balance a 300 crank

[BIGBLOCKCAPRI460]

do i balance as a unit [pistons, rods & crank]
or just use matched weight pistons & rods and
leave the crank alone?

 

[Asa]

the pics i've always seen in the mags have the pistons swingin around offa the crank
so i'd assume the whole rotating assembly

 

[StrangeRanger]

Balancing involves first doing a static balance of the reciprocating parts: matching piston and pin weights, overall rod weight and big end weight, then fitting appropriate bob weights (IIRC each is half the weight of the reciprocating pieces) to the crank and dynamically balancing it. You can do the grunt work at home in the shop. While you're polishing your rods, you can statically balance them. Good pistons and pins will already balance, but check anyway. Then take the whole mess, including flywheel/flexplate and damper to the balance shop.

 

[Thad]

With a straight six crank there is no need to balance with bob weight, don't know the science of it. Just what several engine shop have told me and what I've read.

When building my engine, we spun several 300 cranks on the balancer. All were stock, untouched and all were very close to zero balance from the factory.

Easy to weight piston and match to lightest on drill press or buy a matched set. Most manufactures box in matched weight sets.
Can make a fixture to suspend rod by big end and weigh the small end on a digital postal scale. Match small ends to the lightest by grinding some off balance pad. Then weigh each rod, match to lightest by grind some off the balance pad on the big end.
Bearing and rings are so close to being the same that it is not necessary to weigh. You can then have the crank balanced or trust Ford.

 

[Lazy JW]

Just a question to satisfy my curiousity as I have never actually balanced an engine myself; seems to me that due to the dynamics involved that the big end of the rod would be the more critical to be closely balanced rather than the small end? The big end becomes part of the rotating mass and the small end is mostly reciprocating while the middle does some combination of the two (the hokey-pokey ?). What do you dyno jockeys consider to be important?
Joe

 

[goinbroke2]

Big end is more important, but then I send my stuff to Allyn and John Armstrongs for all balance/machine work. Who are they? Check out national record holders in the NHRA National Dragster, go back as many years you want and look under K/altered or L/altered for Allyn and SS/DA and SS/BA for John. Yup, they own those classes!!

 

[Anonymous]

Three cheers for Thad ! ! ! He has favored us with Actual Controlled-Test Results Using Multiple Samples. A test like this is worth a mountain of the kind of semi-informed speculation and single-example anecdotes that I usually deal in.

Thanks for the info, Thad; good show!

 

[6bangerbill]

I ran across an article and a picture on the net where the counter weights were machined off a 300 crank to lighten the recipricating weight for faster engine acceleration. Im sure some of you have seen it. Any one try this? It looks feasible after looking at my own crank. It seems that each counter weight has a corresponding weight on the oposite end that can be removed to maintain static balance. If the rods and piston weights can be ignored, as stated above, it should work. Each rod journal is placed 120 deg apart for dynamic balance in rotational dynamics. Comments please.

 

[Asa]

it's been done
there was a member here once that machined 'em down for his dirt track car

there's a link in this thread where someone removed about 12 pounds from their crank
http://fordsix.com/forum/viewtopic.php? ... ight+crank

 

[Asa]

found the guy that owns that site

Hi Guys,
I saw one of you had been to my website off a link from this forum so I decided to check it out. I was surprised to see my name mentioned in a previous post. 79indypacecar, if you are allowed to run an aluminum intake as you stated I'd suggest trying an Offenhauser. Either the split or the open plenum will work fine. To be honest we've run both and I personally didn't feel much if any difference. Look around but I think you'll find that JC Whitney has them cheaper than anyone. I just checked for you, go to www.jcwhitney.com, the SKU# is ZX737654R, price is 199.99. It is the open plenum design that I have used in the majority of my wins. Don't worry about there being any bog or hesitation due to the open plenum. With a 500 cfm carb, which I have used, you will still get great response. We are allowed 4 barrels and have used Holley 600 double pumpers for some time and still have crisp throttle response. Something very few circle track racers do is lighten the 300 crank. It can be done easily with a band saw and a hard stone grinder, then balanced professionally. Makes more bang for your bucks than you can imagine! Go http://members.tripod.com/vintage39c/cranks.htm and you'll see a stock crank and one of our modified ones side by side. As stated there is approximately 12 lbs removed, and that's rotating weight! If anyone has any questions about using a 300 you can email me at 39c@cox.net or you can phone any evening between 6:30 & 9:00 central time, just ask for Ron. If you get the answering machine don't be afraid to leave a message and I'll call you on my dime.

http://fordsix.com/forum/viewtopic.php? ... ight+crank