PPONK 470-50 Question

Steve Pierce said:

SJ wines every time he talks about what his P-Ponk cost converting from a J engine.
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Not every time, but most times…

I remember discussing the var issue with you way back then!

sj

stewartb said:

Keep in mind the vast majority of Pponk engines work fine using non-VAR 470 cranks. Just adding a dose of reality.

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That may be true. However it doesn't make them legal if the crank came from an engine as defined by the AD. Just because "everyone does it" doesn't make it legal. And as Mike points out, it can lead to a disaster. I think I saw a picture of his wreck in a BAS shoulder strap ad. He was lucky.

This is a grey area to many and both sides are pretty well covered here, however one thing not brought up is the compression. If it has high comp pistons (naturally aspirated 520) and a NON-VAR
crank it's not per the STC. It takes a field approval to have the high comp pistons and the only guy I know of that's doing that requires a VAR crank.

Good point, but lots of guys have snuck 8.5-1 pistons in and there’s essentially no penalty for doing so. And lots of guys exceed the 2700 rpm redline, too.

Good news for the owner, I contacted the engine builder and he is pretty sure it has a VAR crank but is going to check tomorrow

A good few minute read. Especially the last part about cranks.

https://www.aopa.org/news-and-media/all-news/2016/february/pilot/pe_savvy

Oh boy don’t get started with mike Busch

Fact is it doesn’t matter that var has failed more. The faa said there is an AD and I have to comply with it as a mechanic. I don’t want a grey area. I’m covering my behind.


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I was talking to a FAA friend (one of the good guys) and he said any time the AD calls out, or mentions a SB it becomes mandatory. He said you can't use a non VAR crank in an engine if it has been in an engine affected by the AD.

Another interesting point, he said it is technically legal to sign off AD's on a 0-470-50, which there are no AD's for, but he said its fine until something happens and you're in front of a lawyer. He has done a lot of work, and crash investigations on the VAR AD. Learned a lot about it from talking to him.

The more you know

I think Longsair is right. I just did a 470-50 that was converted from a 470U mfg'd about 1980 with non- VAR. It is good for the original low compression Pponk but would not qualify for the higher compression 8.5 pistons. What I think would be neat is to put a 550 crank with 7.5 pistons and get a few more ponies with car gas.