abwc

I'm fascinated by break-in theory.

As I read about sealing pressure, nobody seems to be discussing piston excursion.

I've long held the belief (based on some motorcycle expert's theory I found on the web 4 years ago) that you need to increase max RPM in small steps to roll the ridge that forms on the cylinder wall at the top of the stroke.

Motoman's technique does not address this phenomenon; is that because it's bunk, or is that because regularly reaching redline is part and parcel of his advice ?<ul><li><a href="http://mototuneusa.com/break_in_secrets.htm">http://mototuneusa.com/break_in_secrets.htm</a</li></ul>

B.S.Rick

Piston moves the same at idle as at WOT, no?

India Whiskey Charlie

The higher the rpm's, the faster the piston's excursion.

VerrÜckt

Bunk.

abwc

...or might we say the "longer" the piston's excursion.

With increased RPM comes increased linear velocity of the piston, and thus increased stretch on the rod.

noobie_boobie

With very low tension rings which are used by all the manufactures these days not a lot of wear in the cylinder walls occur. Everyone wants maximum mileage so low tension is all the rage.

I've seen modern engines with 250,000+ miles on them that have cylinder walls that look (and measure) as new, but they consume a lot of oil, are high in emissions, and are way down on power because the rings are no longer sealing because they've lost tension over time and never were properly seated.

This is why, and a lot will disagree as the "manufacture knows best", that the break in has become much more critical. Since the rings are low tension the only chance you have to properly seat them is when the cylinder wall final hone cross hatch is fresh. After it looses it's very slight abrassion the rings will never seat 100% properly as they don't have enough pressure to do so!

SG

VerrÜckt

And there is also no "window of opportunity" to break the rings in as Motoman claims. This can be done at 50 miles or 5000 miles, the end result will be basically the same.

RI A6

The MotoMan method also seems to assume iron cylinder walls. Alusil walls are a very different beast. There are no cross hatch honing marks. The surface is bored, chemically etched to remove aluminium and expose silicon, and then polished.