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Old 04-26-2020, 03:41 PM   #1
Werner
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Default Bad rod bearing

Bad evening!

Today we made the first big drive after reversing the engine & gear. I'm unlucky with my car! A bearing damage is in the offing. The engine knocks increasingly louder. With the stethoscope I hear the loudest point on cylinder 2 on the oil pan. Does it make sense / is it possible to try to replace the connecting rod without removing the engine? Only the head and the pan away?
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Old 04-26-2020, 03:45 PM   #2
J Franklin
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Default Re: Bad rod bearing

Just remove the pan first and inspect.
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Old 04-26-2020, 06:15 PM   #3
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Default Re: Bad rod bearing

If it is a bad rod bearing, you can easily identify which one by shorting out the spark plugs one at a time. When the noise stops, that is the cylinder with the problem. Then, drop the sump and take off the head. The rod can be removed and replaced without removing anything more. I did it on a friend's car one day on the side of the road.
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Old 04-26-2020, 09:38 PM   #4
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Default Re: Bad rod bearing

As long as the crank journal isn't damaged.
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Old 04-27-2020, 05:06 AM   #5
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Default Re: Bad rod bearing

Hallo und guten Tag.
I get to lay down under the car this afternoon and remove the oil pan to open the bearing shells.

Then we'll see.
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Old 04-27-2020, 06:47 AM   #6
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Quote:
Originally Posted by Flathead View Post
As long as the crank journal isn't damaged.
I should have mentioned that!
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Old 04-27-2020, 07:56 AM   #7
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Default Re: Bad rod bearing

Id pull the engine if it was mine,work standing up,clean and position the engine for installing the pan correctly. It takes longer but youre work is easier and the results will better.
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Old 04-27-2020, 09:55 AM   #8
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Default Re: Bad rod bearing

I have done it. Required removing the pan and head. You will need a ring compressor to get the piston back in. I tried doing everything through the bottom at first but i couldn't get enough room to take the wrist pin out. Others may have had more luck. The trick is finding another rod on the cheap and keeping the oil pump in place while putting the pan back on.
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Old 04-27-2020, 11:35 AM   #9
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Default Re: Bad rod bearing

Werner,

If you can hear it in the pan, it may just be the dipper making contact with the tray.
Pull the pan and look for a mark.
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Old 04-27-2020, 11:58 AM   #10
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Default Re: Bad rod bearing

Gutten tag Werner,

I agree with John, check the rod hitting the pan first. If it is the rod bearing clearance, the babbitt might be able to be adjusted by shim removal?
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Old 04-27-2020, 02:19 PM   #11
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Default Re: Bad rod bearing

Guten Abend.

Thank you all for anticipations.

1) There are bearing damages. The flanks of the soft metal bearing shells have chipped off on the outer edge. Z 2 the damage goes up to 1/4 in the area. That was the cylinder that pounded loudly.
What can the edge chipping come from?

2) Can someone explain why the babbit clearance is set with the shims? The supporting hydrodynamic lubricating film is interrupted by the gap.


The surface of the crankshaft is o. k.
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Old 04-27-2020, 02:32 PM   #12
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Default Re: Bad rod bearing

The damage shown should not cause an audible knock in my thinking. Knock is caused by too much clearance or a mechanical interference. What was the clearance measured on these bearings?
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Old 04-27-2020, 04:27 PM   #13
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Default Re: Bad rod bearing

Just a suggestion, take the rods and make sure they are straight.
It may just be the picture, but the rod looks loaded on the side that is babbitt is broken out of.

Do not worry about the shim gap between the cap and rod, the bearing is not pressure fed anyways.

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Old 04-27-2020, 04:53 PM   #14
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Default Re: Bad rod bearing

The rods & caps are tinned prior to pouring babbitt. Sometimes they don't get a good tin job and the babbitt doesn't stick as well as it should. Even with everything well coated a bearing can experience cracking & chipping of the babbitt if the bearings are well worn or the babbitt is thin.

Shimming is done for several reasons. The most common reason is to be able to tighten a worn bearing set by removing a shim or shims. The other reason is that folks had a tendency to sand the parting surface the cap on a flat piece of glass if the shims were all gone instead of exchanging them for a rebuilt set. This makes the next babbitt job too thin so more shims have to be used to keep from hitting steel while cutting the bores to size.

Last edited by rotorwrench; 04-27-2020 at 05:20 PM.
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Old 04-27-2020, 06:35 PM   #15
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Default Re: Bad rod bearing

Shouldn't the grooves in the bearings be cut like the ones in Herm's picture?
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Old 04-27-2020, 09:11 PM   #16
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Default Re: Bad rod bearing



Hydrodynamic lift principle occurs 90 degrees from the bearing shims..if the rod turns out to be true I've seen where folks have dabbled a little solder in the blown out area and dressed it off with good results
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Old 04-28-2020, 11:32 AM   #17
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Default Re: Bad rod bearing

Guten morgan Werner,
Shims were always installed when new, by Ford, in order for the owner to be able to adjust the clearance as miles were accumulated. This was particularly needed in Model T's as they had no oil directly into the rod bearings. You might try carefully adding solder to the thrust (sides) of the bearings and hand filing to fit. Your bearings look to be still serviceable. Grooves such as you have were mostly used in pressured oiling systems, but yours, IMO, are better than the standard big X grooves as the have more surface area, and are obviously getting adequate amounts of oil.
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Old 04-28-2020, 12:09 PM   #18
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Default Re: Bad rod bearing

When the dippers hit that puddle of oil in the dipper tray, there is pressure to the oil that injects in there with each revolution. There is no way to measure it but it does get a good squirt each time. The higher the rpm, the higher the pressure. The X shaped grooves spread a more even flow of oil over the whole journal than a single groove can.

If the rod bearings still have a usable clearance, a person would need to check the center main journal. They take a beating compared to the others and they will knock if the clearance is too much.

A person would have to get all the oil off of an area that they want to try to solder. Even with flux, it's hard to get it to tin so the stuff would stick.

Last edited by rotorwrench; 04-28-2020 at 12:19 PM.
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Old 04-28-2020, 03:42 PM   #19
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Default Re: Bad rod bearing

Hallo und guten Abend.

I measure a bearing clearance of 0.03 / 0.04 / 0.01 / 0.005 mm (millimeters!). The crank pins are clean and smooth. One has a tiny scar like a cut fingernail. (s. picture).
The cylinders (honing marks) and the slotted-jacket pistons are in a good condition and have modern piston rings (1 nose ring) with no vertical clearance play.

I am considering whether it is feasible to solder the damage of the one of the connecting rods on the tread with SN 40? Who has done this? -


The problem with the shim gap is that the hydrodynamic lubricating film, which has an average thickness of only 0.003 mm (3 m), is interrupted. In order for the hydrodynamics to work properly, a trouble-free (= smooth) 360 course must always be guaranteed. This is independent of pressure pump oil.
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Old 04-28-2020, 05:14 PM   #20
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Default Re: Bad rod bearing

This link is for a similar question: https://www.practicalmachinist.com/v...epairs-207306/

There is a maybe on solder but a person would want as much tin as possible. The connecting rods are a lot easier to rebuild than the blocks. I know your in an area where there aren't a lot of Model A rebuilders but there may be someone close to you that can work babbitt for general purposes. The rods can be poured again and each one fit to your crank as needed or just refit the bad one if you want. It would last a lot longer than way.
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