Author Topic: ST51 C/L (Read 3577 times)

Louis Rankin · « **on:** February 15, 2006, 08:01:21 PM »

Trying to set up my ST51 that I have in my "P Bear". Runs great 4-2-4 first half of the pattern (5.4 - 5.5 lap times) then speeds up to 5.0 or faster by the time it reaches the Clover.

Current set up:

Tank: GRW Profile uniflow 4.75 ounce. Pressure or no pressure runs the same.

Plug: Sig R/C long, very hot plug

Muffler: Big Art tongue. I hate the stock muffler.

Venturi: Stock, 7mm diameter. May try a restrictor made of brass tubing to experiment next time out.

Needle: Tried Stock ST first then tired a Double Star. The DS is larger in diameter, but just a tad. Ran a little more consistant with the DS.

Fuel: Lou's Brew 10/22. Half Klotz and half castor.

Prop: Have tried many. APC 12X6, 12X4, 12.25X3.75, 11.5X4, Zinger 12X6, 12X5. As expected they all give different performance; however, no change in effect on leaning out.

Head shim: One stock shim. I do plan on trying one more shim next time out.

Ideas anyone?

Crist Rigotti · « **Reply #1 on:** February 15, 2006, 08:30:40 PM »

Is the engine hot after the flight? Sounds like a clogged vent line or pinched vent line. Tongue muffler might be too restrictive making the engine run hot thus leaning it out as the flight goes on. Have you tried a different muffler? Try another gallon of fuel. Is the needle tight and not turning in? For the second flight, do you have to turn the needle out or is the needle good after the engine cools down?

Andrew Hathaway · « **Reply #2 on:** February 16, 2006, 07:53:03 AM »

12 years back or so we ran a G51 on a large profile slow combat foamy style stunt plane. Setup was a 12-5 Rev Up prop, K&B long idle bar plug, Sig 10% Champion fuel, GRW profile tank, with the box stock engine complete with the earlier style giant muffler. It didn't look good, but it ran excellent. One flip starts, and consistent flights. Enjoyed it so much that I tried to order another engine and they were on backorder. When they finally became available again I ordered three of them.

Jim P · « **Reply #3 on:** February 16, 2006, 08:48:10 AM »

My one and only G51 works well on pretty much the set ups you describe and does not exhibit any lean out through pattern.
I have seen the same thing in a local expert flyers G51/magnum and he fought it for quite a while. He is a clunk tank guy so I don't know what his solution was. I do know he bought a second G51 to stick in the airplane and all was well at that time but it is unreasonable to assume that was the problem. I do know he did quite a bit of tank switching.
Sounds like a possible leak to me.

RandySmith · « **Reply #4 on:** February 16, 2006, 10:13:08 AM »

HI Louis

That is normally a tank or Fuel delivery problem (something in the fuel system) ie tank lines, cracked tube inside, hole in the tube or tubing, leaky filter etc.

some times it is a heat problem.
try another tank and let us know if the run changes.

if you think it is heat add 2 ounces of castor to your fuel

Regards
Randy

Steve Fitton · « **Reply #5 on:** February 17, 2006, 09:38:49 AM »

Quote from: RandySmith on February 16, 2006, 10:13:08 AM

..........if you think it is heat add 2 ounces of castor to your fuel

Regards
Randy

Randy,
If you have a heat problem like that, can you get away with adding your Aero-1 additive to the fuel instead of the castor? Aero-1 cuts friction, (and hence heat), right?

Steve

dirty dan · « **Reply #6 on:** February 17, 2006, 12:41:47 PM »

While I agree that this probably a fuel-feed issue, just to increase my confidence in the engine itself I would want to have checked the end-gap on the ring.

Dan

RandySmith · « **Reply #7 on:** February 17, 2006, 03:21:57 PM »

""Randy,
If you have a heat problem like that, can you get away with adding your Aero-1 additive to the fuel instead of the castor? Aero-1 cuts friction, (and hence heat), right?

Steve """

Hi Steve

Yes that would help, but I believe it is a fuel delivery problem. I will be keen to hear how it runs with another tank.
Maybe he will get a chance to try the engine again soon

Randy

RandySmith · « **Reply #8 on:** February 17, 2006, 03:25:11 PM »

While I agree that this probably a fuel-feed issue, just to increase my confidence in the engine itself I would want to have checked the end-gap on the ring.

Dan

Dan

That is what I would have done before the engine was ever ran,
However after you have time on it , taking it apart will most likley hurt the ring seal.
The ST 51 is pinned on the intake side of the piston and many get damaged taking them apart and putting them back together.
I hope he can remedy this with another fuel system

Regards
Randy

Jim Pollock · « **Reply #9 on:** February 20, 2006, 05:14:51 PM »

My St .51 exhibited somewhat similar characteristics as you describe. I found that the direction of the hole in the spary bar had changed some over time . After I got some metric wrenches I tightented it down and reset it to approximately vertical and the problem went away. That might not be you problem but it may be worth checking it just the same! Oh, and it was a long hard process finding it out too!

Jim Pollock

Louis Rankin · « **Reply #10 on:** February 20, 2006, 08:51:29 PM »

It has been too cold to fly and Wednesday I go in for some dreaded hernia repair. So, it will be a couple or three weeks before I can go out and try everyone's suggestions. Will update in a few weeks.

Garf · « **Reply #11 on:** March 04, 2006, 10:10:55 PM »

If the mixture change is relativly small, the problem is most likely fuel feed, most likely a tank mismatch. Every airplane/engine combination I have is happiest with a slightly different tank or setup. I finally went to a hard clunk tank setup that has eliminated all my fuel feed problems.

"SAVE ALL THE PIECES"-Phil Brown

Mike Clark · « **Reply #12 on:** March 13, 2006, 08:06:38 AM »

Louis,
How is your tank alignment?
How many laps do you complete at the end of the pattern?
If you change to 5% fuel does the same problem occur?

Louis Rankin · « **Reply #13 on:** March 13, 2006, 12:38:47 PM »

Still have not had a chance to fly since last report. I am not fully recovered but do feel good enough to fly. Soon as the weather permits I will do some more test.

Louis Rankin · « **Reply #14 on:** March 29, 2006, 09:00:16 PM »

Quote from: RandySmith on February 17, 2006, 03:25:11 PM

While I agree that this probably a fuel-feed issue, just to increase my confidence in the engine itself I would want to have checked the end-gap on the ring.

Dan

Dan

That is what I would have done before the engine was ever ran,
However after you have time on it , taking it apart will most likley hurt the ring seal.
The ST 51 is pinned on the intake side of the piston and many get damaged taking them apart and putting them back together.
I hope he can remedy this with another fuel system

Regards
Randy

And, what should the ring gap be on this particular motor?

TigreST · « **Reply #15 on:** January 08, 2007, 01:48:47 PM »

To quote Frank Bowman of Bowman Piston Rings Inc:

"With the fine grained cast iron I use ring gap is .001 to .0015. The rule of thumb is ,001 to .0015 per 1 " of bore.I can pre gap to my bore gage or send them ungapped. I normally send gapped but there are times that bore is larger or smaller than stock, but it is rare. "

Tony

RandySmith · « **Reply #16 on:** January 08, 2007, 02:15:37 PM »

Quote from: TigreST on January 08, 2007, 01:48:47 PM

To quote Frank Bowman of Bowman Piston Rings Inc:

"With the fine grained cast iron I use ring gap is .001 to .0015. The rule of thumb is ,001 to .0015 per 1 " of bore.I can pre gap to my bore gage or send them ungapped. I normally send gapped but there are times that bore is larger or smaller than stock, but it is rare. "

Tony

Hello

You cannot run a .001 ring gap on the ST 51 , or many other motors , There is simply way too much expansion in ST's rings . The ring will simply heat up , expand and lean out and over heat. once you get the ring to expand from heat and the gaps touch ,it is a vicious cycle, the more they touch the more heat builds and the more the end gaps are forced together, this will flat spot the ring and it will never run as it should after that, until the problem has been fixed with a new ring , and maybe even a new sleeve.
If you have special metals that don't expand when hot or expands very little you may can get away with a .001 gap, if your using S.T. parts then NO.
The closest I have ever had them work is with a .003 thou gap, even at that you need to do a careful breakin on the bench or with the plane on the ground, the ring gap will open more as the ring is lapping itself in.
To use a closer gap than that would require using a much much coarser honed crosshatch than comes on the S.T. sleeve

Regards

Randy

Alan Hahn · « **Reply #17 on:** January 08, 2007, 08:38:21 PM »

The following is a copy of a question (and his answer) that I asked
George Aldrich about the ST51 breakin. (This was back in 2000, I think on the CL forum on the RC oriented site (long gone now!)

A question for Nobler,
I have seen you mention the ring gap several times with respect to the ST51. What is the correct gap? I
have a ST51 CL which I plan to use on a Sig Magnum at some future date. I have personally witnessed
the long breakin (and frustration) a fellow club member is having with his ST51. I would like to avoid
some of the long breakin by setting the ring right in the first place.

Every one I have talked to loves their ST51, but they always preface their praise with "..but it sure took
a long time to break in" . Thanks, Alan

added later
Nobler, Thanks for the reply. Alan

[This message has been edited by Alan Hahn (edited 09-30-2000).]

George Aldrich's reply

Everyone of the current ST's I've seen, clear up to the .91, have come with NEGATIVE ring end gap ! The
piston rises to the very top of the cyl. on all of these designs, and if you remove the ring from a new
engine, it will not fit in the cyl. at the top where it get hottest ! The ring ends will actually over-lap !
The end gap should be increased to about .003", and then a more normal run-in will have the engine
purring in about 30 min's. to an hour of slightly rich flying runs.
Above all, at least 20% lube, with 5% min. of castor for fuel.

Bob Reeves · « **Reply #18 on:** January 09, 2007, 09:50:19 AM »

Makes one wonder if the current crop of ST 51's have the same ring gap problem GMA was talking about. I have one on my Skylark that is box stock and seems OK also have another one NIB I was planning on sending to Bowman for one of his rings before I broke it in...

Randy, don't you use Bowman rings? Haven't you discussed your findings with him?

Mike Scholtes · « **Reply #19 on:** January 09, 2007, 12:59:18 PM »

Maybe Alan's observation is why the ring in my 2006-model (ie Chinese) ST51 cracked in half! One run, fine, then...no compression. Sent it to Frank Bowman for a proper ring and deck milling of the sleeve-to-head fit, all done for Frank's ridiculously low prices. 100 flights later, no problems and great power. Using Randy Smith tube muffler by the way.

Crist Rigotti · « **Reply #20 on:** January 09, 2007, 09:04:44 PM »

I send my ST 51 C/L to Tom Lay for his work. They do run great after I get them back.

Ron Merrill · « **Reply #21 on:** January 10, 2007, 08:13:09 AM »

I'am with Crist, i send mine to Tom Lay. Tom told me the tongue muffler was too restictive, use a tube type. I brought two from Scott Dinger. Ron.