Lightening any and everything …

[dunk]

For sh*ts n giggles I have drilled a few cranks...

Yes, the engine it's in still runs!.. quite nicely thanks:) and yes, I had it dynamically balanced afterwards...

To answer some questions above..

re the cross drillings... look down the crank from above, insert long thin rods... drill bits, skewers, socket extensions, pipe, etc whatever you got... all the way through and out the other side of the cross drilled oil holes... you can then mark on the crank webs/journals where they go through the crank and intersect...

If you drill an 18mm hole through the rod journal of a stock forged crank without hitting the oil drilings... it removes approx 100g per journal..

It gets close... but with some planinng and thought you should be able to get a 19 or 20mm hole in there at home with reasonable tools... holding the damn thing is the problem!

Just for some reference - Holes in the beam of stock conrods can get them down to approx 550g... ive only got to about 570 though on the few sets ive done... depends on what they are to start with...

You can also take approx 40g from stock 1600 pistons by drilling holes in the skirts... it runs well and doesn't seem to smoke!

[Dan Ruddock]

The holes Jose drilled into my crank are .973"

My guess is the longer 84mm stroke and being a non-cross drilled has something to do with.

ALB I will get back latter. In the middle of setting cam timing of my current build.

[BFB]

I talked to a guy recently about drilling the crank counterweights and he said they’d run into it causing cavitation , oil foaming.
I have know experience with this but could see it happening.
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"You are the Engineer and the Mechanic.  
Build it your way not the way someone else does it. Their way might not work for you." - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
“ The monkey see monkey do mentality seems to run deep in VW people. "Gene Berg said it was so 30 years ago so thats the way it is" “ - bdkw1

[sled]

[jpaull]

I used a 82mm Bergman Super Light Full Circle crank for years. My buddies called it the "mocha crank". But they never actually used it lol, it was just by looking at it. I put alot of hard quarter mile passes on that and street miles and it worked great. I never pulled the dipstick to find frothy mocha oil lol. It was always normal.

Demello mentioned doing the cranks for him, and Bergman just drilled them for weight savings.

[txoval]

You could also coat the crank post drilling to shed the oil/reduce windage

Might be snake oil, but I did it on my current crank

[oprn]

The difference from windage/frothing losses caused by the extra holes might be too shall to measure.

And no, by the time you shut the engine off and pulled the dipstick the oil would have settled out. I would expect frothing to show up as oil pressure loss/fluctuations at speed not when static checking.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[bugguy1967]

[txoval]

Yep, T is on a whole other level😅 Nicest guy around too. Just wish I could convince him to move to Texas

[oprn]

[bugguy1967]

[txoval]

Counterweights:

Reduce the bending load on the crankshaft.

Imagine a 4 cylinder engine with a flat plane crankshaft. The first cylinder is at the top dead center (TDC), the second is at the bottom dead center (BDC). The conrod and the piston of the first cylinder "pulls" the crankshaft up, the second down, while it is fixed at the main bearings. The crankshaft will be deformed at the main bearings, which means a lot of stress at the fillets next to the bearings, and has a negative effect on the lifetime of the bearing shells. If you add counterweights to the crankshaft at each cylinder, and adjust the size of these carefully, they will pull the crankshaft with the same force as the conrod and piston, but in the opposite direction, and the crankshaft will have no bending loads.

Another good read

http://ohiocrank.com/crankshaft-balance-factors/

[oprn]

From the article quoted above

"The “balance factor” is at best a compromise, and partially suppresses vibration at some RPM and power/vacuum levels."

It's as I suspected then, the counterweighted cranks we buy are just "ball park" weighted for an average piston and rod combination. It's not an exact science, just better than none. I have been noticing over the years that the size of the counter weights varies widely from manufacturer to manufacturer with some actually being full circle which in my mind do not compensate for anything, just add mass.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[txoval]

I would agree regarding “off the shelf” cranks and most builds.

However, you could size/lighten it to match

[oprn]

To do so is above my knowledge and ability and I suspect 99% of others here. Off the shelf generic is still better than the stock one without any.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[ALB]

[clonebug]

[Dauz]

Those DPR crankshafts that people are blasting up to 8k rpm are using 1500 non-cross drilled stockers as their base platform.

Also, I'd rather nix chassis weight before adversely affecting inertia in my motors rotating mass by going apeshit and gutting my motor components for all its' tensile strength. Less weight only means rev up/down faster. You'd especially want the load if force induced.

For most of what you all do, stick with a 12lb flywheel (no less). Leave the rest alone

[Clatter]

Harley-Davidsons have both rods on one crank pin.
It’s essentially almost a single-cylinder motor as far as the counterweight is concerned.
When carefully building one for high-performance,
The balance was ‘factored’ for the intended RPM/use of the motor.
All of the rotating weight and a percentage of the reciprocating weight are added to the opposite side of the flywheels from the crankpin.
You would weigh the crankpin, rollers, and big ends of the rods for rotating,
And the small end of the rods, piston, pin, rings for recip.
IIRC, most of the 7000-7500RPM motors we built had a 60% balance factor (don’t quote me on that number).
Meaning the counterweight would be 100% of rotating and 60% of reciprocating.

Point being,
The counterweights on our cranks could be calculated and created to have an ideal weight for the RPM range we want.

I’m also guessing they’re rather smaller than is ideal,
Just from what they look like based on experience.

FWIW.
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Bus Motor Build

What’s That Noise?!?

[modok]

Can confirm there isn't enough space to approach overbalance. I could cut one in half and balance it, and we could "see" how thick the counterwights would have to be to work as some think they do..... it might make a fun youtube vid or something but I'm not really into that.

So if they are way to small how do they help? IMO it's more like the case of center counterweights on a v8.... they do nothing for the overall balance of the engine, and very little to reduce bearing loading, but still reduce crank flex problems somehow, usually.