Engine Balancing Question?

[avrojockey]

My crank was dynamically balanced, and rods balanced by Aircraft Specialties

I'm in the process of pairing assemblies to balance opposing reciprocating weights.

Dumb question...

Is there anything wrong with mixing and matching assemblies? I know rods and caps can't be swapped because they're honed as pairs, but is there anything else? Everything is numbered 1-4, but not sure this is anything but to ID them. Can you put the #2 rod with #1 piston with #3 piston pin?

FYI...this is a overhaul...some parts inspected/repaired and some replaced new.

Attached are my current weights...

 

[Cayugarandy]

Balance

If your rods were balanced,why a 4 gram difference?And rods are balanced end for end. Rotating and reciprocating weights are figured separately. How are your rod weights,just small end weight,or total weight?

 

[avrojockey]

If your rods were balanced,why a 4 gram difference?And rods are balanced end for end. Rotating and reciprocating weights are figured separately. How are your rod weights,just small end weight,or total weight?

Not sure what the tolerance is at Aircraft Specialties for balance on a Lycoming...I don't have the data from them regarding how they match and balance rods. I understand balancing rotating vs reciprocating, but this is not screaming at 8000 rip-ems so I'm not sure the difference is tangible.

All I know is the total weight as measured by myself. The spreadsheet is total rod weight (sans bearings, bolts, and nuts).

What I can do, given the tools and capability, is match weights as best possible without stacking weight towards unbalance. What I don't intend to do is start grinding on rods to loose 4 grams...I certainly could trim some off a balance pad, but I have no idea what proper treatments and inspections are used after material removal.

Do you have any recommendations? Would you do something different?

 

[lr172]

No issue mixing and matching pistons, pins and rings to get closer total recip weights. I would not move the rods though. Can't give you a reason why, but there could be one. Some engines have radii cut into the rod's big end to match radii at the journals and this is why rod orientation is important. The rod big end faces also wear against one another to form a match on a common journal.

At 2700 RPM. there is no real need for perfection in matching recip weight. I think that the lyc tolerence is around 14 grams for the entire piston assembly, unsure if that includes the rod though.

DO NOT grind on the rods!! They are NOT balanced for total weight alone. You have to do leverage balancing for the big end and indiscriminately removing material will mess that up.
There is a reason that ASI did not get the total weights to match.

A caution. Some suppliers ship a stock ring and expect you to size it (know superior does this); Others may size the ring for the specific cyl; Am not sure as only used new ring kits or superior cyl's. If you start moving the rings around, be sure that you check the end gap, both at the bottom AND the choke area. This should ALWAYS be done, but know of many that do not.

 

[avrojockey]

Thanks Larry...

I looked at the paperwork again I it's possible ASI didn't balance them...at least I didn't get charged for it. Two of my rods got rejected because previous overhaulers ground in the wrong place. They had a hard time finding matching rod for the good two, so they ended up taking mine on credit and supplying a whole serviceable set.

I'll have to do some more research on rod locations before I start swapping positions. Overhaul manual says "...and assemble rods on their respective
crankpins." - Superior Vantange Manual says "Begin with the lowest serial number rod cap and install it to the crankshaft with its matching rod (5) at the #1 (most forward) rod location." - I'll ask Lycoming build folks at Osh to clarify.

Ring gaps will be rechecked. It doesn't look like they needed the gap adjusted when jugs were overhauled...they're Lycoming ring sets. The cylinders and pistons are ECI, oddly the pins are Superior so they may have been swapped out at some point for thick-walled pin with pressed plugs.

 

[avrojockey]

Followup...

I asked the Lycoming folks about moving rods around. There is NO reason they must be installed in their numbered position. In fact, when they're worked up at Lycoming the original numbers are ground off. The numbers are only there to pair up the caps and provide a outside reference for rod orientation...bearing tangs need to be toward sump and so they engrave the numbers on that side of the rod and cap.

Couple other tidbits I learned...POB #4 is no longer produced so Permatex #3 Aviation is the official alternative with 00 thread, but they haven't revised the SI yet. Also, they're changing the recommended crankshaft seal adhesive to Permatex Ultra Black in stead of DC737 or Pliobond

 

[lr172]

Followup...

I asked the Lycoming folks about moving rods around. There is NO reason they must be installed in their numbered position. In fact, when they're worked up at Lycoming the original numbers are ground off. The numbers are only there to pair up the caps and provide a outside reference for rod orientation...bearing tangs need to be toward sump and so they engrave the numbers on that side of the rod and cap.

Couple other tidbits I learned...POB #4 is no longer produced so Permatex #3 Aviation is the official alternative with 00 thread, but they haven't revised the SI yet. Also, they're changing the recommended crankshaft seal adhesive to Permatex Ultra Black in stead of DC737 or Pliobond

I did both my engines with anaerobic sealant (no thread) on the case and both are leak free. Just be sure to come back and re torque the case fasters at 5 and 50 hours if using the specified star washers