so i buy this rotating assembly pre balanced on the latest hines machine. i take the kit to be installed to my local shop, they have it about a week and call me to say i need to re balance it. they said the eagle pistons difference from heaviest to lightest was 3 grams difference. and rods 1.5 grams. the company i bought the kit from said impossible. the shop said my engine would rattld apart at 7000rpm. what do you guys think i should do? oh ya, the shop wants 380 for the pro rebalance

 

If you paid for it to come balanced and it isn't, I'd try dealing with the company you bought it from.

 

yeah the company you bought it from or another machine shop see if they are liars trying to pork you... never know

 

is 3 grams a big deal for a 7000rpm engine? I havnt seen the pistons on the scale yet so I cant say for sure its that off, but I called my rotating kit supplier and he said bullocks that not even eagle sends out these forged pistons that far off.


Oh, does it help I even got a balance sheet with my kit? I didnt understand what all the numbers ment, but perhaps if I posted them, would that help at all?

 

It might be interesting to see what the numbers are.

3 grams is a bit much of a variation in weight. Something like less than 0.1 gram would be a much better.

 

@ 7000rpm 3 grams could easily make some rather expensive 'speed holes' in your block and fenders!


Take it up with the original supplier. Its their problem not yours if it was supposed to be pre-balanced...

 

i should mention that just because the rods are balanced wouldnt mean the entire assembly is...

 

when i bought mine they took into account the rings, piston pins, pistons, rods it even came wit ha new dampener and flexplate. runs smooth to me. i built it myself. even had to grind the rods to clear the camshaft.

 

they should have also balanced with the weight of the rod bearings...

if you had to grind the rods then it is no longer balanced.. as the rods are balanced end to end then the receprocating weight is balanced on the crank

 

i turn it 7500 every time i start it up. no problems here. it has hit 8000. not on purpose.

 

i would say you got lucky.

 

I'd take it to another shop.

 

take it to another shop? what particular reason?

 

to see if the current shop is trying to take your money.

 

Or find someone with a scale. 3 grams difference in piston weight should be easy to find... if its there. Thats something you can verify without any special tools aside of a scale.
Almost sounds to me like the seller of the kit buys some parts that are 'matched' from the manufacturer and calls them balanced. Thats not always true, for more reasons than one. Sometimes its a +/-1 gram tolerance (so they can be off as much as 2), and like what happened to me... got a set of pistons and for whatever reason, 2 were not part of the matched set. I ended up having to return them.

 

Spending $20 on a digital postal scale that can read in grams is a handy thing to have. I always check the pistons and rods myself before taking them to a shop- just to make sure things are "roughly right" before they go off for expensive machine work. I do a lot of stuff where I'm playing mix-n-match with different parts so doing my own home double-check sometimes turns up stuff that is obviously out of whack.

 

I think so, too. They're probably buying a set from the manufacturer and assuming they're already weight matched. Then they take one piece at random and use it to calculate the bob weights for balancing.