ST/46 Upgrade

[EddyR]

There seems to be a lot of interest in motors lately and quite a few on the vintage ST/46. I still run The old ST/46 in a few planes but I had thought for many years about putting a ST/51 in a Juno. Last year I rebuilt this 25 year old Juno to see how I felt about it after 25 years. It flew great but when we had out spring Huntersville contest the weather was beyond normal flying conditions. I kept thinking what it would be like to have higher revving more power full motor in the plane as I flew in the high winds. I just did a rebuilt on a few of my older motors and now have two fresh ST/51 motors. The .51 is a shoe in to the .46 mounts. All I had to do is elongate the rear mounting holes on the motor and it went right in with a little clearance around the cowl needed. The motor extends 3/16 out past the old nose ring and I was not going to extent it but then changed my mind. Two of the pictures are before the extension. It was very easy and took less than two hours all together. I have not flown it yet. The CG moved forward 1/2" with this heavy muffler. When I have some run time on the motor I will switch over to a stub muffler.
EddyR

[Bill Hummel]

Hi, Ed, good job on the retrofit.  Hope this works well for you. FWIW; we've been waiting for ST 51 parts from Tower for well over a year. I'm not sure they are going to continue to support this engine in the future. E-mails to them come back very vague and noncommittal.  Sure hope that is not the situation for the ST 51!

[Bob Reeves]

I did the same thing several years ago in my Skylark. I didn't like the idea of redoing the nose and discovered that the 51 would fit almost perfectly if I used the rear holes and drilled new holes in the engine for the front screws. May have been the other way around, been 4 or 5 years.. Think all I had to do with the nose was go to a Dubro plastic spinner, the airplane was built for a flat back spinner and the Dubro has about 1/8 inch inset which worked out well.

The big problem is getting enough fuel tank in the compartment. This was an early RSM and the fuselage isn't a full 2 inches inside. A standard tank won't fit and the custom one in it isn't big enough to take full advantage of the 51's power even with the wart I added.

[Dan McEntee]

   Hi Ed;
    I think you'll like the set up. Use a APC 12.25 by 3.34 prop, fuel that is 10% nitro and 20% or more total oil that is half castor and half synthetic, hot plug. and that muffler with muffler pressure to the uniflow tank. Take off RPM will be around 9500 to 1200 RPM. That prop was the first one I ever used that I could effectively tell that it was working like it should to help with whip up in the wind. If you can find a Scott Dinger muffler, they are almost as light as a tung muffler, or one of Randy Smith's tube mufflers.
   Good luck and have fun,
    Dan McEntee

[Andrew Saunders]

Ive found parts on ebay. Might wanna look there also

[EddyR]

I ran these two .51's about 8 years ago. One ran for several hundred flights and then the ring went bad. The second one never was very good right from the beginning. When I took them down I found that both had bad rings. One had a broken ring. Both were very soft. I was using very thin 12/4 props on them. This plane is smaller but it has a lot of tank room and it now has the tall gear in it. It weights 53.5 ounces. When I flew this plane at the 1988 Nats it weighted 49 ounces. I put 1500 flights on it and it weighted 58 ounces when I quite flying it 20 years ago. I cut off all the oil soaked parts, put it in a box and forgot all about it. I have about 50 flights on it with the .46 since I rebuilt it. At 58 ounces it flew just as good as it did at 49 ounces. Billy's Juno's weighted 52-54 ounces.
Bob the spinner idea is a good one to bad I did not think of that. I may go to plastic to reduce weight and I have some light stub mufflers that are light. I will fly it next week for sure.
 Here is a picture of the same plane taken at the 1988 KOI
Ed

[M Spencer]

youre running the G-51 ? schnerle .

++++++++++++++++



heres a mean and nasty one !




The Lesser Spotted Super Tigre G- 21 / 51 !  part No for liner is as per ' V ' 51 in the 51 , 56 , 60 series . But rod piston & gudgeon might be awkward . dunnon if flat top or baffled .
My catalouge / parts list , is for the earlier upturned intake one .

[Paul Allen]

Ed
    Good idea on retro fit of St 51,if sloting the hole does not appeal
they can be redrilled.
Paul
In OZ

[goozgog]

Please. Does anyone know what the old ST/46 weighs?

[pipemakermike]

I have been gathering the weight information fo a while now  and the attached spreadsheet is my repository!

[goozgog]

Thank you VERY much Mike!

[EddyR]

I weighted 6 ST/40&46 motors. They weighted from a low of 8.2 to a high of 9.2  Only one had muffler lugs. Most had the head fins shaved down to 3/32 depth.
Ed