The short story is I had to replace a cylinder and send one out for repair.

The repairs necessitated a re-boring and a P10 piston and I'm now looking to install the repaired jug. Some curiosity has been expressed on where to best position the repaired jug given it's slightly heavier weight when compared to the other three original jugs.

Any engine guru's within the community who might have experience with this kind of a "balancing act" ?

Not an engine giuru but built a shitloaf of air cooled VW in another life, most engine shops can balance pistons. Bring you old one and have them match the new?

Rocket

rocket wrote:Not an engine giuru but built a shitloaf of air cooled VW in another life, most engine shops can balance pistons. Bring you old one and have them match the new?

Rocket

Sounds like a good idea however to do that I would have to remove an installed cylinder, retrieve a piston and all the work associated to do so. If I must I will but I'm trying to limited down time during the float season.

But a new or overhauled cylinder that isn’t oversized. Sell the P10 one.

Jug weight doesn't matter much for how smooth the engine runs since it just sits there (hopefully). The weight of the reciprocating parts matters a lot. The only way to ensure the engine operates smoothly is to remove all of the pistons & connecting rods and balance them, but that's a whole lot of extra work. If you want to keep the job simple, you'll just have to accept an engine with whatever vibration the new reciprocating weights cause. There is no magic cure.

Flyhound wrote:Jug weight doesn't matter much for how smooth the engine runs since it just sits there (hopefully). The weight of the reciprocating parts matters a lot. The only way to ensure the engine operates smoothly is to remove all of the pistons & connecting rods and balance them, but that's a whole lot of extra work. If you want to keep the job simple, you'll just have to accept an engine with whatever vibration the new reciprocating weights cause. There is no magic cure.

I should have been clearer on the original question. It is the moving parts I'm referring to, specifically the piston and not the jug per say. I've been told that Lycoming does publish a weight difference limit, just working on finding the technical reference for it.

Last cylinder I replaced, the engine guy had me send him the old one so he could weight match the piston.

StillLearning wrote:Last cylinder I replaced, the engine guy had me send him the old one so he could weight match the piston.

Was he removing material from it somewhere? Maybe grinding it out of the recess on the underside?

I'm just a dude on the internet but... You're planning on removing all 4 jugs so that you can mix and match them for balance while simultaneously not wanting to buy the correct piston and cylinder?

How much money do you save by using an overhauled cylinder and +.010 piston? To me it wouldn't be worth it. I would consider oversized pistons if i was topping the whole engine.

Realistically... Once you slap this thing back together you can use a dynavibe and figure out how bad its shaking. At this point I vote you do it for science and keep us posted!

Zzz wrote: Was he removing material from it somewhere? Maybe grinding it out of the recess on the underside?

Potentially. Also might have just cleaned and weighed the old piston and picked a new one which was close in weight. Maybe both!

Mapleft, don't you have the old piston you are taking out?, Clean it up and compare the weight to the new one. If it is within a few grams don't worry about it. If it is off quite a bit then yo can remove mass from the underside of the piston but I think you will need to consult someone who knows at to exactly where you can remove material without creating a problem.

I just tore down several SBC V8s, factory remans and they had completely different pistons in them! One had three different style pistons in it as a factory crate engine.

Not saying that is a great thing to do just saying that there has been a lot of pretty crude things done to engines and most of the time nobody ever knows about it.

shorton wrote:Mapleft, don't you have the old piston you are taking out?, Clean it up and compare the weight to the new one. If it is within a few grams don't worry about it. If it is off quite a bit then yo can remove mass from the underside of the piston but I think you will need to consult someone who knows at to exactly where you can remove material without creating a problem.

I just tore down several SBC V8s, factory remans and they had completely different pistons in them! One had three different style pistons in it as a factory crate engine.

Not saying that is a great thing to do just saying that there has been a lot of pretty crude things done to engines and most of the time nobody ever knows about it.

You make a good point, I haven't actually compared the old piston to the new one so maybe they are close in weight, thanks for the idea.

shorton wrote:...
I just tore down several SBC V8s, factory remans and they had completely different pistons in them! One had three different style pistons in it as a factory crate engine.

Not saying that is a great thing to do just saying that there has been a lot of pretty crude things done to engines and most of the time nobody ever knows about it.

And that's in a motor that spins more than twice as fast as an aircraft engine.
Balance matters, of course. Building a high compression fire breather for Reno that you're going to spin to 3500RPM, definitely tear down and balance to the nth degree.
Normal airplane motor? I'd guess most mechanics for the entire history of Lycoming/Continental/Franklin would swap the jug and move on. I'd probably compare to old piston weight and shave as needed to match.
There's probably orders of magnitude more imbalance force from fuel mixture distribution from our tractor carburetors than a gram or two on one piston.

StillLearning wrote:Last cylinder I replaced, the engine guy had me send him the old one so he could weight match the piston.

This. Match the weight of the old piston.

StillLearning wrote:Last cylinder I replaced, the engine guy had me send him the old one so he could weight match the piston.

If matching the weight means removing material how is this safely accomplished ?

Does Lyc/Conti leave "extra" material in the cavity of a piston so that an overhaul shop can do this safely via an approved method ?

skyward II wrote:

StillLearning wrote:Last cylinder I replaced, the engine guy had me send him the old one so he could weight match the piston.

This. Match the weight of the old piston.

Of course, this is assuming that the old piston set weight matches.
I'm curious if anyone has actually weighed std pistons vs oversize,
it may be that the mfr produces them all to the same weight spec.

Some of the best lessons in life come from screwing up,

I did a poor man’s top overhaul on my wagon when I was putting it together years ago. I literally built it with other buddy’s hand me downs, and the engine was no different. I paid no attention to piston weight when I replaced a couple.

It shook like a dog shitting a peach pit.

Weigh the old one, and match that weight as close as you can.

I ended up pulling that engine and installing one I got with another project. I’m pretty obnoxious about balancing now.

Curiosity finally got the better of me so I put the new and old assemblies on a scale.

Old piston with rings tips the scale at 3.000 lbs or 1360 grams
New piston with rings tips the scale at 3.002 lbs or 1367 grams

I might be overthinking this all a bit to much.

Mapleflt wrote:Curiosity finally got the better of me so I put the new and old assemblies on a scale.

Old piston with rings tips the scale at 3.000 lbs or 1360 grams
New piston with rings tips the scale at 3.002 lbs or 1367 grams

I might be overthinking this all a bit to much.

I’d whittle off 7 grams

AEROPOD wrote:

Mapleflt wrote:Curiosity finally got the better of me so I put the new and old assemblies on a scale.

Old piston with rings tips the scale at 3.000 lbs or 1360 grams
New piston with rings tips the scale at 3.002 lbs or 1367 grams

I might be overthinking this all a bit to much.

I’d whittle off 7 grams

Any available guidance on where to apply my whittling knife

Mapleflt wrote:

AEROPOD wrote:

Mapleflt wrote:Curiosity finally got the better of me so I put the new and old assemblies on a scale.

Old piston with rings tips the scale at 3.000 lbs or 1360 grams
New piston with rings tips the scale at 3.002 lbs or 1367 grams

I might be overthinking this all a bit to much.

I’d whittle off 7 grams

Any available guidance on where to apply my whittling knife

Looks like the wrist pin is available in different weights.

https://www.lycoming.com/content/replac ... or-pistons

That seems like the easy button.