Allot of engines will still run with a pressure tap hole open to the outside but, it should be plugged. JB weld should work well if completely degreased.


MM

OK thanks for the reply's

Same sort of subject

I have a few new ringmasters and a soon to be built SkyRay as well as another Larger Ringmaster from Pat Johnston...the 526 RM will get one of my new in box Evo .36

I have been somewhat impressed buy the Bret Buck recommendation of the OS 20 and associated BBTU commentary and my personal experience is this system works a tad bit better than the Old skool Fox 35

That all said, I am a casual flyer...no contest aspirations. I just want to find myself at the field with a power system that does not demand a lot of fussing around

The Fox 35 (no burp plug) on one (Mike Griffin ARF RM) is prefect for my pseudo stunt flying
I built a RST with RM tail and it is powered by a blue La 25 and near perfect for me also

I have bought two FP20s but they are the large hump so called "iron liner" versions and run fine on the bench
I recently won a FP 20 no hump, assumed ABN version and it too starts and runs fine on the bench

I am using the OS Venturi and NVA assy as well as the 2030 muffler fed with home brew 15% N...22%oil half half and each starts and needles with a fairly broad NVA range from 8000+/-Rpm up to 10,700~12,200 rpm using a  typical 9x4 prop

OK now the question....

I thought the ABN version was the preferable one until I read recently that the Iron liner one was stronger....in this thread
http://stunthanger.com/smf/open-forum/ringmaster-with-a-os-25/?topicseen

where Phil Spillman claimed the Iron version was preferred.......so I am confused

Am I concentrating on finding the wrong OS FP engines

"It fires easy, needles just fine and runs a steady 8800 RPM rich up to 12,400 lean with a MS 9x4 S2 Series thin blade prop......NOTE: MY last APC 9x4 is not balanced yet

Why the hell will this 2 stroke engine even start and run with a vent to atmosphere in the Crank case...

Fred, with all due respect but out of curiosity .... why are you gonna' mess with it .... especially since you said it runs so nice??  To me, it seems like you might be preparing to kill the Golden Goose!

Jim sorry I did not see your question until today

I am still curious why it runs so well with the hole in the CC

a few times in the past an erratic engine run was tracked down to a air leak at the Back plate and once a crack in the crank case from one too many vertical arrivals

While running it does NOT spew fuel OUT of the CC hole.  I wonder if there may be something similar to sub piston clean air induction happening due to the timing of the crank shaft counter balance passing this very small and oddly placed hole

I think I will cover it temporarily with a small piece of gorilla tape and see if there is any run difference that I can detect

If no difference I will JB close the hole just to keep dust n grass seeds out of the Crank case

If there is a noticeable difference with the hole temporarily plugged I will be even MORE curious

Thanks Phil

I have a hard time understanding why the Tapped (I looked with a 9x Loup) is directly under and centered below the exhaust side mounting lug. For profile mounting I can not think of an easy way to use it as a pressure tap....the other curious about this TAPPED hole is how thin the CC is right there and how close the crank shaft is to the inner wall... any screw or tap would only have 1.5 threads engaged and not be a very strong fit

Bottom line is thanks to all who responded I think I will just close the hole and go flying....

I do plan on using the 2030 muffler ---with or without Muffler pressure depending on run with my clunk tank options

Tim...because the weather is 100+ every day now for last 2 weeks--- I may just bolt it up, get a run or two noting ease of start, Needle range, rpm with typical 9x4 prop

Then Cover the hole and repeat--- noting any differences with same fuel and prop on the bench

I am sort of thinking there may be some little sub piston type fresh air charge being introduced so maybe there will be a noticeable difference...at this point just a curiosity

The original owner claims it was NIB when he put it into service and never knew there was a hole and it (in a RC application) started and ran fine when he used it

The engine came to me in the OS box and was clean on the outside and piston looks nice and un-scored with light brown piston top (seen in the plug hole)

While I was removing the carb and installing the venturi/NVA is when I noticed the hole

I refuse to believe OS shipped it with this hole...if posting a photo was not such a pain on this site...but i digress

BTW the included 842 muffler was never put into service and I recently sent it to a Flying Lines want ad..you know him

I got it for a good price, it runs well, but I have a hard time believing the hole was not noticed....BUT--- it just may be as simple as he is older like me and thinking of a different engine...he sold about 5 engines at the time I bid on this one

Again...a big tanks to all following this way out of production and curious engine I got for $40

No matter where I go on this and a few other sites I continually learn and have started to really enjoy this hobby  quite a bit more than my frustrating efforts of my youth

I have not yet ever had a engine explode...crank shaft break, or even a shaft run....but when it eventually happens ...I will know what caused it and probably laugh my ass off. Just as I do when I make a PERFECT figure nine early landing with no flair to final...you know the vertical landing and passenger -immediate- disembark operation!....grin

all you guys are making my late fifties early sixties real fun...again thanks to all who respond and offer your wise and sage advice