Sportster 65 has dark gray oil in exhaust and some binding

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Sportster 65 has dark gray oil in exhaust and some binding

Postby Lardog » Tue Jul 14, 2009 2:48 pm

Hello,

I own 12 to 15 K&B aero and boat engines and have always had great success with them. I have 3 brand new .65 Sportsters (old stock, just never used), and just put one on my Hangar 9 Twist 60.

I ran 2 tanks of Omega 10% fuel through the engine while on the plane to break it in. (It stayed on the ground the whole time.) During the first fuel run, I was running pretty rich (needle valve set based on the Sportster break-in instruction manual), and the were massive amounts of dark gray oil coming out of the engine. (I assume that's from aluminum being honed by break-in.) After that run, compression was very good and the engine was turning more smoothly. I leaned the engine a few clicks for the next tank, and it ran better and with less gray in the oil.

I leaned the engine another click or two, flew the plane for the next tankful, and the gray color in the oil was almost gone. I still had a lot of oil on my plane, but it was pink (the fuel color) and the engine was running fairly well, but still somewhat rich.

The next tank of fuel, I leaned the engine 1 click. Before flying I checked cylinder head temp, and it was around 185 at idle, around 230 at mid-range, and about 275 at full throttle. I flew the plane and the engine ran well and was alternating between two-stroking and four-stroking. (Just what I was going for.) It sounded great, and it was a great, though somewhat tame flight. (It was a break-in and test flight, after all...)

The 3rd flight was with the same needle valve setting, and all was fine for 6 or 8 minutes. Then the engine lost a little power and sounded a little weak. I landed and the engine died as soon as I reduced it to idle speed. I found that very dark gray oil was again covering the airplane. I also noticed that there was some drag or binding as I rotated the engine crank. It didn't feel like piston/cylinder drag, as it didn't change at BDC and TDC. It felt more like drag on the crankshaft. I was able to restart the engine, but it needed a few clicks of throttle (fast idle) in order to overcome this newly-induced drag. I decided to take the plane and engine home and check it out.

At home, I opened the back of the case of the engine, expecting to see where the crank was dragging the case or backplate, but it looked OK. There was quite a bit of oil in the engine, and it was very dark gray. The piston has a somewhat shiny ring around it near the top (top 1/8 inch I'd say) and the motor still has great compression.

By the way, I was pretty easy on the engine during all 3 flights, mainly running between 1/3 and 1/2 throttle with occasional full-throttle bursts. I didn't do any extreme manouvers or vertical climbs which could have over-leaned the engine.

Any idea what is causing the dark gray oil? Is my engine being damaged? What cylinder head temperature should I be shooting for on this engine?

Thank you for your help.

Larry
Lardog
 
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Joined: Tue Jul 14, 2009 11:02 am
Location: Peoria, IL

Postby SteveM » Tue Jul 14, 2009 3:12 pm

From my experience with a K&B 20 Sportster, it takes ages for these motors to break-in properly and mine ran sloppy rich and blubbering goo for well over a dozen tanks. The shiny area at the top of the piston is normal.
SteveM
 
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Joined: Mon Nov 20, 2006 10:33 am
Location: Ottawa, Ontario, CANADA


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