buzzard bait

I just picked up an old used ST S25 without knowing anything about it, and wondered if someone here could clue me in. It is not the X25 that seems so sought after; I think it's probably an earlier model. It has a slightly dished head, ball bearings, a carb with a BIG throat, twin needles, and a extra little vertical screw on the carb whose function I don't know.

Mine has good compression and smooth bearings, the muffler is an OS 842 (25 FP type) that appears on the small side for this engine. Unfortunately it's an odd screw spacing so I can't swap out something larger.

Any insight on performance to expect, prop, fuel and glow plug choice would be much appreciated. I can post pics in anyone is interested. If no one is familiar with it, I'll start with 10% nitro, 22% oil (1/2 castor) and a 9x5 or 9x6 prop, and report what happens. When the weathers warms...

Nice looking engine. Thanks in advance,
Jim

jeffie8696

Photo?

buzzard bait

Here it is:

jeffie8696

ILike It!! Sounds to me like you are on the right track.

modeltronics

My Feedback: (27)

If I remember right the S25 came after the 25X. I have several of the 25X engines and I had one S25. I have flown both in Sig Wonders. The 25X is the winner for speed spinning an 8X6. Both are good quality engines. I always thought the ST muffler was too restrictive (and hard to find in this size). If you can lay your hands on the Tigre Paw mini pipe it is much better.

mike109

G'day Tigres. Back in the 1970s I was racing Goodyear control line and rat race using Super Tigres. There were two series of engines at that time. The sport series - which were the G20 series in various sizes and the G15 which was an out and out speed engine. The original G20 15 had been a speed motor too but over time, the G20 15, G 20 23 etc became sport engines and by the late 1970 the G15 too was becoming dated. All these engines used Super Tigre's own porting with flat top pistons and two large transfer ports. Liners were all steel and pistons iron though I think some of the larger engines were ringed. I only had 15 (2.5cc) engines.

The X series were the first Schnurle ported Super Tigres and also saw the introduction of ABC construction. I seem to remember that initially, both steel/iron and ABC were available at least in the 15 size. The X series were an attempt to regain the top spot in the performance field. This had been taken by Rossi and other engines in the late 1970s. I owned an X15 though I never ran it as I left the hobby at that time. I still have one of my G15s and a very tired G20 15 D which was built from scrap parts. I wish I still had the X15 and my Rossi 15.

When I got back into buying model engines in the early 1980s, the S Series were current. They were sport engines with a dished top to the fins on the head. In 1990 when I dropped back in again, the G45 was the thing to have and so I bought a couple. They were great engines too.

I still like Super Tigres. My latest model is a Sig Mid Star 40. A shiny new G51 is going in it though most of my models now have Saitos.

buzzard bait

Yipes, a hot 25 in a Sig Wonder...must have been a handful!

So do I gather correctly that the S series was designed to use larger props at lower rpm than the X series?

Sounds like a 9x5 to 9x6 is about right. I've also got some Bolly 9.5x5s, so I'll try one of those too.

Too bad Bolly shut down production of those props.

Jim

mike109

G'day As I remember, there were different versions of the X15. Some were intended for pipe use, others not. I am not sure about the 25 size though I think the X40 was also available in pipe and non pipe timing.

Ah Bolly props. As an Australian it is particularly sad for me to see them go. I really liked them especially the 10.5 x 5, 11.5 x 5 and 12.5 x 5. Sadly cheap imports killed them off. I found they worked better than any other props I tried for most purposes. And were quiet into the bargain.

summerwind

Jim,

just sent you another email about the Tigre...........i miss it now that you posted the picture

summerwind

you hit the nail on the head.................the X's were designed to run high RPM, while the S dropped things back a notch to pull the larger props and had a bit more torque at the lower RPM band.
i ran a 9x6 on it, but for the 880 square inch winged Satellite i used a 10x4. the Satellite was an RC assist that weighed 38 ounces.

the original muffler was dumped in favor of the OS muffler for a 4-500 RPM gain.

djlyon

I have the S29. I don't remember the 25. But back then you didn't know month to month what Super Tigre was going to make. My 29 was moderate in power, less than most other Super Tigre 29s. That would be expected all other Super Tigre 29s I remember were designed as Proto speed or high performance Free Flight engines.

Denis

buzzard bait

Here are pictures of the mystery screw, nestled vertically right in next to the carb throat in a little groove on the HS NV side. There is another screw that must be the barrel retainer/idle stop screw in the usual location on the exhaust side, and then there is the nice big low-speed needle on the exhaust side. FOUR adjustable screws. I know what to do with three, so any enlightenment on the fourth would be much appreciated.

I'm enjoying the comments. Nice to know about the properties of the S series, and I like to use larger props. Lost my taste for high pitch screams after several years of Cox .049s with 25% nitro. Sounds like this engine is probably comparable to the OS 25 FSR? Maybe a little stronger? Anyway I'll enjoy getting to know it.

The ST mufflers I've seen of that vintage were flow-through types, if I recall correctly. Interesting that it didn't do as well on the engine as the OS muffler.

Yes, it is sad about Bolly; I noted the posts from Australia. I used to use a 10.5x5 a lot and liked it. I got a stash of 8.5x4 and 9.5x5 from Graves in the States when I saw they were closing out the Clubmans; the 10.5s were already gone.

I'll take good care of your engine, Mike. Great story about the Satellite 800...will send PM reply to your message about it.

Jim

djlyon

It's the low throttle stop screw. Used to adjust how far closed the throttle will go. It's seldom used. Most folks make the adjustment with the throttle trim on the transmitter.

Denis

summerwind

Zactly........you could even remove it if you wanted to........but i'd leave it in there just so long as it doesn't restrict closing of the barrel.

buzzard bait

The issue is FOUR adjustments. But I figured it out. The screw on the right holds the carb barrel in place just as similar screws on on other carbs do. But on all my other carbs, the same screw that holds in the carb barrel ALSO serves as the limit screw for the idle. ST didn't do that on this engine, so they have a separate screw to adjust the idle limit. Seems oddly complicated, but that's how it is.

I really don't know why they bother. Even before computer radios I never set a limit on the carb barrel rotation.

sgilkey

My Feedback: (180)

The S25 looks very similar to the S29, it's the same basic engine. I have never run an S25 but have lots of S29s. It is a fine running powerful and durable engine. The muffler spacing is the same as the 25FP. The stock ST muffler that looks like it has a long funnel on the back end is HORRIBLE and very restrictive. The FP muffler actually works very well. The ST29/34 "swing" muffler also works great. You can also make a mousse can pipe (MCP) with the Macs header for the 25FP/LA engine, this will REALLY wake the engine up, it responds very well to a tuned muffler. The ST "Tiger Paw" is a factory tuned muffler and is very effective but heavy, the MCP works even better and is lighter and cheaper.

The S-series engines of this era often came with a small restrictor in the carb- look to see if yours has one. It is a small aluminum piece that fits in the barrel. To get it out, you have to remove the barrel from the carb, and the low-speed needle from the barrel, then it simply presses out. Removing it will have no affect on running, as long as you are using muffler pressure.

You can also thin the spraybar to further open up the carb. This was done on the ST34 heli engine, which uses the same basic carb. The spraybar is soft brass and can be easily thinned with a file. Just file flats on both sides of the spraybar to knock the "round" part off- if the "inlet" of the carb is 12 o'clock, make the flats at 3 and 9. You don't need to take much off to get a big reduction in restriction, it will be obvious when you look at it. This will tend to make the midrange a bit fat, though, but it will really open up the top end.

Don't know about the S25 but the S29 loves turning small props up in the high18k range on a MCP. It will also happily turn in the 14-16k range with larger sport-type props such as the 9x5APC. It's a very flexible engine.

buzzard bait

Finally got some spring weather here; still have snow piles but they're melting fast.

I disassembled and cleaned the engine, then put it back together and up on the test stand, 15% Morgan, 10x4 Zinger. I got 11, 200. Then I tried a Bolly 9.5x5 and was surprised to get 11, 900. That was much better, but still kind of low. Then I remembered the head shim I noticed when I disassembled the motor, so out with the head shim. That got me 11,450 on the 10x4, and 12,100 on the Bolly.

These are pretty ordinary figures. Then engine is old but holds compression at TDC very well, so I imagine it wasn't much stronger when new.

What makes it a keeper is the throttle and the smooth, steady running. Vibration is low, and you can idle as long as you want, then snap the throttle wide open and then engine responds instantly without a hint of hesitation.

I wish I had tried open exhaust, because I still think the muffler is rather restrictive. Unfortunately, there aren't many alternatives due to the bolt spacing.

Overall, I had fun playing with it, it is a very pleasant engine to run, power is not bad, so I got my money's worth, which wasn't very much anyway. The Bolly prop is probably the way to go on this engine.

Jim

summerwind

LOL......what you paid me was only half, you still owe me the other half.....kindly pay up....

buzzard bait

Hi; well, as I said once before, all's well that ends well! I'm happy with it.

Cheers,
Jim

sgilkey

My Feedback: (180)

make sure the carb restrictor is out! there aren't many "factory" mufflers that will be less restrictive than the 25FP muffler (make sure it does not have a baffle in it), you could ream out the taipipe to 1/4". A mousse can pipe will probably really wake the engine up, most tigres respond well to tuned mufflers. Use the Mac's header for the 25FP. If you want to use a 10x4, we use the MA G/F3 for r/c combat, it gives excellent thrust.

buzzard bait

I meant to check on that baffle...will do. What do you mean by "carb restrictor"? I don't think anything is restricting the carb...I had it apart and it looks good.

That's interesting about the MA 10x4. I'll give it a try. It will probably turn up much better than the Zinger, which seems like kind of a clunky prop, i.e., thick trailing edge and a little broad. The Bolly ran amazingly well, considering that by the numbers, a 9.5x5 should create a similar load as a 10x4.

Thanks,
Jim

summerwind

Jim,
don't worry, there is/was no restricter in the carb.
actually, none of the 23's or 25's i've owned from NIB ever had a restricter.

this engine will suprise you though, but give the 9x6 APC a try.........you'll smile

sgilkey

My Feedback: (180)

I don't have any knowledge of this specific engine but many NIB STs and Comos of that approx. vintage that I have had all came with carb restrictors from the factory. It's easy to see, it is an aluminum ring in the carb barrel that reduces its ID, if it's not there, great. Takes two seconds to look for and about two minutes to remove if it's there.

buzzard bait

Thanks, but SW is right...no restrictor.

jeffie8696

Iam still looking for a nice Super Tiger Sanything for my collection,,,,,,,,Pete!!
Wanna trade sumthin?