Piston pin and balancing dilemma!?

[Thuppu]

Just got my bottom end from balancing. But now I realiced that my JE piston pins are with quite thin wall thickness(compared to AAN stock pins) and they are only mild steel versions. E-mailed JE's info about it and they recommend 9310 alloy steel ones for the power target I'm aiming at. They do not cost much, but the problem is that the stronger pins weight 27g more than the mild steel ones. How does this affect the crank balancing? Can't belive I didn't notice this earlier before sending the bottom end for balancing.

Can the heavier pins be lightened few gramms by machining the ends or something?

[Billman]

ask your machine shop. (did you also removed the sharp edges of your je pistons?)

Maybe you can lighten the piston by 27 grams to compensate (not sure If it is possible....just make suggestions)

Ask the shop that did the balancing or wait input from JP or others who know that kind of stuff.

[JP]

27gramms is a lot to take of from anything pistons or wrist pins.

Was your assembly externally ballanced like stock? Or internally ballanced for race application?

If externally ballanced and staying below 7200-7500rpm you can get away with it as you are adding an equal amount at 5 equal points around the crank. And in the grand scheme of things you will only be out by approx 1.5-2% compared to the old bobweights for ballancing.

However if internally ballanced and you are intending to rev much higher it should really be double checked as you really want to be working to a much lower percentage variation.

Hth JP

[Thuppu]

Hmm, I'm not sure what the difference is between internal and external balancing, but the crank was balanced to zero with the bobweights, then the damper and flywheel added and balanced ot zero.

[JP]

That is internal ballancing you have described. Although I'm surprised how little material had to be removed on the crank to achieve a zero internal ballance unless they didn't do the correct percentage ballance factor? The weight removal from the front pulley confirms internal ballancing

If you are not going to be revving it past 7200 and sitting there continuous round a racetrack I wouldn't worry about it too much. People put their stock engines more out of balance by just changing over the flywheel.

[Thuppu]

I'm not yet sure where we gona set the limiter. If the engine pulls nicely all up and it seems that the tappets follow nicely it could be at 7800-8000rpm's, or so I planned... The use is most street and fun driving with a couple of trackdays per year and maybe few drag strips.

I was suprised though that the flywheel and pressure plate havn't need any balancing, or there was no material removed from them..?

[DJones]

These things play with you mind....

If from what has been said, it should cause no problem, you either have to forget it and put it behind you. If your the sort that cant do that, then get it back to the balancing shop...

[prj]

I'm not yet sure where we gona set the limiter. If the engine pulls nicely all up and it seems that the tappets follow nicely it could be at 7800-8000rpm's, or so I planned... The use is most street and fun driving with a couple of trackdays per year and maybe few drag strips.

I was suprised though that the flywheel and pressure plate havn't need any balancing, or there was no material removed from them..?

You won't really need that many revs with that turbo/hotside. 7600 will be plenty.
You should have a good powerband between 4500 and 7500.
Without some exotic high end cams your engine won't really flow all that well up top anyway.

[Thuppu]

ask your machine shop. (did you also removed the sharp edges of your je pistons?)

No, I didn't do that, but that's not gona do much, 1g or so..? Do you mean the edges on the valve pockets?

Maybe the pins can be lightened few grams without making them bad.

Stock pin
 __________
|          |
|__________|

vs

lightened pin
 __________
\          /
/__________\

lol

[Thuppu]

...unless they didn't do the correct percentage ballance factor?

What is the correct balance factor?

You won't really need that many revs with that turbo/hotside. 7600 will be plenty.
You should have a good powerband between 4500 and 7500.
Without some exotic high end cams your engine won't really flow all that well up top anyway.

Ok. I was thinking of setting a gear change light to something like 7500-7600 and if you miss that you don't hit the limiter stright away. But this was just a tought.

[prj]

What is the correct balance factor?

Ok. I was thinking of setting a gear change light to something like 7500-7600 and if you miss that you don't hit the limiter stright away. But this was just a tought.

You will probably shift at 7300, not at 7600...
With 7A cams that is... with stock ones earlier.

[Billman]

No, I didn't do that, but that's not gona do much, 1g or so..? Do you mean the edges on the valve pockets?

Maybe the pins can be lightened few grams without making them bad.

Stock pin
 __________
|          |
|__________|

vs

lightened pin
 __________
\          /
/__________\

lol

Yes the piston sharp edges remark was separate to the balancing....it just occurred to me.

[JP]

Was the flywheel an aftermarket item? If so these come zero balanced from manufacture which would explain why it wont have any drill holes. Pressure plates are usually out of balance a little bit and I rarely see more than 5 grams being removed unless it's from a vr6 which are often out by as much as 20 grams.

Balance factor of an I5 engine is 50% if the company knows what they are doing they'll know what that means. The best thing to do is ask them what balance factor they used without giving them your information otherwise they'll just say yes to whatever you say for ease.

[Thuppu]

The flywheel is a Alu Fidanza and SRE pressure plate.

What I know they have used 50%, at least so it reads on the balancing document. Here is a better pic of it:

[JP]

Looks spot on to me. And fidenza flywheel very unlikely it will need weight removal.
From the figures looks like they done it right.

So if we do some maths

27grams difference on small end. 50% gives 13.5grams. Original bob weights are 737.5 giving a percentage error of 1.8% so in the grand scheme of things not that bad.