Piston ring gap size exactness

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rebelrouser
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Re: Piston ring gap size exactness

Post by rebelrouser »

ring endgap is a minimum clearance not a maximum clearance, if its a thousands or so bigger I personally don't sweat it. If they are too tight the rings can butt and break under running temps. A little loose a tiny bit more blowby.
I have an old set of KD feeler gauges that are double ground one thousand difference on the tip. It takes away a lot of the issues with drag or feel when checking end gaps and adjusting valves. If the tip slides in and the main blade will not you have the right measurement to one thousandth.
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Re: Piston ring gap size exactness

Post by CGT »

Drag from the feeler gauge can be deceiving when filing rings. Sometimes it takes getting them deburred and them rechecking them to get a good feel for whats going on. If its a conventional headed, firing ordered sbc, throw the looser ones in one of the center cylinders.
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Re: Piston ring gap size exactness

Post by engineguyBill »

I don't believe that there is any advantage to installing a torque plate when gapping the rings. Once you have final-honed the cylinders with torque plate properly installed, you are good to go. The cylinders are as round as they are going to be. A ring squaring device is absolutely necessary to insure that the rings are square in the bores.
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Re: Piston ring gap size exactness

Post by jed »

Can u use a flat top piston of the same bore size to square the ring in the bore??
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Re: Piston ring gap size exactness

Post by zums »

engineguyBill wrote: Mon Mar 19, 2018 1:25 pm I don't believe that there is any advantage to installing a torque plate when gapping the rings. Once you have final-honed the cylinders with torque plate properly installed, you are good to go. The cylinders are as round as they are going to be. A ring squaring device is absolutely necessary to insure that the rings are square in the bores.
Cant say that is true if it was honed with a plate, ive seen more than once the end cylinders on a Bowtie SBC which is quite a bit stronger than your typical block go out of round .0008-.001 with the plate removed, so now before you even start to gap your rings there is a .003 difference in gap from the top of the bore to less than 2" down the bore
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Re: Piston ring gap size exactness

Post by engineguyBill »

jed wrote: Wed Mar 21, 2018 7:27 am Can u use a flat top piston of the same bore size to square the ring in the bore??
Yes.
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Re: Piston ring gap size exactness

Post by rebelrouser »

For a squaring tool, I go to the Dollar store and buy cheap rolls of masking tape, pull off the tape until the roll fits the bore perfectly and use it to square the rings.
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Re: Piston ring gap size exactness

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jed wrote: Wed Mar 21, 2018 7:27 am Can u use a flat top piston of the same bore size to square the ring in the bore??
Captain Obvious here: Just be sure to leave a ring on it as a stop to keep the piston square in the bore and don't try it on your 348/409 Chev. :lol:
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Re: Piston ring gap size exactness

Post by Mark O'Neal »

I need a feeler gauge that will measure 5 ten/thousandths....... :D
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Re: Piston ring gap size exactness

Post by Mark O'Neal »

jed wrote: Wed Mar 21, 2018 7:27 am Can u use a flat top piston of the same bore size to square the ring in the bore??
If you make sure the piston is flat. I've made a lot of flat tops that were .010 to .020 taller on one side.

The rules said flat, they didn't say parallel to the pin.
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Re: Piston ring gap size exactness

Post by David Redszus »

As stated earlier, ring end gap should be sufficient to prevent ring ends from touching under any operating condition.

We can measure cold clearance and we can calculate hot running clearances. It becomes a bit more complex to determine the ring end gap clearance during warm-up and transitions when the bore, ring and piston are not at the same temperature.

Ring end clearance should be measured at several vertical locations within the stroke travel. Any cylinder that has a taper will cause end gaps to change as the rings move vertically.

While most all engine blocks will show some change in ovality with and without a deck plate, the rings used for rebuilds are typically flexible enough to conform to first order distortions. An oval bore is acceptable, a triangular or clover leaf shape is not.

Also note that combustion forces will cause a deformation of bore shape. After run-in, it is a good idea to check bore surfaces for wear using a surface profilometer, not a bore gauge.
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Re: Piston ring gap size exactness

Post by MadBill »

Some racing side valve air cooled motorcycles were notorious for developing a shiny low spot in the cylinder wall adjacent to the exhaust port, where it bulged in due to exhaust heat. A re-bore would lose power until the new surface wore similarly.
Maybe they could have used a torch up the port during honing... :-k
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