"Reversing Pressure" on Rings During Break-In ??

[Earle]

A possible clarification, If I may, on the subject....

Please read my last post under "Engine Break-In Conflicting Advice". I should have started a new thread but I don't feel like re-typing it all again here.

Comments and missed insights welcome!

Earle

[MikeK]

Originally Posted by Earle

A possible clarification, If I may, on the subject....

Please read my last post under "Engine Break-In Conflicting Advice". I should have started a new thread but I don't feel like re-typing it all again here.

Comments and missed insights welcome!

Earle

Earle! I'm a lazy typest too. "cut/paste" brings your post here easily. (So would a link to that post) Here 'tis:
OK, Gents, Two posters have now mentioned it and I have to try to get some clarification - or maybe offer some clarification? : I'm paraphrasing here, but the statements were like this: "During break-in, be sure to spend some run time decelerating and coasting against compression. This will reverse the pressure on the rings and load both sides of them to help them seat better."

If the posters are implying that deceleration and coasting against compression causes the gas pressure on the rings to switch from coming from the top down to coming from the bottom (crank case) up, I beg to differ.

The pressure on the rings is ALWAYS in one direction - from the top down, even when "coasting against compression." There is no way, especially in a vented crank case, to develope and maintain gas pressure from the bottom up against the underside of the rings to "reverse pressure" on them. The only thing you're doing by letting off the gas and coasting against compression is depriving the combustion chambers from a supply of gas to ignite. This causes the pistons to move upward on the compression stroke only against non-combustable "air" resulting in no "power stroke". This air compression effect is what you feel as a "drag" or resistance in the engine that slows the car down (like a "Jake Brake" on eighteen-wheelers?). Maybe it's this lack of ignition and the resultant lower pressure on the rings that the posters are referring to as varying or "reversing" pressure to help them seat. But the term "reversing the pressure" on the rings is misleading. It is not literally reversing.

Steer me right if I'm off track! - but I don't think I am!

The nature of the gas pressure on the rings in one thing. But I am still trying to reason out in my mind why constantly varying the force with which the rings press agianst the cylinder walls (accelerating then coasting, etc.) will result in a better break-in than loads that are more "constant" (long trips at one steady speed, etc.).

Earle

My two cents: Coasting in an engine will incur a very high intake manifold vacuum, 20+ inches. The rings will be subjected to that during the intake stroke, causing perhaps a bit more reverse load than normal, and questionably pulling more oil. Even at WOT, when intake vac. is zero, during the intake stroke nothing is pushing the rings down, they are being dragged by the lands on the pistons. A true "Jake Brake" is a different thing. A true diesel jake plays with the valves making it compress against much more than atmospheric pressure. Imagine your cam keeping the exhaust valve closed 3/4 of the way up the exhaust stroke, then opening under all that pressure. PoP PoP PoP Pop...

[PC/SR]

Accelerating inceases the pressure of combustion gases around and behind the rings resulting in increased pressure on the cylinder walls and wearing them "in" until smooth with the rings. Declerating creates a vacuun which sucks some oil from the valve guides until they are set, and maybe some oil from the mist in the crankcase. YOu know your valve guides and/or rings are worn when you get a puff of smoke when you hit the throttle after decelerating.

[Earle]

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