The International Cessna^® 170 Association

This might be interesting to you guys, since this is the same engine that powers most of our beloved 170s. A friend of mine owns a 1960 172, with just under 1,700 hours total time, airframe and engine. In 45 years, it has had exactly two cylinders pulled for re-work. The oil pump was replaced a few years ago. That's been it for the core! This airplane was first owned by Steve Wittman of air racing fame, who also invented the spring steel gear later licensed from him by Cessna.

Recently, a third cylinder started having exhaust valve leakage, due to a worn guide. My buddy decided it was time to major the engine. I'd say after 45 years and 1,700 hours, someone got his money's worth.

I think it is an O-300A, but I'm not sure and didn't think to ask. It has that funky belt-driven vacuum pump, which is original. We pulled the engine and split the case on the bench. The crank looked like brand-new, with no grooves or anything you could catch with a finger nail. Rick Romans in Tulsa will check it out. The lifters looked great to my untrained eye, and so did the camshaft.

The most interesting part was the HUGE amount of sludge in the oil pan. Measured nearly one inch in places...When this engine was new, A.D. oils didn't exist, and weren't widely available until the early 1970s, I think. He installed an F & M filter about five years ago, which at least trapped the gunk broken loose by the modern oils. There was a nice funnel shaped area in the area of the oil drain.

Pretty impressive...I will mention that this airplane has always been hangared. The fuselage was re-painted, but the wings are original, with the 20 inch numbers still present. I still maintain that Continental built much better cylinders in the old days...

I've asked this question before, but it's been awhile. Who out there has the oldest overhauled or original engine? As an aside, I was flying my 1946 Stinson 108 as recently as 1993 on the original Franklin at 400 hours since new, airframe and engine... Russ Farris

Thanks for sharing that story, Russ. It brings up an interesting topic of discussion I think.
Is sludge/gunk in an engine harmful? Is it a good idea to use solvents to remove it or make attempts to "clean" the interior of engines?
We see it all the time. Folks who use so-called "snake oils" and aftermarket cleaners or kerosene or ??? whatever they imagine will do the job.
My belief is that such efforts are detrimental to the long term health of an engine. "Sludge" and varnish that build up inside an engine are not harmful by nature of their static condition. They are not circulating aroung causing damage until someone breaks them loose with solvent and cleaners. In fact, they are coating the non-moving parts and preventing moisture from attacking the base metals and causing rust and corrosion. I believe my view is confirmed by the wise, old advice never to start using detergent oils in an old engine which has always used mineral (non-det.) oil, because it will break up the sludge and send it thru the engine to cause damage. If that is so, then how can using powerful additives and snake-oils to "clean" the interior be any better?
BTW, as a point of interest, back in 1960 so-called "detergent" oils were already common. (In fact, by 1964 multi-grade oils were being promoted in the automotive world. I remember it (SAE10-40)being recommended in the first new car my Dad ever bought...a 1964 Dodge with a push-button transmission. They didn't start using the "W" in the moniker until the 70's tho'.) The multi-grades were the hot, new trend in motor oils in '64.
Even with AD oils, an engine that sits idle a lot will build up sludge that AD oil won't budge. (And reading about it's low time over 45 years, that engine has done a lot of sitting. Don't forget to check the sump just forward of the two drains for possble thinning due to corrosion, especially the forward drain.) It's possible that original O-300 engine was operated on modern ashless dispersant oils most of it's life.

What George said. For some reason, I thought A.D. oil was introduced to the aviation world in the late 60/early 70s, but I was talking to Howard Fenton in Tulsa yesterday on another matter and he gave me a little history lesson. For thoses of you that don't know him, he is the former owner of Engine Oil Analysis, now part of Blackstone Labs. Howard said that the first multi-grade, A.D. oil for aircraft use was developed by Sinclair in 1963; I didn't even know they were ever in the aviation business. After trials in Sinclair's fleet of pipeline patrol, which were highly sucessfull, it went on the market in a major advertising campaign...and promptly flopped. Aviation types are conservative by nature and it took years for the multi-grades/ A.D. oil to gain general acceptance. By then, Sinclair was long out of the aviation oil business having pioneered the modern oils. Howard worked for Sinclair during this time and provided the information here...Russ Farris

russfarris wrote:.....................................................................
It has that funky belt-driven vacuum pump, which is original. ...............................................

Dave, really, I didn't put Russ up to this.....oops, I just remembered that what your airplane has is a belt-driven supercharger. Never mind.

Eric

Oh boy, and I held back when I really wanted to suggest that you upgrade from your 170 experimental to one of BL's evolved 55's! HELLOOOO, obviously it was the funky belt that allowed that engine to last that long. Because of the 180 style catfish mouth nose bowl in front, there is more airflow directed across the cylinders to help keep the engine in that kind of shape.

What engine did they start putting the engine driven vacuum pump on? I thought it was later than the 0300-A (1955), like maybe the D.

Randal

I believe the O-300D engine's vacuum pump was engine-driven off the accessory case-- maybe a pad on the right-angle adapter for the starter?

Eric

For all practical purposes, it was the O-300-D which introduced the right-angle drive for a starter and allowed provision for an accy case mounted vacuum pump. (Technically, all O-300-C engines subesquent to SN 21001 were capable of being so equipped, but it was the D engine which actually left the factory with the standard.)