Cylinder #4 - Fire ring replacement

[unicom]

Hi all,

I need some technical advice. I just had the #4 cylinder fire ring replaced (due low compression) along with the valve guide plus resurfacing of the valve (exhaust valve I guess).

My maintenance facility has replaced the synthetic oil I had, with straight mineral oil and is asking me to run 20-25 hours with that oil. A friend of mine is telling me that doing so there is a risk of "glazing" (not sure of the exact word in english) the 3 other cylinders.

The engine is a IO360 with 500 hrs (Mooney M20J).

What are your thoughts on that matter ? Do you believe I should return to synthetic oil sooner than that ?

Thanks for your help.

Philippe

 

 

 

[tony]

I'd sell the rest of the case of unused oil to your friend and stick with the mineral oil.

 

All kidding aside, some people think a synthetic blend is OK, some do not. In my airplane I prefer to run mineral oil. It absorbs the products of combustion better and these products stay in the oil and are not deposited in the engine (sludge).  So when you do your oil change those byproducts are evacuated with the oil. I’m sure this subject will start a good debate here.

[N601RX]

Cylinders need to be broken in with straight mineral oil until the rings seat and oil usage stabalizes.

[jetdriven]

Running your engine for an extended time on mineral oil (hundreds of hours) can cause sludging as straight (non-AD) mineral oil does not have detergents to suspend contaminants.  For a 50 hour periods to seat the rings and cylinder is fine. 

Many people use Philips 20W50 X/C oil to do this but I understand it is an AD oil anyways. You could use it untl overhaul.

Glazing of cylinders happens when the new rings fail to seat and, instead, polish the bore. Then the ring won't seal and that cylinder uses lots of oil. Fly at the recommended high power setting until oil consumption stabilizes. 

[KSMooniac]

Quote: N601RX

Cylinders need to be broken in with straight mineral oil until the rings seat and oil usage stabalizes.

[RJBrown]

 Using mineral as the shop recommended will not cause glazing of the other 3. That statement is absurd and indicates that whoever repeated it to you has NO understanding of what those words even mean. 

 When rings are installed in an engine the cylinder walls are honed with a "glaze breaker" of some sort. This process leaves a crosshatched pattern inside the bore. This "roughness" wears into the ring face and wall surface so the rings and the bore mate together. Some oils lubricate so well that they interfere with this process. This is why "break in" oil of some sort is used. The other 3 cylinders are already broken in. Using mineral oil will not affect them.

 

[Bill_Pyles]

Mineral oil is superior for break-in.  Synthetic oil molecules are so slippery that they impede the seating of the rings and lead to the glazing or polishing.  Rings need to abrade against the cylinder walls and take on their shape so as to ensure good sealing.  The mineral oil lubricates and cools, but still allows the rings to acquire the shape of the cylinder at the micro level.