M20F 360-A1A Crankcase to Crankcase Bolts do not appear correctly torqued

[Rivermoney]

IO-360-A1A on a '75 M20F. Lycoming Reman with 500 hours. Doing some PM and noticed some weeping oil wetness on top front seem of crankcase where the two halves are joined with nuts/bolts (area between number 1 and 2 cylinder. The paint on a couple of the nuts was peeled off - no torque stripes evident. Lycoming manual states torque is 300 in-lbs (25 ft-lb) for the nuts. I went to check the torque and the three nuts I sampled were all torqued well less than 20 ft-lbs. I started to torque a few and after a few turns I stopped thinking maybe I should not mess with it and accept the slight weeping. So, do I torque them all to the correct torque? Or, just leaving them along and accept some weeping. I have no major oil burn or leaks. Slight weep/wetness around one nut on number 1 top left cylinder nut. Other than that, nothing. I appear to use less than 1/4 quart of oil per 3-4 hours of operation - but I have learned to just keep it at 6.5 quarts so have been adding well less. Worldly advice appreciated.   

[Greg Ellis]

I could be wrong about this because I am not an A&P or a mechanic of any sort but I would think that you may not want to torque these two bolts.  Seems that most things on our engines are torqued in a certain order for a reason.  For instance, when torqueing a cylinder to place you do it in a specific order for a reason.  I would be concerned that if you all of a sudden just torqued two bolts randomly that it may make things worse.  Just a thought.  Maybe wrong  but I am sure someone will be along anytime to provide the correct response . 

[MikeOH]

I am NOT an A&P, so this is just my concerned opinion:  I agree with Greg that randomly retorquing in random order is not a good idea.  Further, the fact you could not achieve the proper torque after 'a few turns' REALLY concerns me!  Perhaps if they were not properly torqued initially, but if they 'loosened' on their own...I'd be worried something bad is going on.

Finally, when was the engine OH'ed?  The general appearance seems like quite a bit of time, if not hours, has gone by since OH.

[Prior owner]

Where on earth did you get that torque value from? Those upper crankcase bolts are something like 96-106 inch lbs, not 300 inch lbs. if you’ve over torqued them, they should be replaced. Contact an A&P! Also, it is doubtful that’s messing with those bolts will affect any seeping at the crankcase halves….

Edited July 5, 2021 by PilotCoyote

[EricJ]

19 minutes ago, PilotCoyote said:

Where on earth did you get that torque value from? Those upper crankcase bolts are something like 96-106 inch lbs, not 300 inch lbs. if you’ve over torqued them, they should be replaced. Contact an A&P!

This is even too high from the overhaul manual I have, which indicates 75 in-lbs for those 1/4" fasteners.    If one of them turned a few times on the way to 300 in-lbs, it likely needs to be replaced.

Edit:  I have the Lycoming "Overhaul Manual, Direct Drive Engine", Dec. 74.    See P 7-17, Items 7-92 and 7-94, Fig. 7-21.

Edit edit:  See the Lycoming SI 1029D linked below.   96-108 in-lbs.

The order for certain of those around the entire case is important during reassembly, but once it's together those adjacent fasteners can likely be checked and re-torqued in any sensible order.

The leak is probably worth looking at, but it might be blowback from a leaking main front seal, maybe?   

Edited July 5, 2021 by EricJ

[Prior owner]

3 minutes ago, EricJ said:

This is even too high from the overhaul manual I have, which indicates 75 in-lbs for those 1/4" fasteners.    If one of them turned a few times on the way to 300 in-lbs, it likely needs to be replaced.

The order for certain of those around the entire case is important during reassembly, but once it's together those adjacent fasteners can likely be checked and re-torqued in any sensible order.

The leak is probably worth looking at, but it might be blowback from a leaking main front seal, maybe?   

Lycoming Service Instruction 1029

 

[EricJ]

2 minutes ago, PilotCoyote said:

Lycoming Service Instruction 1029

 

Yeah, that's better.   ^^Do that.

 

[Prior owner]

15 minutes ago, EricJ said:

The leak is probably worth looking at, but it might be blowback from a leaking main front seal, maybe?   

My thoughts, as well…

[Guest]

If it’s leaking between the case halve, there is little to nothing that torquing the bolts will do to stop the leaking in my experience, but there is no harm in trying.

The case is sealed with a thin glue and a silk thread.  I’d clean the area really well and monitor.  I’ve seen them bubbling oil out between the halves, removal and disassembly is the real repair when they leak that badly.  Some people try to seal externally with fuel tank sealant.

Clarence

[flyingchump]

I had the same thing on my 66E when I bought it.  Io-360-a1a.  2 of the lower crank case bolts were loose.  Like not even finger tight.  I had oil blowing everywhere...  My 2 loose bolts were the hardest ones to get to.  The ones where the starter and generator are pretty much in the way.  I saw this as laziness on whoever maintained my plane prior to me and no brownie points were earned for the guy who did my pre-buy.   Anyway,  My IA and I checked the torque of every nut and bolt on the engine.  No more oil leaks!

[A64Pilot]

The bolts that were overtorqued need to be replaced, they have been stretched and may break, the good news is that they are real cheap and easily replaced, and I doubt you hurt anything.

The concern if bolts are actually loose isn’t leaking oil but the possibility that the case halves are moving against each other and causing wear.

If there is a silvery grease look to what’s leaking then you may have a concern, but I doubt it

Check that the crankcase vent is clean and isn’t bent flat or something

[Rivermoney]

Thanks all. I will clean the area and look for new leaks next time I take the cowl off for an inspection. I typically take the cowl off every 25 hours just to do a quick inspection. The engine was a remanufactured engine, not OH. So, when Lycoming did the reman they sprayed the crankcase and bolt/nuts with gray paint. What caught my attention was the the oil sheen on the area AND the two nuts which exhibited cracked, flaked, and missing gray paint. That led me to believe the nuts had loosened thus putting torque wrench on to see what the existing torque was. The Lycoming service instruction torques attached in the threads above do match the Lycoming IO-360 manual I have - crankcase through bolts/nuts at 300 in-lbs. These two nuts were definitely not even near that. The engine has not been started and run since checking them, so I will replace the nuts/bolts as a precaution, torque stripe them, clean the area and monitor it over time. I have seen no other leak issues. I acquired the AC earlier this year - the engine was installed in 2004. So, the previous owner had 400 hours in sixteen years. I have added 100 hours in the last four months. 

[EricJ]

53 minutes ago, Wreindollar said:

The Lycoming service instruction torques attached in the threads above do match the Lycoming IO-360 manual I have - crankcase through bolts/nuts at 300 in-lbs. These two nuts were definitely not even near that.

The crankcase bolts/nuts that are referred to as "through bolts/nuts" are 3/8" shank bolts that go through both sides of the engine and hold the front bearing in place around the snout the cylinders on on each side.   They are not the 1/4" shank bolts that hold the edges of the case together near your oil stain in the pic you posted.   If you put 300 in-lbs on those 1/4" bolts holding the case together, or anything much over 108 in-lbs as noted above, the fastener should be considered compromised and discarded and replaced.

Don't loosen or retorque the actual 3/8" shank bolts holding the cylinders on without A&P/IA supervision as that has greater potential of compromising the integrity of the engine.

Just to clarify, there are no "crankcase through bolts/nuts" in the red circled area in the pic.   Those are 1/4" shank fasteners that should be torqued to no more than 96-108 in-lbs per SI 1029D.    If you've put more torque than that on those fasteners, they should be removed and replaced with proper replacement fasteners per the Lyc IPC.

Edited July 6, 2021 by EricJ

[EricJ]

The page from the Overhaul Manual makes it a little clearer which are the 3/8" though-bolts that get 300 in-lbs (around the outside of the crank snout to hold the main bearing in place), and which are the 1/4" bolts that get the lower torque spec (75 in-lbs in the manual, 96-108 in the SI):

 

[Prior owner]

50 minutes ago, Wreindollar said:

Thanks all. I will clean the area and look for new leaks next time I take the cowl off for an inspection. I typically take the cowl off every 25 hours just to do a quick inspection. The engine was a remanufactured engine, not OH. So, when Lycoming did the reman they sprayed the crankcase and bolt/nuts with gray paint. What caught my attention was the the oil sheen on the area AND the two nuts which exhibited cracked, flaked, and missing gray paint. That led me to believe the nuts had loosened thus putting torque wrench on to see what the existing torque was. The Lycoming service instruction torques attached in the threads above do match the Lycoming IO-360 manual I have - crankcase through bolts/nuts at 300 in-lbs. These two nuts were definitely not even near that. The engine has not been started and run since checking them, so I will replace the nuts/bolts as a precaution, torque stripe them, clean the area and monitor it over time. I have seen no other leak issues. I acquired the AC earlier this year - the engine was installed in 2004. So, the previous owner had 400 hours in sixteen years. I have added 100 hours in the last four months. 

If you are not an FAA certificated power plant  mechanic, you are delving into things that are far outside the “preventive maintenance” that you are authorized to perform as an FAA certificated pilot…..it would be in your best interest, and in the interest of every person who might operate that plane in the future, to seek the services of an A&P who will, at the very least, supervise your work. It will keep you safe & legal…. 

[carusoam]

Nicely stated PilotCoyote.

Thank you.

WreinD, when you get a chance… see if you can mention that you are working with a mechanic on this project, or you are a mechanic…

Best regards,

-a-

[Rivermoney]

10 hours ago, carusoam said:

Nicely stated PilotCoyote.

Thank you.

WreinD, when you get a chance… see if you can mention that you are working with a mechanic on this project, or you are a mechanic…

Best regards,

-a-

Yes, I am actively working with an A&P on this and always do so with any matter that is outside the the scope of authorized PM and often even when items are in the scope of PM.