Masnart39

If you keep your current components, you only need to grind rods # 1, 2, 5, & 6.

If you get another cam, and it's .615" lift or less, 1.050" base circle will clear most rods.

quickSS

Good info above. File for future reference.
Karl

hosspwr94

if its an internal balance motor I recomend re-balancing after grinding the rods. you could get some vibration at different rpms. better safe than sorry and loss of time tearing down a second time.

RallyBoy1

Well, I found out today that rod #5 was not clearanced at all. I have to wait till tomorrow or Monday to find out how this will be handled.

Masnart39

I'm sure some will disagree with me, but I wouldn't bother with re-balancing the crank after clearancing the rods. At most, you'll probably grind off 2 grams, which will be 4 grams in the bobweight. In my opinion, that doesn't constitute a re-balance. If the bobweight was to change by 10 grams, then I would consider it.

rskrause

When you lighten the rods or pistons you create "overbalance". While the typical internal balance is "neutral", i.e. a 50% balance, many people prefer 51 or 51% anyway. You will be creating far less "overbalance" than this. You will never notice this and it will work fine. End of story. I have a rotating assy in my race car that was neutral balanced for 600gm pistons. I replaced them with 585gm pistons and it runs fine to 8,000rpm with no vibration, wear on bearings, etc.

Rich

hosspwr94

not trying to argue but the pistons aren't being "thrown around" like the rods are. if you grind 4- 5 grams off two or three rods and not the others, it is possible that you 'could' feel some vibration.
the crank sees the pistons as just a push and pull weight, if they are all the same then it won't care. the rods are actually creating opposing stresses with each "throw" of the crank therefore the weight difference between rods changes the stresses. and in a race car you probably won't feel or ever notice the vibrations but in a daily driven street car this poses a longevity problem.
again not trying to argue just giving some facts.

Masnart39

Rich is correct. Most shops and crank manufacturers will overbalance.

As far as noticing vibration, or adverse long term effects...... in my experience, it's just not the case.

Most computerized balancers have a setting that you can input the number of grams + or - of perfect balance that the machine will show as "0". (typically 2 or 3 grams) The reason for this, is that you can litterally spend hours chasing perfect zero balance. It's nearly impossible, and quite frankly, isn't necessary.

Another scenario, which anyone who has balanced crankshafts for a living will agree...... You can set up your bobweights, and balance the crank. Then take the bobweights off of the crank and remove the crank from the machine. Now put the crank back into the machine, and re-install the bobweights without changing anything, and spin the crank. 9 times out of 10, the balance will be off.