited with my '48. I have another video w/sound taken from inside the cab.

Sound from Inside Cab. [sandeace.com]

I've received good suggestions (above and other friends). I've already looked at some of them and gave the results above. I'll look at others in order of how easy the checking would be.
I will:

1. pull the valve cover and idle up the engine. The sound begins at 1300 RPM. Using a stethoscope, the sound is much louder on top of the crankcase vent tube than the valve cover but this only costs one gasket.
2. pull the harmonic balancer. Check it out and run the engine up to the 1300 RPM.
3. remove the timing gear cover and check for rubbing marks. I understand the timing gear can get a bit catywompous and rub on the cover if I understood correctly.
4. get back in touch with you guys!

Thanks for your help so far and into the future!


1948 3/4-Ton 5-Window Flatbed Chevrolet [sandeace.com]

28 Years of Daily Driving but now on hiatus. With a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 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 #1372499 Fri Aug 07 2020 11:01 PM
Joined: Feb 2004
Posts: 21,062
H
Boltergeist
Unless the harmonic balancer slips forward on the crankshaft snout, there's virtually no way for the crankshaft gear to touch the timing cover, and I'm pretty sure the angle of the gear teeth and the rotation of the crankshaft will keep the cam gear pushed back against the thrust plate. Not saying it's impossible- - - -you might also find a chicken with lips one of these days! If there's a bunch of big dents in the timing cover, all bets are off, however!
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 #1372556 Sat Aug 08 2020 02:57 PM
Joined: Feb 2020
Posts: 4
G
New Guy
Try using a piece of broom handle about 3' long. Put one end on the engine (like you would the stethoscope) the other to your ear. You will be able to hear noises in the area you are touching and not picking up all the other noises like you would with the stethoscope.

Re: Horrible Sound from my 261
Wally / Montana #1372593 Sun Aug 09 2020 01:13 AM
Joined: May 2001
Posts: 1,534
W
Shop Shark
Took off the valve cover and things look hunky dory. The noise comes from below the rockers, etc. and to the front.

Next in order would be to remove the harmonic balancer and see if the sound persists at accelerated idle (1300 RPM). I might also try to find a good engine man.

Any other more "minor" checks I could make?

Thanks!!!


1948 3/4-Ton 5-Window Flatbed Chevrolet [sandeace.com]

28 Years of Daily Driving but now on hiatus. With a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 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 #1372638 Sun Aug 09 2020 02:26 PM
Joined: Mar 2002
Posts: 9,031
Master Gabster
I use a piece of 3/8" plastic tubing to listen. I can point the end and it is very directional.


1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed


My Chevy Master 4 Door is on the Road!
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