Topic: 750 Crank Balancing?

[Garage_guy_chris]

I decided to do the oil passage ball removal, clean out, drill, tap and set screw approach. I actually did a little tutorial on it:

http://forums.sohc4.net/index.php/topic,146287.0.html

The question Im trying to get some input on is if I should be concerned about its balance after the work I have done?

I realize a re-balance will likely find some imbalance just due to the fact it was last balanced with 1960's-1970's technology. But what I can't get my head around is would the modification be likely to throw the balance out enough to cause problems down the line? 

Im at that point where this and a small issue with cutting the quench band is the only thing keeping me from assembling the engine and finishing the bike

[MRieck]

Balancing is big....I do it for everything.

[Old Scrambler]

Your crank-work may be modest.........but the pistons and new pins should be considered.

[Jerry Rxman Griffin aka MuthaF'er]

Lightening and balance perhaps.

[Garage_guy_chris]

I had to brush up on my engine balancing knowledge a little as its been a while Big Jay sums it up clearly in a older thread

No. Inline four cylinder cranks are "self canceling" Meaning the  design ( two thows up, two down) cancels itself out. The crank is spun up and balanced alone then if the component weights, are the same, no matter what they are, and the entire assembly is still in balance. Inline sixes and flat fours are the same. All other crank configurations require bobweights to be attached to simulate the component weights.

This means, you can take the stock lightweight oem pistons out of your 750 and swap them for heavier, say, 1000cc pistons, without screwing up the balance.

Jay

Old Scrambler: I have checked the weights on the rods pistons and pins everything is very very good in that regard the heaviest and lightest were 1 gram between each other.

Jerry Rxman Griffin aka MuthaF'er: Lightening would be nice but I think Im gonna save my $$$ for now

I think the moral of the story here is that getting the crank dynamically balanced would be a good idea. all its gonna do is make the engine better and smoother.

[PeWe]

"Self canceling.." was something I had in my mind when I replaced the pistons at last restore. How I placed the pistons and which to carve 1 gram or 2 from. My pistons are of 2 types so I could not place them everywhere, 2 or 4, 1 or 3. Valve pockets differ.
1+4 same weight as 2+3
1 equal to the meeting 2
3 equal to the meeting 4

I hope it is OK, but I felt better back in the days when my tuner balanced the entire crank with rods, pistons.

I regret I did not order lightened crank and  better rods mounted and balanced from APE or equal. My engine is done, too much work to pull it and open it again. I know the weak point everytime I pass the red line and enter the green area on the other side.

[SOHC4 Cafe Racer Fan]

I did a mild lightening and balancing of both the crank and rotor.

[Retro Rocket]

Regardless of what anyone says, if balancing wasn't important on these engines, no one would do it, I'm definitely balancing mine...

[bear]

Regardless of what anyone says, if balancing wasn't important on these engines, no one would do it, I'm definitely balancing mine...

PM me if you need a lead on a good crank man Retro.

Cheers,
Brian

[Retro Rocket]

Regardless of what anyone says, if balancing wasn't important on these engines, no one would do it, I'm definitely balancing mine...

PM me if you need a lead on a good crank man Retro.

Cheers,
Brian

Answered in a PM mate...

[Big Jay]

As close as we balance the cranks, changing the balls for screws would change the balance.  As for the components, it doesn't matter what they weigh as long as they all weigh the same.

[Garage_guy_chris]

Well I just dropped off the crank and the flywheel/alternator rotor at the machine shop. Hes gonna give the crank journals a polish and balance up the crank then put the flywheel on and check its balance. Should be done in a week or two.

Im lucky to have a local guru, Gord Bush. He knows the Honda MC engines and any other Japanese bike or car engine very well, He is the guy to go to if your in or around Toronto.

[SOHC4 Cafe Racer Fan]

Well I just dropped off the crank and the flywheel/alternator rotor at the machine shop. Hes gonna give the crank journals a polish and balance up the crank then put the flywheel on and check its balance. Should be done in a week or two.

Im lucky to have a local guru, Gord Bush. He knows the Honda MC engines and any other Japanese bike or car engine very well, He is the guy to go to if your in or around Toronto.

I just noticed your avatar.  Yikes!!