Engine Balancing Qs?

DieselNasty

DieselNasty

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Apr 28, 2008
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Got my whole rotating assembly balanced by PDR and everything was perfect! One of my pistons got messed up so I got a new one and it was said to be very close in weight. Then I decided I wanted to get the pistons cut for valves after I balanced them so Scheid cut them and then checked the weight and the new one was 2 grams lighter. Scheid said that chasing 2 grams from all the 5 pistons was not worth it without the rest of the bottom end.

My questions: Should I worry about the 2 grams in the pistons or am I worrying for nothing?

Shouldn't I re balance the crank since I removed weight from the pistons?

Thanks
 
2 grams is nothing

how much does a piston weigh?

slap it back together

you wont be able to tell the diff from doing that or starting over and rebalancing the whole assembly

for sure
 
oh, just reread it

how much did they weigh before they did the valve reliefs?

how much afterwards?

are you willing to spend the cash to start over?

i wouldnt worry about it but it is too bad you had it balanced before having the valve reliefs done

n too bad you hurt a piston too

i still say slap it together!
 
Yea thats what I was thinking just putting it together but then I starte thinking hey this is my race engine I should do it right haha. I'm a bit ocd with this stuff so I like to make it right, but will it really effect performance if i wont really rev to 5k for drag racing.
 
Machined piston is 1126 and un machined is 1157(may not be perfecty accurate since I used a smaller digital scale)
 
DTanklage said:
2 grams is nothing

how much does a piston weigh?

slap it back together

you wont be able to tell the diff from doing that or starting over and rebalancing the whole assembly

for sure
Click to expand...

A piston w/pin is somewhere in a 1,950 gram range. before cutting
 
on all the ones weve done the crank, pistons, and rods are balanced seperately. on a v8 the assembley has to be balanced using bob weights on an I6 it does not.

If your really worried about it all you would have to do is have them weigh all the pistons and then take the lightest one and remove weight from the others until it matches the lightest one.

our machine shop gets them all to within 1/2 gram however we leave the line at 6000 so it is a litle more crucial.
 
So your saying an I6 doesn't need the crank redone because of the weight of pistons changing? Ok then I'm good with what I have becasue PDR balanced it all separate like said.
 
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I have a question for ya'll, when balancing the rods and pistons you find the lightest one and then match the rest of them to it. But in doing so where do you remove the material from those heavier ones? Do you just use a grinder on the rods until they all match?
 
Typicaly use a belt sander and remove material from the big flat area on the outside of the rod cap. And the edge of the skirts on the pistons.

Just try to match the lightest one.
 
yikes

piston design limits where the weight can be removed. have not held a cummins piston in my hand so i cant tell you for sure but prolly up under the wrist pin boss. think most balancers use a mill for this tho and dont know if you should try this at home. you cant balance the crank there either...

you need special fixtures to weigh rods and i am gathering by your questions that you do not have them. why not just send it all off together and have it balanced?
 
DTanklage said:
yikes

piston design limits where the weight can be removed. have not held a cummins piston in my hand so i cant tell you for sure but prolly up under the wrist pin boss. think most balancers use a mill for this tho and dont know if you should try this at home. you cant balance the crank there either...

you need special fixtures to weigh rods and i am gathering by your questions that you do not have them. why not just send it all off together and have it balanced?
Click to expand...

I was asking mostly out of curiousity, my truck will never be at a level where that sort of thing will be needed. If it was something I could do at home safely I would though for sure...
 
My pistons all have a small amount of weight taken from under the piston if you flip it over it will be dead center. Almost hard to tell because of the small amount removed. The rods have material taken from the flat part on the outside of the cap. You can tell that they are way out compared to the pistons because of the material differences.
 
rods have a hole in ea end

so they support the center of one end and weigh the center of the other

(with the rod horizontal)

then they spin them around and do the same thing to the other end
 
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