Cylinder gaskets and leaks

[lmb118]

I am installing new cylinders on my Lyc IO360. My last ones seeped at the base and I would like to avoid that this time. The case mating surface is smooth. Is the O ring the only thing that seals. Has anyone used a non hardening permatex (just a very thin film) or the stuff that is used to mate the case halves . Both would seem pliable enough not to cause torque problems. Are there any procedures that are not obvious.

Thanks.
LMB

[az_gila]

Originally Posted by lmb118

I am installing new cylinders on my Lyc IO360. My last ones seeped at the base and I would like to avoid that this time. The case mating surface is smooth. Is the O ring the only thing that seals. Has anyone used a non hardening permatex (just a very thin film) or the stuff that is used to mate the case halves . Both would seem pliable enough not to cause torque problems. Are there any procedures that are not obvious.

Thanks.
LMB

LMB ... Lycoming requires a "very thin" layer of zinc chroate on this surface, and no paint. I think sealer would be more pliable than paint... I say follow the instructions, very thin primer layer only.

gil in Tucson

[MrNomad]

If you can wait a day, I'll email the expert who helped me build our Superior.

[RV6_flyer]

Originally Posted by az_gila

LMB ... Lycoming requires a "very thin" layer of zinc chroate on this surface, and no paint. I think sealer would be more pliable than paint... I say follow the instructions, very thin primer layer only.

gil in Tucson

What Lycoming Document says that this is required?

Go to Lycoming Overhaul Manual Part number 60294-7 dated December 1974 on paragraph 6-124 says use the seal.

Paragraph 6-141 talks about cylinder painting and "is intended to alert personnel to extreme caution necessary when painting the cylinder base flange. An excessive amount of paint between between the cylinder hold down plate and the cylinder flange will lead to a loss of torque on cylinder base nuts and eventual stud and / or cylinder failure."

I have seen one engine that almost self destructed because of paint between the cylinder flange and crankcase. There was no accident but there was a large repair bill for an improperly assembled engine.

DO NOT use anything other than the O-Ring unless you hear from someone like Malon that is an "Engine Expert".

[MrNomad]

Gary is correct. I am absolutely certain we did not paint the engine where the barrels meet the case.

I expect the reply from the engine expert (30 years building these engines) in a few hours.

We used LOCTITE 515 between the halves, BTW, no silk thread.

Barry RV9A

[Allen Barrett]

Use only the o-ring. NO SEALANT. an almost transparent coat of zinc chromate on the skirt and bottom side of the cylinder flange is required. Check for nics or burrs on the chamfer where the o-ring seals, also verify that the cylinder deck on the case is flat particularly at the corner studs and thru-bolt locations. Proper torque sequence should be followed during assembly.

Allen

[DanH]

The issue is loss of preload on the short cylinder studs. Theory says when tightened properly they are stressed in tension to a level higher than the tension loads due to cylinder pressures, thus they see don't see cyclical loading and avoid fatigue. Paint, sealer, or anything else that can crush or extrude out of the joint will relax the preload. That wouldn't bother the long studs much as the change in clamped thickness is a very small percentage of the stud length. However, extruding a thick coat of paint will relax a significant portion of the preload on the short studs. That includes paint under the washer and nut.

Dan Horton

[chaskuss]

Originally Posted by RV6_flyer

What Lycoming Document says that this is required?

Go to Lycoming Overhaul Manual Part number 60294-7 dated December 1974 on paragraph 6-124 says use the seal.

Paragraph 6-141 talks about cylinder painting and "is intended to alert personnel to extreme caution necessary when painting the cylinder base flange. An excessive amount of paint between between the cylinder hold down plate and the cylinder flange will lead to a loss of torque on cylinder base nuts and eventual stud and / or cylinder failure."

I have seen one engine that almost self destructed because of paint between the cylinder flange and crankcase. There was no accident but there was a large repair bill for an improperly assembled engine.

DO NOT use anything other than the O-Ring unless you hear from someone like Malon that is an "Engine Expert".

Gary,
My overhaul manual, 60294-10b, dated 2002 DOES contain the direction to apply zinc chromate primer to the cylinder base flange. It's contained in 6-141-c. It states:
"Spray a very light coat of zinc chromate primer (.0005" maximum thickness) on the cylinder flange. See figure 6-35. If the correct amount of paint has been applied, the color will be green, with a yellowish tint, and the metal will show through. If the paint is to thick, the color will be zinc chromate yellow."

This is followed by a paragraph cautioning against applying the primer to thickly, and how to properly accomplish applying it as directed.
Charlie Kuss

[MrNomad]

Originally Posted by lmb118

I am installing new cylinders on my Lyc IO360. My last ones seeped at the base and I would like to avoid that this time. The case mating surface is smooth. Is the O ring the only thing that seals. Has anyone used a non hardening permatex (just a very thin film) or the stuff that is used to mate the case halves . Both would seem pliable enough not to cause torque problems. Are there any procedures that are not obvious.

Thanks.
LMB

Per my promise, here is the wise words from someone who has been building these engines since forever.

ONLY USE THE O RING SEAL. IF IT LEAKS YOU HAVE A BIGGER PROB.
SOUNDS LIKE THE OIL IS LEAKING FROM THE THRU STUD. THERE IS A SEAL BETWEEN THE ENG TO PREVENT THIS FROM HAPPENING, AT LEAST ON THE NEWER ENGINES. OLDER ENGINES DO NOT HAVE THIS SEAL. IF O/H WAS DONE RIGHT THIS WOULD BE CORRECTED AT THE ENG SHOP THAT DID THE O/H, MIKE.

[az_gila]

Originally Posted by RV6_flyer

What Lycoming Document says that this is required?

Go to Lycoming Overhaul Manual Part number 60294-7 dated December 1974 on paragraph 6-124 says use the seal.

Paragraph 6-141 talks about cylinder painting and "is intended to alert personnel to extreme caution necessary when painting the cylinder base flange. An excessive amount of paint between between the cylinder hold down plate and the cylinder flange will lead to a loss of torque on cylinder base nuts and eventual stud and / or cylinder failure."

I have seen one engine that almost self destructed because of paint between the cylinder flange and crankcase. There was no accident but there was a large repair bill for an improperly assembled engine.

DO NOT use anything other than the O-Ring unless you hear from someone like Malon that is an "Engine Expert".

Gary... you didn't have enough caffeine this morning.....

Paragraph 141.c is exactly what I was saying - and yes I have the same revision as you of the manual - it even gives a maximum thickness of the zinc chromate primer in Figure 6-35 of 0.0005 inches.

All I was saying was "follow the manual" - good advice I think for engine assembly....

If the thickness of paint in this particular location is that critical... then ANY type of sealer in the same spot would be bad.

I thought my posting was clear and correct....

gil in Tucson