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Oil Leaks Are Normal - Curtiss Jenny & A Lycoming Angle Valve (AV) IO-540 Tear Down

Slidin Gator

Well-known member
When removing cylinders you end up dealing with the crankcase cross bolts. Item #15 on the diagram below is a 10-5/8" long, custom stud with 1/2-20 threads on either end to match the cylinder mount holes. The Lycoming 4 & 6 cylinder motors stagger the cylinder mount bolts such that these studs capture 50% of the 1/2" cylinder stud points on either side of the case.

These bolts effectively preload the crank bearings. If you think about it, Lycoming didn't change from the Narrow Deck to the Wide Deck to make it easier on the mechanic. Lycoming made the change to increase the crank bearing diameter, they had to widen the bolt pattern to allow for a heavier duty (and heavier) crank.

Crankcase Assy.jpg
 

Slidin Gator

Well-known member
I found oil leaks at some of these cross over bolts. They had been sealed with an old school silicone. That will be resolved.

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A 12 Gauge cleaning kit comes in real handy at this point!


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Slidin Gator

Well-known member
When dealing with a half-worn engine, the primary concern is the heads and valves, tune them up and it will light up a used engine (or make it throw a rod, either way you know).

This is where we get into special Lycoming tools vs. my hacks. Attached is the special tools catalog from Lycoming, you won't find anything in the catalog for under a C note but it's a great starting point.

First the overhaul manual says to put the cylinder in the cylinder fixture (or something like that). Luckily I had my old man on site to think this through and we ended up with a plan. A wooden plug to hold the valves closed and a barely applied press to hold the cylinder steady.

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Next I was looking for a valve spring compressor tool. The Lycoming tool is over $1K, I found this tool all over the internet for $50-$60 with reviews like "Broke on my 5th cylinder, make it out of steel" etc. But that pic is enough to understand, use the rocker arm pin for leverage.

OIP.pptDlrMnS9CLoCxWWrpgJAAAAA



So after a morning of tweaking, welding, grinding etc. I ended up with this.


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That didn't work exactly right, so a bit more welding and grinding and away we go.

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Slidin Gator

Well-known member
some of the finest afro engineering I have seen lately! :D
I don't have a fully outfitted shop, my goal here is to show what can be done on these things with typical hand tools, some basic welding equipment and Enginuity (engine, get it). Over my life, beyond a hammer and punch, a torch and welder have been key tools for getting stuff done vs. reaching a road block and spending a week to sort it out.

Note that several aviation threads talk about doing the following with the engine assembled and on the plane via working through the spark plug holes. There is actually a Lycoming service advisory calling for filling the cylinder with rope via the spark plug hole, turning the prop to hold the valve closed, removing the springs and then checking the valve operation to look for carbon build up leading to the potential for valve sticking. If the guide needs to be cleaned it goes on to how to ream while still working through the spark plug holes.

Sounds like a PIA to me, just pull the cylinders and get it done.

I cleaned up all the valves with my wire wheel tools and wash tank, none had any issue with carbon build up/sticking and the valve guides are still smooth and tight. All the valves show good wear with no burned valves or seat issues. So the only operation I am doing on the valves is to lap them in place to clean up the fit. I have done this same process when replacing a burned valve, but the lapping process just takes more work to get a good fit. Here, It only takes a minute with the drill (forward/reverse/forward) followed by some hand oscillations to finish. I don't intend to grind out the pits seen in these pics, I just want to maximize the surface contact area and make sure there are no high spots, particularly the exhaust (that is how the exhaust valve gets cooled).
 

Slidin Gator

Well-known member
The valves and seats are not new by a long shot, they probably just got a lap job 500 hours ago.

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This is #2 Exhaust before lapping.

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The Exhaust valve stem is 1/2", I had some 5/8" tranny cooler hose. The intake valve stem is 0.4" diameter, so I used some 3/8" fuel line. Keep reversing the drill on low speed, push and pull. Then finish by hand, back and forth while pulling to load the valve.

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John Fenner

Well-known member
Need to run a 15° stone on the intake seat then a 30° to center the seating area on the valve face.
A 30° stone and a 45° stone on the exhaust seat, when lapped in the pattern should resemble this.
A fresh 45° reface of exhaust valves and a fresh 30° reface of intake valves would be beneficial as well, this is what keeps the guides from wearing out as well.
 

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John Fenner

Well-known member
About the through studs, there are O-rings in the main bearing saddles where they pass through at case mating surfaces to seal off oil from weeping out to the threads of the cylinder hold down nuts.
I looked over the studs in the pictures, I have not ever seen floating studs in a lycoming, interesting!
Every one I've built had the studs threaded to lock into the case half. Or if it was actually built by Continental lol.
 
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Slidin Gator

Well-known member
About the through studs, there are O-rings in the main bearing saddles where they pass through at case mating surfaces to seal off oil from weeping out to the threads of the cylinder hold down nuts.
I looked over the studs in the pictures, I have not ever seen floating studs in a lycoming, interesting!
Every one I've built had the studs threaded to lock into the case half. Or if it was actually built by Continental lol.

John,

The parts catalog I am working from has matched this engine well and does not show any O-rings between the case halves. It specifies Lycoming P/N 76220 for the cross over studs. The catalog describes them as STUD, 1/2-20 x 11-45/64 long. But Googling that part number comes up with 10.7" length which matches what I have. I found an Ebay link with some up for sale for $65 each.

P/N 76220 Lycoming Standard Crankcase Thru-Bolt Assy. | eBay

Ebay 76220 Studs.jpg


Crankcase Assy #3.jpg


Item #15 is 8x 10.7" cross bolts. Also, Items 14 & 20 are 3/8" cross bolts right on the prop end bearing, those were not leaking so I am not touching them.

Crankcase Assy #2.jpg

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Slidin Gator

Well-known member
Need to run a 15° stone on the intake seat then a 30° to center the seating area on the valve face.
A 30° stone and a 45° stone on the exhaust seat, when lapped in the pattern should resemble this.
A fresh 45° reface of exhaust valves and a fresh 30° reface of intake valves would be beneficial as well, this is what keeps the guides from wearing out as well.


Thanks for the input John, wish I had a nice set of cylinder tools, but then I imagine everyone would be bringing their stuff to me to work on. 🤔

I am glad you weighed in on the contact patterns, I have been trying to interpret what I have and if it really does need to be addressed. I started with a 500 hour SMOH motor that runs well but leaking oil and definitely not balanced. My primary goals have been to address the oil leaks, sort out all the stud issues, reset the valve lash, freshen up the paint and aim for another 500 hours without going too anal and spending money. Rather than spend money on full cylinder overhaul, I plan to buy some spare cylinders (and get on with building my next boat!).

The valve you posted shows a contact pattern in the middle of the valve contact face, while mine are contacting near the tip. My exhaust seats show contact towards the bottom of the seat and the intakes are contacting towards the top. One of the things I noticed when I pulled the first cylinder (#5) off was no valve preload, the rocker arm shafts came right out without pulling the cylinder. So no doubt that the valves have seated in vs. the original lash setting.

Figure 6-30 from the overhaul manual shows desired, acceptable and un-acceptable contact patterns. The acceptable graphic shows a wide contact pattern in the middle of the valve. The desired graphic would show a relatively small contact band towards the outside or tip of the valve.

The Unacceptable graphic would show a narrow contact band towards the inside of the valve seat.

From my read of this, I think I have good contact within the bounds of "Acceptable", but absolutely open to opinion! I also think that the exhaust seats are getting near the limit where the next time they get ground they are likely to go out of spec, calling for valve seat replacement, something I'd just assume avoid for now.

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Slidin Gator

Well-known member
Just to be complete, here are the sections of the overhaul manual covering valve and seat regrinding and replacement.

Valve Seat Grinding #1.jpg


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John Fenner

Well-known member
I have these pages imprinted in my mind.
Ok, this must be a late model case, they must have revised to the floating studs due to the ones that were threaded and affixed into the case halves,,, the only reason I can see why, is that the threaded and locked in through studs would cause the fractures in the case.
I would say split the case, inspect bearings, anaerobic sealant around each stud and case halves, throw away the silicone
 

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Slidin Gator

Well-known member
I have these pages imprinted in my mind.
I assumed you would! I'm posting all this for everyone else (me included) Going through all of these I am finding that they are really just ground at the 30/45 degree angle and never got the 3 angle treatment called out. Also, I find that I have 3x Inconel exhaust valves and 3x steel. The overhaul manual says the valve stem diameter must be consistent for steel valves and maximum 0.002 thinner in the valve guide area on Inconel. It turns out that the Gator tolerances are a bit bigger with steel exhaust valves up to 0.0035 undersize.

Just to be clear, if you ever get on a piston plane in the Bahamas (etc.) and you see my bald head under the hood, get off the plane immediately, take a boat.😬

Fig 6-12 Valve Inspection.jpg

Earlier today I looked at the calendar, damn, Bow season opens in 2 weeks. So yep, if there is a short cut to finish, I'm taking it.

Ok, this must be a late model case, they must have revised to the floating studs due to the ones that were threaded and affixed into the case halves,,, the only reason I can see why, is that the threaded and locked in through studs would cause the fractures in the case.
I would say split the case, inspect bearings, anaerobic sealant around each stud and case halves, throw away the silicone

See the part about less than 2 weeks to be done with this project, I'm not splitting the case, then I'd have to address the cam wear and tappet spalling I see, etc. etc.. Floating studs would certainly even out the stresses on the case. I'm gonna use old dependable on these studs.

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John Fenner

Well-known member
I assumed you would! I'm posting all this for everyone else (me included) Going through all of these I am finding that they are really just ground at the 30/45 degree angle and never got the 3 angle treatment called out. Also, I find that I have 3x Inconel exhaust valves and 3x steel. The overhaul manual says the valve stem diameter must be consistent for steel valves and maximum 0.002 thinner in the valve guide area on Inconel. It turns out that the Gator tolerances are a bit bigger with steel exhaust valves up to 0.0035 undersize.

Just to be clear, if you ever get on a piston plane in the Bahamas (etc.) and you see my bald head under the hood, get off the plane immediately, take a boat.😬

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Earlier today I looked at the calendar, damn, Bow season opens in 2 weeks. So yep, if there is a short cut to finish, I'm taking it.



See the part about less than 2 weeks to be done with this project, I'm not splitting the case, then I'd have to address the cam wear and tappet spalling I see, etc. etc.. Floating studs would certainly even out the stresses on the case. I'm gonna use old dependable on these studs.

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If you see spalled cam followers, split the case and address them, you have it this far down why not?
After all this is a fine tutorial for those who are scared to wrench on an aircraft engine.

That said,,, Lycoming engines are notorious for cam wear due to spalling of the cam followers, as the cam is in the "roof" of the case, plane lands hot "airboat parks after a weekend" oil hot and thin, drips off of the cam followers, and once it cools it draws in moisture which gathers at the "roof" causing a rust event on the cam followers faces, thus the small rust pits turn into the spalling and then camshaft wear, metal in the oil to imbed the main and rod bearings, wearing on the crankshaft journals.
Hence the need of Cam guard oil for lycoming engines,,, now, if there was a block heater of a sort to disburse moisture from the case while the engine(s) are dormant, that would help.

I may have stated before or on another thread that,, I have rarely seen spalled cam followers in a Continental, as the camshaft is below the crankshaft, so take into consideration the "roof" theory!
Great post, I enjoy learning as well as letting others learn.
 

Slidin Gator

Well-known member
If you see spalled cam followers, split the case and address them, you have it this far down why not?

Damn you John Fenner:giggle: The case is all wrapped up and called done. 2 weeks left and all that.

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But I did skip over the cam system and I am waiting for the ospho to do it's job on the cylinders before paint, so here goes.

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Slidin Gator

Well-known member
The lifter (and cylinder) spacing on the Lycoming engine is configured so each cam lobe (except the 2 ends) alternates between port and stbd cylinders. The exhaust and intake tappets are opposed. The cam rotates in the same direction as the crankshaft, but at half the RPM.

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Lycoming Cam & Lifter Assy.jpg

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Slidin Gator

Well-known member
That said,,, Lycoming engines are notorious for cam wear due to spalling of the cam followers, as the cam is in the "roof" of the case, plane lands hot "airboat parks after a weekend" oil hot and thin, drips off of the cam followers, and once it cools it draws in moisture which gathers at the "roof" causing a rust event on the cam followers faces, thus the small rust pits turn into the spalling and then camshaft wear, metal in the oil to imbed the main and rod bearings, wearing on the crankshaft journals.
Hence the need of Cam guard oil for lycoming engines,,, now, if there was a block heater of a sort to disburse moisture from the case while the engine(s) are dormant, that would help.

Sounds like the solution is to drill and tap 7x grease zerks into the top of the case where (wear, get it) I can lube up the cam proper 🤔

The worst cam lobes I find are the singles at each end, #1 & #6 Exhaust. The rest of the lobes look better, I don't really see a lot of spalling on the tappet bodies, just years of wear. From what I see the tappet bodies are in decent shape. The cam is going to wear out eventually and if following the manual I would be following your advice above for sure, that and posting a cam for sale on Southern Airboat Classifieds (just removed from a plane even)!

As it is, I know what parts to start collecting for the future. I will be watching the #1&6 exhaust valve lash. As usual I got too many projects in the pipeline.

I don't think I'ma gonna be splitting the case just to make content for Rick. Rick seems to be doing well pimping Ukrainian women (that don't look Ukrainian).


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