How Do Rings Bed In?

[Winston001]

I was talking to an engineer today and he referred to the bedding in of rings to create a perfect seal with the cylinder sleeve. Always heard about this but how does it actually work? Why doesn't it work sometimes? How does "running in" an engine help?

I enjoy learning about this stuff.

[Drew]

When the cylinder sleves are put in, they are scuffed up with a stone, which works like sand paper, so when the the rings first start gonin up and down past tehm they wear a bit to the exact shape of the bore.

Nowadays the running in thing is actually less for bedding in, and more a safety period incase something is very wrong, at least that is what I've heard from some reliable sources.

[homer]

It also allows for the heating and cooling effects in the engine
allows the working parts to polish and lets them get used to being placed under stress

Lets say i run over you foot

And lets say i do it another 100 times an hour later
do you think it will hurt more the first time or later on

[Motu]

The piston rings and cylinder go to bed together (with your permission of course) They pump up and down together quickly,generating heat....if they go too fast it's all over very quick and everyone is disappointed.By varying the speed the process can be extended.....and it all becomes very blissful and everyone is happy.

Rings can't go to bed with other rings,and cylinders can't go to bed with other cylinders - in the engineering world we have rules,and you cannot break them,no matter how hard you try.

[homer]

The piston rings and cylinder go to bed together (with your permission of course) They pump up and down together quickly,generating heat....if they go too fast it's all over very quick and everyone is disappointed.By varying the speed the process can be extended.....and it all becomes very blissful and everyone is happy.

Rings can't go to bed with other rings,and cylinders can't go to bed with other cylinders - in the engineering world we have rules,and you cannot break them,no matter how hard you try.

Yeah thats very clever

[Winston001]

You guys are great. Here I am laughing my head off having been gently threatened with pedial assault by Homer to illustrate his point, only to read Motu's classic description of how it all works.

[homer]

oops yeah
well its just to give the idea
i was laughing at the time as well

Where does that leave the lord of the rings
is he situated at the top

[Ixion]

The piston rings and cylinder go to bed together (with your permission of course) They pump up and down together quickly,generating heat....if they go too fast it's all over very quick and everyone is disappointed.By varying the speed the process can be extended.....and it all becomes very blissful and everyone is happy.

Rings can't go to bed with other rings,and cylinders can't go to bed with other cylinders - in the engineering world we have rules,and you cannot break them,no matter how hard you try.

Yeah? Wot abart the Knight sleeve valve engine then ?

[Motu]

Yeah? Wot abart the Knight sleeve valve engine then ?

That's a strap on.....one of the cylinders has to turn onto a piston.

[Winston001]

Enough of this levity and general chuckleheadeness. I have questions.

So a piston reciprocates within the cylinder. The rings touch the sides and flatten off high spots during the first few hundred thousand cycles. At this stage the motor is referred to as tight. Fine.

Pistons do not simply reciprocate up and down. There are lateral forces transmitted by the conrod to the gudgeon and thence to the sides of the pistons. The conrod converts a turning force from the crankshaft into a vertical force but there is some sideways pressure.

So logically, since the lateral forces only go to each side, the bore should become slightly oval. Right?

But rings are floating. How can they turn and flex and move yet form a seal if the shape they are forming changes every 90 degrees?

[Ixion]

It is actually more complex than that, in fact the crystalline structure of both a (new) bore , and the rings is usually changed in the process.

Not all rings float, two stroke rings are usually pegged as are some four strokers.

But in general terms you are right. Bores do become slightly oval with wear (in fact that is the most precise measure of bore wear, and why a hone on a lightly worn bore improves it ). And the ovality (though bear in mind that rings are flexible) no doubt is a major contributor to ring wear.

[jonbuoy]

I believe its the gasses from the explosion trying to force their way past the rings that pushes them out onto the bores and makes an even tighter seal. They do move and wear the bore and piston on the thrust faces - you can see scoring marks on the piston skirts to show this. Still amazes me that engines can be so reliable when you think of all that metal on metal contact and only a wee film of oil between them.

[007XX]

I just want to ask something, pretty please:

So, when someone says that the bike runs better after the running in period, is that because the bore has now become smooth(er) and is offering less resistance to the rings?

*and Motu's explanations rocked! *

[imdying]

Hush woman! The men are speaking bikes!

But yeah, that and lots of little bits all gelling together nicely.

[007XX]

Hush woman! The men are speaking bikes!

.

You talk to your momma with that mouth?
And there was I, trying to learn and take part in a serious bike thread...That''ll learn me!

Now, back on topic...does the "bedding in" time vary from bike to bike? For example: would a Vtwin take longer than a normal in line four?

Reason I ask: still doing research for potencial next bike.