Overhauled engine means relearning how it operates

QUESTION: First, let me say thanks for your excellent column. It’s always one of the first things I flip to when GANews arrives. In my 1947 PA-12 (I’m new to the plane, purchased after complete restoration), I have an O290-D2B with about 18 hours on a new limits field overhaul, including new exhaust valves, seats, guides and springs, rings, pistons, lifters, oil pump and gears, inspected and reused crank case, rods, crankshaft and camshaft. I have installed a spin-on oil filter kit and my crankcase vent/breather line runs below the cylinders.

My questions:

1) How much oil should be put in the engine? All the documentation I got with the plane, history, records and advice from other 0290-D2 owners says fill to six quarts and add at five. But the Lycoming Operator’s Manual indicates the oil sump capacity is eight quarts.

2) It seems to have too much oil blowing out the crankcase vent/breather line. I read your article of Aug. 20, 2004, indicating camshaft pn 74167 (bolt-on gear) is the only camshaft that should be used, so I checked the documentation and inspection tags from the overhaul and they indicate my engine camshaft pn is 74166. Is this a possible camshaft for my engine? Or is it more likely they made a error writing down the part number?

Other field advice says to relocate/run the crankcase vent/breather line over the top of the engine. Any thoughts?

3) Early on, the engine had a #3 CHT overheating problem at full power (high 400s, but EGT was OK). This was traced to a sticking intake valve not seating and was corrected. Now the engine runs nice, but on occasion at full power the #3 EGT now rises to 1,470° (and will keep rising) while the others are at around 1,335°-1,390°. The only remedy is immediate power pullback to about 2,000 rpms. But this high EGT only happens on occasion. Oil temp stays at 190° max and oil pressure is at 80 psi. I plan to do another compression check at next oil change but I’m really puzzled about this erratic EGT. Any ideas ?

Roby Denman

Boca Raton, Fla.

ANSWER: Roby, I really appreciate your kind comments regarding the articles. It sounds to me as though you’ve got a great aircraft and you’ve asked some good questions, so let’s see if I can offer some good advice. First of all, the O-290-D and D2 have an eight quart oil sump. The documentation you got with the aircraft was probably based on the past owner’s historical data he collected over many hours of operation of the engine. It very well may have been suitable for the operation of the engine given the way he operated the aircraft and the specific oil consumption at that time. All of that data went out the window when the engine went through its most recent overhaul, which sounds quite extensive.

What you have to do now is learn how the engine is going to react with all of the new components. I’d suggest you service the oil in accordance with the Operator’s Manual and very carefully check your oil consumption and how much comes out the breather. You may find it blows excessive oil out the breather when serviced to eight quarts, so then I’d drop it back to seven quarts and check it there. I think you’ll find starting there and adding a quart when it goes down to five or six quarts on the stick and you’ll be ok. What we must use caution with is that the engine doesn’t breathe or consume oil at a high rate and we end up running out of oil before we run out of fuel on a long cross country.

Regarding the camshaft and the inspection tags, you’ve got no problem with the 74166. That particular part number is of the camshaft only, but after the locating dowel is installed, it then becomes a 74167 camshaft assembly.

When it comes to routing the crankcase breather line, I’m afraid I’ll have to leave that to someone who knows the specific aircraft installation better than I do. You may want to contact the Cub Club and see if they might have some experience with different routings. I’d use caution routing it over top of the cylinders though because that’s a cold air area and depending on your location, you may freeze the breather up and then you’d have real problems. At least with the breather line mounted under the cylinders you’ve got nice warm air in the area.

The non-consistent high EGT on number 3 cylinder sounds more like a probe, wire, or gauge problem to me. If it goes to 1,470° and keeps climbing, that’s a pretty high number for a normally aspirated engine and could indicate an induction leak. Just to be certain, I’d recheck the induction system, paying close attention to the intake pipe gasket, flange, and the tube where it enters the sump. If you have access to a manifold pressure gauge you could hook that up. If you notice a high MAP (12 inches or greater) at idle (500-700 rpm), that could indicate an induction leak. I’m not sure it’s worth going through all the trouble to do this since you say it’s not constant. Is there enough wire to just swap the lead from the #1 to the #3 and see if the oddity stays with the cylinder or the wire? Remember, this will only tell you if it’s the wire or not, but if it’s the probe, then you’ll have to swap that too.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.

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