thrilla135

i have a 406 that has been completely taken apart...the motor was built at a race shop about two years ago..everything ready to run...unfortunately when we were putting the motor together the cam was in wrong and so the valves were the hitting the pistons..all pistons were fine but one...and for some reason the motor got taken completely apart without numbering the rods with pistons....so my question is what kind of issue will have with balancing? everything was balanced before ( minus the new piston had to buy) does each rod and piston have to be matched to each other? or since they already have been balanced would be ok to just put them back together and just get the new piston balanced?...i can build the motor but when it comes to balancing i have never done it before and really dont have much knowledge on it....i would really rather do this myself if i can and save alot of money...any and al answers is greatly appreciated

mxcrazed

I'm pretty sure that you are at square 1 with the balancing the weight of the pistons will vary up to about 1.5 grams then you have to take into account the weight of the rods varying, i would bring the whole rotating assy. harmonic balancer and crank pulley also your clutch and flywheel if it is a standard

ross

As long as the rods have there original caps you will be fine thay dont care what pistons are on them. And for the bal. job bring one of the old pistons and have the new one mached to the old pistons to keep your bob weight the same.

AlkyIROC

The big end and small end of the rod can have different weights. If your replacement rod has a lighter weight on either end then it can't be matched to the rest of them. Same thing with pistons. They're adjusted to weigh the same as the lightest one but if they're cast too heavy, you can't take enough material off in the proper location to make it lighter. Even wrist pins come in different weights. I had to change a couple a few years ago and the wrist pins that arrived were way too heavy to lighten up. I had to reorder another pair of wrist pins closer to the required weight.

Unless you're using floating wrist pins, you're not going to be able to replace your own pistons. The old wrist pin is pressed out and when installing the new one, the con rod is heated up to allow a slight expansion to install the pin. An engine shop will have a special jig for doing this without damaging the piston.

You also won't be able to do your own rebalancing. You just don't have the proper equipment to make sure it's done properly.

thrilla135

i have all of the original rods with their matching rod cap and they were previously balanced...as were 7 out of the 8 pistons...so that leaves me with one piston needing to be balanced to the others? and that should do the trick? the pistons are aftermarket forged aluminum mahle pistons .. floating wrist pins i do believe

ross

Yes all you need to do is have the one piston set to the weight of the rest of your pistons and you will be ready to go back together.

thrilla135

ok awesome ...hopefully a machine shop will do that for pretty cheap...i have only built one motor before..this will be my second...im estimating 5-600 hp and over 4 grand in parts...i hope i dont mess up lol first one turned out good though...

mxcrazed

not every shop will balance things the correct way some will use other parts of the rotating assy (pulley,harmonic balancer, flywheel) to balance the crank properly so that they don't have to drill as much out of the crank if someone cut a corner you may be up a creek without a paddle

I have heard of this happening but i don't know what the chances of this happening to your engine

somoeone else please chime in and please correct me if i am completely wrong

ross

He will be fine and on ext bal motors yes somtimes thay will take a little from the flywheel or bal. But he only needs one piston balinced to what he had he will be fine cost about $20.00.