What causes rings to "seat"?

[billncolo]

I have heard a few theories, but not sure I have heard the right one. I would like to better understand the process so that I can have better results on my third attempt.

[tryan]

your right foot........
seats the bottom of the ring land.

letting off seats the top of the ring land.

time and friction seat the ring to its bore . a function of ring tension, ring and cylinder material and surface roughness.

( edit ,and the oil properties )

500 to 3000 miles depending on how you drive and the motor.

all of the diesel trucks that i have had take about 17k to 20k to "break in"

[J P Stein]

You'll notice that there is a "top" marked on the compression rings. Some say "top" some have a dot. In some cases (Porsches come to mind) the upper and lower compression rings are different and are marked.....mine were color coded.

The face of the ring is tapered with the acute angle being the top.....in my experience (always gotta cover your a** here).
This knife edge is what wears fairly quickly and allows the ring to seat....or match the bore. You don't even want to put them in upside over.....it's been done.

There are many variables
Iron rings seat quickly.
Chrome moly rings take longer, as they are harder.
I believe 911 rings are iron.

I built a Chebbie motor long ago with moly rings, blew it up after 2000 mi and the rings still hadn't seated.......that's how I learnt'
about ND oil

The bores of the clys can create some problems for the rings to deal with.
Since the rings migrate around the pistons (and we are so careful to set gaps 120 deg apart ), if the bore is very far out of round, WAG, half a thou (but see your spec book), the rings will never seat. This tolerance should....OK, must be checked using a bore gage......nothing else will work.....I inspect machined parts for a living and have the "touch" but I wouldn't try it with an inside mic. This check is best left to pros with the tooling.

Surface finish of the bore comes in here, also.
The crosshatch hone on an iron cylinder is necessary for either ring material.
When puting together the 2.7L with Nicasil clys, I was quite concerned with their smooth finish....not to worry, I was told (yeah, right), the rings will seat.....if the cyls are in spec.

Thas about all I think know about that.

[ChrisBennet]

Break In Secrets
-Chris

[makaio]

Thanks for the link Chris!

[HawgRyder]

With the number of engines I have built over the years...bikes, cars, snowmobiles, trucks, and really big diesels...I use the same oil that I am going to use for the life of the engine.
Break in - when you start the engine for the first time...do not turn off for 25 - 30 minutes! (varying the rpm's)
Very important...if you turn the engine off before the valve train seats in...all of the special lube you put in when rebuilding will be washed away.
The cam to lifter (rocker) mating surface is pre-lubed and will seat in quite fast...but the rest of the engine takes more time.
After the first run....drop the oil and filter...I like to cut open the filter at this time to see what's going on.
Then...fresh oil and filter....run for 500 miles...oil and filter change again.
After this...change every 3000 miles (5000 Km)...and enjoy.
I try to run in the rings quickly....with 2nd or 3rd gear pulls from 2000 to 3500 rpm several times in a row....run for 5 minutes or so...then do it again.
After 20 - 30 runs...the rings will seat to about 75%...and will finish seating in the next oil change period.
Some of the big block chevy engines I have done this way are still going strong after more than 400K miles.
Bob

[RoninLB]

Originally posted by billncolo
I have heard a few theories, but not sure I have heard the right one. I would like to better understand the process so that I can have better results on my third attempt.

3rd attempt on same engine.. how many total miles on rebuild? did you do new pistons and cyl? and what oil are you using? how many miles did you run the engine at each start up? What kind of roads? these flat 6s are a PIA, IMO... I thought my leak down tester was damaged when I did a test after 3k.. it's tighter than a crabs ass.. and that's water tight.. maybe I got lucky........Ron