Merco .61 tank size????

Can anyone with some experience with Merco .61 powered stunters tell me what size tank is needed for the 7 minute run?

Thanks in advance.

Charlie

Which Merco 61 Charlie? The black case one from the 90s was a bit of a disaster even though Tom Dixon showed us that they could work! About the same fuel used as the ST 60 was my experience which was about 5 1/2 to 6 oz but less power and rather inconsistant with engine runs. Could have been the result of the poor fit of the cylinder jacket on the liner resulting in hot spots on the cylinder. I still have a NIB earlier natural finish case one but never enough time to build a model to use it in!

The older 60s 49 and 61 production ones were a far better engine and lighter.

HH

Dallas, all that I know is that is has a natural finish case - one of the heavier ones and a single rear facing angled plug. It was made when Merco engines were being produced by Premier engines and plastics limited. This one probably came via the States as it had a type written note saying to send to Hobby Lobby for service or repairs.
I got it NIB but old and stripped it down to find out why it was so hard to turn over. The answer to that was that the front bearing was fitted
with steel shields both back and front and pre-lubricated with a bitumen like grease. Removal of the rear shield and the offending lubricant cured that. One of the rings was also a strange oval shape that let daylight past when you squinted up the bore. A new ring fixed that one and now it feels really healthy. I have only bench run it though.
Charlie

Looks like this Charlie? This was the R/C version with twin plugs and single ring. Well I think that was the ring gonfiguration! Maybe I swapped the pistons 15 years ago to try and get some more compression out of the other thing. Doesn't like it's been apart though. The C/L version had only the rear plug and 2 rings. This configuration continued to the black case ones. Pitty they didn't leave the 1/4" shaft rather than go to the heavy 5/16" one. The R/Cers must have been planting too many of them and bending the shafts!

Just checked on the venturi size and it is 0.300" dia and used with an Enya spraybar. Incidently, that is the same size as the old 60s original 49 Merco venturi. Maybe that's why I made this one the same and fed it on 10% nitro. The 49 in the 60s used standard 4:1 fuel. Couldn't afford the nitro.

HH

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Yes that is what it looks like, except that it is the C/L version with 2 rings and 1 plug. So your guess would be about 5 1/2 to 6 oz then?

Thanks for the help.

Charlie

That's it Charlie. Let's know how it goes. What are you running it in?

HH

I have drawn up a standard sort of stunter for it. Not one of the classic designs, but due to a few health issues I am not spending too much time in the workshop at present. When I do get there I am not only slow, but also have a couple of vintage engines to finish preparing for flying duties (hopefully). They are both Westbury designs, a Kestrel from 1937 and an Ensign from 1949.
Charlie

G'Day Charlie: Tom Dixon always claimed that the Merco 61 used less fuel than the ST-60. I would still go with at least a 6 ounce tank just to be on the safe side. I too have a couple of Merco 61's but have never used them in a plane - one of these days.

Thanks Peter, I will be guided by Dallas and your suggestions and make room for a 6 ounce tank.

Charlie

I'm using a 6 oz on mine which I'll have at the Nats in a few days, but I would put in 6 1/2 if you can. I may have to adjust the venturi to limit the power and extend the engine run so I can do the full pattern.
Happy Landings

Thanks for the tip John.

Charlie