@XfbodyX that first link is not 100% working for me, but that might because of my work limiting it (maybe).
Bruce, there is an art to engine balancing. My brother used to work in a huge race car engine builder (GM engines), back in the ‘80’s, and some of their engines would turn 8-9k RPMs, mostly for sprint cars and for other high speed circle track cars. My brother knows more of the things they do more than I do (I know the basics). They would also purchase pistons and rods by the hundreds, weigh (and mark) them then sort them into groups by weight. This was before a lot of the lightweight parts came out. I’ve heard them say when they get an engine balanced exactly to factory specifications, then they are very happy.
What gets me is if the factory specifies certain specifications for parts (weights, sizes, clearances, and so forth) – then their engines wouldn’t it leave the factory that way. Sizes and some clearances, yes - but weights and balancing are definitely not at specs.
Even taking a brand-new engine and blueprinting it (ie: getting it to factory specifications) eliminates vibrations, blowby and uneven wear.
I have two new 400 short blocks in my garage. You can see numbers hand painted on the sides of the cast iron blocks:
After the factory builders bore/hone the cylinders, they measure the holes and mark the size as a letter. In this case “C”, “D” or “E” as shown. Then they go a roomful of pistons (with pallets marked “C”, “D” or “E” and so forth), retrieve and place the pistons on a tray (in order) so the rods can get pressed in.
It is possible the pistons gathered might be made a month apart or even from a couple different venders, sometimes. I have removed pistons from these engines (back in the day) that are evident there were 2-3 different style pistons used – so there might have even been compression differences as well (I didn’t look that hard for I was getting paid by the job, not by the hour). I would say most factory engines are a long way away from being close to factory specifications.
If you look closely, you can see “D”s handwritten on the piston tops (but covered with cosmoline) and one notch indicating front of engine.
Now look at this (the other block), This one has two notches indicating front of engine. The lower piston you can see a “D” (or maybe a "C"). The top piston might be a weird “D”, maybe (not sure).
What I’m trying to get to are both engines are using different (brand, maybe) low compression pistons. Both are brand new short blocks. The blocks cast within a day of each other (one on 3-13-78 (see top picture, above) and other on 3-14-78) – but not sure of machining date or assembly date (not looked). There might have been a couple of weeks of the blocks being machined and/or assembled. It is hard to have two different pistons weight in at same amount – even from the same casting. Even notching the pistons will make them weight in differently.
Also, one block has a heavy coat of cosmoline on it and the other, not so much.
Block 2 - I wonder if it was cast on a Friday?
The good news is I have new stroker crank kits for both engines, so the cast cranks and these low compression, um, pencil holders/paper weights won’t have to worry about balancing.
On the underside, there is all kinds of paint markings on it. Each main cap bolt and rod cap nut has a dab of paint – which I would assume verified it is at correct torque. The crank has a lot of blue, which I suspect means a 400 with cast crank with normal rod/main bearing sizes. The connecting rods have orange paint on them – which I assume is standard size bearing inserts installed. I think it is interesting on the story each of these engines have – but once you paint the outside of the blocks and coverup the pan – that story is gone.
When I get ready to rebuild both engines, I’ll take the old pistons/rods out and weight them for giggles. The builds will be listed here – just not yet ready for that, yet.
BudW
