The Stovebolt Site Forums The Shop Area Engine Shop crankshaft balancing importance?

Hey Guys,
The engine shop ordered a re-ground crank for my 235.
I asked if it had been balanced and they responded; 'inline cranks don't need to be balanced'.

Not sure if I buy it, but then again they're the experts.

Sure, I get the thing about all the pistons cancelling each-others momentum.
But it seems like it would be important to make all the counterweights evenly pull on the crank?
It's just a street engine (4x4 & roadtrips) so maybe I should let it slide?

Advice would be appreciated.
Thanks

I asked the guy wo has been grinding my crankshafts for the past 35 years that same question a few weeks ago, and got the same answer- - - - -inline sixes don't need the crankshaft balanced at any normal operating RPM. The 120 degree separation of the counterweights creates an inherently stable condition. Recently, I had a 235 crankshaft in my lathe, and turned about 1/2" off the OD of all the counterweights to create clearance for a shortened connecting rod and piston combination I'm using with an increased-stroke engine I'm building. Just for grins, I turned the spindle RPM up as fast as it would go. No shake! A V8 crankshaft would have made the lathe walk across the floor without properly calculated bobweights on it!
Jerry

I don’t know about anyone else, but I am picky that way. So I have always balanced my 235/261 and 230/250/292 motors. For the little bit extra, I think it’s worth it to assist with a nice smooth running motor.

I weight match all the moving parts to 1/10 gram tolerance or closer (A dollar bill weighs one gram) but in my experience, inline six crankshafts just aren't worth the trouble, especially stovebolts. The cylinder head won't let one turn fast enough to get into dangerous RPM territory. Now a Datsun 280Z or maybe a Toyota Supra with a twin cam cross flow head and a 7K+ RPM redline might be a different kettle of fish!
Jerry

The guy who worked on my 235 crankshaft "balanced" it and then had to go back and unbalance it by adding weights where he had ground off counterweights. He believes that he either read something wrong or there was a glitch in the balancing machine.
He admitted that he doesn't get many (any) old inline sixes in his shop. Lesson learned, he said.

Quick replies, thanks!
I'll skip the crank balance, but will be sure to match piston & rod weights.
Very interesting to hear about crank on the lathe!

Another thing I would believe is that crank bending moments induced by piston reciprocation would dwarf any counterweight mismatch centripetal forces.

My stroker engine will be using stock 235 pistons with about 1/4" trimmed off the bottom of the skirts, but the rods will be considerably lighter weight than the originals. They're recycled NASCAR H-beam rods, and are only 7/8" wide at the big end. The material I've machined off the counterweights and the reduction in reciprocating weight should just about cancel each other out.
Jerry

Sounds like a unique form of stovebolt!
Hope to see pictures at some point!

This ^^^^^^^ a very “long” crank.......poorly supported ( mains Too few, too far apart) is the main concern at high rpm if your going up there.

Fortunately, "high" RPM on a stovebolt is somewhere just below 4K, unless some pretty exotic work is done to the cylinder head, camshaft, carburetion, and exhaust system! It sort of seems like the guys who designed the engine knew what they were doing!
Jerry

If all the constellations in the Zodiac get aligned properly and I actually get the engine built, I plan to mount it on a trailer with a portable dyno and attend a few swap meets and other stovebolter gatherings. I think a 260+ cubic inch engine with about 150 HP or so that looks like a 216 from the outside just might attract a few potential buyers!
Jerry