When to retorque cylinder bolts?

[kenpilot]

I did my recent condition inspection with the help of a local A&P IA. Most of the "inspecting" I did myself, but some projects required specialized tooling. And the second set of eyes was helpful.

We noticed a bit of oil wetness at the bottom of one Cyl #2 (this is an O-320-E2A). Prior to the engine being washed down, prior to any attempt to prove the source of the leak, the mechanic recommended the cylinder bolts be retorqued, and then if that didn't fix the leak we'd dig further. He also said that it is the normal recommendation with piston engines to retorque ALL cylinder bolts at EVERY annual inspection, and offered to do that for me on a follow-up visit.

At the time, I said it sounds good, let's plan for that when I return. But now that I've completed the CI and understand a ton more about my engine, I'm looking at that project and really wondering... Is that true? Do people really retorque on every annual? Doing so would require all the baffling to come off, perhaps even the intake & exhaust tubes, perhaps even the oil lines to the oil cooler. What a project!

Thoughts?

 

[lr172]

never heard that to be normal or required and I don't do it every year, just as I never check the torque on the cyl heads in my auto engines. If it was initially done correctly, it should never loosen. If that were a risk, they would have safety wire, like all of the other fasteners that are at risk of loosening, though much safety wire is applied in areas that arguably have very little risk. Not saying that it is always done correctly and therefore never have loose nuts, but I believe is not common.

The leak there is highly unlikely to be related to bolt torque. several things it could be, including oil wicking through the threads on the 3/8" and some of the 1/2" studs that are exposed to oil inside the case along with several others. Through bolts on WD engines are interference fit and wear can cause oil to migrate from the journal area out to the nut and drip. The cyl doesn't need to be that tight in order to not leak oil. There is a big o-ring that stops oil migration around the base flange and this only requires moderately firm contact to work. IOW, if the nuts were loose enough to leak for that reason, the nuts would have vibrated off by now.

 

[kenpilot]

Thanks for the reply. So it's not just me that finds the mechanic's recommendation unexpected. And I found it funny that he didn't recommend I also retorque the propeller bolts.

Not trying to discuss the oil leak source just yet. There's so many things it could be. Without the tools to do a proper solvant wash, what I did for the CI was just a rag wipe down, so the engine run could confirm I didn't have any devastating leaks. But now I'm hoping to spend some extra time on this, to see how close to a dry engine I can get.

 

[blaplante]

You could call Lycoming customer support and get an opinion from the horse's mouth.
... and I've never heard of retorquing those bolts on each annual either ...

 

[Toobuilder]

Only periodic retorque of cylinders I’m aware of is the head nuts on the Lycoming O-145 but with cylinders cast into the block, apples to walnuts…

That said, your oil seal is a big fat O ring at the base of the cylinder and if leaking due to loose nuts, the whole cylinder has moved A LOT. So much so that you have likely lost several studs already due to the pounding of combustion and fatigue. Unless you have missing nuts or they are finger tight, can’t see where a periodic retorque will cure an oil leak.

 

[Bavafa]

Thanks for the reply. So it's not just me that finds the mechanic's recommendation unexpected. And I found it funny that he didn't recommend I also retorque the propeller bolts.

The torque on the propeller is a different case if that is a wooden prop and I do believe they need to be retorqued.

 

[kenpilot]

The torque on the propeller is a different case if that is a wooden prop and I do believe they need to be retorqued.

Yes, I've seen that on various condition inspection checklists... Retorque prop bolts (N/A for metal). I have a standard aluminum prop.

 

[[email protected]]

Spring for some spray cans of brake/electrical cleaner and it will make fast work of getting to be able to see the leaking area.
My luck varies Fixit

 

[planenutz]

It is normal for an engine shop to check the torque of the Cylinder Base Nuts and Crankcase Thru Bolts after the engine has completed its test runs prior to delivery to the end user. It is good practice to go over these again at around 50 hours when you would typically change the oil from straight to multigrade, and check the filter. Similarly the Cylinder Base Nuts should be checked after 50 hours if a lung is removed for any reason in the life of the engine.

After that there should be no reason to revisit these on your average 4 or 6 cylinder Lycoming.

 

[OKAV8r]

Horizontally opposed Lycomings don't require, or normally need, base nut retorque. Some round engines do, and a few have an AD requiring it. But, that's for radial engines. Maybe this IA is a round engine guy.
Probably most common source of your leak would be the rocker box oil return line rubber couplings.
Also, if it IS leaking at the cyl base, retorque won't be very effective (unless the cyl base nuts are VERY loose, and that can be determined by checking a couple of the more accessible nuts). If the leak is at the cyl base, you most likely have: 1) a twisted cyl base o-ring, or 2) a nick in the case chamfer, typically caused by a connecting rod impacting during cyl removal/ install. OR both.

 

[rv6n6r]

Careful

Read the full procedure for torquing at installation time in the Lyc. overhaul manual or service instruction. Given how specific (and critical) that procedure is, it seems likely that re-torquing months or years later is going to be increasingly inaccurate given what corrosion and other factors will have done to the threads.

Anyway there's always some oil coming out somewhere, if it's not a lot then best to live with it rather than risk making something worse.

 

[Roadjunkie1]

Engine oil leaks..........

Anyway there's always some oil coming out somewhere, if it's not a lot then best to live with it rather than risk making something worse.

Especially as an engine ages, if you DON'T have oil coming out of SOMEwhere, worry about having run out of oil........

 

[daddyman]

If you are still looking for an oil source

I've found using an oil dye in the engine oil, then inspecting with a blue light and yellow glassed (comes in the kit) readily available at your local auto parts store to allow me to pinpoint a pesky oil leak.
In my case (pun intended) the line from the prop governor to the prop.
Dogged me for almost a month until it worsened to the point that I grounded my plane.

Daddyman

 

[kenpilot]

Given how specific (and critical) that procedure is, it seems likely that re-torquing months or years later is going to be increasingly inaccurate given what corrosion and other factors will have done to the threads.

I knew that it was a very specific procedure. That alone gives me great pause. Letting someone touch a critical part of my engine requires more trust than I currently have in this mechanic. But I hadn't thought about the inaccuracy over time. Thanks.

Also, if it IS leaking at the cyl base, retorque won't be very effective (unless the cyl base nuts are VERY loose, and that can be determined by checking a couple of the more accessible nuts). If the leak is at the cyl base, you most likely have: 1) a twisted cyl base o-ring, or 2) a nick in the case chamfer, typically caused by a connecting rod impacting during cyl removal/ install. OR both.

Good tips.

It is good practice to go over these again at around 50 hours when you would typically change the oil from straight to multigrade, and check the filter.

Yes, this one I had heard about. The 50-hr follow-up is often overlooked by field mechanics doing cylinder changes. We learned that one the hard way years ago when my Dad had a cylinder depart the engine mid-flight because our mechanic never told us about this.

---

Thanks for the tips, everyone. I'll close the discussion at this point, before it becomes a thread about how to find an oil leak. UV light and dye is on order.

 

[kenpilot]

I just completed the deep clean with Brake Cleaner, followed by a 20-minute engine run with UV dye in the oil sump. Pretty cool idea! It didn't just show me the leaks. It helped me see what was NOT leaking! It turns out the wetness around my fuel pump is a leak at the elbow for the oil cooler line above. And of course I have all the other common leak points... magneto clamps, oil sump seal, minuscule leak on the crankcase top seam, and one oil return line clamp. All that is easily fixable.

----



Anyway, back to the main topic... Unfortunately, the UV dye revealed that I really do have a leak on the #2 cylinder, lower front two nuts. On the positive side, at least it's not the cylinder base itself, right? And these nuts happen to be the easiest to access of all of them.

The Lycoming Service Instruction 1029D Part 2 is for full cylinder removal. But if I'm just tightening up two nuts that are leaking... does anyone know if that's acceptable without catching the other 6 on that cylinder?

(I'm only asking because accessing the other nuts would probably require removal of exhaust tubes, intakes, etc. to even get in there.)

 

[tgmillso]

Loctite is your friend.

Just tightening the bolts will likely not fix the problem, as the oil is tracking around the thread, and regardless of how much torque you apply, you will not solve this with torque alone as there will always be a tolerance gap between the threads. The issue is that the oil is leaking through the case half split onto the through bolt, then working out to the threaded portion, onto the thread and tracking out. You either have to split the case, machine things and re-set the seals ($$$), or you fill the threads with loctite and block the oil from making it's way past the threads. I sent a similar query to Lycoming last year on this matter. Here is the subsequent response. I would encourage you to contact their support team directly. They were very helpful.

"Leaking through body fit through bolts would be repaired by following SI1290F. For cylinder base studs that are bedded into the case the two options would be to remove the cylinder base nut, clean the base of the stud thoroughly with solvent, and apply wicking grade Loctite 290 to the base of the stud or to remove and replace the stud. I recommend using the Loctite 290 as it is much less invasive than replacing a stud and in most cases is a successful repair."

Although this is not an "authorized repair" and hence no Service Instruction, I can confirm that with approximately 10hrs and 20 starts since performing the Loctite solution, it has worked flawlessly.

Regards,
Tom
RV-7

 

[kenpilot]

I suppose this is more a Lycoming question than it is a Van's question. Thank you, Tom, for the loctite idea. I'll look into that, and also chat with Lycoming; I should get to know them more anyway.

 

[lr172]

JFor cylinder base studs that are bedded into the case the two options would be to remove the cylinder base nut, clean the base of the stud thoroughly with solvent, and apply wicking grade Loctite 290 to the base of the stud or to remove and replace the stud. I recommend using the Loctite 290 as it is much less invasive than replacing a stud and in most cases is a successful repair."

Although this is not an "authorized repair" and hence no Service Instruction, I can confirm that with approximately 10hrs and 20 starts since performing the Loctite solution, it has worked flawlessly.

Regards,
Tom
RV-7

Had one leaking on my 540 (ironically #2) and this mostly solved it. Not perfect, but leak is very minor now.

 

[OKAV8r]

... does anyone know if that's acceptable without catching the other 6 on that cylinder?....

Suggest you put a torque wrench on it, and see if it is tight. if it is, or it's close enough that you don't see perceptible rotation, then I wouldn't worry about the torque on the remaining nuts. Then, remove the nut, clean and reassemble to final torque with the locktite applied.

FWIW, I've done this repair on a few engines over the years. Sometimes it is worth the effort, sometimes not. Doesn't hurt to try.

 

[Majorpayne317641]

Loctite is your friend.

Just tightening the bolts will likely not fix the problem, as the oil is tracking around the thread, and regardless of how much torque you apply, you will not solve this with torque alone as there will always be a tolerance gap between the threads. The issue is that the oil is leaking through the case half split onto the through bolt, then working out to the threaded portion, onto the thread and tracking out. You either have to split the case, machine things and re-set the seals ($$$), or you fill the threads with loctite and block the oil from making it's way past the threads. I sent a similar query to Lycoming last year on this matter. Here is the subsequent response. I would encourage you to contact their support team directly. They were very helpful.

"Leaking through body fit through bolts would be repaired by following SI1290F. For cylinder base studs that are bedded into the case the two options would be to remove the cylinder base nut, clean the base of the stud thoroughly with solvent, and apply wicking grade Loctite 290 to the base of the stud or to remove and replace the stud. I recommend using the Loctite 290 as it is much less invasive than replacing a stud and in most cases is a successful repair."

Although this is not an "authorized repair" and hence no Service Instruction, I can confirm that with approximately 10hrs and 20 starts since performing the Loctite solution, it has worked flawlessly.

Regards,
Tom
RV-7

The reason why it’s happening is case fretting has caused the case seam seal at the through bolt to become damaged and leak. I had this happen on my engine. Improper torque when originally overhauling a single cylinder 700hrs prior by the previous owner was the cause. Loctite or even the lycoming repair SB is just delaying the case fretting problem. There is no way to check bearing clearance once you tighten down the case to repair it. It may have fretted to beyond service limits and you will just never know until the next overhaul or until it seizes.

The bolt circled in the OP’s problem is not a through bolt. You will need to pull the cylinder and then remove the stud with a stud puller to reapply whatever Loctite lycoming prescribed for the blind stud. You could call Divco and ask them what they do. When I had my case overhauled by them I paid extra for them to install all brand new studs into my case.

 

[kenpilot]

"Leaking through body fit through bolts would be repaired by following SI1290F.

@tgmillso Do you happen to have a copy of SI1290F? Could you DM me? It seems this is one of the view that Lycoming does not post on their website, and I've already tried all my Google skills to find it.

The bolt circled in the OP’s problem is not a through bolt.

Thank you for pointing that out. I was just assuming it was a thru-bolt. You are correct. This appears to be just a simple stud. Perhaps that makes everything worse.

I still haven't heard back from Lycoming yet.

 

[RV8JD]

@tgmillso Do you happen to have a copy of SI1290F? Could you DM me? It seems this is one of the view that Lycoming does not post on their website, and I've already tried all my Google skills to find it.

Not @tgmillso, but below is a link to Lyc SI 1290F:

 

[kenpilot]

Not @tgmillso, but below is a link to Lyc SI 1290F:

Perfect. Thank you, thank you! I'll add that to my collection of Lycoming bulletins. Regardless if my leaking stud fit the criteria, I really wanted to see what you all were talking about.