One of the joys of owning a somewhat peculiar engine is that sometimes conflicting information arises. I’ve read the Franklin overhaul manual which states one thing, read my POH which gives a little different criteria, I’ve been told that the POH supplement when installed in a 172 gives yet a different figure and I’m not quite sure what to think. I’ve been schooled a bunch on the premise behind a mag check being more aimed at checking L vs R mag for signs of trouble but also know that at some threshold, excessive rpm drop is indicative of other issues. I’ve read/heard numerous times that Franklin 220’s are known to have big mag drops due in part to them being a high compression engine among other design factors. I’m interested to hear what those of you with firsthand experience accept as normal. What’s your mag drop and at what RPM on a 220 Franklin?

Thanks in advance folks,
Zack

2200 rpm you should get a 250-300rpm drop

Thanks Farmaule!

Anybody else?

In the 172, Franklin book says drop should be 125-250 at 1200 rpm, I forget off the top of my head what it is at the high 2200 rpm check. In ours the drop is less at 2200 than at 1200. Biggest thing that was told me was to really look at difference between the two mags so you can catch any small issues before they become big $$ issues.

Thanks a bunch for the input guys, I was able to get a 250-ish drop after a thorough warm up today and was subsequently able to complete a successful test flight for the first time ever!!! Things are lookin’ up

Zack

I get 250-300 at 2000 RPM.

Thanks Jim, I love the way your bird turned out!

Straydog wrote:Thanks Jim, I love the way your bird turned out!

Thanks! I meant to add that I've read several places that the max allowable drop for the Franklin is 500 rpm for the 215/220 engines.

3rd the 250-300 typical