K&B .35 Stallion Restoration

[ghostler]

Back in June, I purchased a K&B .35 Stallion FF/CL engine for one of my profile control line aircraft. Engine appeared to be clean except for casting defects mentioned in the very brief E-Bay description.

In a post in another engine forum, where I showed photos, one poster 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.

About a week 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 soaked it in heated anti-freeze for 2 days, freed the head from the cylinder and cylinder from the crankcase by careful prying prying with my knife blade and after, a putty knife.

[ghostler]

The slightly diluted antifreeze discolored the engine aluminum exterior parts a uniform darker color. Using fine steel wool, I cleaned the aluminum exterior surfaces, then removed the brushed look using Mother's Mag & Aluminum Polish.

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

This engine may have been a run away free flight or 2 channel R/C without throttle control. Much of the internal corrosion is near the cylinder gaskets at top and bottom. It appears that moisture was wicked in from these locations. The engine stopped at top dead center based on the rust in the cylinder combustion chamber and crankshaft at venturi, so there is minimal rust in the crankcase cavity. This most likely would have been a stopped location during a crash.

Now that I have had a chance to further forensically examine this engine, the circumstantial evidence reveals that the engine was corroded by water exposure possibly as a field find and not by occlusion imperfections during the manufacturing casting process.

[ghostler]

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.

[ghostler]

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 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.

[Konrad]

It does look like she took a dirt nap. I like finding Free Flight engines as they normally have good internal part. This is because of the short engine runs there rarely is much damage from lean runs. 

Now a problem I often find is with the connecting rods. That is they stretch and the bores often are out of round. Do you have a set of gauge pins to measure this?

Looking at the parts it looks like there is some distress on the journals. Do you polish the wrist pin and the crank pin? I do polish these, even with brand new engines, with 600 grit. I'm sure you know that with the 2 cycle engine the lubrication of the wrist pin is problematic. Putting a nice 600 to 1200 grit cross hatch on the wrist pin seems to help keep lubrication there.

Does the K&B 35 show Sub Piston Induction? That is does the piston open the bottom of the exhaust port at top dead center (look like the piston skirt is too short)? If so this allows moisture to flow into the inner working of the engine should the piston stop near TDC.

A nice thing about lapped P&Ls is that there often is a layer of varnish on the inner cylinder walls and on the piston that protects these surfaces from corrosion a bit. Ringed P&Ls often don't have this protective varnish.

It is my experience that RTV silicone actually makes a horrible gasket.

What type of anti freeze did you use to clean the case?

What can you tell us about Duplicolor High Temperature Ceramic Engine Green paint? Is this like a powder coat that needs to be baked to fuse the ceramic?

All the best,
Konrad

[ghostler]

It does look like she took a dirt nap. I like finding Free Flight engines as they normally have good internal part. This is because of the short engine runs there rarely is much damage from lean runs.

Much of what I say about its history is speculation. I really don't know for sure. It is obvious it was an environment that exposed it to water moisture to cause parts corrosion.

I doubt if it would have been a free flight competition engine, although it might be used to power say, a sport cabin type FF. For a cross scavenge, plain bearing engine, it is a little heavy at 8.8 oz., 0.2 oz. more than an Enya .35-V TV and 1.8 oz. more than a McCoy .35 Red Head. It is a touch weaker on power, 0.42 HP at 11,000 RPM (see http://sceptreflight.com/Model%20Engine%20Tests/K&B%20Stallion%2035%20%282%29.html). Looking at Peter Chinn's data, I'd probably go with an 11x4 prop for a free flight. It's lower peak RPM tells me that it is probably better suited as a CL stunt engine. Others have mentioned it doesn't do the 4-2 break well, so they run it in a wet 2. (Breaks from wet-2 to dry-2.)

Now a problem I often find is with the connecting rods. That is they stretch and the bores often are out of round. Do you have a set of gauge pins to measure this?

Not needed, bosses are definitely not stretched and I doubt the rod is either.

Does the K&B 35 show Sub Piston Induction? That is does the piston open the bottom of the exhaust port at top dead center (look like the piston skirt is too short)? If so this allows moisture to flow into the inner working of the engine should the piston stop near TDC.

No SPI, again this is in the standard cross scavenge construction patterned after its ancestor, the Torpedo, which also doesn't have SPI.

A nice thing about lapped P&Ls is that there often is a layer of varnish on the inner cylinder walls and on the piston that protects these surfaces from corrosion a bit. Ringed P&Ls often don't have this protective varnish.

True, there was very little pitting on the piston travel area, so whatever Castor protected it.

It is my experience that RTV silicone actually makes a horrible gasket.

Depends on the application and circumstances. I did it because I wanted to get it up and running quickly. As I said before, if I find I need gaskets, will manufacture them.

What type of anti freeze did you use to clean the case?

The standard older style stuff, plus I added this time a touch of water to stretch the liquid to cover the engine (running short, usually I don't do this). However, even the slight discoloring of the aluminum was of no effect. I steel wooled that oxidation off and the sand blasting roughness, then polished with mag polish.

What can you tell us about Duplicolor High Temperature Ceramic Engine Green paint? Is this like a powder coat that needs to be baked to fuse the ceramic?

Can't tell you much because this is the first time I've used this paint. It is not like exhaust paint, it doesn't require heat to bake on. Once I put the engine in service, I'll know more.

[Konrad]

Thank you.

Please let's us know about the paint. Not just how well it holds up against the heat but also how it tolerates nitro fuels.

All the best,
Konrad