VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 how do I replace pushrod bearings?

Hello All,

Have a coffee, this will take a while! As you can tell by my postings It's been on again, offf again with the renovation of my car. I was making great headway with my 51 today, was checking the engine with my new vacuum gauge, got the vacuum advance unstuck, and the engine was running as smooth as when it was rebuilt in 92'. Then a thudding started in the engine- sounded like a bad diesel. I imediately shut off the engine. Pulled out the dipstick, which had silver flecks on it!! There seemed to also be small flecks in the engine compartment outside as well! Using the shop manual I took off the oil pan, and #4 definitely had the pushrod bearing go. My questions are this.

Do I need to replace all of the engine's bearings in the bearing caps and pusrods, (for a total of twelve halves)? Or just the one bearing (two halves) that went bad?

How can I find out why the rod bearing went bad in the first place? The oil pan nozzles seem to be correctly aimed, but I'll check. I'll also check the dipper height and trough depth, and check the oil pump. (how do I make sure that it is operational, there was oil pressure while the car was running)?

How do I find out the size of the bearings I need? The engine was rebuilt by a professional in 92', (already the oil pipe going to the rocker assembly got worn through by a pushrod). All he states in the bill of work perfomed is that the crankshaft was re-ground, to what? I don't know. He did write down that he used bearings "micms 163810" does this ring a bell with anybody? I know it is not the cam bearings- that's m/c sh2095. I have put no more than 10,000 miles on this engine, I have changed the oil annually. What gives?

I bought this car way too early in my life, but with your help I'll get this girl back on the road!


Thanks again!

Steve

Push rod bearing? Do you mean a connecting rod bearing instead?

A push rod is the long round rod that goes from the valve lifter to the rocker arm on the cylinder head.

:) :grin:

Hi Steve,

It will not be necessary to replace all 6 rods. You will have to remove the head and remove the bad rod along with the piston. Now comes the catchy part. The crankshaft throw must be inspected for damage. If it is damaged, then you will have to remove and disassemble the engine to remove the crankshaft. Depending on where you are going with this engine determines what you do next. It is possible to turn just the damaged journal and obtain a rod of the correct size for re assembly. If this will be a hard driven car on tours ect, it will be necessary to start from scratch and turn all journals on the crankshaft, and a new set of rods to fit the new dimensions.

The cause may have been a tight bearing on the rods big end. Could have been starved of oil, or any number or reasons. This calls for a professional engine re builder to diagnose the problem, solve it and rebuild the engine.

It is highly important that the block be thoroughly cleaned to remove all the pieces of babbit that is throughout the system.

Its possible that the rebuilder used replacable insert type connecting rod bearings. The 1951 engine originally had the bearing material bonded directly to the connecting rod and bearing cap.This required replacing the entire conn. rod. With the insert just the insert or shell am be replaced.
Its very unusual for the bearing to "go" while the engine is running at low speeds.More common at high speeds. I would suspect one of the rod trough oil pipes is restricted.

Hello all,

Thanks so much for the quick reply. Antique Mechanic, when you say crankshaft throw, I assume you mean the bearing surface on the crankshaft where the connecting rod attaches to the crankshaft. In the old chiltons manual, (I also have the chevy shop manual) it says you can take a penny, (I guess I need to find an old penny that is 100% copper) and run it across the surface, and it should feel smooth. How do I find out what size bearings I need? Thanks for all three of you gentlemen's help!

51Steve

This will rquire a micrometer.For standard size will measure 2.311" to 2.312". Undersize would be in the steps of .010', .020" or .030" less in diameter. If its been rebuilt there is a 99% chance thats its undersize.
Are there insert type bearings?...Did the insert spin in the rod?.
If this occured at idle speed I would doubt if the crank journal surface was harmed.

Before you get the engine all apart it may be a good idea to purchase a passanger car shop manual 1949 - 1953 with a 1954 supplement from one of our vendors. Read the engine section until you have an understanding of what you are attempting to do. Just My Own Opinion.

Hello Everyone,

Sorry to keep you hanging. Haven't worked on the engine yet. Hopefully next weekend. I hate to say this, but where is a good place to sell a parts car? I was thinking of posting on this website, chevy talk, and hemmings, I think I'll avoid ebay. If I get the motor running, you can be rest assured the purchaser will be told that a connecting rod bearing had gone out.

Thanks,

Steve

Steve,
Sorry to hear of your problems. I can understand where you are coming from. Hope you decide to repair it, but if not the places mentioned are good outlets.

If you decide to sell and if you have a 'local' Auto Trader - (and it looks like you do) - I'd give that a try. Especially with a car that isn't running; just for parts; etc. Certainly makes 'local pick-up' easier if you sell it locally....

Click here for Tampa Bay Auto Trader

Good luck....

Bill.

Hello Everyone,

After another hiatus, I’m back to getting the 51’ up and running.

I’ve done all the trouble-shooting I could to diagnose why the connecting rod bearing went bad in the first place- to no avail. I’ve turned the oil pump with a screwdriver shaft attached to a variable speed drill, and it seems to be pumping well. I’ve also checked the dipper height, trough depth, and checked the oil pan nozzles for blockage and aim, and all checked out good.

I was educating myself about the installation of the new connecting rod bearings when I came across this in an old Chilton’s manual. “Increase engine speed to just above idle. At this point, rods which are defective or loose will give off a dull thudding sound, the sound will slowly fade out as the engine is slowed down to idle.” Shazam! This is exactly the sound I had while tuning up the engine before all *#$@ broke loose. This might be common knowledge to most of you, but I’m learning everything from a book so please bear with me! I knew that you could tell the general health by revving the engine and listening for metallic noises, but not so precisely!

Might the loose connecting rod bearing be the reason why, even before I had any obvious problems that my oil pressure gauge would sit in between 0 and 15 psi. at idle? But as soon as I would have the engine under load (driving) the oil pressure would be right on 15 psi. Ever since I had the engine rebuilt the oil pressure would sit at approximately 7 psi at idle. It was this way since I had the engine rebuilt. Personally, I think there is no correlation between the two, but I would like your opinion.

So my questions are… Since the bottom is open already should I check the clearance of the rest of the bearings with the plastigauge? What should I rinse the block out with and what viscosity of oil should I use after a repair like this? Any tips on installing the piston/pushrod assembly?

Thanks,

Steve

Did the babbit melt or did the bearing just loosen up? Does the engine have insert bearings or is the babbit directly in the rod and cap. Was the crankshaft turned under sized and under sized rods installed ? If the bearing burnt out the carnkshaft surface would be damaged, would need to be "turned" so it has a smooth surface or new rod bearing will not hold up.
Reason a connecting rod bearing will burn-out (babbit melt)
No oil to bearing due to plugged oil line in pan.
Oil contaminated with gas.
Bearing adjusted too tight.
Rod cap on back-wards
Poor quality replacement babbit material
Dipper broken off. Under normal driving conditions will tolerate the stream being off, dipper hight or trough depth being off. If the rod burnt out at a lower speed, under 60 MPH some thing did cause it that should be corrected.
The normal oil pressure with hot oil and at idle speed will be 5 to 8 pounds. Normal pressure at 50 MPH will be 14 pounds. This is what the pump is designed to deliver. The rods do not get oil under high pressure.
Will the non-pressure to the rod bearings a loose or burnt out or even a missing bearing will not affect oil presure.
Best way to adjust rods is by following the shop manual ....remove shims until bearing is tight and then add one shim - rod then should be able to be moved back and forth by hand.see manual and for get the plastigage.
Use 10W-30 oil. Will give instant lubrication at start up and have good "body" with hot oil.
I have never burnt out or loosened up a rod bearing in a "dipper" Chevrolet engine. This gose back to when I was a teen ager. Often would them up through the gears and ran them at top speed....and still do.

Morning Gene,
Read your reply about winding up your babbitt pounders through the gears and running them at High Speed. This prompted me to did through the archives in search of any discussions about RPM limitations on the 216's. And I got my usual results from the "search" engine, Zip!
Of course the HP specs that are published in the manuals are taken on dyno when the engines are new and under ideal or controlled conditions so I’m somewhat reluctant to run a 60year old 60,000 mile engine that has its share of rattles at 3300 RPM.
In my '50, 3600 I'm running the stock SM420, 4.10 gear and stock diameter tires and it runs somewhere around 2500 an 2700 at hiway speeds, i.e., 55mph. I’ve kicked it up to 65 once or twice momentarily and have some serious doubts that it would hold up very long at those speeds. Even when up shifting in traffic she feels about maxed out at 2800 or 2900. I would say the sweet spot is about 2400 RPM and I think she could run there all day long. I might feel different if the rings and bearings were in newly rebuilt condition.
So what are your feelings on the RPM range of the 216’s?
Denny Graham
Sandwich, IL

Back in the '70's and early '80's a few of us regional members drove our cars to meets in various parts of the country. There were two 1937's, a 1938, my 1939. and a 1940. All were Master Deluxe models with the 4.22 ratio (1940 had 4.11). We would run them at about 60 MPH with the cars at the end of the line often needing to go faster to "catch-up". 60 MPH with a 4.22 is about 3200 RPM. All engines were stock but in good condition. We never had any connecting rod problems,etc. My '39 had aluminum pistons, the others had cast iron. Trips included crossing the great Plains with two to Colorado with 100+ degrees across Nebraska.
When on my own I always drove my '39 at 65 MPH and thought nothing of running it up to 70 or 75 (will do only 80). Five years ago I replaced the ring gear and pinion with a 3.73. That makes 70 MPH a breeze on the Interstates.
When I was young and foolish I drove my Chevrolets at 65-70 MPH often. Never had a problem. I would not advise doing this today though with an engine in unknown condition. If rods are loose or the condition of the bearing babbit or oiling system is sludged up keep under 2800 RPM.
In 1952 a friend had a 1949 with about 50,000 at the time. He drove to Madison, Wi and back, a one way trip of 70 miles, wide open. Was early in the morning on a good straight road...had no problem. Later he milled the head, installed dual carbs and exhaust, bored it out, etc, beat the heck out of it and never had rod problems.

Hello Everyone,

Thanks for the suggestions. I should get to working on the engine next week. As you have said, these engines have gone through a lot of abuse, that's what frustrates me to no end, this engine has maybe 5,000 to 10,000 miles on it since it's been rebuilt! I've heard from the "old timers" back in the days you could go to a used car dealer and buy a chevy, two for the price of one, and beat the @#$% out of the chevy full throttle without a problem. Oh well, off to get mine on the road!

Well just got back from draining another tankard of petrol and a couple of quarts of Rotella-T. That's about the average time I'm putting on it every week in the summer time, that is, at least until my allowance runs out which, is getting smaller and smaller with these markets the way they are.

Since I put the 4.10 gear in I'm getting bolder and bolder about driving her at the higher R's. Pistons are slapping a little, the crank gives me a little thump for a few seconds or when I first start her up and rods are thumpin’ some but as long as I have good oil pressure the temps are in the green and I don't see any smoke in the day light I guess she will make it home. If I don't I'll tell the mechanic in the tow truck, "I can't understand it, Gene S. told me it was OK to run her all day at five grand!!!"

On that oil pressure Steve, that 15-15 lbs is about what I carry on my, pretty much worn down 216. I just ran across those specs that Gene called out earlier while scanning the shop manual, 14 lbs at 2000 RPM and on the low end I’m right about where he said at idle also, 5-8 lbs.
Denny Graham
Sandwich, IL