The International Cessna^® 170 Association

If it was mine, I'd give it a try slipping new O rings in with plenty of lube on them.

I'll have to check the photos from my 2006 overhaul when I get back to California, but I think the through-bolt holes in the case at the split are chamfered for o-rings. Also, I think the center shoulders of the through bolts are precision ground; that's what aligns the case halves. The rough part of the web castings don't necessarily line up exactly, but they don't have to.

Aryana wrote:After disassembling two engines (one C-145 and one O-300) only half of the through bolts were able to come out without splitting the case. After lining them up without any bolts, you can see there isn't perfect alignment between the left/right case halves and the o-rings would catch on a small lip.

Like I said, I'm no expert and just interested to know if anyone has actually been able to successfully remove and replace the center o-rings without splitting the case and how they did it in a way that renders the engine airworthy.

Sounds like a defective case to me.

cessna170bdriver wrote:I'll have to check the photos from my 2006 overhaul when I get back to California, but I think the through-bolt holes in the case at the split are chamfered for o-rings. Also, I think the center shoulders of the through bolts are precision ground; that's what aligns the case halves. The rough part of the web castings don't necessarily line up exactly, but they don't have to.

Your recollections are exactly right Miles. I have a dis-assembled case out in the hangar. The through bolts are chamfered for the "o" rings on a machined raised area that helps align the case halves. I can slide these through very easily. Of course as noted in this thread, is this the right way to assemble the engine ?...no. The question was can they be removed to replace the "O" rings without splitting the case ? Yes.

I had an oil leak at #6 cyl and the engine mount thrubolt which I stopped by removing the mount leg, cleaning the stud where it exited the case using aerosol electronics cleaner. After it dried, I packed Permatex #2 gasket sealant where the stud exits the case beneath the engine mount leg, slipped an O--ring onto the stud, then reassembled the mount leg and let it dry overnight. It worked like a charm at that location.

For looking for an elusive oil leak, Please see my comment in the "Oil Leak" subject above.

Hey guys, I’m hoping you can help me with an oil leak issue. After a 45-60 min flight I am seeing 5-10 drips on the ramp within 5 minutes of shutdown. Oil is dripping onto the inside of the cowl and dripping at lowest point. Also, a fair amount is showing up on the belly of the aircraft and the foot step down posts. I keep the oil level at 5-6 quarts. Freshly overhauled engine.

From what I can tell, the left middle rocker cover may be dripping and maybe the alternative shaft seal. I also have found oil on some of the cylinder head bolts. And some oil coming from the silver looking plug at the bottom of my magneto. I confirmed the gasket joint between the magneto and engine is bone dry.

I cleaned the engine, did a 5 minute run up, then placed in the hangar to inspect with a flashlight. I have 32 pictures on this Dropbox link. Let me know if you are able to view the pictures. Any help would be appreciated. My old engine would drip less than this new one.

Pictures link: https://www.dropbox.com/sh/twew08n8uc81 ... NiiUa?dl=0

mmcmillan2 wrote:Hey guys, I’m hoping you can help me with an oil leak issue. After a 45-60 min flight I am seeing 5-10 drips on the ramp within 5 minutes of shutdown. Oil is dripping onto the inside of the cowl and dripping at lowest point. Also, a fair amount is showing up on the belly of the aircraft and the foot step down posts. I keep the oil level at 5-6 quarts. Freshly overhauled engine.

From what I can tell, the left middle rocker cover may be dripping and maybe the alternative shaft seal. I also have found oil on some of the cylinder head bolts. And some oil coming from the silver looking plug at the bottom of my magneto. I confirmed the gasket joint between the magneto and engine is bone dry.

I cleaned the engine, did a 5 minute run up, then placed in the hangar to inspect with a flashlight. I have 32 pictures on this Dropbox link. Let me know if you are able to view the pictures. Any help would be appreciated. My old engine would drip less than this new one.

Pictures link: https://www.dropbox.com/sh/twew08n8uc81 ... NiiUa?dl=0

You describe what sounds to be a magneto oil-seal/gasket problem….and a rocker-box-cover which needs a new gasket and/or resealed. (Caution: The “Real Gaskets” folks make their rocker cover gaskets out of a “silicone” or epdm type of gasket material…which if “over-tightend” …is guaranteed to leak as the excess torque squeezes/spreads the gasket too much. Do not overtighten those gaskets.

Mark,
I recently helped a friend find an oil leak on his O-320 powered C-172. We were about to remove the sump to replace the gasket as the leak appeared to be coming from this seam. But prior to going to such an extreme we pressure washed the engine to remove any vestige of oil and then ran the engine very briefly at idle with leak detector dye in the oil. Using a UV light like George describes here the leak was discovered at the top of the case leaking from the inboard ends of two pushrod tubes -- far from where most of the oil was visible to the naked eye. It appears from some of your pictures that you have been using a UV light.

Your overhauled engine looks great! Being as it is a fresh overhaul I would think the overhauler should take some responsibility for fixing the oil leaks. One would hope that they installed all twenty one o-rings shown in figure 3 of the IPC and followed the instructions in fig. 3-5 of the M-O manual regarding crankcase threading to the letter.

A lot has been written on this forum about using Permatex and other sealants. The Continental M-O Maintenance Manual writes in bold lettering, at least eight times:

WARNING
Do not apply any form of sealant to the crankcase cylinder deck, chamfer, cylinder mounting flange, cylinder base O-ring, or cylinder fastener threads. The use of RTV, silicone, Gasket Maker or any other sealant on the areas listed above during engine assembly will cause a loss of cylinder deck stud or through-bolt torque. Subsequent loss of cylinder attachment load, loss of main bearing crush and/or fretting of the crankcase parting surfaces will occur. The result will be cylinder separation, main bearing movement, oil starvation and catastrophic engine failure.

See also NTSB accident report NYC03FA043 and NTSB report NYC95FA049. Sealant clogging oil passages is another reason not to go crazy with RTV as this NTSB report shows. This is not to say that sealants should never be used. In Table 3-4 Continental lists approved sealants and where they can be used. Table 3-6 lists approved adhesives. Appendix C-9 and C-10 give instructions on using Gasket Maker.

Were your accessories -- magnetos, starter, alternator -- overhauled at the same time as the engine? If so, they should have new seals. If not, here are some p/n that may help.
-It appears you have Slick 6364 magnetos. If there is oil contamination on the inside of the mags replace seal p/n M3062.
-Your Ford alternator uses two seals, drive seal p/n ES4142, and an o-ring seal ES4140.
-I see you have a Tempest oil filter adapter. As I'm sure you've read, there have been a lot of issues with this leaking. This is the first place I would look for a leak.
-The tach drive adapter seal has been another common source of oil leaks, often it seems to be installed backwards. There are two style of adapters; the old style shown in fig. 9 and the new style shown in figure 10. My old style adapter has the part number cast into it -- p/n 35342. It had seal 21163 installed. The IPC p/n 640087 has been superseded to 642714. Alternative part numbers are CR3751 or 3752 which is made from Viton. The new style adapter uses p/n 641533 which I think crosses to National p/n 50197S. It is a smaller diameter than the old style seal.
-The gasket under the alternator/generator and the tach drive adapter, p/n 36100, seems to be a frequent source of leaks. Often this is because mechanics, shade tree or otherwise, cut the gasket in two so they don't have to remove both the generator/alternator and the tach drive adapter to fix one or the other. As you can see in the attached picture, there is a scribe mark where someone has done this on my accessory case. This leaves around 1/8" between the cut and the oil pump gear hole -- a recipe for a leak.
-I think it's also important to ensure that the oil return passages are open on the accessory case. There are no oil seals to the oil pump gears so oil is free to squirt into the tach drive adapter cavity from the top gear and is blocked by the generator gasket on the lower gear. But, to lubricate the lower gear shaft with fresh oil, there is a slight channel cut into the accessory case to allow oil to drain back into the case. For the top oil pump gear, oil returns to the case through two holes in the oil pump gear shaft. These can be seen in the attached photo. -Although I doubt this is an issue with your newly overhauled engine, Continental Service Bulletin M76-4 gives instructions for replacing the crankshaft oil seal. Chapter 10-10 of the M-O manual covers this subject. There's a link to this manual here.

Thanks for the replies.