New Piston Heavier Than Original Piston

[MaximumMini]

I found that removing 5 grams of material from an aluminum / tin coated piston would require substantial butchering.
Probably better of all the options to have the hardened steel wrist pin bored out a few thousandths.

 

[Cujet]

If you can match the weights, do it.

You may not feel much difference if you don't take any action at all, especially at normal cruise RPM's. However all of us have experienced an engine that was just "right". Ran right, was responsive, smooth and fun. Those engines are properly balanced engines, both mechanically and with regard to airflow balance. That's the secret.

 

[MaximumMini]

If you can match the weights, do it.

You may not feel much difference if you don't take any action at all, especially at normal cruise RPM's. However all of us have experienced an engine that was just "right". Ran right, was responsive, smooth and fun. Those engines are properly balanced engines, both mechanically and with regard to airflow balance. That's the secret.

I agree.
Only problem is removing 5-6 grams of aluminum from a piston will result in quite a bit of removed material.

 

[meep]

Does the counter balancing on the crank play a role in the balanced assembly??

 

[MaximumMini]

Anyone ever had a wrist pin bored out to decrease weight?
The Factory Service Manual calls for 433g min to 443g max (just the piston alone)
My piston started at 446g and I got it down to 443g.

The Original Piston weighed 434g with a wrist pin weight of 134g
The new piston is still 9grams heavier than the OEM piston.
This is not acceptable EngineTech !

The new wrist pin is 6g over the old one so I must use the old wrist pin as well.

I have not weighed the other 5 pistons but being factory I would take a WAG they are very close to 434g as well.

I would really like to get the net weight of the piston and wrist pin down 3 more grams but I'm leery of compromising the piston structural integrity.

 

[MaximumMini]

Does the counter balancing on the crank play a role in the balanced assembly??

Absolutely. But I'm not touching the crankshaft.

 

[meep]

Absolutely. But I'm not touching the crankshaft.

Hmm

https://www.v8buick.com/index.php?threads/5-gram-variance-in-wiseco-pistons-balance-problems.251752/

https://www.offshoreonly.com/forums/general-q/241310-balancing-pistons-how-much-too-much.html

 

[MaximumMini]

Hmm

https://www.v8buick.com/index.php?threads/5-gram-variance-in-wiseco-pistons-balance-problems.251752/

https://www.offshoreonly.com/forums/general-q/241310-balancing-pistons-how-much-too-much.html

Ok, I read that entire thread. there's no way I'm going to modify the crankshaft, still installed in the engine. I would modify the piston and wrist pin long before I even considered that.

As far as the out of balance. I may work to get 2 more grams off the piston then go with it.
The EngineTech casting is what I would call "sloppy" compared to the really precise OEM casting. A lot of that extra weight seems to come from just the sloppiness of the casting.

 

[meep]

Right. I wouldn’t touch the crank… you’d have to ADD weight to it… maybe shave the piston some. Seems that yours is very close to usable depending on some odd mix of “experience” vs “personal standards”

 

[MaximumMini]

Right. I wouldn’t touch the crank… you’d have to ADD weight to it… maybe shave the piston some. Seems that yours is very close to usable depending on some odd mix of “experience” vs “personal standards”

Right.
Did you see the line in that link you posted about the radial force of an unbalanced piston? Wow!
5grams or so equating to hundreds of pounds of radial force at rpm's.

 

[meep]

I did. And it’s hard to “feel” those numbers, right? I mean, how many times does it change directions per second at 3600 rpm? And balanced vs unbalanced (who cares in this example?) what is the force at the pin just as it slows, stops, moves - at the top and bottom of the stroke. If I understand correctly, thrown rods happen more often from rod stretch, unloaded, zero throttle moment at high rpm, than under loaded compression. Balance doesn’t matter there, it’s about tensile force.

 

[MaximumMini]

I did. And it’s hard to “feel” those numbers, right? I mean, how many times does it change directions per second at 3600 rpm? And balanced vs unbalanced (who cares in this example?) what is the force at the pin just as it slows, stops, moves - at the top and bottom of the stroke. If I understand correctly, thrown rods happen more often from rod stretch, unloaded, zero throttle moment at high rpm, than under loaded compression. Balance doesn’t matter there, it’s about tensile force.

I guess I'm more concerned about the vibrations felt in the drivers seat of by the engine crankshaft and it's bearings.
It's very difficult to imagine the stresses.

 

[MaximumMini]

For anyone facing this situation........

I ended up buying a set of rasps for my dremel tool and was able to shed 6 total grams off the piston.
Hopefully I did not compromise the integrity of the piston. Only time will tell.
I doubt that I did and just used common sense in where I removed metal and 6 grams is less than a Quarter so it's not a whole lot in any circumstance.

Here is the set of Rasps I used.....
Amazon

 

[Nessism1]

Nice work on the piston.

Are you going to run the original pin? As long as it's the same length, you should be okay.

 

[Hohn]

I think it's pretty obvious where material was removed on the factory pistons, I'd remove material from the same area. I'd check the wrist pin for material removed from the centre.

It seems to me that “hole” is the location of material removal for factory balance.

 

[Hohn]

That is for ONE cylinder
No. I'm only considering the weight of the old piston vs the weight of the new piston. I "trust" that the factory got the original rods the same weight or well within tolerances.

The set of 6 pistons I bought from RA is EngineTech, P5043(6)STD brand.
I did notify RockAuto of the piston weight being out of factory specs.

What are the factory specs?

 

[Nessism1]

What are the factory specs?

I've never seen a service manual that listed piston weight specs.

 

[Hohn]

I've never seen a service manual that listed piston weight specs.

Precisely my point. Someone is asserting the pistons do not comply with a spec that doesn’t exist.

 

[OVERKILL]

It seems to me that “hole” is the location of material removal for factory balance.

I'm looking at the area above the wrist pin boss, it's milled flat on the OE piston and raw casting that protrudes upward on the aftermarket one.

 

[OVERKILL]

I've never seen a service manual that listed piston weight specs.

I assume it would be mentioned in the service manual for the 302HO, since the engines were factory balanced. Material was removed from both the rod caps an the pistons, and each one numbered. Was one of the neatest early wrenching discoveries for me, as prior engines I'd torn down had not received this treatment.