druidjaidan Posted Sunday at 08:40 PM Report Posted Sunday at 08:40 PM Just discovered a broken cylinder bolt during an oil change. Pretty yikes. We had our alternator go bad at the end of an 8 week vacation with like 80 hours flown. When I picked up the plane I noticed they had topped up the oil to 8qts for whatever reason. At the end of the first leg home of course I noticed a fairly substantial amount of oil in the gear door near the breather, but chocked it up to the 8qts blowing out some. Flew the rest of the way home and got around to the oil change today. Immediately noticed the lower cowl and everything had more oil than I expected, started looking for leaks. And I found a sheared off bolt hanging out next to the governor. 1
N201MKTurbo Posted Sunday at 09:28 PM Report Posted Sunday at 09:28 PM I’m not real familiar with those engines, so I can’t tell if that is a through bolt or not. If it is, I would be very concerned. It might be worth a call to the factory for advice.
redbaron1982 Posted Sunday at 10:15 PM Report Posted Sunday at 10:15 PM Sorry to hear this. What part of the engine the first picture shows? I can't tell. I mean I do see the nut backed off, but I can tell where that is.
druidjaidan Posted Sunday at 10:18 PM Author Report Posted Sunday at 10:18 PM 1 minute ago, redbaron1982 said: Sorry to hear this. What part of the engine the first picture shows? I can't tell. I mean I do see the nut backed off, but I can tell where that is. Sheared side of the bolt is cylinder 6 toward the propeller. The backed off side is in front of cylinder 5
druidjaidan Posted Sunday at 10:20 PM Author Report Posted Sunday at 10:20 PM A bit more context on the engine.
IvanP Posted Sunday at 10:21 PM Report Posted Sunday at 10:21 PM Looks like a through bolt. How many hours are on the engine? Any recent work on the cylinders?
druidjaidan Posted Sunday at 10:33 PM Author Report Posted Sunday at 10:33 PM (edited) 5 hours ago, IvanP said: Looks like a through bolt. How many hours are on the engine? Any recent work on the cylinders? No recent work, at least since I've owned it. Around 1550 hours on the engine. I'll check logs for any work before I owned it. Edited Monday at 03:54 AM by druidjaidan
jetdriven Posted Sunday at 11:25 PM Report Posted Sunday at 11:25 PM If it is not torqued to spec, or not torqued at all, it has low or no preload on it, it will fail in cyclic fatigue. That looks like maybe what we have here. 1
N201MKTurbo Posted Sunday at 11:58 PM Report Posted Sunday at 11:58 PM 27 minutes ago, jetdriven said: If it is not torqued to spec, or not torqued at all, it has low or no preload on it, it will fail in cyclic fatigue. That looks like maybe what we have here. It could be the case was fretting, or some sealant got on the case halves where the through bolt went through. This can cause a lack of stress (torque) leading to what you describe. Lycoming has a service bulletin warning people that the use of any type of sealant around the through bolts can lead to this failure. Some were putting sealant around the through bolts to stop oil leaks. Lycoming says that is a very bad idea.
Utah20Gflyer Posted Monday at 02:50 AM Report Posted Monday at 02:50 AM During an oil change last year I found a broken cylinder hold down stud. Fortunately it wasn’t a through stud which I think would complicate the process of fixing the problem. Fixing mine required removing the cylinder and an interesting process to remove the broken stud piece that remained in the case - but was broken off below the surface. I’d imagine the fix for a through stud will require removing two cylinders. I would certainly contact the manufacturer for their input on the proper procedure for removing and replacing a through stud. Hopefully there is a precedent for doing so while the engine is still installed. 1
druidjaidan Posted Monday at 03:56 AM Author Report Posted Monday at 03:56 AM (edited) Double checked the logs. Last cylinder work was quite a while ago 10/14/2014 at 962 TSMOH. Last annual 6/19/2025 we were at 1567 and we've probably flown 90ish hours since then. Calling the local mechanic on the field tomorrow. Unfortunately mechanic availability is absolute crap at KPAE so I'm likely down for quite a bit for something as severe as this =( Edited Monday at 03:57 AM by druidjaidan
EricJ Posted yesterday at 12:01 AM Report Posted yesterday at 12:01 AM Often through-bolts require the case to be split to replace them. I don't know whether that's the case with this one or not, but it would be nice if not. Even if not it might be worth consulting with Continental or a relevant shop on what inspections might be a good idea if the engine ran for a while with no tension on that bolt.
druidjaidan Posted 15 hours ago Author Report Posted 15 hours ago Continental Tech Support says: Given this through bolt provides clamping pressure to the main bearing they recommend IRAN and I might as well overhaul it since it's been more than 12 years. 1 1
Ragsf15e Posted 15 hours ago Report Posted 15 hours ago 18 minutes ago, druidjaidan said: Continental Tech Support says: Given this through bolt provides clamping pressure to the main bearing they recommend IRAN and I might as well overhaul it since it's been more than 12 years. That’s probably reasonable based on your hours as well. Glad you found it, but sorry this happened to you.
MikeOH Posted 11 hours ago Report Posted 11 hours ago 4 hours ago, druidjaidan said: Continental Tech Support says: Given this through bolt provides clamping pressure to the main bearing they recommend IRAN and I might as well overhaul it since it's been more than 12 years. Sorry to hear this. But better than having an engine failure! At least you got some hours and over 12 years out of it. Thread drift warning! I've heard that the worry with loss of the clamping pressure runs the risk of spinning a bearing insert. But I've never quite understood that. Don't the inserts have tangs that 'locks' them in place in the case like automotive bearing inserts? Or, do they only rely on the friction provided by sufficient clamping?
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