shimming connecting rod bearing

A friend of mine told me that when he was in the USAF (Eglin AFB) back in the 60's he bought a 1950 Dodge that had low oil pressure due to worn bearings and journals. Because he was too broke to buy new bearings he took some govt owned shim stock (don't tell anyone) and shimmed the bearing inserts. He drove the car from Florida to Alaska and back and when he sold it a couple of years later it was still running.
 
Shimming bearings use to be a common practice and most auto parts stores stocked shim stock until sometime in the 70's. It is a patch not a repair by todays standards. Just like you can get rings that are standard on the inside to fit the piston but 10 over on the outside to compensate for cylinder wear. Again a patch. Both repairs would allow a cheap way for you to get some extra wear out of an engine but not what you would get from a proper rebuild. Shops don't do it anymore because the customer expects the engine to last like a new one and if the shop installs a reman the reman company has the warranty. Keep in mind that years ago a customer could be told "ok, we will do it cheap but no warranty" and they would be ok with it.

If you want to try it.....
Get the stock that is tapered on the ends. The internal action of moving parts in an engine stretches the caps a little and it compensates for that stretch. Use plastigage, be sure to get all of that plastic off of the journal and bearing surface or else it dams up the oil and you will take a bearing out.

You can cut it with a decent pair of kitchen scissors.

I myself wouldn't do it, but then again I have machine shops close enough that do good work at a fair price and can afford the parts. If you are looking to get by for a few weeks to finish up some work it would be ok too....but as a long term repair??? Might be ok for a trailer queen/parade tractor.

Rick

Rick
 
(quoted from post at 07:19:11 10/20/10) Has anyone any advice , other than don"t, to shim a connecting rod bearing.

Shell insert bearings are made slightly thicker in the middle, thinner on the ends, and higher than the parting line to produce a pre-engineered amount of "crush" when the cap is torqued down. This crush is part of the insert design and causes a slight bore distortion which produces a carefully engineered ecdentric bore along the thrust line and a wedge shape in the clearance area to promote formation of the oil film. To do it "right" you need to grind the ends of the insert down by the thickness of the shim in order to maintain that "crush". You also need to grind a small relief on the ends of the bearing parting line to prevent the crush from raisng a ridge in the bore.

In other words a lot of careful engineering goes into the bearing geometry - it's not as simple as it looks on the surface and that's why shimming is no longer done.

TOH
 
Had a 54 Ford Mainline for a while and was going to re-motor it with a 327 after the stock 6 cylinder jumped time. Took it apart and the mains all had tobacco can shims and the pistons were knurled.... Not saying its right......
Ended up moving to CA before the re-motor was complete and sold the 327 and car to different people.
 
(quoted from post at 07:19:11 10/20/10) Has anyone any advice , other than don"t, to shim a connecting rod bearing.

First thing I would do is check the rod journal to see if it is egg shaped .

Myself I would either run it loose , resize the rods , or grind the crank , but it would be a good idea to find out why the bearing is loose .
 
To do it "right" you need to grind the ends of the insert down by the thickness of the shim in order to maintain that "crush". You also need to grind a small relief on the ends of the bearing parting line to prevent the crush from raising a ridge in the bore.

Wouldn't that depend on whether you are shimming because the crank is too small or shimming because the rod is too big .
 
(quoted from post at 20:13:43 10/20/10)
To do it "right" you need to grind the ends of the insert down by the thickness of the shim in order to maintain that "crush". You also need to grind a small relief on the ends of the bearing parting line to prevent the crush from raising a ridge in the bore.

Wouldn't that depend on whether you are shimming because the crank is too small or shimming because the rod is too big .

Yes. I was assuming he was trying to reduce the ID - worn crank and/or bearing.

TOH
 
Take your time and do one at a time. Know what rotating the engine feels like with and with out shims. I can't find tapered shims any more so if you want taper on the ends you have to make your own taper. Is time consuming so if you value your time you won't gain anything. But it works for me cause I can't see turning a crank if it has less than .002 out of round. This is for my own stuff only. Let the beatings begin.
 
Shimmed the rods on my IH340 with aluminum foil 2 years ago and haven't had a lick of trouble from it.

Not sayin' it's the right way to go, I'm just sayin'...
 

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