Randy, I've got a Big Jim ST 60 in my new Shark 45. I've only got about 10 flights on the ship .The issue that I'm having is that the engine wants to begin breaking at about 12 O'clock. Consequently I don't have the punch where I need it . Here is my set up at present:
13x5 prop Rev Up
5%/23% oil half castor half synthetic
Fox long idle bar plug
Plane weight is 68 oz
Line length C/L to C/L is 69' 6"
ST needle valve in 310 venturi
My question is: should I change the "Big Jim" Hemi head for the higher compression stock head.....or raise the % of nitro or both??? Thanks.PhillySkip

Hi Skip   to make the engine  break faster  DO NOT run pressure,  running teh engine in a faster 4 stroke  will put it breaking quicker,  The setup your  using  should be launching at about 9500 RPMs  if your  launching at  88 to 8900 RPMs  you do not have a 5 pitch prop,
If you raise the nitro, you will have more power but you will  get  LESS  break, or you will get the break later in the maneuver , and it might  make it accelerate  going down hill
Are you running pressure ?
Did you look at the head to make sure it is machine to lower compression?  how many head shims?
If you go to 10% nitro you may need to add a head shim
are you loosing  tension at the tops of maneuvers?
is it slowing down at the tops , or speeding up/winding up ?

Here s  the normal  stock setup to start with:
13 x 6 prop
88 to 8900  RPM launch
5 to 10% nitro 23 % oil part castor
this is assuming 301 to 310 venturi
This should come on at 2 cycle 10 O Clock  and off to a 4 cycle at 2  O Clock   so its sounds like we need to see  why yours if differant

Randy
 

Randy thanks for your help on this. I pulled the head off of the engine and found two shims totaling .045  that seemed excessive so I pulled the head on another ST 60 I had (also with "hemi head) and the shim was .024 . What I did was use the .024 shim in the engine powering the Shark. I'll see how that works.
I do use muffler pressure on the uniflow line. One other thing, the prop was a 13x6 not 5. My launch RPM was right around 9000.
I do not have the uniflow vent into the wind, it's attached to the muffler. If I pull it off the muffler and just let it hang below the plane will this help?  If not I'll make up a tube that is in the slipstream.
Since I have not got my set up working properly I have not tried any of the overhead or vertical stuff. I think the plane has less than 12  flights....Cheers,Skip

Hi Skip
Pressure makes  the engine  dumb. it comes on late and off a weird ponts, try the  1 head shim take it OFF pressure, that way it will break faster, The uniflow should be  above centerline, and pointed  into the slipstream,  This should make a substantial change in the right direction

Also you may want to pick up a 13 x 5  prop  to try too

Randy

Any Chance of a photo of the B J combustion chamber Skip .

Incidently , while we're here ;

.25 over venturied ( 7.5 mm )  vent into wind ( Fwd ) Vs perpendicular cut 45 Deg - to wind ( The end slashed 45 Deg to fuse )
Was 1/4 turn to lean to same air setting . Worse into / out off - wind richen / lean  aimed fwd .

Some people do hide in cowl , as in Out off Airstream - for that reason . Generally . Not ST 60 specific .

Ive Decided if on the ground ' the break ' is at 20 to 25 degrees Nose Up . Upright & inverted - same ,
your V Close o the in air setting , so need to prop to get that .Can you video it ??

Uhh  NO it is  not  over venturied, the lower compression takes a larger venturi, if he runs the stock head, them , YES  switch to a 285 venturi, but he  is  not running  high comp heads.  jms  setup used a larger venturi

Randy

With an old engine that has obviously many versions of carters and heads, often modified using not so accurate machining work, it would be wiser to talk about head volume instead of amount of shims.
It’s very simple to measure; you just need a small syringe with needle, put piston in tdc and measure the volume with fuel.
That’s the easiest and most accurate way to compare and copy this important parameter between engines.
Without knowing ST.60, I’d guess that it has a head volume in 1,2 milliliter ballpark.

Sorry for off-topic..

Lauri

Did I ever mention that I positively HATE Fox glowplugs? Cannot remember ever replacing one with a Thunderbolt that didn't make an immediate improvement. Most times on anybody else's engine that wasn't running right. With Hobby People gone, I'd get some Merlin plugs from Randy!


Funny local ST .60 stories...

Bruce Hunt got a Tom Lay version somewhere, plugged it into his new Shark (many years ago) and it wouldn't draw fuel, always cutting out in the RWO. Brett was watching, and suggested more nitro, which helped a lot. Later, Bruce pulled the head off and discovered it had an immense number of head gaskets being stored there. The previous owner didn't want them to get crumpled, and figured that the next owner would certainly pull the head and set the shims where he wanted to start and would adjust from there. Curiosity isn't a bad thing, apparently.

Pete Ferguson had one in an ARF Strega, and it went pretty well. But not quite right. He pulled the tank out and fiddled with it, and the next time we flew, it would run one lap and quit, time after time. Turned out he'd put the tank in with the wedge on the inboard side of the fuselage. We got a good giggle out of that one.  Steve

   The ST.60 is an interesting engine. It kind of 'talks" to you and can tell you when it is propped correctly. I had a Cardinal that I bought from a local guy mainly because it had a T&L .60 in it. It weighed 72 ounces or  more, but I knew if I could get a good prop it would fly a pattern. Maybe not the best pattern, but fly none the less. I just wanted to experience the ST.60 for use in some later projects.
  I had learned that he usual prop of choice for the ST.60 is the 13-6 Rev-Up, but try find some of those!. The previous owner had a Zinger cut down to 12" for some reason, and would barely fly the airplane. I started to hunt around and try different props. I had read about Vess props and tried one of those one flying session. Up to that point, I had been using a Brodak 13-6 and it was the closest to doing the job, but not quite there. One flying session I had the Vess prop in hand, but put up two flights with the Brodak just to have a base line on RPM and fuel load. Next I tried the Vess 13-6. I had to start this model inverted because of the cowling and prop extension, and the guy helping me had some experience with the engine also. I started the beast up and it had the Tigre sound immediately! My friends eyes got real big and he smiled! I turned the airplane over , and in that process it broke into a two stroke for a second and went back right away. That made me get all goose bumpy!  I had put in the same fuel load as before and I remember tweaking the needle just a bit for some reason, but not much. I proceeded to fly the flight with much improvement! Actual line tension up top and such. When I got to the over head eights, it broke a little more like it was running out of fuel, so I pulled out of it and after two more laps it quit, out of fuel! I had to add fuel to get the pattern in after that, that's how differently the prop was loading the engine. And as mentioned, a good, hot plug makes al the difference also. And every Fox glow plug on the face of the earth should be destroyed IMMEDIATELY!!! As it was already mentioned, I have witnessed a simple replacement of the Fox plug to be a cure for many, many engine woes!
  Type at you later and have a safe Memorial Day Holiday,
     Dan McEntee

 PS to add, I always use an idle bar hot plug. That give jink and carbon a place to form instead of on the element. I mainly use Glow Devil R/C Longs, part number RC300, I think.

APC makes a 12.5 x 6 that you should try. Probably not available at the LHS, but what is?  Steve

Steve ,what local hobby shop? None exist around here.

 Ok, so today I got out to the field early and got some "testing" done. I switched the Big Jim head for the stock one with stock shim and actually had a nice run. I was running a 12x6 Rev Up .No runaway very consistent. The break was coming in about 10 o'clock and back at 2 o'clock. I did get to finally fly the plane thru the pattern. I'm satisfied with the engine run ,but will try  some of the other aforementioned props. I switched back to the Big Jim head for comparison, the engine began to run away about 1/2 way thru. I'm putting the stock head back on immediately. Cheers,Skip

Skip

The  TT Cyclone  or  Yoshioka  12.5 x 5.5  is  excellent on the  ST 60  I have those n stock  now

Randy

Randy this ST 60 is driving me nuts! I installed one of the 12.5x5.5 props I got from you and it pulled very nicely,but my "stunt runs" are not consistent. The plane is either too fast or too slow. I can't seem to find the needle setting. I use a tach and as little as a 300 rpm difference really has a big effect on the flight performance.

Here is my set up from today:
12.5x5.5 prop Take off RPM from 8900 to 9200
.310 venturi.OS NVA.
stock head,.025 shims
tongue muffler (I'm still with muffler pressure to uniflow) I will change that tomorrow and eliminate the pressure.

I gotta get a inflow vent into the airstream to see the difference.

Randy .....Eureka ....I got the ST 60 purring now. I did install a side vent for the uniflow line.Took it off pressure. I reinstalled the Big Jim head with .035 shim. I used your 12.5x5.5 Take off rpm was 9100. She's going great now. Thanks for your advice.

I had to figure it out,Leaving for Brodaks in the morning.