Wait a minute....I was just thinking....When I said that .030" of end gap would equal such and such for the outer arc and such and such for the inner arc.....Does it work that way? Because the .030" is a linear dimension....and it wouldn't necessarily equate to a curved dimension would it?

I'm tired and it's too late to be doing this.....

ok, weigh the bugger and then measure it's thickness. you know the specific gravity of the material. should be easy to back into it's surface area, once you calculate it's volume and measure the thickness, no?

First off, is this noodle with or without cheese.

Second, as long as the ability of the first and second rings to scrap the bore as they travel is not compromised, the gap will be the blow-by control, as the engine ages and wears, the end gap become less of a factor and the residue left becomes more of a factor. Did you add the residue factor into your equation for itterations into the life of the component?

So, if you plot a curve of gap blow by versus wear blow by where the two curves cross is the apex of "Time to rering the engine".

Why would you want to conjure up old rotten memories of classes no one really liked.

Calculate the area of a circle of the larger diameter (L).
Calculate the area of a circle of the smaller diameter (S).

The area of the total ring (R) is R = L -- S.

Take the area R and divide it by 360 degrees or 2 PI radians (or even 3600 degrees or 20 PI radians) to get the area per degree or tenth of a degree.

Measure the opening as number of degrees or radians of a circle. Multiply that figure by the area per degree.

Sound right?

Ok ....... here are the areas - with some assumptions.

1. Cylinder diameter = 3.550 inches. Given
2. Piston diameter = 3.45 inches. Assumed
3. Depth of ring groove in piston 0.125 inches. Assumed
4. Ring outer diameter = 3.550 inches. Given
5. Ring inner diameter = 3.250 inches. Assumed
6. Ring end gap 0.030 inches. Given
7. Ring end faces are parallel when ring is in cylinder. Assumed

These numbers allow for the piston to move 0.025 inches either side of the centerline of the cylinder. Then the inner diameter of the ring is against the bottom of the piston ring groove.

This means that the area for blow-by varies. It will be a minimum when the piston moves toward the cylinder wall in a direction exactly in line with the location of the end gap.

The shape of the area is per that attached bmp image earlier. The outer arc is the cylinder wall, the parallel lines are the ring end faces and the inner arc is the piston. Note that the 2 arcs do not have a common center due to the pistons movement. They will only have a common center IF the piston is sitting exactly in the center of the cylinder.

The minimum area for blow-by using the figures above is 0.00075002 sq. in., the maximum is 0.00225002 and if the piston is perfectly centered the area is 0.00150002 sq. in. If the piston moves toward the cylinder wall in a direction exacly 90 degrees to the end gap location the area is 0.00150545 sq.in.

What I do not know is ....

1. How much blow-by is from gases getting in behind the rings.
2. How much blow-by gets through the first ring end gap AND then gets through the second ring end gap.

Is it always assumed that there is never any blow-by from gases going in between the piston and rings ?
As the end gaps do not line up vertically is it assumed that what gets past the first ring will always get past the second ?

regards
Doug I

PS If someone could given me the real world numbers for those that I assumed, I can give you the real world areas :)

...

The ineer diameter of the rings ?

This allows the piston 'slop' to be figured.

And to keep it simple let's say that ALL the blow-by ONLY goes through the end gap, and that everything that goes through the first goes through the second.

Actually what you have already measured is the nett blow-by after going through the 3 rings (2 compression and 1 oil). If I'd thought about it I'd have realized that sooner :rolleyes:

Ok ...
cylinder = 3.5511 in.
piston = 3.5507 in (4/10000 clearence ?)
end gap = 0.030 in

piston perfectly centered in cyliner

Blow-by area = 0.00000600 sq.in.

If the piston moves over and touches the cylinder wall the area less than 0.000000005 sq.in.

If it moves the other way the area is 0.00001200 sq.in.

regards

I did notice that there were few Gasholes replying to this thread!
I know the answers but I am not telling. Y'all won't learn unless you do it the old fashioned way. :D

What ? you mean counting on ya fingers ?

Just run it tight...............

Dang, I need an asprin and I only skimmed the threads.

Is the drawing you attached to the thread at a 1:1 scale? If so, I can import the image into AutoCAD, trace it with some lines, and come up with a real close section area for you. let me know.

Is the drawing you attached to the thread at a 1:1 scale? If so, I can import the image into AutoCAD, trace it with some lines, and come up with a real close section area for you. let me know.

Hey Jay......nah....it was something I freehanded in Paint.....hehehe....I was just trying to let everyone get an idea of the shape.

I think I got everything I need so far...I made an Excel spreadsheet with two different sheets....one for a "riemann sum" of the area....and one that's more exact. They're not too far apart.

I really appreciate your offer though.

ain't physics fun ya'll :)

I love it when I'm not rusty at it. Sitting here trying to figure out stuff that I knew like the back of my hand 2-3 years ago sucks.

You don't need any math higher than simple algebra to calculate the area of the gap.

big circle - little circle = area of ring that is exposed
bore circum/ring gap = percentage of area that is gap

Thank you mr Fixit for taking what was developing into a complicated work problem/equation from Hell and putting it into terms Humans will understand.


Excuse me while I take a gew asprin and try and calculate the volume of Beer of my Miller Lite using the old mouth to stomach equation. ;)

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