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Ring end gap question
Posted by: rlp11 ()
Date: March 06, 2022 12:55PM

Hi All

Book says .013" -.025" for top two rings. I would like to know what you gap them to. Closer to .013 or closer to .025? This motor I am building is .105" over bored and will be 8.75:1 compression. Will this make a difference in the end gap?

Oil rings .015" to .055".
Do you gap all three or jut the top and bottom ones? And closer to which end of spec?

Thanks

Roger Parent
El Cajon, CA
1964 Monza Driver
1964 Monza Project

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Re: Ring end gap question
Posted by: dryenko ()
Date: March 06, 2022 01:03PM

I use .003 -.0035" gap per inch of bore .
Remember out cylinder bores expand more than a water cooled engine does.

Bob C aka Dryenko
Dobson, NC 27017

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Re: Ring end gap question
Posted by: 66vairman ()
Date: March 06, 2022 01:32PM

Basically take the increase in bore circumference, vs. stock. and take the percentage increase and apply it to increase the ring gap.

Keep in mind a piston ring expands and will bind, or break something, if the gap is too small.

A gap too large means a little more blow-by.

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Re: Ring end gap question
Posted by: JimBrandberg ()
Date: March 07, 2022 08:58PM

I seem to usually end up about .016-.020 on the top ring. I haven't had to file any in years.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Ring end gap question
Posted by: gerg ()
Date: March 08, 2022 06:45AM

I have only built 3 Corvair engines now using Hastings rings. I found it interesting that the gaps all measured at the upper end of the range THEY specify out of the4 box.

Every VW engine I have built had tight gaps out the box that you would file to desired and / or required gap.

gerg
Monroe, LA


Current cars and other fun stuff -> [gregblakeney.smugmug.com]

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Re: Ring end gap question
Posted by: vairmech ()
Date: March 09, 2022 03:20PM

You say you have an overbore so you need to increase the gap accordingly. You can't use the book other than a reference of where to start your figures.

So any numbers quoting the book for stock numbers are useless in your case.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Ring end gap question
Posted by: rlp11 ()
Date: March 09, 2022 03:40PM

Ken

That is why I ask where to start. With my .105" over bore and using 1986 Cavalier .040 over pistons. This gives you a 3.543" bore. Yep a 2.85L motor. I would like a place to start. I have just finished gaping a set of rings with a .020" end gap. Hope this will work.

I'll let you know.

Thanks

Roger Parent
El Cajon, CA
1964 Monza Driver
1964 Monza Project

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Re: Ring end gap question
Posted by: wittsend ()
Date: March 09, 2022 05:00PM

.105 is roughly a tenth of an inch. Using the mentioned .003-.0035 per inch above it would seem the gap increase would only be .0003-.00035 for an additional .105 diameter increase.

If the whole circumference of the ring is a factor to consider then multiplying by 3.1416 barely gets you slightly under/over .001 gap (.000942/.00109) using .003/.0035 and given the .013-.25 specs mentioned I'd say Op's .020 gap is right in the middle of that.

At .003 X 3.542 (the .105 overbore) the gap number is .0106 which is actually under the spec .013 and at the .0035 x 3.542 (the .105 overbore) the gap number is .0123 which again is slightly below the .013 minimum in the book.

.105 is a very sizable increase in bore. Thus as the overbore decreases to more common .060, 030 etc. the difference would be roughly half a thousandth and with a feeler gage is that even detectible?

I don't mean to be decisive, but are these small differences even worth being concern about except to an engine that has gaps right at the lower limit and one that will be run hot? The math seems to say the difference even with a rather large bore increase is very minor and there seems nothing wrong with hitting it right down the middle (.020 in this case) of a rather large difference (.013-.025). If my math is wrong please let me know I don't want to ill advise anyone.



Edited 1 time(s). Last edit at 03/09/2022 05:02PM by wittsend.

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Re: Ring end gap question
Posted by: vairmech ()
Date: March 10, 2022 05:48AM

rlp11 Wrote:
-------------------------------------------------------
> Ken
>
> That is why I ask where to start. With my .105" over bore and using 1986 Cavalier .040 over pistons. This gives you a 3.543" bore. Yep a 2.85L motor. I would like a place to start. I have just finished gaping a set of rings with a .020" end gap. Hope this will work.
>
> I'll let you know.
>
> Thanks
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

BTW, that is the same piston I use for the kit I put together. Why didn't you say what bore you were using? I use .020-.025 end gap. You also need to increase your piston to cylinder clearance, I use .003 as a minimum there.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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