[Tom McCutcheon]

I just realized that I should have put my question here. I also put it in general discussion.

I'm about to put 4 new cylinders on my Lycoming O-320. Is there any advantage to match balancing the pistons? If so, where is the best place to take material off the pistons so as to match balance them to the lightest piston? Thank you all in advance for any help you can provide.

Tom McCutcheon

 

[Allen Barrett]

Sometimes it is, other times it's not. The pistons and rods are a match balanced set (at least at our shop they are) If you still have the old pistons and depedning on who built your engine last, then balance the new pistons to the old weights. it ran before, it should continue to.

.02 only,

Allen Barrett
BPE, Inc.

 

[eric_marsh]

If my memory serves a horizontally opposed four cyl doesn't need to be dynamically balanced so it's just a matter of making sure that thr piston assemblies weigh the same and the rods are balanced end for end. For a decade I worked as an automotive machinest and engine builder and my experience in that field is that matched sets tend to be well balanced. Why don't you buy an electronic postage scale if you can find one with the correct capacity and chech them yourself?

 

[Geico266]

If my memory serves a horizontally opposed four cyl doesn't need to be dynamically balanced so it's just a matter of making sure that thr piston assemblies weigh the same and the rods are balanced end for end.

I have to respectfully disagree. Every aircraft engine / aircraft airframe benifits from being dynamically balanced. If nothing else to confirm it is the lowest possible IPS (inches per second) attainable. I've only seen one engine that did not need to be balanced. I call that one just plain lucky.

 

[rocketbob]

Usually when you buy a set of pistons, if they come in one box from the manufacturer they'll be in a matched set within 2 grams.

 

[eric_marsh]

I guess I misremembered the info about dynamic balancing. I worked in a shop that specialized in VWs back in the early 1970s and yes we did dynamically balance the cranks and flywheels. Here's what I found on the subject of balance and boxer engines.

Boxers are one of only three cylinder layouts that have a natural dynamic balance; the others being the straight-6 and the V12. These engines can run very smoothly and free of unbalanced forces with a four-stroke cycle and do not require a balance shaft or counterweights on the crankshaft to balance the weight of the reciprocating parts, which are required in other engine configurations. Note that this is generally true of boxer engines regardless of the number of cylinders (assumed to be even), but not true for all V or inline engines. However, in the case of boxer engines with fewer than six cylinders, unbalanced moments (a reciprocating torque also known as a "rocking couple") are unavoidable when the output is a crankshaft due to the "opposite" cylinders being not exactly opposite but offset slightly.