Dismantle ST46

Any of you guys able to tell me the best way to remove the prop driver & crank from an ST46?
Thanks.

LAST EDITED ON Feb-09-04 AT 04:59 PM (CDT)
 
I fashioned a drive washer "puller" from a automotive battery terminal puller. Cheap at a auto parts store. Had to grind the tips slightly to get a proper fit behind the drive washer. There are probably more expensive tools out there but it works. As to the crank shaft, you can put it on a pan in the oven, rear opening down, and the shaft will fall out when heated. Sorry, but I can't remember what temp I used for the oven.
Bill <><

The Crankshaft should fall out once the dust cover is removed.Watch out for the spacer on the front of the crankshaft that goes up against the front bearing and it must be put back on the same as it came off.Heat the case and the rear bearing can be removed by hitting case on a piece of wood. If the bearings are good don't pull the crank.
Ed

I agree with what's already been said. When you get it apart, make sure that the rear bearing hasn't been turning on the shaft. If it has, use locktite or similar to make sure that it doesn't in future.

Not to hijack the thread but seems like a good place for another question.

It's been over 20 years since I pulled apart a ST 46 and I seem to remember having to heat the case to get the liner out. I also remember carefully opening up the case a little with sandpaper so the liner would fit without the heat.

What I don't remember is... Are all ST 46 liners a press fit to the case and is it a good idea to open up the case so the liner is a snug fit?

What about installing one of Tony's ceramic coated liners, the liner is aluminum instead of steel so the expansion properties would be the same as the case. Should this be a press fit or would it be better if it fit like say the FP case/liner?

It is certainly usual to have to heat the case to remove the liner, but that is usually because of the varnish that builds up on the outside of the liner. Brand new liners usually fit brand new cases very well (I used to work for the UK ST importer). I think that easing the fit will effect the heat transfer and also allow more varnish to build up and effect things even more.

Thanks for the input guys. Having never dismantled one of these engines before I wasn't sure how the prop driver was secured.
My liner slid out without any heat but it was almost size for size.
Getting the gudgeon pin out was another story......
I'll be using one of Tony's liners when it goes back together so I'll let you know how the fit is.

Please tell us how you got the Wrist (Gudgeon) Pin out!!

Just pulled one of my ST 46's apart, at the risk of not stating a "Gold Standard"... I made sure the wrist pin was free then stuck a round tooth pick in the hole in the pin and pulled it out. Only problem is when I tried to remove the tooth pick from the pin the tip broke off in the hole. Nothing a small drill bit won't take care of.

I was told by two very esteemed engine builders to use an old ST needle screwed into the pin to pull it out. Not my original idea.

Bill <><

>I was told by two very esteemed engine builders to use an
>old ST needle screwed into the pin to pull it out. Not my
>original idea.
>

That's what I always did. After I got it apart, I drilled and tapped the hole for a 2-56 screw. That way, I could get it apart the next time much easier.

When things are stuck, I use a heat gun and an oven mit to hold. The wrist pin can be tough. If it won't just pull out, try to turn it to loosen it. Pull while turning.

I used a tapered screw extractor, or ezy-out to remove the gudgeon pin.

The ST .46 is not a hard engine to work on but it is a little different in some ways. The only tools needed are a propane torch, a plastic tipped hammer, 3/8" wood dowel and good glove. The thrust washer is easy to remove by heating it with the torch and tapping the side of the thrust washer. It will pop right off without damaging the thrust washer.

The wrist pin can be a little more trouble but only slightly. Warn the case until the cylinder liner slides out. Note: In some of the ST .46's had a screw in plug on the back of the crankcase just below the cylinder fins. Remove this plug and line up the wrist pin with this hole. Again, using the torch with a low flame, heat the bottom side of the piston and the connecting rod. Tap the case on a block of wood and pin will slide out the hole.

The rear bearing is removed in much the same manner, by heating the bearing seat on the outside of the crankcase and tapping the case on a block of wood. Remove the front bearing by heating the bearing seat and tap the bearing out with a wood dowel.

I my opinion, never dismantle a ST 46 without removing the bearings and inspecting them carefully. That is the only way to see both sides of the ball bearings and inspect the bearing race.

To assemble the engine (after clean up) slip the rear bearing onto the crankshaft until it is up against the back of the counter weight. Warm the rear bearing seat on the out side of the case and drop the crankshaft and the bearing in place. The bearing should seat itself completely. To verify that the bearing is fully seated, tap the back of the crankshaft with a wood dowel and hammer and allow the case to cool. The front bearing is just as easy to install. Heat up the front bearing seat on the outside of the case, and drop the bearing over the crank shaft and tap it in place with a deep socket on the outside of the race only. While the case is still warm add the forcing cone and thrust washer onto the crankshaft. Attach a prop and securely tighten in place. Spin the prop making sure it spins freely and smoothly. Allow everything to cool and spin the prop again. It still should be free and smooth. If not, disassemble the engine again and look for burs and dirt. Remove any burs and dirt and assemble the engine again. It has to be smooth and free from any binding or roughness.

Attach the rod to the crank pin and slip the piston in from the cylinder head end of the case until the wrist pin bosses and wrist pin hole in the rod are aligned. Slip the wrist pin in place until it is centered in the wrist pin bosses of the piston. With the piston at top dead center, warm the case around the cooling fin area and slip the cylinder into the case with a twisting motion. Line up the notch in the cylinder and the alignment pin in the case, and press the cylinder in place. Make sure cylinder is fully seated in the top of the crankcase. This must be done quickly before the cylinder heats up.

The most important thing about a ST .46 is the fit and seal of the ring in the cylinder (like most ringed engines). If anyone is interested I can write down all the little things we used to do to make the ST .46 a fantastic stunt engine.

Mike,

Please do, it would be nice to have all the in's and out's of the ST 46 in one thread. Most of us know there are better engines available today but for a classic 4-2-4 in the right airframe the ST is hard to beat.

Thanks
Bob

Since it is not a S.M.A.L.L. size engine, a sledgehammer is recommended!

As I recall, didn't Harry Higley use an ST .46 as an example in the chapter on disassembly and cleaning in his book on model engines?

Nope, Harry used a ST .35 C

St .46 Mods. First let me state that almost all of these changes were incorporated by many different people and I don't know who thought of the specific procedure or change but they were used by many modelers flying the ST 46.

Crankshaft: On some of the early models of the ST .46 there was a brass ring that was pressed onto the outside of the crankshaft counter weight. This brass ring would sometimes come loose while the engines was running and send shaving through the engine. Most of the modelers I knew removed them before they became a problem.

Rings: Were the biggest problem with the ST .46. You could buy a dozen and only three or four were any good at all. To check them we would place them in the cylinder bore about a 1/4" from the top of the cylinder and hold them up to the light. If we saw any light between the inside wall of the cylinder and ring they were unusable. In addition, the ring end gap had to be very close at .002" to .004" maximum. Any more than that then very noticeable amount of power was lost.

Cylinder: For the most part, the cylinders were pretty good but the cross-hatching inside the cylinder was very important. We would use a brake cylinder hone and give the inside of the cylinder with a quick (about 1 or 2 seconds of run time with the drill) while moving the hone up and down in the bore. This added scratches to the cylinder wall would give oil and place to cling to. This also worked well on used engines for a short time and could help you get through the season.

Connecting Rod: Put a large radius on the oil holes on each end of the rod. If it didn't have an oil hole at the wrist pin end of the rod, then add one. This allowed more oil to get to the wrist pin and crank pin increasing the life of the engine.

Piston: One experiment I tried was gas porting the piston. This was an old drag racer trick of drilling four equally spaced .015" holes in the top of the piston on the outside edge. These holes stopped as they entered the ring grove of the piston. During the compression stroke the compressed air would pass through these holes and push the ring outward against the cylinder walls. It worked extremely well but you would go through rings like crazy. They would last about three or four gallons of fuel then you could feel the power start to drop off. But it was great while it lasted.

I have to admit that I never tried one of the after market ABC, AAC, or Plasma piston and cylinders in the ST .46, but my feeling is they would be great and well worth the money.

Bearings: Good quality bearings were always the trick item. The front bearing were replaced with a bearing that had metal seals on each side. One of these metal seals was removed with a sharp pick. When the bearing was installed in the crankcase the seal was to the front or to the outside of the engine. This greatly increased the fuel mileage of the engine and kept the nose of the model much cleaner.

Cylinder Heads: Mostly stock but some preferred that half the height of the cooling fins be cut off. This was OK in cooler climates but extra fins were needed when it was really hot in Lake Charles or Texas.

Venturi & Needle Valves: Many fliers had great success with the sprinkler type venturi, but I was not one of them. I found it far better to place the needle valve assembly through the center of the venturi. The little holes in the sprinkler system always clogged even with a fuel filter causing a lean or inconsistent run. Venturi size ranged from .275" to 310" depending on the size of the model.

Muffler: Open faced, tongue, or tube type all seemed to work just fine.

Props: In their hay-day the Rev-Up was king. The most popular props were 11" X 6" EW, 11-1/2" x 6", or the 12"x 5" W with .030" of under-camber sanded into the back of the blades. The modern C/F props such as the Bolly and Either should work like a dream on these engines with performance far superior to the wood props.

Fuel: I may be a little prejudice but I used nothing but Sig Champion 5%, 10%, and 15% for many years without a single engine failure. Some swear by all castor and others there own brew but the St .46 never cared one way or the other.

I am sure that I forgot something but this is all I have on my notes for the ST 46.

just been peeking the back of one or two of my ST46s. early ones (no muffler lugs) show a completely cut away crescent shaped counterbalence either side of the crankpin. Later version appears full circle from the rear but when removed reveals milled slots in the web on either side of the crankpin - no band though. There is also a spacer on the front, reduced diameter part of the shaft, behind the front bearing - did they make the large diameter portion too short? Rear bearing is a SKF 6001 - any recommendation for upgrade? Front is not marked.

Piston has two rings, is this type any good.

Thanks,