The International Cessna^® 170 Association

In prep for our October annual Leroy, my airplane partner and I changed the oil in the 170, It has gotten to the point in our lives that the 170 does not get flown enough but to do one oil change a year. When we pulled the screen, it was full of metal. We immediately went into denial. Cleaned the screen and did not keep any samples and disposed of the oil without further investigation. Later, the next day over coffee, I mention to Leroy we had a lot of metal on the screen. He said "yes there was, I wondered if you saw it."

We decided to fly the 1 hour to our annual and then maybe another 4 hours and pull the screen to see what we would see. Annual went as it always does and we even mention the metal to him. He said fly it a few hours and pull the screen and see what you see. And so the plan was in place. As it turned out, on our return to home base we noted oil dripping from the screen crush washer. The following day we pulled the screen with 1 hour flight time to replace the crush washer and recalibrate our torque wrench for the installation. And there it was, more metal. Not nearly what was there from the past change that had 35 hrs on it, but much more than we should see from one hour. A few of the flakes several times larger than a pencil lead. There was fine ferrous metal which actually did not concern us so much and shiny plating that was non-ferrous. It was the plating that had us concerned.
We decided at the least a few cylinders would have to come off to allow further examination. We choose #1 and #3 for no particular reason we will admit. Both cylinders looked great. Connecting rods, bearings pistons and wrist pins, cam and followers that we could see looked great good. It was decided to pull cylinder #5 so we could examine the front of the cam. And there it was. Two cam followers and a cam lobe on its way to perfect roundness. The engine was coming apart. We congratulated ourselves for being so smart taking the third cylinder off. But on the way home I realized we still hadn't found the source of the non-ferrous metal in the screen.

Today we finished the tear down. Here is the bad piston pin cap. You can see how a skin of thin aluminum was flaking of accounting for the aluminum we found. Here are 3 of the 4 cam followers which are obviously bad. The one obviously worn cam lobe. The main and rod bearings were worn very thin as can be seen on this example with cooper showing through. What can the logs for this engine tell us. The engine is a '58 0-300A taken off a 172 in 1961 with 181 hrs for a prop strike inspection. It was rebuilt will all new parts including the crank and then installed on my 170. At 1016 TTSN and 834 SMOH the engine was given a top overhaul with 6 cylinders, pistons and piston rings .015 over, valve springs and all the other cylinder head parts necessary.

At 1548 TTSN, 1367 SMOH the engine was again given another top overhaul with the cylinders repaired as necessary and also the connection rod bearings, bushings and piston pins where replaced.

At 1646 TTSN, 97 hours later an impulse coupling let loose into the engine and the bottom end was torn down. New crank, cam and bearings and reconditioned followers where used. As no cylinder work or inspections where logged at this time it could not have been a major overhaul but it was not long till that is what it was called in the log. In fact every year since 1978 it has been reported as such.

Fast forward 39 years and 1715 hrs with remarkable trouble free running and no real work other than the occasional mag rebuild. The engine now has 3361 TTSN, 3180 SMOH that could be called a overhaul and 1715 since the IRAN of the bottom end.

The cylinders we took of, which were running just fine and actually look pretty good, have 2345 hrs since they were topped the first time and punched out .015 over. We have no idea if these where the original cylinders to this engine in which case they have 3361 hrs. No one takes new cylinders and punches them out so these cylinder have much more that the 2345 logged in the book. We measured one of the bores and it still measured in service limits. We're looking at new cylinders for the overhaul.

As we tore down the engine I notice something strange in the prop flange. It did not have a welch plug but instead a c-clip holding a piston in place. Yes the "new" crank installed 1715 hrs ago is for a C-145-2H or 0-300B. Hmmm. Leroy and I always wondered what happened to the crank for the 0-300B case we have with the aircraft spares. I think we found it. Good thing our spares also include a 0-300A crank from the spare 0-300A case we have. We'll have them both checked out and use the 0-300A crank which is correct for this engine if we can. BTW we also have a spare 0-300C/D crank supposedly new in the box. I might have to talk Leroy into selling this to help pay for the major on this engine..... fat chance.

The last thought on this engine. 1715 hrs ago it had new bearings installed. Most were found pretty thin. We often hear the bottom ends on these engines will go 3000 hours. Based on what I see in this engine, no way.

Sucks.

What's the thought of just repairing the motor with required new parts and putting it back together again?
Not really an overhaul but just enough to get it back in the air.

It would be uneconomical in the long run just to repair the engine as the gears have eaten some of that metal also . Personally it would be a full overhaul for me . Also check that sump for corrosion and gunk.

David, we have thought long and hard about that believe me.

I missed a few costs such has cleaning, checking the case halves. Here is a quick break down using Aircraft Specialty pricing. I really like Aircraft Specialty having used them 3 times already.

There are some assumptions such as we will have to grind something on the crank and we will have to grind a cam. We already own a cam we think can be ground (not the one that just came out of the engine)
There are a few parts or services I did not include such as rockers and rocker shafts and thrust bearings. I also don't have thru bolt nuts or any common AN hardware for the case.

We will inspect our mags, carb, generator and starter.

As you can see saving about $1700 on the stuff Continental says we now have to replace that the overhaul manual doesn't and not calling it an overhaul is not worth the savings. We may have considered it if we felt we could reuse our cylinders as that would lower the cost significantly.

Actually the sump looks remarkably good. BUT one reason it looks good is there is two small areas that have what is probably an illegal epoxy coating. This will have to be investigated more closely but it looks like it covers some very small creators. They do not go all the way through.

BTW this repair was likely done in '61 as my partner is the last one in 1977 after that to have the sump off He wouldn't have done it.

If you have to buy six new power packs, yeah - you're into an overhaul.

I thought the damage might be limited enough to replace a few parts, clean up the bottom end and get a few hundred more hours out of it before doing the motor in.

Ok, lets look at the oil pump and see what's chewed out there , how much back lash in the gears etc . Are you going to x.ray the crank and other associated components ? Some of the PMA manufacturers make a better jugs than continental . This came to light recently when the original jugs on the O-300 were cooked and replaced with Superior brand[i think???] I test flew the aircraft and WOW it appeared to have more grunt for the gallon of fuel used. I had flown the aircraft [172] previously and flew like a dog.

Yes, all parts will be checked for cracking and condition. That is what the charges are for in the list. The oil pump looks good. All parts of course need to be investigated closer. But other than the cam and followers and piston pin caps, all looks good.

Cylinders are actually a little disappointing. There seems to be very little choice today. Basically Continental old design and new design. Both steel. Can tell you what the difference is. Superior also seems to have a cylinder but it seems no one has any stock. That's about all I've found.

Bruce sorry the Continental has got to have major surgery. You guys have got to do more flying. Get it all back together and a trip to NM in July will be good for both the plane and its pilot Are you and your partner going to do the reassembly under the watchful eye of your A&P or are you going to have him do a turnkey OH for you? Good luck whichever route you choose. Go big GREEN

Bruce Fenstermacher wrote:Yes, all parts will be checked for cracking and condition. That is what the charges are for in the list. The oil pump looks good. All parts of course need to be investigated closer. But other than the cam and followers and piston pin caps, all looks good.

Cylinders are actually a little disappointing. There seems to be very little choice today. Basically Continental old design and new design. Both steel. Can tell you what the difference is. Superior also seems to have a cylinder but it seems no one has any stock. That's about all I've found.

Are your cylinders so far gone that they need replaced? Could they be freshened up?

Frank, the plane will fly again. It may be 6 months. Partly because winter is about on us and our plane is tied down outside. There is no hanger. We'd have to disassemble it and trailer it to a hanger.

I was not planning to fly the 170 to NM Just to far to do it cost and time wise. It will be the big silver tube for Teresa and I this coming convention.

bagarre wrote: Are your cylinders so far gone that they need replaced? Could they be freshened up?

Yes David anything is possible. However, realizing these cylinders likely 56 years old and have 3380 TT on them, is that a wise move. I'm thinking these things have to crack sooner or later. Probably sooner.

Sorry to hear about your engine Bruce. We are pulling my motor off the plane this week for a tear down. I was able to get six new Superior cylinders from AS a few months ago. Had to wait about a month for the backorders to come in. Mine will be a full overhaul. I plan to start a thread on the build once I get some pictures going.

Come on guys, all about 170's