CrankShaft - Equilibrate

[Nuno Cristiano]

I´m a bit confused. Today went to my mechanic to give pistons, rods, bearings, rings that came last week.

He speak that my crankshaft ( 7A engine ) is not calibrated to my new pistons ( JE ) and forjed rods. He said that equilibrations is made into Pistons + Rods and crankshaft.

Normaly engines inline of 4 and 6 cyl have crankshaft equilibrate. Right?

So, my question is necessary recalibrate my crankshaft to my new setup of pistons + rods?

Regards,

Cristiano

[Error404]

i think he means balance. your new rods and pistons will not weight the same as your original ones so you need to get the whole assembly balanced.

[Nuno Cristiano]

Yes, balance.

Where i can buy it or i will need manufactured this part?

[Error404]

you can't buy a crank balanced for your spec, you need to find someone who knows how to balance the 5 cylinder engine

[Nuno Cristiano]

Understand!

Thank you by all!

Regards,

Cristiano

[Billman]

many people run with other/lighter rods and pistons without to balance the assembly. Some say one need to balance them when going with higher than stock RPM.

[quattrofrank]

On an inline 5 you need to balance the whole assembly in one go. It doesent help to balance the parts separatly

[Nuno Cristiano]

Can you give me some company that make it?

[Error404]

many people run with other/lighter rods and pistons without to balance the assembly. Some say one need to balance them when going with higher than stock RPM.

IMHO you'd have to very lazy and/or very stupid no to
If you change the mass of any of the reciprocating components you should have it balanced.

[Thuppu]

Can someone give a explanation how to balance a I5 crank correctly, and why does it need to be so complicated? If you need to balance the crank in one limp with the flywheel and damper, what then if you need to change one or both of them, total engine dismount?

[JP]

Balancing is covered towards the beginning of my bugswatter build thread.

[Billman]

IMHO you'd have to very lazy and/or very stupid no to
If you change the mass of any of the reciprocating components you should have it balanced.

experience shows otherwise....how many people in this forum changed rods and leave the rest as is without to balance the assembly?

I once met a guy from Austria with a Lehmann tuned RS2 with 500+ and said that his crankshaft is untouched.
Dahlback said the same in an interview i was reading a couple of years ago about the Golf.

The flywheel has an imbalance from the factory. Also stock pistons and rods have massive deviations that shows that there is always imbalance.

however there also also many opinions about it. As JP states above there is much said in his thread also.

[UrS4boy]

Sorry. I have to say something. This thread implies that if Nuno does not balance all his rotating parts (crank, pistons, rods, flywheel and clutch), the end of the world will be upon us or, at the very least, his engine will blow up in only a few revolutions.

Let's get real. The factory did NOT do any such balancing. Yes, the crankshaft is balanced (i.e. counter weights drilled out in strategic places) but it was NOT balanced with rods, pistons, etc. attached. The factory allowed for some tolerance in the weight difference between the combinations of rods and pistons that would be pulled from the parts bins, such that the total weight of a rod and piston combination could not be more and "n" grams different than its other 4 neighbours.

Complete rotating unit balancing might be something that high revving F1 engines get but for our 3B, AAN, ABY and ADU lumps, it is NOT necessary. Sure things *might* be better, i.e. smoother, higher RPM (but why do you need more than 7200 anyway?) with a complete balance but for non-race applications it is overkill.

That said, for Nuno's install, he should weigh all five pistons and weigh all five rods separately and then match the rods and the pistons together such that the combined weight of the pairs minimizes the total difference in weight between the pairs. Easy with a computer spread sheet (or a piece of paper and a pencil).

Hope that makes sense.

[UrS4boy]

Example Rod and Piston Pair Matching Exercise

One the left are the hypothetical weights of the five rods and five pistons, with their average weights and their average total weights. On the right are the weights of the rods arranged heaviest to lightest and the corresponding piston weights arranged lightest to heaviest, i.e. the heaviest rod is paired with the lightest piston and vice versa.

In the end, even though the pistons weights have a 4 gram spread and the rods have a 5 gram spread, by carefully matching the pairs as shown, the difference in weights across the pairs is only 1 gram. (If purely random pairing had been done, it would have been possible to have one pair 254 gms (152+102) and another pair 245 gms (147+98), an overall difference of 9 grams. By selectively pairing, that difference drops to only 1 gram.)

............ Pistons....Rods...............Rod.......Piston.... .Total

1........... 100........150................152.........98...... .....250
2........... 102........147................151.........99...... .....250
3........... 101........151................150.........100..... ....250
4........... 99......... 148................148.........101.........249
5........... 98......... 152................147.........102.........249

Average= 100........149.6...249.6.......................... .....249.6

[mcandmar]

You are right in saying it will work, but its not right. As you point out Crank, flywheel, and front pulley are balanced from factory assuming a rod/piston assembly of X weight. And sure there will be some deviation between each piston and rod as per manufacturing tolerances. Problem is aftermarket rods and pistons have very different weights from stock components, and personally i would want it balanced. I made sure my own engine build was balanced because of this, and also because i replaced the original ABY flywheel and front pulley with 3B items. If you spending a few grand to rebuild an engine, spend the extra few hundred quid and do it right IMO.