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Sep 05, 2018, 07:42 AM
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Venerable K&B .35 Stallion CL/FF Engine Clean Up

I'm always on the lookout for good condition control line engines, especially in the .29 to .40 displacement for older technology cross scavenge engines of 30 to 70 years ago. Several months ago in June, I got from E-Bay what I thought was low time K&B .35 Stallion CL/FF venturi engine.

The seller mentioned the engine had occlusions that were typical of the original castings some 60 years ago. A poster in another forum pointed out that engine could have possibly been sand blasted recently. The great extent of the irregularities in the surface appeared to be caused by surface corrosion versus claimed occlusions. (Occlusions are basically trapped air bubbles or fleck impurities in the hot pour casting.)

Normally during bead or say walnut shell blasting, the manufacturer does this prior to assembly. Then cleans the crankcases of all dust prior to assembly. When I took a closer look to the engine, there was a small amount of residual aluminum flecks beneath the cylinder fins. The extra clean and bright aluminum exterior seemed to give credence that it had been carefully sand blasted. The screws on top, normally either finished in galvanized or black oxide appeared to be sand blasted. There was no evidence on the fins, so it is possible this area was masked during grit spray. The "new in box" finish just seemed to be too good to be true.

Two days ago, I started to disassemble the engine. Any sand or grit that got into the engine could only spell harm and thus needs to be washed out. I removed the back after the screws by prying with my Leatherman tool knife blade. There is a rusty grit inside resembling rust particles.

Then I removed the head screws. They did not come out easy. Once broke loose, like they were Locktite'd down. One 4-40x1/4 screw broke at the screw head, fortunately allowing me to remove the stud with needle nose pliers. Removing the head required carefully wedging the edge of my Leatherman knife blade. I worked slowly, tapping on the back of the knife blade with my needle nose plier handles to work my way around the perimeter of the head, until I could remove the head.

There is heavy rust inside the top of the cylinder combustion chamber and along the edge of the aluminum head. This engine was exposed to water or to a high humidity atmosphere.

The crankcase threaded prop shaft, nut and prop washer look like new without rust, so I can't quite make heads or tails yet about the seller's occlusion story. Was an NOS set installed?

Since I was the only bidder (I wonder why? ), I got this engine for a song, $20.00 US plus $10.00 US shipping. Rust is in the combustion chamber, not the cylinder area the piston rides in. I think I can salvage this engine and make it into a good runner. I'm going to soak in hot anti-freeze and see if I can't free the cylinder liner from the crankcase. Otherwise seems to have good compression. The crankshaft turns reasonably free without binding or looseness. I have stainless steel 4-40 socket cap screws to replace the originals. The prop nut, washer and shaft appear to be new and rust free and hardly any wrench marks. These may be new parts.
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Sep 05, 2018, 07:47 AM
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A day passes soaking the partially disassembled engine and parts in hot antifreeze in my Polyperk Coffee Percolator. (In warming mode after boiling, its temperature is in crockpot range.) I took my Leatherman knife blade and by gently tapping on the crack between aluminum crankcase and steel cylinder all along its perimeter, worked the cylinder loose. Then with gentle prying and further tapping with a putty knife, I edged the cylinder until it fell out.

There is surface rust on the cylinder port and mating surface area. I was able to scrape most of the surface rust from the cylinder inside top that forms the combustion area at TDC. Darkening of the piston top is surface rust. There is rust on the back side of the crankshaft opposite the intake hole. Most of the rust was removed when the crank was turned.

I scraped away the gasket on the steel cylinder, both bottom and top. They appear to be the old graphite paper ones, similar to the car head gaskets of the early 1970's. Then I put the separated parts back into the percolator's antifreeze for further soaking before final clean up and polishing.

An interesting fact with this engine is that it has a steel piston pin full length without any pads. A friend and long time experienced modeler with this engine recommended that I round the pin edges and polish the ends, because the pin can can wear against the cylinder gouging it, ruining the cylinder. Parts for this earlier "economy engine" are hard to come by. Connecting rod is unbushed solid aluminum. Running this engine with a slug of healthy Castor in the fuel is a must. Crankcase has a crankshaft bronze bushing.

This appears to be a low time engine that was probably only bench run at the factory. Was it worth my $30? At this point I think so. Rarely does one get a low time engine at this cost. Most seem well used, although they may have some life in them. It's current condition looks worse than it really is. The rust will clean up as I continually work on it.
Sep 08, 2018, 10:06 AM
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I did things a little different in that I added a small quantity of water to the antifreeze in the coffee percolator since I was running low. Now, the engine is darkened similar to a few engines with dark aluminum finish, like the Sanye AP .09, some Enyas and MDS engines. I removed the items, started scrubbing with dish soap and a green Scotchbrite pad. The outside of the cylinder that sits inside the crankcase has heavy rust, similar to the inside top where the piston at TDC sat for a long time. It is not enough to severely weaken the steel or severely pit it, but it is there. This piston shows some rust outlined where it was exposed to the exhaust port. I got most of it off with the green pad, will later use fine steel wool to remove the remainder on both the steel cylinder and iron piston.

The head gasket is well stuck to the aluminum head, wonder if the owner used some form of gasket shellac. Will need to do further work. I did a test case of applying and rubbing with a paper towel Mothers Mag and Aluminum polish on one side of the bottom of the crankcase. The brighter aluminum is coming back, with a mild aluminum gloss it looks like a die cast factory finish. I'll be able to restore the crankcase, back and head to natural aluminum color and get rid of the odd sand blasted finish with some elbow grease.

With it soaking and cleaning the aluminum exterior pores in the so called casting occlusions has made me see more clearly that this engine was subject to a damp environment. For all I know, it may have been a field find near an old model flying field. The head and crankcase on the intake bypass, left side of the engine have similar continuous corrosion pattern from crankcase to head. Parts are cast separately, so if there were casting occlusion imperfections they would not look uniform between pieces.

It is now more clear that at one time, it was in fact mounted to an aircraft. The diameter outline of 4-40 lock washers show on at least 2 locations, one on each side. The sand blasting must have removed enough that the other two holes look as though they were untouched.

Now on its way to recovery, this bride of Frankenstein will live again.
Sep 08, 2018, 11:47 AM
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Great thread! If you want a brand new Stallion never run for $40.00 including shipping go here:

I have two Stallions with one NIB otherwise I'd by it ASAP.

Sep 08, 2018, 02:00 PM
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Originally Posted by knuckleball
Great thread! If you want a brand new Stallion never run for $40.00 including shipping go here: I have two Stallions with one NIB otherwise I'd by it ASAP.
Thanks, knucleball for the tip, I'll check it out.

The slightly diluted antifreeze discolored the engine aluminum exterior parts a uniform darker color. In real life they look better than in the photos. After the soak, the so called occlusions, which are surface corrosion is more evident. In one photo, the surface polished with Mothers Mag and Aluminum Polish cleaned up nicely, however, I'm almost tempted to put the crankcase back in the antifreeze and let it re-discolor.

The crankshaft shows signs of rust in various places, but this is cosmetic. It will run fine as-is.

The cylinder has its share of rust, but where most rusted is not located in the piston travel area. I was able to remove the gasket fragments and some rust from the top and bottom fins using a utility knife with sharp box cutter blade. My suspicion of gasket shellac was wrong, the "glue" is simply impregnated rust and the affinity of the ancient gasket material for the machined metallic surfaces.

You can see from these photos where the engine piston rested at top dead center during much of its "abandoned and unloved" life. Evidence of surface rust outlines the cylinder bypass port on one side and the higher exhaust port on the other side. Both top and underside of piston has surface rust, but this is cosmetic.

The head shows evidence of rust in the mount screw holes.

Now that I have had a chance to further forensically examine this engine, the circumstantial evidence reveals that the seller's story of occlusion imperfection occuring during the manufacturing casting process was stretching the truth a bit.
All is not lost, though. Franken-girl will live again!
Last edited by GallopingGhostlr; Sep 08, 2018 at 02:09 PM.
Sep 09, 2018, 06:40 PM
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Today, I did further cleaning up of the engine parts using fine steel wool. This removed the sand blasted finish from the aluminum parts, imputing a fine brushed metal finish to the aluminum. I could stop here, or I could further remove the brushed look to polished with Mothers Mag & Aluminum Polish. The steel wool also removed the rust residue from the steel parts, cleaning them up considerable. Now, with the majority of the rust removed, once reassembled, oil will take care of the rest to prevent further rusting. I think you will see that the parts cleaned up quite well.

Last photo of the piston, you'll see a steel wool "hair" strand. I will blow all engine parts with compressed air prior to assembly.

The engine may look worse for wear from the photos. Actually it isn't as bad as it looks. The photos are up close, magnifying flaws. To the naked eye the engine looks much better.

The crankcase roughness does reveal the extent of the effects of weather upon the metal finish. This engine may have sat for a while, up to 2 or 3 decades in a midwestern field. If the engine could talk, I'm wondering what free flight or simple R/C aircraft (1 or 2 channel without throttle) it might say it belonged to. In the mid 1960's multi-channel was very expensive, akin to costs associated with flying turbine jet aircraft. Many who gave RC a try would settle for 1 or possibly 2 channels, escapements would be the least expensive. May be it was on a Goldberg Senior Falcon flown without throttle control?

We don't know at this point, but as you see from the photos, it was definitely not manufacturing defects but rather corrosion that played a major part in marring the exterior finish.

And, after closely looking at the piston pin, the ends are radiused and polished, which should help it from scoring the cylinder walls since there are no pads at piston pin ends. Without any serial numbers, I can't tell whether this was an earlier or later Stallion. Also I learned from Peter Chinn's engine tests (see Sceptre Flight) that if one removes the plastic venturi insert, suction is still strong enough that the HP gain will be close to the engines it competed against, the Foxes and Testor McCoy Red Heads.

With the plastic venturi insert in place, it should be a fine engine for .35 CL aircraft toward the lower end of wing area, such as the Sterling Kit S-1 Ringmaster. The extra suction should prove it to be a very bullet proof engine for that aircraft.
Sep 09, 2018, 11:47 PM
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Here's what the engine crankcase looks like now that I have applied and rubbed in, then polished with a paper towel - Mother's Mag & Aluminum Polish. Final step was to use a clean paper towel, which then really adds the shine.
Sep 14, 2018, 08:09 PM
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Stallion is done except for final tightening of screws and fittings. I deviated a little from the historical presence of this engine by painting the head with Duplicolor High Temperature Ceramic Engine Green paint. I know that this engine followed the green heads by at least a decade and was left in plain aluminum.

However, seeing that it suffered as an unloved child to corrode, thought that with the appearances of surface corrosion, it could use a little dressing up. This certainly beats telling people that it suffers from casting occlusion defects. "Why, didn't you know the first Stallions out of the factory were green? This is an early one!" (Actually, one lie to cover up another one never really worked.)

To clean the head of sand blasting was too much work. A slightly roughened surface for paint sticking lent itself to me thinking, "Why not?"

To expidite, I used Permatex Ultra Grey Maximum Torque Gasket Maker to seal the cylinder and head. This holds pressure well and can stand the temperatures. It is also used on motorcycle engine cases and heads. If I find that the compression is too high, I can roll my own gaskets or seek sources later.

I think it actually came out quite well. So that the RTV gasket material could bond, I did not use any oil and assembled the engine dry. Once it cures and I torque down the screws, I can liberally oil it and such will fill the interior voids and surfaces.

Now I'm letting it sit and cure, hope to bench run in the near future.
Sep 16, 2018, 09:24 AM
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Yesterday I torqued down the head screws, mounted a 10x6 prop then applied liberal amounts of 5-30W motor oil to the exhaust port and venturi opening. Flipped the prop and rotated the engine through all angles to get the interior surfaces coated. It has like new engine compression.

The back plate has light wear on it from the nylon crank spacer rubbing against it along with Castor residue on interior surfaces of the engine before I cleaned it, so it was run in the past. I'm stoked. What first appeared to be a mistake in buying has turned out a decent engine anyway.

When I locate where I stored my engine stand, will do a run up report.

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