Breaking in a new engine

[Bakes5]

dup

[Ken_Jamieson]

Of course the pistons will move further at higher RPM's with the addition forces when you double the revolution speed will cause the all the materials involved to strain more from the crane shaft bearings to the crank itself to crank bearings to the piston rods, etc, they might be mostly metal but metal is constantly expanding and contracting and stretching and contracting. This is what eventually leads to metals sometimes hardening because of this and then eventually becoming brittle and breaking....metal fatigue. Any physics, mechanical engineering course, metallurgy, etc., texts will tell you this.

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[cbath]

Most engines now days are using low tension piston rings with some sort of coated piston... it's pure speculation that "breaking in" an engine one way or the other is better... I say run it like you plan to use it from day 1 and maintain it like you want to use it for life.


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[UNSTUCK]

Can someone explain to me how ridge rings will form if I run it at a constant 2000 RPM vs vary between 2000 and 4000 RPMs? Are you saying that the rings move around differently at one RPM vs another? That is to say, hypothetically at 2000 RPMs the ring moves say 4.125 inches up and down but at 4000 rpms the ring moves 4.130 and at 1000 RPMs the ring only moves 4.120 inches up and down.

Any new engine you need to vary not the speed so much as the rpms for the first while including wide open as the new pistons and rings move up and down in the cylinders there will be some sizing happening to the cylinder walls causing a "ring ridge" at the top and bottom of the piston movements. Running at the exact same RPM causes there to be a large ring ridge in the same place in the cylinder, then if you happen to gun it and the piston rings end up moving further in the cylinder it can blow the rings, pistons, seals and/or crankshaft. So as a minimum as others have said vary your RPM's constantly for the first 10 or so hours but don't be afraid to work it as you want any ring ridge to be as high and low in the cylinders as the pistons will ever move during the rest of the engines life. Also change the oil after the first 10 or 20 hours minimum as there will be metal fillings in it as all the parts wear in together and those small manufacturing tolerances match up.

I can only think of two things that form these ridges. High miles/hours or excessive carbon (usually both). Over time a ridge will form, but with today's oils we are seeing diesel engines go 1.5 million miles with no ridge formation. Keep in mind, formation of a carbon ridge will reduce the ID of the cylinder at the top. I believe the ridge that Ken is talking about would actually be an increase of the bore in the stroke area from removal of material. For example, a ridge is present in a older engine with an original bore of 3.500 and the stroke section of the cylinder may have a bore of 3.501. This engine is worn out. .001" of material has been removed.
I for one am not trying to create a ridge when I break in a motor. If this was the case, I would want the ridge to be at the highest and lowest points of the stroke, like Ken said. So to do this I would WANT to run at max RPM the whole time. Not vary the engine speed as he suggests.

Ridges are an indication of engine wear, not a properly broken in engine, in my opinion of course.


This is a pretty neat video I was looking for earlier but couldn't find it. It's a promo video for Chevron, but the take away is that with proper servicing using good oils you'll have a good engine for a long time. Not so much how you break it in.