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Re: Horrible Sound from my 261. Part 2.
Wally / Montana #1376440 Wed Sep 09 2020 12:47 AM
Joined: Feb 2001
Posts: 1,133
D
Shop Shark
If that were my engine , I would be concerned with the damage done to that bearing surface . Also I see the rod bolts have no lock nuts (pal nuts) on them .

I'm inclined to go with tom moore suggestion .

Re: Horrible Sound from my 261. Part 2.
Wally / Montana #1376441 Wed Sep 09 2020 12:53 AM
Joined: Jan 2001
Posts: 5,017
P
Master Gabster
Just a FYI, Chevrolet stopped using pal nuts when they went to full pressure engines.


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Re: Horrible Sound from my 261. Part 2.
Wally / Montana #1376442 Wed Sep 09 2020 12:56 AM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
That bearing isn't badly damaged, but the wear pattern is all wrong. It would be interesting to see what a piece of Plastigauge would show in the way of clearance. Now, to be thorough, there are three more main bearings and six rod bearings to inspect. That engine was designed to be able to change main bearings "in the frame"- - - - -notice the small anti-rotation tab on the bearing that's up in the block? It's possible to loosen the other bearing caps a little, insert a home-brewed tool made from a cotter pin into the oil hole of the crankshaft, and roll the top bearing shell out by turning the crankshaft. Earlier engines with dowel holes in the block and corresponding nibs on the main bearings required the crankshaft to be lowered 1/2" or more to change mains. That modification to the block and the bearings happened about mid-year 1955, the same time as the change to the low water pump position.

So far, I haven't seen anything bearing-related to cause your squeal. I was expecting to see much more damage to the front main bearing, and possibly a badly scored crankshaft. the surface of the bearing that rides on the crank is made of soft metal, a lead/tin/antimony/copper alloy. "Babbit" metal is one type of bearing material, but there are others as well. The next few layers of the bearing will be copper, and then a steel backing shell. The soft metal is there so debris can score, or "imbed" into the bearing with little to no crankshaft damage. It looks like your bearing has done its job of protecting the crankshaft quite well. Now- - - -slip the lower bearing shell out of the cap, look at the back side, and see if it shows an "undersize" It will probably be marked "STD", .010, .020, or .030, indicating the size of the crankshaft. Reground shafts have been ground down to a smaller size to make the shaft round again, and eliminate out of round or tapered wear. As long as a shaft is round, and not scored or tapered, new bearings can be installed without regrinding the shaft. You're getting close to the point where removing the engine will let you do a better repair job, although untold thousands of stovebolts have been rebuilt with the engine "in the frame" under the old shade tree in the back yard!
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. Part 2.
Wally / Montana #1376447 Wed Sep 09 2020 01:36 AM
Joined: Apr 2005
Posts: 9,003
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
Wrist Pin knock?


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Re: Horrible Sound from my 261. Part 2.
Pre '68 Dave #1376448 Wed Sep 09 2020 01:41 AM
Joined: Mar 2010
Posts: 9,443
5
Master Gabster
Originally Posted by Pre '68 Dave
Just a FYI, Chevrolet stopped using pal nuts when they went to full pressure engines.
I have a '53 W/Powerglide 235 (Chevrolet's first full pressure engine) which has pal nuts. (A little off topic since it is not a truck engine. Just thought that I would share some trivia since a lot of car engines end up in trucks.)

Re: Horrible Sound from my 261. Part 2.
Wally / Montana #1376449 Wed Sep 09 2020 02:00 AM
Joined: Mar 2010
Posts: 9,443
5
Master Gabster
Did you ever inspect the thrust plate behind the camshaft timing gear? You can see it through the holes in the gear and maybe from the side with a flashlight.
You need to make sure that the screws which hold it in place are there and tight and actually going through the holes in the thrust plate.
I just got done tearing down a 235 which was parked by the previous owner soon after a re-ring job because of a "horrible noise" (his words!).
I removed the 2 screws which hold the the thrust plate to the block and removed the cam to find that the screws had not been installed through the holes in the thrust plate! The ears of the thrust plate were completely broken off. No wonder it made a "horrible noise".

Re: Horrible Sound from my 261. Part 2.
Wally / Montana #1376459 Wed Sep 09 2020 03:07 AM
Joined: May 2001
Posts: 1,522
W
Shop Shark
How do you slip the bearing out of the cap? Tool required?


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. Part 2.
Wally / Montana #1376461 Wed Sep 09 2020 03:34 AM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
That one has a dowel built into the lower bearing shell to keep it from moving, so rolling the bearing out of the cap isn't possible. I use a sharp instrument like a gasket scraper or a pocketknife blade to lift one end of the bearing away from the cap.
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. Part 2.
Wally / Montana #1376465 Wed Sep 09 2020 04:03 AM
Joined: May 2001
Posts: 1,522
W
Shop Shark
10/02 (date?) 0.010
Clevite, etc.

0.010 means it's smaller in diam by 0.010" than stock?

It was rebuilt in 2003-2004. Has about 30,000 miles on it.

Last edited by Wally / Montana; Wed Sep 09 2020 04:07 AM.

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. Part 2.
Wally / Montana #1376488 Wed Sep 09 2020 01:57 PM
Joined: Feb 2004
Posts: 21,002
H
Boltergeist
OK, you need to order .010" undersize bearings if you choose to replace them. It's not a particularly difficult process. Simply remove the main caps one at a time, and loosen all the others a couple of turns to let the crankshaft drop down a little. Then bend a cotter pin into a T shape that will slip into the oil hole in the crankshaft journal with the cross piece of the T lying flat against the shaft. It won't be a perfect 90 degree angle since the oil passages are drilled to point toward the rod journals. Roll the crank against the bearing shell and keep turning to push the bearing out of the block. Be sure to push the anti-rotate tab out of the block, not force in tighter! Roll the new bearing into the block the same way.

I'd suggest checking the oil clearance with Plastigauge, using the bearings you have in there now. Pay particular attention to the front to rear clearance, as the bearing in your picture appears to have more clearance at one end than the other. That's not a good thing! The only way to correct a tapered crankshaft journal is to regrind it to the next smaller undersize, .020". That requires a complete engine disassembly.
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!
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