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IO-360 - oil leak from case bolts

SteveR

Active Member
I have an oil leak from one or two of the lower case-half bolts at the front of the engine, in front of the oil sump. I removed the bolts and added Permatex form-a-gasket to the bolts/washers, but the leak got worse. Permatex worked where I had this issue on the top of the case, but on the bottom I can barely get to these bolts to clean them and add Permatex.

Has anyone dealt with this and found a definite fix?
 
sometimes when you think it's the lower case bolts leaking, it's actually the nose seal and the oil is running down the split between the cases and collectin on the lower case bolts.
Good Luck,
Mahlon
 
sometimes when you think it's the lower case bolts leaking, it's actually the nose seal and the oil is running down the split between the cases and collectin on the lower case bolts.
Good Luck,
Mahlon

I’m with Mahlon on this one (as I generally am!!). Those bolts are OUTSIDE of the line where the case sealant goes, so they shouldn’t have any oil reaching them - unless the motor was built by someone who didn’t understand how to apply the silk thread (or other….).

Paul
 
I have had those lower bolts loosen early on and tightening them worked. However, if it is has been loose for a while, the sealant may have worked itself out of the seam and nothing can be done about it. While it is a hack, the exterior of the seam can be coated with RTV to stop it or at least minimize it. The right stuff is preferred for this application, as it has a tenacious grip. However, case must be perfectly clean. Per Mahlon, need to be sure it is not the front seal first.

Bolts are well outside the sealant area, so they will not leak unless the sealant between the case halves has been compromised.

Larry
 
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I've seen these do the job on leaking fasteners; Grainger is one source.
61JX54_AS01
 
sometimes when you think it's the lower case bolts leaking, it's actually the nose seal and the oil is running down the split between the cases and collectin on the lower case bolts.
Good Luck,
Mahlon

Y'know, I've been starting to suspect this on mine, too, but I'm not 100% sure.

I've taken a pretty hard look at the lower part of the bulkhead and tried to get my endoscope up there to see but I haven't seen any oil. Maybe I'm not looking in the right place.

Is there a guide anywhere on checking that nose seal?
 
Standard procedure to finding leaks is to get it clean enough to eat off of. Clean clean clean. I use brake cleaner or other such stuff to get all the oil off everywhere. Fire it up, run for a bit and look with a black light. Oil should have a glow to it in the DARK.
If it doesn't show up with just oil. Got to Amazon and buy some leak detector.
It will show up then for sure.
Rinse and repeat as they say.
It works for me Art
 
sometimes when you think it's the lower case bolts leaking, it's actually the nose seal and the oil is running down the split between the cases and collectin on the lower case bolts.
Good Luck,
Mahlon

Nose seal…..are you speaking of crank seal ?

Thx
 
I’m with Mahlon on this one (as I generally am!!). Those bolts are OUTSIDE of the line where the case sealant goes, so they shouldn’t have any oil reaching them - unless the motor was built by someone who didn’t understand how to apply the silk thread (or other….).

Paul

I’m trying to visualize what bolts on a Lycoming case are inside the line of where case sealant or silk thread goes ? What am I missing ?
I’m sure that ALL case bolts are outside the sealant line. Case bolts start leaking when that particular sealant method has failed. The top bolts above the camshaft journals are especially vulnerable. Some case shops are cutting relief slots above the cam and below the sealant line giving the pressurized oil an alternate path. I’m a proponent of LyCons o-ringing cases by cutting a grove in one case half with a C & C machine then putting a thin o-ring ribbon in the grove. This grove follows the pattern of the standard silk thread method. I’ve never had a leak in any of the engines I’ve built using this method. LyCon now has an STC for this process so the certified guys can utilize it as well.

Duff
 
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I’m trying to visualize what bolts on a Lycoming case are inside the line of where case sealant or silk thread goes ? What am I missing ?
I’m sure that ALL case bolts are outside the sealant line. Case bolts start leaking when that particular sealant method has failed. The top bolts above the camshaft journals are especially vulnerable. Some case shops are cutting relief slots above the cam and below the sealant line giving the pressurized oil an alternate path. I’m a proponent of LyCons o-ringing cases by cutting a grove in one case half with a C & C machine then putting a thin o-ring ribbon in the grove. This grove follows the pattern of the standard silk thread method. I’ve never had a leak in any of the engines I’ve built using this method. LyCon now has an STC for this process so the certified guys can utilize it as well.

Duff

Yes, all of the EDGE bolts are outside the sealing line - but lots of folks here have never taken one apart, so they might not know that. Of course, there are lots of case bolts inside the line - the through bolts for instance….which is why you can get leaks that through their holes unless they have been O-ringed as well (another great modification for older engines….).
 
Leaky Through-Bolts

Yes, all of the EDGE bolts are outside the sealing line - but lots of folks here have never taken one apart, so they might not know that. Of course, there are lots of case bolts inside the line - the through bolts for instance….which is why you can get leaks that through their holes unless they have been O-ringed as well (another great modification for older engines….).

Hey Paul hope you didn’t take my comments as being snarky 😎! I was just trying to be concise. Always enjoy reading your comments.

Lycoming Case bolts leak because the crankcase seal has failed and permatex or silicone around the bolts doesn’t fix that. I’ve seen it tried lots of times, and you have nothing to lose at that point, but have not seen it work other than a temporary slowing of the leak.
In the case of the through-bolts you mentioned it is a different story. Body fit through bolt leakage can be fixed by reaming the through bolt hole oversized and using the appropriate oversized through-bolt. If I recall they come in P1 P2 P5 and P10 oversized. Lycoming SI 1290 details this procedure.
The through-bolt o-ring #72075 oil seals you spoke about are utilized in all modern cases (post 1975 ish) and anytime an older case is overhauled by a certified case repair facility the recess is cut for the O-rings as well.
Just my 2 cents and probably not worth that much.
Duff
 
I've seen these do the job on leaking fasteners; Grainger is one source.
61JX54_AS01

As Walt said above... and use Loctite 518 sealant on the bolt. A tip from the engine shop on the field. I used it for a couple top bolts and it worked, stoping the drips.
 
Mine too

I had the same bolts showing oil and traced it to the crankcase seal. It was leaking between the seal and the case, not the seal and crank. You have to remove the ring gear to get a good look to find it.
 
In the case of the through-bolts you mentioned it is a different story. Body fit through bolt leakage can be fixed by reaming the through bolt hole oversized and using the appropriate oversized through-bolt. If I recall they come in P1 P2 P5 and P10 oversized. Lycoming SI 1290 details this procedure.

I would definitely get things really clean and do the UV light trick. With the way air flows, oil with collect areas nowhere near the leak.

I had oil collecting at the lower case half bolts like you and it was coming from thru-bolt so I ended up doing the SI1290 above. I also had a leaking drain back tube and oil was going as far forward as the starter and alternator mount.
 
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