How to spend a BUNCH of time obsessing over what things weigh and how to fix it


runs with scissors
May 26, 2001
This is a step by step how-to of balancing rods and pistons at home with the minimal of expensive tools.

Since I've had horrible luck with FM hypers in my 4.1...

I decided to spend waaaay to much time making my own custom 'earlborwn' forged pistons. The original idea was to pull the engine pop the pistons out, measure the exact bore, then slam it back together as soon as my slugs were made. Actual practice was a much different outcome. A few months ago, I pulled the engine, measured my bore (3.996" right at 1 thou greater then I thought it would be. Glad I went through the extra trouble. Having 4 thou clearance instead of 3 is an additional 33.3%.

So when it came time to 'slam' my engine back together I decided at the last minute to use a set of NOS rods I've have stored in my nudie book shelves for a few years.

Then I fired up my scale and took a total weight just to see what I was dealing with.

As you can see the range is from 691.33 grams to 699.75. 8.42 grams between high and low.

I went back and forth as to if I wanted to have pressed pins or floating. After many days of drinking beers and looking at naked women on the internet, I decided to go ahead and float them. I hate the idea of additional noise if I don't need it, but ti's so much easier to R&R pistons when they float. Not to mention allowing the rod to find it's 'happy place' since it's offset.
first I set up my cheep Harbor Fright mini drill press with a small center drill. Then poked a hole in the little end for oiling.

Normally I would have done all the beam polishing and balancing before I floated the rods but I was already at the machine shop, the rods were with me,and there were beer. Now most people, including myself don't have a precision honing machine at home. This step will most likely have to be farmed out for floaters.

Next, to save time and belts, I took my $13 tool show grinder and knocked off about 80% of the casting flange. DO NOT try and get it flush as you'll end up having to sand the grinding scratched out of the beam.. You DO NOT want the lines going across the beam. Those are stress risers and will give a crack a place to start.

Next I fired up my brand new Harbor Freight 4" belt sander and started sanding.

Once the beams were looking good and the casting flash and roughness were gone, I swapped out to a finer belt and got them all as smooth as possible.

Then the fun began. And by '''fun'' I mean "This thread is brought to you by lies". First is to get an initial baseline weight on both ends.
My 'rod balancing fixture' is a chain that hangs from my vaulted ceiling with a custom hook on the end made out of a coat hanger. The disk is a scrap piece of UHMW I had laying around that I made to balance my BBC rods for my jetboat. Turns out it's only a smidge smaller than the Buick big end, so I ran with it.

For some reason I couldn't get repeatability for anything on the big end. Luckily the little end did offer repeatability. If I didn't have a scale that would report 1/2 of 100th of a gram it might have helped out some! This scale is so finiciky I have to do EVERYTHING the same when I weigh stuff. That includes the way I breath, the A/C can't be running, no open doors or windows and I can't move anything on the table it's sitting on.... INCLUDING my Mickey Mouse stool (and my house is on a slab!). That scale is badass :)

.So I decided to make all the rod caps with their bolts weigh the same first. Same technique as the beams. Get it close with the grinder, then smooth it with the belt sander. At leas on the rod caps the grinder marks are oriented the correct way.


Once the caps were all the same, I moved back to the little ends. Now even though the caps were the same the big end could still vary. as the cap weight hangs off past the centerline of the big end. Since the fixture acts like a 1st class lever, removing weight off the big end will cause the little end to weigh more and vice versa. I spend the next few hours killing beers and going back and forth between total weight and little end weight. Once I got to .75 grams I called it a day (my repeatability was right at 1/2 gram. It was taking so long the weather was changing and it was screwing with the scales internal weather station)

Next was the easy part. The pistons don't require any balancing or fixtures to the repeatability is dead nuts accurate. First I weighed all the wristpins by them selves and then all the bare pistons with locks. I married the heavest slug with the lightest piston and the lightest pin with the heaviest piston. Since my pistons started out very close to each other, doing that step put me VERY close to perfect. Since I knew what hole each slug was going it, I married them to their respective rings

After I knew who goes where and what they weigh, I fired the belt sander up and make them all match. Without the rings, my slugs settled in at 713.08 grams without the rings (bare slug was 573.28g to 574.02g)

I gave the rods and caps a quick hand lap. Even though the rods were new, they weren't blueprinted and I wanted to improve on the factory finish. I also wanted to make sure there were no boogers on the parting faces.

It's a good thing I checked...

Hand lapping is a 'feel thing' in a lot of ways. You can also tell what your workpiece is up to by sound as well. Boogers make fine scratch lines and a scratching noise. Flat surfaces make more of a hissing sound. When they get really flat that act more like a puck on an air hockey table and the media pretty much stops eating.

I also wanted to tighten up the vertical clearance to the minimum spec of 2.3738" for maximum bearing crush and heat transfer.

Time to get out the precision toolies. On my home bore gauge I have no problems with this cheap Shars unit. I think I paid $35 for it and I've put it side by side doing comparison runs and it read the same as the Mitatoyo it was copied from and a Starrett unit. From my personal experience it's possible to cheap out on that one as long as the dial gauge is in good shape and smooth. As long as there's repeatability, you're good to go. Now the mics on the other hand, DO NOT cheap out on those. Old ass name brand like Starrett, Mitatoyo, Craftsman (made by Starrett), or, like mine, Sheer Tomico are light years better than brand new Chinese crap. Mics have to be smooooth to be repeatable, the screw has to be DEAD NUTS precision machined, the anvils need to be hardened, and the ratchet needs to have the same drag every time.

Now back to it... Once I got the big ends where I wanted them I broke the rods down, loaded up my clean wider bearings for a 95 Park Ave and torqued them up.
I measured my rod journals and noted what journals were the biggest to smallest.

Then I dropped the bore gauge into my rods and did the same thing.

Now I know what rod goes with what journal and I know what piston goes in hole.

Now I can set the bore gauge to each journal and measure the oil clearance on each rod.


What's odd is that I had 1.1thou before I tore it down. Going back with the same (new) bearings netting me 1.7 to 1.7 thou on the big end. That just goes to show to always measure EVERYTHING!

Time to marry them up. For those that can't remember what way a rod faces, the easiest and most foolproof way it to look at the side of the rod. one side of the big end is machined lower than the other three. Those low areas face each other. That was done to make room for the lip between rod pars on our even fire cranks. By making a split pin, it pushes the rods out from the bore centerline. Releaving that lip allows the rod to come back towards the center a little bit.

After that it's just a matter of spending 2 hours looking for your ring compressor just to learn than the SS band rusted through and you're lost the last warm day for months and can't build the short block :D

This should show the amount of precision stuff that you can do at home. Taking things to this level (and control) generally isn't something you can pay a shop to do. Most of what I used is very cheap and can be used around the house for other stuff like the drill press, belt sander, etc. Anormal scale would be much easier as it wont' have the resolution that mine does. This job would be much easier if I had a scale that only read down to 1 gram.

it's also funny seeing all the leaves and crap in the background. All of this stuff except for the very end was dirty work. My living room and back porch were fine as the clutter and debris aren't there during final assembly.


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Nice to see what you've been doing. Haven't seen you post anything in a while. I was afraid you might have gotten married or something. :)
I'd never buy a car without test driving it first.

I'm a fan of multiple test drives :)