Thread: balancing pistons/rods

Tweet

Hey Gang,
I took my piston rod assemblies to our local market after hours and got the first weigh in .
#1 1420 g
#2 1430 g
#3 1440 g
#4 1410 g

looking at the #3( the heaviest ) the casting marks were rough looking
then looking at #4 ( the lightest)) it was smooth with no casting marks

I used our air die grinder with a tungston burr and now have
#1 1410
#2 1415
#3 1417
#4 1410
I'll do a little more grinding and
Tomorrow I'm going back and weigh them again

does 30 g seem like a lot of difference between two rods?
I'm shooting for all the same
hank

Originally Posted by TOW'D

Hey Gang,
I took my piston rod assemblies to our local market after hours and got the first weigh in .
#1 1420 g
#2 1430 g
#3 1440 g
#4 1410 g

looking at the #3( the heaviest ) the casting marks were rough looking
then looking at #4 ( the lightest)) it was smooth with no casting marks

I used our air die grinder with a tungston burr and now have
#1 1410
#2 1415
#3 1417
#4 1410
I'll do a little more grinding and
Tomorrow I'm going back and weigh them again

does 30 g seem like a lot of difference between two rods?
I'm shooting for all the same
hank

In what area are you grinding on??

a big belt sander works the best i try to sand on the weight pads on the rods i hang each end for weight with a connecting rod balancer the big end come in most of the time good i get them with in less then a gram .on the pin end there is some times not much steel there . no steel to take off. i like some meat there so i will match up the light pin ends with heavy piston and light pistons with heavy rods pin ends i then add the weight and tune in the heavy ones just abit on the piston or if press pin throw the pin up on the lathe and trim the pin down two grams is not hard to get when it time for the pistons to get hang on the rod you re set the stop so the pin is on center the short pin this works for me

I'm removing the metal from the rod seam casting marks --all around the side of the rods and on the big end cap
there are cast spots that have been ground off before on these rods from the factory

hank

Just got back from the market scale and #3 is still 1415 and no more metal to remove
looks like its plan #2
get 4 more con rods and weigh them before sending off to get rebushed
I've got a few donor engines

Do you guys balance the rods seperate from the piston?
then weigh the pistons/rings/wrist pin/clips

Over all weight or big end on scale and small end supported on a jig?

I can see after weighing these rods and getting such a wide range of weight
I better shooting for all the same with in a gram

A big plus for air tools ripping the donors down

hank

Weigh each end seperately and if you sand on the sides of the rods be sure to sand up and down, NOT across!!

Scales are cheap, build one,and weigh them yourself at home.

Pat

Man that is COOL ! In the 70s we used a Baby scale on the Rods .

Thanks for the pix Pat
just what I needed to see

Where do we grind on the pistons to balance them(if needed)
Looks like the only place is on the inside of the piston on the thick skirt ??

hank

you trim on the pin boss in side of were the pin goes thru the piston >(-)<

You'llneed to give the machinist the acurate count of grams for bob weight when he spins the crank up for you. Total count of grams at rotating end and 50% of the reciprocating end (upper end).

Originally Posted by nitrowarrior

You'llneed to give the machinist the acurate count of grams for bob weight when he spins the crank up for you. Total count of grams at rotating end and 50% of the reciprocating end (upper end).

yep the best thing to do is let him use his scale to get the weight of one piston and rod this is what i do so the same scale making up the bob weight then all weight can not be off from your scale to his