Question for Paul McBride, the General Aviation News engines expert: The #2 cylinder thru bolt stud and deck stud nuts broke off a Lycoming O-360 180-hp engine. The engine has more than 1,600 hours. The cylinder has never been off.
I thought something like this happens early on, after overhaul or cylinder replacement. Have you ever seen this?
Two touch and goes and the pilot quit for the day after a rough idle noticed on the second landing. When he parked and got out of the airplane, there was oil all over the nosewheel.
Mark
Paul’s Answer: I found this question interesting and something I may have difficulty in coming up with a good answer.
The big disadvantage I have with this is a total lack of specific details and the history of this engine other than its being an O-360 series and 180 horsepower.
Even with the total time being reported as 1,600 hours, not knowing if this was since new and or field overhaul leaves me with a lot of unanswered questions, such as has the engine ever suffered from a sudden stoppage from a prop strike.
From my experience when an engine thru bolt fails, it’s typically caused by one of two things: Under torque or over torque.
So which is it in this case?
One thing that may provide a clue is if after the cylinder was removed, were there signs of fretting between the cylinder base and the crankcase face? If there is an indication of fretting between the two surfaces, then my suspicion would be that the cylinder was under torqued for some reason.
If the thru bolt broke off inside the crankcase and appeared to have a necked down section where the fracture occurred, then the cause would be an over torqued situation.
Please understand that I’m not saying this is what happened in your situation, but I’m just pointing out how something like this could occur.
