Oil leak

[LBPilot82]

Has anyone had a problem sealing a cylinder base from oil leaks? Replaced a cylinder last month and upon replacement, coated the o-ring with some oil and installed. Leaked right away. Pulled it back off and dispite some suggestions to use tight seal, used permatex #2 as per my mechanic. About three hours later, leaking again. Not only that cylinder (#5) but #4 is now leaking as well. It has been on and leak free for just over 800 hours now, kinda wierd. We thought we may have had excessing crankcase pressure so we checked the breather line and all is fine. If we had excessive blow-by, the oil would be very dark very soon. Got almost 20 hours since oil change and it still looks quite clean. (My mechanic is convinced it is a crankcase pressure problem.) Tommorrow we're going to hook up an airspeed indicator the the breather and check it. Anyone know what it should read?????? Best way to "plumb" it in???????? Trying to get a hold of M89-9 service bulletin from TCM (can't download it from their website), it has to do with excessive crankcase pressure.

Oh...I should mention that when I pulled the cylinder the second time, I removed all cylinder studs and lightly coated threads with permatex. I didn't put an o-ring over them but I have heard this can solve oil weaping problems through the threads. I have no way of knowing if the oil is coming from the threads or the cylinder base o-ring. After coating with baby powder, cyl #5 shows oil coming from the cylinder/case mating surface, cyl #4 shows oil from between the cyl. nut and cylinder base.

[mit]

I would be looking for a Cracked case.

[johneeb]

LB,
Sense you now have an oil leak on both the left and right bank of cylinders this sure sounds like the O-rings on the through bolts are either missing or displaced.

[GAHorn]

I agree with John.. I believe you have a leak emanating from the thru-bolts which cyls #4 and #5 share.
Here's what commonly occurs: the thru-bolts have an O-ring at the case parting line. R & R one cylinder shifts that bolt/O-ring slightly, due to the torque (pull) effort placed upon the (now relaxed) bolt/O-ring by the opposite cylinder (in this case #4). Now the replaced cylinder is reinstalled and torqued down, but the thru-bolt shifts and TURNS due to nothing/no-one holding it on the opposite side of the engine to prevent the bolt's rotation as the replaced cylinder is torqued down, and due to the shifted bolt, ...oil pressure now slips by the dislodged O-ring and travels out the bolt and exits at the cylinder base.
Further manipulating the #5 has now dislodged it to cause oil to also escape out the #4 cylinder base via that thru-bolt.

The fix:
#1- Tell your mechanic to quit wasting your time and money chasing a non-existant crankcase pressure ghost.

#2. Pull those two cylinders again, clean up the mess created by the previous failed attempts. Thoroughly clean the area of the thru-bolt exit-points with solvent such as electronic cleaner spray or degreaser and let it dry. Inject Permatex #2 into/alongside the stud exit points, and reinstall the cylinders with new O-rings. Don't use any kind of "pookie" on the cylinder base. Inject more Permatex into the area of the cylinder-base where the thru-bolt exits the cyl-base, install an O-ring beneath that nut, and torque it to the specified torque ...using EQUALLY increasing torques on opposite sides of the engine simulaneously. (Avoid rotating that thru-bolt in it's hole, as that is likely what has already contributed to the problem.) Allow the Permatex to "cure" overnight before starting the engine.

This should work for you. I've cured several oil leaks on such engines. The only other fix I know is to completely disassemble your engine and start over.

Sorry not to have better news for you.

[LBPilot82]

Seems too simple for me to have not thought about that!!! Thanks. The parts manual isn't very clear on which cylinders have which studs going through to another cylinder. My concern is that if I pull #5 and #4 again, when I pull #4, will #3 be affected as well??? When #3 is fixed, then #2 leaks??? and so on. I've got 850 hours since major and all but two cylinders are original. I hate do think drastically like this for an oil leak (especially since compressions are mid to high 70's) but topping the whole thing might be an option.
For future work, is there a better way to R&R a cylinder so this doesn't happen again??

What p/n o-rings should I use for the through bolts? And just to verify, they go between the nut and cylinder base, not between the case and cylinder base right?

Thanks again.

[Brad Brady]

For future work, is there a better way to R&R a cylinder so this doesn't happen again??

What p/n o-rings should I use for the through bolts? And just to verify, they go between the nut and cylinder base, not between the case and cylinder base right?

Thanks again.

In order to get a good seal, follow George's out line....I will disagree with him on one count.....I always put a VERY THIN coat of tight seal on the cylinder bases....Also the o rings are on the thru bolts in the center(almost) of the engine not on the ends of the bolts. I don't have my overhaul manual with me, so I can't give you a part number ......Brad

[jrenwick]

....The parts manual isn't very clear on which cylinders have which studs going through to another cylinder. My concern is that if I pull #5 and #4 again, when I pull #4, will #3 be affected as well??? When #3 is fixed, then #2 leaks??? and so on....

Wherever the rear nuts on one cylinder are directly opposite the front nuts on a cylinder on the opposite side of the case -- those are the through bolts. If I'm figuring this right, there are four of them. They go between the rear nuts of #5 and the front nuts of #4, and between the rear nuts of #3 and the front nuts of #2.

[GAHorn]

The O-rings which I am recommending you to install under the nuts (but above/outboard of the cyl. flange) is for the purpose of assisting in keeping that oil inside the engine. Use any tight-fitting O-ring that is handy.

In the future, whenever removing a cylinder...BE AWARE...of the thru-bolts and make every effort NOT TO TWIST them when R & R -ing the cylinder. When bolting the cylinder back on...use a wrench on BOTH ends of the thru-bolt so that when you torque the repaired cylinder....you don't also twist that thru-bolt upsetting it's center O-ring. (And always use sealant such as Permatex #2 where the bolt exits the case when re-installing the cylinder.)

If you are very very lucky, you may not have to completely remove #4...if you can get the thru-bolt nut off the cylinder, use aerosol cleaner (carb cleaner, electronic cleaner, etc.) to clean around the thru-bolt threads within the cyl base flange, ...and inject Permatex, install an O-ring, and replace/re-torque that base-nut. OR.... you may get away with placing that piston at TDC and only pulling the cylinder partly away from the case for the cleaning, etc. You'll have to decide. But you'll want to do it as thoroughly as possible only ONCE... rather than to have to do this again and again.

Look at the following illustration and (being aware that for clarity not all the thru bolts/tie bolts are depicted) look at the cylinder mounting pads and at the crankshaft mains areas. YOu can see which are studs...and which are thru-bolts. Each thru bolt and each tie bolt has an O-ring on it at it's mid-point where the case halves come together. Those are the bolts that we must make every effort not to disturb when we do cylinder work. There are 4 thru bolts and 9 tie bolts, plus 1 "stud" which actually hold those cases together and which require mid-length O-rings. Make every effort when performing mid-life engine repairs to leave these O-rings undisturbed by avoiding any twisting or movement of these bolts.

crankcase assy.JPG