VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Shimming upside down rods

I'm trying to shim up 6 re-conditoned rods for the first time w/o the pistons attached by hanging them upside down off the crank. I'm thinking I might save a little time before I mate them up with their pistons. The cylinder head is off. Does anyone see a problem setting the clearance adjustment by simply swinging the rod through 180 degrees instead of normally using the hand crank with pistons attached to check for drag ?

Researching the topic, I know I should be looking for .0005 to .0001 but doubt I'll get there not knowing if the journals are true. That's a job down the road someday if needed.


I've done one rod this way by removing shims just enough to eliminate any rotational resistance. I plan on going back in once I put things back together for a final check. I used Plastigauge with limited success.

These rods came with the car in a box, all with bowtie logos, must have been sent out and re-babbitted years ago still in their Federal Mogul boxes. They have an odd mix of shims, from .002 to .034. They are all shimmed differently but the bore diameters appear uniform and true according to my calipers.

Doing it in that manner I would get them to the point of just a bit of resistance in turning. Being new rods the high spots will pound down in a short time.

Thanks Chevnut.
That helps get me going. I'm going shim crazy here.

Charlie,
If you flip the whole car over you can then work from above and won't have to lay on your back or take the motor out and the rods won't be upside down anymore.

Uhhh……no comments from Olds owners please.

You got me there my friend!

The fact that the rods have different shim thicknesses suggests they may have been fitted previously, perhaps to specific cylinders? Ordinarily a company babbetting rods puts an equal number of shims on each side, same amount on all rods before boring them to suit crank.
Oh well, process you suggest may work depending on whether journals are out-of-round much. Personally, having removed my rod caps a couple of years ago (because engine was loud on bottom end), I found play ranging from 30 to 50 thousand. Rods had been freshly rebabbetted and never run (thanks goodness because dippers were in backward). Anyway, I removed shims one rod at a time, until I got within about 10-15 thousand, and as I tightened each one, I turned crank to ensure not too tight (remove sparkplugs to eliminate compression). Worked great. So my advice, wait until you have pistons in place, then do it like GM recommended.

Maybe they were babbitted and custom fit years ago but never installed for some reason. There seems to be no rhyme or reason to the different shim thicknesses. I tried to match them up on my different journals but nothing clicked so I'm doing it the old fashioned way, manually by feel, one rod at a time. Once I get them pretty close, I'll re-install the pistons and test again like you said, with emphasis on the dipper direction !
How did you arrive at 10-15 thousand ? With instruments taking measurements of the bore & journal, or with Plastiguage ?
I would think if the journal is out of round by the slightest, I'd be trying to get that 10-15 thousand with no high points until the cows come home.
Anyway, we'll see what happens….I think I'm good. With no shims left and paper thin babbitt on my originals, I had to do something. Thanks Smoke

I never found where a new rod and its shims would fit a new or used rod journal with the furnished shims.
The test will be to tap the rods back and forth (front to rear) as per the shop manual after the pistons, etc. are installed.
wroperly adjusted you should not be able to move them back and forth by had but the will move with a tap of a little 8 ounce hammer.

That's where I'm stuck. No matter what I do, I can't get to the point where the back and forth (front to rear) requires a tap to move AND the have the rod swing without binding. I don't mean the high spots either. There is considerable resistance on the rod unless I remove a shim BUT then I can move the rod back and forth by hand. Maybe my hands are too strong, or I need .001 shims. My smallest is .002. Or perhaps I should just accept some back and forth movement and concentrate on when the rod offers slight resistance, then lock her down.

A .001" shim will increase the clearence by .0005 and that is what you need. Try cutting a shim out of Renolds Wrap.

Thank you ! I'll give it a go tomorrow. I'll also try just one on one side (cam side) for fine tuning. I should develop a feel for it as I go along. Glad it's only a six cyl.

I have 6 packets of GM shims that came with the car. Inside there are a pair, each held together in groups of 3's. But the smallest is .002.
Yep, I think the prior owner was trying to tell me something.