.40 stuka stunt (Tower) eng.

I just learned of your heart attack today by reading the forum.
Glad to hear every thing seems O.K. My question concerns a .40 that I have in a cavalier profile. This engine will not give a decent run under any circumstances we have tried. I am using a new fuel, powermaster 22% lube, 10% nitro, rev-up 12/5 prop, and have tried several tanks, all uniflow. The only way to get this engine to calm down is to take-off with barely enough rpm to get it off the ground, and then it still leans out to a fast 2-cycle about mid-way thru the flite. If we set the rpm @ 7800 - 7900 on the ground, it results in a total runaway. I got this engine from Tom Morris a while back and just got around to using it. You might be interested to know that one of our fliers here has the identical set-up, except that it is a O.S., not a tower, and has worked like a charm from the start. He is using 5% nitro, on a cavalier profile, 12/5 prop,etc. He is extremely pleased with it. Any sugestions would be appreciated. THanks.

Sorry to hear about your problems, but we will work you through it to make it work. One thing I would suggest is trying your friend's fuel--or any 5% for that matter. These engines are set up to develop optimum power with 5% nitro. 20% to 25% oil is fine (you are using 22%) and, although we prefer all castor, so long as it is a mix using at least 50% castor in the oil, it should be OK. You didn't say if it was a 50-50 blend or all synthetic. If all synthetic, get some 5% nitro fuel with 20-25% all castor--or at least 50-50 castor/synthetic.

These engines are also intended to be heavily loaded. I even warn in my instruction sheet that if you use a prop with a substantially lighter load, it will run away. A 12 - 5 Rev Up prop is very light. We have had good success using a 12-6 Rev-up, but even this was rather light. A 12-6 Zinger works fine. Some have used 12 - 5 Zingers with good success and the best wood prop we have used is the 12 x 6 BY&O.

As to the difference between the Tower 40 and the FP 40, there is very little. These engines are part for part compatible with one another. You can take any part from one and put it on the other and it will work fine--except--the Tower uses a .010 head shim and the FP uses a .016 head shim and the Tower compensates by machining the head slightly to restore the same compression and head clearance. I use a single .016 head shim on the FP and two .010 head shims on the Tower, but drop the sleeve accordingly to maintain the same clearances. You could swap heads and shims one to the other and they would be the same. Other than that the Tower uses the fully machined crankshaft as used on the very early FP engines, and the Tower is also true ABC (chrome plated) whereas the FP is nickel plated. When run properly, the nickel will hold up well, but I still like the chrome better.

So...try it with 5% nitro. (See the thread just a little lower discussing the increasing of nitro in fuel.) This is the way it is set up and that is all you should need for this engine. If you must use 10% nitro (it is all you can get, or whatever) then you should probably replace one of the .010 head shims with a .016 made for the FP. That would raise the head .006 which should be enough to accept the higher nitro content in the fuel. If you can, get a 12 x 6 BY&O prop. Brodak is now making these again in limited quantities and I even have some in stock. Or try a 12 x 6 Rev UP or a 12 x 5 Zinger.

Just remember, not all props are made equal. Whatever is marked on the blade is kind of a guide line, and will vary immensely from brand to brand. A 12 x 6 BY&O will actually measure out to 12 x 5.5. A 12 x 6 Rev UP is closer to a 12 x 5. I don't know what a 12 x 5 is. Also, a wood prop can obsorb moisture and warp, shrink, whatever. We once put a new 12 x 6 BY&O prop on our plane, set it at the desired rpm, and lap times suddently went from 5.3 seconds to 4.7 seconds. We later put that prop on a prop gauage and one blade measured 7 and the other 7.5. I would imagine it was merely the result of the wood drying out and warping. I then checked a dozen new props I had in stock and they were all "right on" (5.5 pitch.) We sanded the blades of the offending prop to proper pitch and it worked fine from then on.

One more thing, you did break the engine in on the bench, didn't you? Here is where you can put a little smaller prop on it, but bring it up to operating speed and temperature right away. Some of these will seat in with about half an hour of running. Some will take an hour and a half or longer. The pinch on these engines at the top is quite tight on some of the Tower engines. One of these engines that I sold to Tom had about two hours on it and it still wasn't broken in. It will be a good engine when finally run in, but it will just take a little longer.

You may also want to check for fuel foaming. We have had an experience where an inline filter was causing a problem. We removed the filter and the problem went away. And don't use an air filter over the venturi unless you also increase the size of the venturi. For that matter, don't change to an ST needle valve without changing the size of the venturi. If you are using the stock muffler that is going to choke it down. We have 1.3 ounce tube mufflers and also half ounce tongue mufflers both of which work well. These engines do not like back pressure. Along the same lines, don't put an exhaust deflector at the back of the muffler. This, too, will increase back pressure and the run will be "different". On some engines these things may work. With these engines it is a "no-no" without increasing outlet diameter or venturi size.

Give it a try, see how it works, then let us all know. When you get it running right, you WILL be happy

Thanks for your quick reply Sun. p.m. - after reading your input, I decided to check anything/everything I could here @ the shop before going to the field in order to try and save time, etc. - I pulled the head off and thought I would check the actual gasket(s) thickness- - BUT THERE WERE NO GASKETS- none. Interestingly, I have a new Tower .40 that has never been out of the box, all brand new, and I pulled the head on that motor. No gasket under the head, although there was one in an envelope in the box. I am not sure what this means, unless the mfgr. intends for the owner to install. At any rate, I searched thru my stuff and found a gasket that mic's out @ approx. .022, so this should be close to what you are recomending. Should be able to test fly tomorrow (wed.) Your thoughts would be appreciated. Hope your recovery is going well.
ED

LAST EDITED ON Aug-08-00 AT 08:19 PM (EST)

Several problems. When I add a second head gasket I also drop the sleeve an appropriate amount depending on the engine. Each engine (and this goes for OS, Fox, you name it) has built in manufacturing tolerances that affect the deck height (distance between top of piston and squish band of head) and also the timing of the ports. I drop the sleeve to where I want it and then add the second head shim. So you will start out with too much head shim to begin with. It wouldl be far better to go back to 5% nitro than to try to add head shims. If you insist on adding head shims, adding .005 should be enough. If youo add .022 to what should already be there, we are going to be out in "la-la" land. And If I was aiming for two head shims of .010 each and both got left out, the piston would be hitting the top of the head.

So...are you sure there was no head gasket? Some of these are hard to see. The bottom of the head that fits against the shims is very shiny--shinier than the shims themselves. If you poke in alongside one of the bolt holes with your number 11 knife, you can sometimes snag the shim that you at first didn't see. Check again before you add any shims.

Now, your getting a Tower 40 with a head shim in a package is a new one on me. This may be one of the very early ones and it included an extra shim for your use. OS used to be kind enough to do that. Now to get a shim from them you pay $3.50 and get one head shim and one back plate gasket you didn't want. (Or if you wanted a back plate gasket you get a head shim in the deal, too.)

So, check again to see if you have a head shim (actualy two head shims). I will venture to say they are there and your problem is using too much nitro for the way the engine was set up.

Leonard, I just got in a new Tower 40 to replace the sleeve in my OS 40 with and it had one gasket installed,and another one in a package in the box. You know the other day when I discussed my engine quitting in the hourglass etc. Well nothing I did corrected it . As you suggested, I even changed the tank. When I ordered the Tower P&C they said none in stock, so I ordered the entire engine and another spare P&C along with two wrist pin assys just to get the little teflon pads. The new P&C assembly cured my OS MAX quitting problem. It's back to running good again. Thanks for your input and assistance.
Bigiron (Marvin Denny)

The addition of the new head shim must be something new then. I ordered ten of them about a month and a half ago and these did not have the extra gasket in them. It may be that too many RCers are going to 15% and higher nitro and they felt they had to do something about the situation. Meanwhile I have about 350 of these head shims on hand (aftermarket made) and then they go adding an extra to the box. Oh, well, these work on the 35 and 40 FP as well as the 35S engine, so they have a bunch of uses. The .010 size comes in handy when OS has .016 because then you can mix and match in smaller increments.

0.K.-you convinced me to have another look for any head shims. I had somene else look earier today, and he used a #11 blade and was sure there were no shims. However, the area where they are was dull,just as you said. The third time I tried with the point of the #11 was sucessful in dislodging a head shim. It checked @ .010 and I am sure there is another one there, although I could not dislodge it. (looks dull). So, the new engine I have must also have a shim (or two?). These things are really in there hard and tight! So tomorrow's flying session will primarily be one of trying a BY&O prop and the 5% fuel, Thanks for your input- I'll let you know the results. Ed

The continuing saga of the ss.40-Tower eng.- today I used the new 5% fuel, 22% lube, 50-50, and installed a BY&O 12/6 prop. THis seemed to calm the beast down, so we launched @ approx.7800 rpm. The thing ran about 4-5 laps and suddenly quit. It had locked up. The crank had become tight as a drum, from heat, I suppose. After sitting for a short time, and gently moving the prop back and forth, it returned to normal. We could only suppose that the new heavier load caused the front of the engine to heat up. The second flite was better, but too lean and too fast. Ran about 7 min. on approx. 4-1/4 oz. From experience with Bill N's here, (OS 40), it should run about 5-1/2 to 6 min. to get the best speeds and power.Before I could adjust and fly again, a storm ran us off. This engine has approx, 1-hour total on it including original bench run of 15 min. and subsequent runs in the plane.It certainly ran differently with this prop, and the line pull is astounding. Maybe next time I can get it adjusted. Any sugestions apprec. Ed

What this sounds like now is that the engine does not have enough bench time on it. A plain bearing engine needs a fair amount of time just to break in the shaft. But some of these Tower engines have a nice "pinch" at the top. Then when I drop the sleeve 5 to 7 thousandths or more (depending on tolerances) the pinch gets tighter. It is not uncommon for these engines to take as much as two hours of break in before they really begin to run the way they should. The break in needs to take place at opereating temperature, which means normal rpm, but maybe a little less load at first. You are zeroing in on it now with 5% nitro and 22% oil, but if it froze up, it probably wasn't the shaft, but the piston that froze at the top of the cylinder. If you have a tight pinch on top, try putting a bit more bench time on the engine before putting it in the air. When running the engine on the bench you can monitor it at all times and keep it from going too lean (no lube) or too rich (not hot enough for the cylinder to expand). Try putting another hour on the engine on the bench, then take it out and fly it. At this point you should see quite a difference in the way that it runs and you are going to be pleased with it.

I've got a Tower 40 with an RJL diesel head on it. I havn't gotten it into an airplane yet, but running on Davis Plane fuel and set 1/4 turn rich and a little undercompressed (like I would set it to fly a stunt ship) it turns a Zinger 13 X 5 at 9,200 on the bench. Isn't that about what an ST 60 will do?

The Tower engine (40) that I just bought for the P&C toreplace the P&C in my OS has the shaft to case fit so tight that it actually binds when I turn it over even with the P&C removed. In my opinion, that is WAY too tight and could cause galling of the case bearing. I also found that the thrust washer doesn't run true. It causes the prop to wobble when tightened down.
Denny

Interesting, because I have never run into that. I always reassemble by putting the shaft in first using Marvel Air tool oil for reassembly. I then put the thrust washer on and check for front to back "slop" and also spin the shaft to see that it is free. I have never let one out that wasn't. I have had two engines--none of them tower--where the sleeve to case fit was too tight. A different sleeve fit fine so I knew it was the sleeve that came with the engine. These I turned down to get the proper slip fit before reassembly. At any rate, his shaft should not have been binding because I would have checked that. If the shaft is too tight and it is the bearing, not the shaft itself, this is an easy thing to fit, but, quite frankly, if I felt the shaft was off I would return the engine. I returned a batch of OS engines once. They weren't too happy with me, but I didn't like the piston/cylinder fit and wouldn't accept them. They did replace the engines.

I always check things out before I do anything so if I find something I don't like that isn't easily correctable I can simply return the engine.

Sorry Leonard, I didn't know that the engine came from you. If I had paid attention, I'd probably have known. Yes I know you would never let one out like that. Neither would I nor the silver Foxx. I talked with him, and he said that he had run across a couple of the thrust washers that didn't run true, but no shafts as tight as mine was. HMMMM
Bigiron

Leonard,

I didn't understand Denny's comments to mean that the engine that he just bought was one that had come from you. Did I miss something?

Old Sourdough

Yes OS, You missed something. I was talking about the guy's engine that locked up, and related it to the condition of one that I had just received from Tower and I didn't realize that he had gotten his from Leonard. I know that Leonard would never let one get out of his shop as tight as mine was.I thought that the guy had just got his from Tower.
Did I confuse you enough now??
Bigiron

BigIron wrote:

".........Did I confuse you enough now??"
==============
Ayup. But we're having a heat wave...above 70°F, and my mind wants to go into your basic slumber state.

After mulling over what happened on Wed., I am more concerned than ever, not about the eng., but what may have caused the lock-up. My flying buddy, (the one running the OS), said that he could not see any smoke trail on either of these runs, which REALLY concerns me. This was a brand new gallon of fuel,but I have not used this kind before. Leads me to believe the oil content may not be as advertised.I had occasion to talk to Randy Smith today about an order, and mentioned what happened yesterday. His reaction was that the fuel mfgrs have a tendency to, well, be less than than accurate with their claims re oil content. This can't do your eng. any good. I believe that you are recomending as much as 25% or more lube. The more I see various eng. run, the more I am inclined to agree with you. I'll probably add some more castor to this gallon, maybe to all of it.

My personal opinion for what it's worth, is, If there is no smoke, there is not enough oil. Some time back, I opened a new case of fuel from the company that I had been doing business in fuel for many years and had had NO trouble with their quality of fuel. All of a sudden ,I started having trouble getting a good needle adjustment and the engine tended to run away at the later part of the flight. When I got to looking for reasons, I noticed that there was very little if any oil on the wing and fuselage from the exhaust (there used to be gobs of it) So, I added four ounces of castor to what was left of the gallon (alittle over three quarts) and immediately the engine ran much better, so I added another four and it started running like it had before I went to the new case. Also I started getting oil down the wing and fuselage again. I added eight ounces to each of the other three gallons of that case and have since burned it all up with no more trouble. I guess that shows that occasionally even the best and most consientious of manufacturers can err. You might try a tank of fuel with a little more oil and see what happens.
Bigiron