Q: I have a 1977 Piper Lance, which has 1,800 total time on engine and airframe since new. The engine is now starting to consume excess oil, about one quart every hour or so.
I’m wondering if it makes sense to hone the cylinders and replaced the rings versus an overhaul?
I do not really know much about engines, and really cannot afford the cost of an overhaul, so I’m looking for a fix to get another 200 hours out of the engine to get it to TBO.
Compressions at the July annual were 74, 76, 78, 77, 77, 77. The underbelly of plane is oiled. There’s also a few drops of oil under the engine when sitting.
Todd Ciavola
A: Todd, your particular situation is one that many others have been confronted with in the past and I can assure you that many more will be in the future, so let’s look at the options.
Without knowing any of the engine’s history other than what you have provided in your email, I’d be inclined to approach your decision depending on the answers to a few questions.
If the hot differential compression readings are continuing in the range you mentioned, I’d be inclined to continue operating the aircraft as is. If you reference the Lycoming Operator’s Manual for the IO-540 K series engines, you’ll notice that the maximum allowable oil consumption for this model is one quart per hour at rated RPM.
Even though you are nearing that amount, and acknowledging the fact that the consumption will never get better, you’ve still got a normal operating engine at this point.
What type and weight of oil are you presently using? There is a slight chance that if you are using a multi-viscosity weight oil, you may improve oil consumption slightly by switching to a single grade Ashless Dispersant oil of the proper weight as set forth in Lycoming Service Instruction 1014 M.
Unless you are aware of some other engine health issues, I’d say this may get you the additional time you’re looking for.
The next question is what are your plans for this aircraft in the future?
Depending on how many hours you fly a year, the 200 hours you’re looking for out of a top overhaul could take a couple of years of your typical operating habits.
It all boils down to a money issue: Do you decide to do nothing now — which could be reasonable — or do you go for the top overhaul?
My suggestion is that you make some inquiries from a few highly respectable, well-known facilities that are capable of doing a good top overhaul. Once you’ve got those estimates, you can compare that amount against what it would cost for a field overhaul or a factory overhaul since a factory re-manufactured engine may be out of your price range.
If you intend to sell the plane within the next two to three years, then maybe more serious consideration should be given to the factory engine approach. From my experience, when selling an aircraft with a low-time factory engine, it’s quite common to recoup the money you’ve invested.
The other issue here is the fact that prices very seldom, if ever, go down and no one can guess where prices will be in a couple of years.
So, I believe you have three options. A little further research on your part should provide you with the most logical answer.
- Continue to operate the aircraft while closely monitoring any sudden change in oil consumption,
- Check closely the cost for a complete top overhaul, which should take you well beyond the 200 hours you mentioned you were looking for, or
- Consider swapping out the engine for a fresh factory overhaul, which would certainly increase the total value of your aircraft.
Unfortunately, I can’t make the decision for you, but hopefully I’ve provided a few things for you to think about so you can come up with the correct decision for your particular situation.
I like that you said that using viscosity weight oil, has greater chances of higher consumption. My friend likes working in his car to keep it working at its best performance when driving it. Thank you for helping me understand the importance of using the proper weight oil.
Great advise Mr. Klaus, I think you hit the problem right on the head !!! Everything you mentioned was right on. Nice going..
What level is the oil quantity? If full, two quarts low might reduce the oil consumption.
Manny; good point. These engines were designed in the 1940s, per the U.S Dept of Commerce, ‘Aircraft Powerplant Handbook, No. 107, dated 1949.
It states on page 198;
“…1 gallon of oil for every 25 gallons of fuel, but not less than1 gallon for each 75 horsepower. ”
So, my 300 cubic inch engine, making 175 HP and 52 gallons of fuel, is required to have a 12 quart sump.[ I’ll let you do the math] However if we fill it to more than 7 qts, it blows out the oil until the 7 qt level is reached, within 1-2 hrs.
Newer engines, like the Rotax 900 series were designed to newer standards, and carry 4 qts of oil. Being water cooled helps a lot, allowing tighter fit of pistons and rings.
Our 1961 Continental GO-300 engine, with 1800+ hours on it had oil use climbing past 2 hrs per qt.
We pulled the middle cylinders and found both with shattered #2 rings.
We replaced the cylinders with new TCM cylinder assemblies and we now have oil use at 5-6 hrs per qt.
Continental had revised the ring gap on the #1 and #2 rings from 0.013 inches to 0.022. The tighter gap was causing the rings to seize and break.
With your engine having that many hours, I’d advise on buying new cylinders from TCM. The cost difference between rebuilding you old cylinder and new is about $200; and you get phosphate coated pistons, new valves, springs and guides. You will need to reuse your rocker arms and shafts. Don’t damage these since new parts are $300-$400 each…
I would definitely borescope it before removing cylinders.
Look over the entire engine for signs of external leakage. The push rod seals and retainers, prop shaft seal and those of the accessories tend to leak over the years anyway.
The breather tube is probably full of oil mixed with moisture gooey gunk. Remove the whole breather tube assembly and clean it all out. The internal pressure of the crankcase needs to be very low and not pushing oil past 1800 hour worn valve guides and other orifices. Look at the manifold pressure gauge, it’s a low pressure, especially when the power is pulled back for decent. High crankcase pressure goes up the push rod tubes to the valve area and pushes past the intake valve guide to the much lower pressure intake manifold. Excessively worn exhaust valve guides will also produce pressurizing of the rocker arm intake valve area.
Common problem with engines that have lots of years of use. The manufacture recommends the engine be overhauled each 12 years. Things like plugged breather tubes is one reason why.
When reinstalling the breather tube be sure to have the open end in a low pressure location. The angled cut in the end should be opened facing aft. Do not have it face forward and pressurize the crankcase.