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IO360 that’s a leaker

ERJDriver

Well Known Member
Hey all, recently acquired an 8A. Been slowly cleaning it up and fixing things. Biggest issue was an oil leak that would coat to midship after 30 mins of flying.

I’ve totally degreased it and done a few things.

Oil pressure sensor was leaking, replaced
Tightened return tubes
Check compression all mid 70s
Checked TQ on through bolts

It’s still leaking.:mad:

Cylinder base o rings bad?

Engine has 374 hrs SMOH
 

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Even though I can see in the first picture that it's safty wired, I would check the base of the dipstick tube. Not saying that's your problem, but it's easy to eliminate before you start digging in to the harder stuff.
 
I'll try that. It looks like it's coming off the cylinder at the front of the dipstick. The second photo of the bolt legging is the upper front through bolt to that cylinder
 
The second photo of the bolt legging is the upper front through bolt to that cylinder

...distant from the dipstick.

I've never tried it, but an engine leak should be findable in the same manner as a tank leak...low air pressure and a bubble solution:

https://www.amazon.com/Bubble-Liquid/s?k=Bubble+Liquid

I've been brushing it on welded aluminum tank seams for years. Finds tiny leaks and porous spots very well.

Plan B might use UV oil dye. Plan C would be the trusty can of powder.
 
Looks like the thru bolts may be leaking. Could also be some of the other base studs. They are not always into bling holes. If it is the thru studs, before attempting any fix, retorque them and make sure the engine doesn't get tight. Big leaks at the thru bolts are often from extreme case fretting at the bearing parting surface. This in turn can squeeze the main bearing when they are properly torqued. Could also be that the thru bolt fit is way to loose since the beginning but that allows fretting too. Hopefully, it is one of the other non thru bolt studs.
Good Luck,
Mahlon
 
I have a friend with an RV9 and IO320. He was getting oil at the front of #2 cylinder. Turned out to be the dipstick tube. Some crazy air currents going on around our engines.
 
Just retightening hose clamps is very iffy.

On my new M1B, the rocker return tubes were removed for access during baffle installation. I could not get them seal again and after 25 hrs of trying to seal the leaks, constant force (spring) clamps with new hose completely dried the area.

Also, although the engine is wet, don't discount belly oil coming from the breather as a significant contributor.
 
Looks like the thru bolts may be leaking. Could also be some of the other base studs. They are not always into bling holes. If it is the thru studs, before attempting any fix, retorque them and make sure the engine doesn't get tight. Big leaks at the thru bolts are often from extreme case fretting at the bearing parting surface. This in turn can squeeze the main bearing when they are properly torqued. Could also be that the thru bolt fit is way to loose since the beginning but that allows fretting too. Hopefully, it is one of the other non thru bolt studs.
Good Luck,
Mahlon

This was my guess as well. A month or so ago, another poster went through this and posted a lot of good data.
 
Leaker

I had a heck of a time finding an oil leak when I began Phase 1 of my -6. I used all new stainless steel wrapped teflon hoses for oil lines and one had a crack in it. As the oil leaked it was diffused through the stainless steel web and took forever to track down. Good Luck!
Joe
 
When I originally got the plane I check the TQ on all the cylinder bolts, they were all at the proper TQ. just confirmed they still are. So I guess I should try the 1 or 2 oversized thru bolts.
 
This was my guess as well. A month or so ago, another poster went through this and posted a lot of good data.

Mine guess also...I think I was that poster. https://vansairforce.net/community/showthread.php?t=191165 As BillL mentioned, there's a couple other threads I posted when going though this process. Just search my post history.

From what it looks like in the picture it's the middle main upper thru bolt on #3. I had the same leaking thru-bolt on middle main, but it was coming out the other side. I removed and replaced with oversized bolt per SI1290 and it's been bone-dry ever since. SI1290 is not applicable to 360s as it appears the higher HP could effect longevity.

Per lr72 and mahlon_r...make sure retorquing thru bolts doesn't change engine tightness. That would be a sure sign of fretting and lead to improper bearing clearance.

Sure is nice having a clean and dry powerplant...worth the effort.

If you're shopping around for an oversized bolt...It's worth calling around. I've seen them as high as $200 eventually found one from Duncan Aviation for $75.
 
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Yeah just now looking into the bolts, seeing average prices of 170 bucks :eek:. I’ll give Duncan a call. Is there a list of lycoming parts dealers, or is it just a google around type of thing?

What size did you end up going with? I figure I’ll order the .01-.02 size due to not having the ream them. They were all at the proper TQ values so hoping the case isn’t fretted. Tired of the leaking
 
Yeah just now looking into the bolts, seeing average prices of 170 bucks :eek:. I’ll give Duncan a call. Is there a list of lycoming parts dealers, or is it just a google around type of thing?

What size did you end up going with? I figure I’ll order the .01-.02 size due to not having the ream them. They were all at the proper TQ values so hoping the case isn’t fretted. Tired of the leaking

For parts, try Aircraft Specialties in Tulsa (http://www.aircraftspecialties.aero/) - they seem to have every part imaginable, and at good prices.

Paul
 
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