View Full Version : Connection rod balance

07-04-2012, 12:18 PM
I had to rob 2 rods from another engine and they happen to be slightly heavier.. I hear I need to stagger them.. Should I run it with the 2 heavier ones on #1 and 3 or 1 and 2?

07-04-2012, 02:45 PM
I had to rob 2 rods from another engine and they happen to be slightly heavier.. I hear I need to stagger them.. Should I run it with the 2 heavier ones on #1 and 3 or 1 and 2?
I've weighed and balanced mine by taking off the excess molding flashing material to get them even

07-04-2012, 02:52 PM
I would match them if you have the time

07-04-2012, 03:06 PM
I would match them if you have the time

Match em up fo sho. Way easier on your engine

07-04-2012, 04:36 PM
can you afford to have to live with the consequences if you are wrong and this goes south?

if not, find a way to avoid a result that you cant live with going south.

07-04-2012, 07:36 PM
other 2 heavier ones aren't good?

07-05-2012, 12:27 AM
tp properly balance rods you need to hang small end
so you are weighing the big end
big end off rod is rotating mass
small end is recipricating mass
make all the big ends weigh the same by grinding the pad on bottom of rod
then weigh rod over all make them the same by grinding the pad on top of rod wrist pin end
pistons need to all weigh the same too
crank shaft is nuetral ballance on inline motors
good luck

07-05-2012, 08:18 AM
Just out of curiosity, what engine are we talking about and does it have floating pins that can be easily removed freeing the rods for easy work?
All grinding on rods should be done lengthwise or finished ground so any marks left are parrallel with the long axis of the rod.
The easy way to balance rods is with a fixtures that fastens the small ends of two rods together (starting with the lightest rod) and balances them across a pivot.
Material is removed from the heavy rod till they are neutrally balanced.
After all the large ends are done the same is done to the small ends using another fixture that holds the rods in the large ends.
When done the rods will be perfectly balanced end to end and for total weight.
I made my own fixtures but i think Comp Cams sells a kit. i will look for a part number and post it up if i can find it.

07-05-2012, 08:27 AM
I know CompCams sells one but i found this one being sold through Jegs.

07-05-2012, 08:27 AM
Thanks a lot everyone.. I guess it's time to pull out the die grinder... It's a 22r So it has the floating wrist pins so it's no big deal to disconnect the pistons I just assembled

dirka dave
07-05-2012, 10:04 AM
22r are not too fussy.

I have mixed and matched rods.

07-05-2012, 10:19 PM
22r are not too fussy.

I have mixed and matched rods.
and your shit never gets driven other than 1 weekend a year[f]

07-06-2012, 07:21 AM
Well I made a measuring jig at work and found a good kitchen scale that measures in grams... I tried to take a little bit off one rod but I stopped because it didn't seem right...
The two newer rods measure

Large end:577 small end:190 overall:772
Large end:565 small end:190 overall:770

Older ones

Large end:550 small end:203 overall 737
Large end:560 small end:202 overall 741

So by the looks of it I could take some off the heavier big ends to match those up but it seems like I would have to take off quite a bit... So back to the offsetting idea.. Pairing them up they only have a 3g difference between the stroke...

07-06-2012, 07:24 AM
Also I'll note there is no "pad" on these.. I'm guessing off either side of the large end where they look to be machined and then it looks like some had been removed along the length of them

07-08-2012, 02:01 PM
so i gave up on the balancing... i made it so there is a heavier and a lighter one on each set... but now ive installed them and they all went in perfect, all the plasti gauge is in spec.. cleaned each one up, oiled and installed... now the last one wont allow the crank to rotate ( i loosened off 1 by 1 to figured out the culprit ) i cant see anything wrong with the crank or the rod.. the crank was polished and checked at a shop.. ovalized rod mabye???

07-08-2012, 02:24 PM
So u where spinning the crank after u installed each piston to make sure it spun freely or u didn't do it till all where installed?

07-08-2012, 02:26 PM
i put them all on after i plasti gauged and cleaned them and i did the front 2 they were fine and then i did the last two and it didnt work.... so then i backed off the last one till it was snug and it spun freely

07-08-2012, 02:31 PM
Check underneath the bearings make sure there isn't anything underneath that could be giving u trouble.

07-08-2012, 02:37 PM
yea im gonna pull the one and clean the lube off and look for any marks..

07-08-2012, 02:40 PM
hopefully its just that simple[cheers]

07-08-2012, 09:09 PM
well it was almost that simple...... i feel like a retard now.... when i took the 2 rods n caps from the spare motor somehow i mixed a cap up... well got the right one on now and it works...... easy fix but man do i feel stupid.....

07-09-2012, 12:07 AM
bent rod ?? take the rod and lay it flat on a flat surface
and see if theres any gaps between rod and surface
a piece of thick glass and a set of feeler gages works good
unless you have acsess to a milled plate
table on a drill press would work
or try plastigage across bearing journal width of bearing
see ifits crushed more on one side than the other

07-09-2012, 07:01 AM
No it's good to go now some how I managed to grab the wrong rod cap when I robbed them from the parts motor

07-09-2012, 08:03 PM
Just glad u didn't find that out after u tried to fire it up[cheers]

07-09-2012, 10:58 PM
lol mised the second page last night
good you got it figured out