Piston balancing

Talkwrench

Talkwrench

Well-known member
Where's the best area for weight removal for balancing. Any tips would be helpful.
Cheers.
 

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In the old days, I instead wire-wrapped the rod small-ends to add weight to match the heaviest piston if more than a few grams difference. I just couldn't bring myself to mutilating the pistons. 8^) Jack E/NJ
 
It is not easy to remove much weight from aluminum pistons. Sometimes a little can be removed under the heads, sometimes from the pin bosses, sometimes the scallops of the skirts can be enlarged, and usually some material can be machined in the lathe from inside the skirts below the pin bosses. In extreme cases for racing, I have drilled many 1/4" holes in the skirts. I figure the minimum head thickness at .175 for cast pistons and .150 for forgings in unblown, gasoline applications.
 
Talkwrench said:
Where's the best area for weight removal for balancing. Any tips would be helpful.
Cheers.
Click to expand...

When I need to remove material on a piston like the one in your picture I take it from the inside diameter of the piston at the bottom. I use my lath to remove the material. Another option you have is removing the weight from the inside of the wrist pin using the lath.
Ronnieroadster
 
ot sure what you project is but piston weight isn't very important in a street aplication. However the rods are . The rods and crank are a match set and will remain in balance even in an expensive race engine with a change of weight piston set Many race teams have changed pstons and never re balanced the crank. Back in the pre 60's most rebuild engines were ever balanced. At Danbury we never balanced our engines, because thw=ere were no place the get it done. Bells in nJ had a 6 month back log. so I tried t keep my crank assys together,
Gramps
 
That circular land just up inside the skirt is where the material has been removed for balancing. Like stated above, it would have been done on a lathe.

(Probably).
Mart.
 
I remember seeing a video on the tube of them building the Ford V8 engines .
One scene was how they balanced the pistons .
They had a fixture that locked the piston in place above a cutter .
Then as it cut,,,the chips fell into a catch basin and when the chips weighed out right the machine stopped cutting .
It was really amazing to watch,,,,and really fast as well .

Tommy
 
Ol' Ron said:
ot sure what you project is but piston weight isn't very important in a street aplication. However the rods are . The rods and crank are a match set and will remain in balance even in an expensive race engine with a change of weight piston set Many race teams have changed pstons and never re balanced the crank.
Click to expand...

The weight of the piston needs to be included when balancing a crankshaft.

You can't change pistons from XYZ grams to ZYX grams without affecting the balance of the system.

Race teams that are replacing parts between runs have ensured all the components - old and new - are the same weight before reassembling the engine.
 
Itslow, I don't disagree with you, however the weight of the piston is factored in differently than rotary weight, as the pistons weight is reciprocating. I keep all my cranks and rods together as rotating weight is more important .However, when turning 8 grand all dy long might be different.
 
First of all, weigh all the pistons on an accurate gram scale to determine how close/far they are apart. Many forged pistons are delivered with a very accurate weight between them - like Ross.

The cast ones (as you show) tend to have a lot more variance. If you don't have a lathe and the weights are close, you can always use a air grinder with an aluminum rotary file - you can fairly accurately remove material around the inside perimeter of the bottom of the piston.

I've seen some cast pistons where a wide drill bit is used to remove slight amounts of material up inside the crown . . using a series of small drill removal areas (drill bit size like .500). Might see a half-dozen drill areas inside the crown - each maybe only a slight dish (like the size of the drill bit when the outer radius reaches the material).

Obviously you don't want to weaken the crown, but a lot of times the heavy cast pistons have quite a bit of material up top.

Good luck!
 
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