This came across my FB feed yesterday from a well known engine builder here in Alberta. These were not engines built by him, but engines that hes had come in to the shop after failure.
Anyone else having issues?

How do we prevent this?, or what are the signs rods are going bad?

I did a bit more digging this morning. It seems that the engines were built reusing the counterweight retaining clips and washers, or they weren't listed as new parts on the build sheet at least. The clips came out, then the pins and the counter weight then came off wreaking havoc.
So I guess check your build sheets and confirm new clips and washers were used is the best action plan.

Here is a picture of one counterweight. The ohmther one is shattered. Not the pins and washer with no damage. They were found in the bottom of the pan.

Great info, I already had a flight planned to Pponk next week, will talk to Steve about this.

Thanks for the info.

I have a Pponk being built up by one of the authorized builders currently and was told this morning that everything in the counterweight is a mandatory replacement and all new. Went on to say that in over twenty years of doing these, they have seen two cases of counter weights letting go. Both on Lycoming engines, and both with new plates. The plate actually broke in both cases. One case was with Lycoming plates, and one with Superior.

A Pponk O 470-50 is a different engine than the Pponk O 520's correct?

motoadve wrote:A Pponk O 470-50 is a different engine than the Pponk O 520's correct?

Correct. The 470-50 is an overhaul to 520ci displacement, but uses the 470 as the core. The O-520 takes an IO-520 and converts to carbureted induction, which is the route I'm taking. Pros and cons to either approach, but the latter does not involve any engine internals modification.

I've not read a CMI rebuild manual, but in any other engine I've worked on replacing things like retaining clips is always part of it for this exact reason. Those parts are consumable and not designed for repeated installation as they can weaken and eventually fail. Talk about spending $30-40k to save a couple bucks, wow.

I'd be interested to know if this was a shop authorized by P-Ponk, and if the failures connect back to any particular shop or builder, or if this is somehow common practice in more than one shop.

colopilot wrote:

motoadve wrote:A Pponk O 470-50 is a different engine than the Pponk O 520's correct?

Correct. The 470-50 is an overhaul to 520ci displacement, but uses the 470 as the core. The O-520 takes an IO-520 and converts to carbureted induction, which is the route I'm taking. Pros and cons to either approach, but the latter does not involve any engine internals modification.

I've not read a CMI rebuild manual, but in any other engine I've worked on replacing things like retaining clips is always part of it for this exact reason. Those parts are consumable and not designed for repeated installation as they can weaken and eventually fail. Talk about spending $30-40k to save a couple bucks, wow.

I'd be interested to know if this was a shop authorized by P-Ponk, and if the failures connect back to any particular shop or builder, or if this is somehow common practice in more than one shop.

The engine pictured came from Steve's shop, so pretty sure its authorized.
I checked the logs for a Pponk I work on and the retaining clips are listed as new parts. So whether they missed an entry or didn't get replaced on these other engines is a question Steve may have to answer. I know if it were my motor I wouldnt be pleased.
Funny you mention spending so much and trying to say a few $$. On the Pponk I work on all the rocker cover gaskets were cheap cork gaskets that were leaking in 5 years. Why build a nice expensive engine and not use good gaskets is crazy to me...