View Full Version : gapless rings

01-03-2006, 05:51 PM
I finally got some time over the holidays to finish hone the cylinder on the 1/2 scale. So now it's on to the piston and rings.I know there have been several posts about making rings,but they have been for rings that are split straight across.So now for the question...How do you make gapless rigs?Played around this afternoon making one out of scrap.I could not get the ends to match up with the step.There is something I'm missing here and can't figure out what.

Alistair Hosie
01-03-2006, 06:10 PM
Good question I suppose if you want to be scientific a piston ring with a gap is not a ring. So all rings are therefore as far as I not gapless.Alistair

01-03-2006, 06:25 PM
Not an answer to your question but in my experience with drag race engines gapless rings don't yield noticable power. A good set of rings hand fit work very well. As I recall my top rings where toolsteel but it's been awhile.

-Christian D. Sokolowski

01-03-2006, 06:32 PM
I agree with you Alister.But I do know that the step feature in a so called "gapless" ring does make a difference on the longevity and how much blow by you get on a large bore steam cylinder.

[This message has been edited by burnlast (edited 01-03-2006).]

01-03-2006, 06:44 PM
I think they're refered to as rings because they are circular not because it's closed. A ring doesn't necessarily have to be round to be a ring either.

There's several types of piston rings that are called gapless. It's really a misnomer because they aren't truely gapless. Some use overlapping parts and some use a dual ring design. In truth, they still have a gap to allow for cylinder wear and/or some dimentional changes to the cylinder and piston during operation.

To be accurate, steped or overlayed rings need to be ground at the contact point. The contact point or joint has to be able to move.

01-03-2006, 06:47 PM
RSR911,not looking for any power gains out of this.The steps I think restrict the blow by a little better especially when the ring gets a little worn.I have had a friend of mine replace the rings in his full size engine that were "gapless" with straight cut ones and in the middle of his 2nd season of running them,the blow by was worse than with the old original gapless.

01-03-2006, 09:35 PM
Automatic transmissions use step rings if you can find a supply house that is heplfull.

01-03-2006, 09:44 PM
One form of gapless ring is a sort of spiralock affair. Others have a stepped or notch alignment. I like file fit. Moly tops, cast seconds. Determine the gap by examining the thermal characteristics of your cylinder/piston.

Is your engine a four stroke? JRouche

01-03-2006, 10:44 PM
If he got that much blowby after two seasons he didn't hand fit the rings properly. Basically you set a ring square in the bore, measure the gap (or lack thereof) and the file until you have the right gap. It's been about 8 years since I last built a drag motor but I seem to remember gapping the tops a little loose due to the tremendous and rapid heat buildup during a 1/4 mile blast. Essentially the block doesn't have time to expand like normal yet the forged aluminum pistons would expand a lot during a run. A true drag motor is worn out before it's ever run in everyday vehicle terms. bearing tolerances and piston tolerances are really loose, when I put mufflers on for short street drives I could hear the piston slap while warming up.

Depending on what it is your building a good hand fit ring should work real well, however I can appreciate the craftsmenship in making gapless rings, show us a pic of your work.

-Christian D. Sokolowski

01-03-2006, 11:02 PM
My experience is that gapless rings do indeed work. Since I changed to them on my blown alky motor I've had a lot less trouble with alcohol dilution in the oil.
A leakdown test shows they do seal better than standard rings....and for a far longer period of time.
I use the dual ring type...with the thinner sealing ring under the thicker ring.


01-03-2006, 11:26 PM
alky motor, now that's a whole different story. I almost went that route but didn't want to deal with the wear from cylinder washdown or the invisible flames. I love the smell when they run though.

-Christian D. Sokolowski

01-03-2006, 11:51 PM
Ooop's!!!!! Thought I had mentioned that this is for a steam engine.Sorry about that,got ahead of myself.On steam,blow by causes all sorts of problems on double acting steam engines.Also ring grooves are a lot deeper and wider than what would be on a modern internal combustion engine.The dimensions on the ring is 4.500 OD, 4.0 ID by .250 wide.The bottom of the ring groove is going to be 3.500 dia.

01-04-2006, 12:57 AM
Okay,since nobody else has an answer here goes http://bbs.homeshopmachinist.net//biggrin.gif

Make your blanks to the finished thickenss,but oversized by an 1/4"on the od and undersized by 1/8" on the id.

Clamp the ring on the mill table and mill a 1/4"wide x 1/8" deep slot through from the side.Flip the ring and repeat with the groove milled offset from the other by 1/4".

This should split the ring and provide you with your overlaping .

Next mount the ring on a faceplate clamping the ring on the inside with the overlap closed so you can machine the od to the finished size.Once the od is machined reverse the setup and hold the ring by the od with the overlap closed and machine the id.I found it easier to make a jig from roundbar to chuck up in the lathe that had a shoulder turned to the same id as the ring and the length of the shoulder slightly less than the thickness of the ring with five or six button head screws tapped into the end so that the heads clamped the ring to the jig.

Check the fit in the bore like mentioned above.If all is well file .005-.010" of the tips of the overlapping joint for clearence.

Next put them in the oven at 450-500F for couple hours to normalize.

It's tedious,but it does work.I had to make a few for an old Gardner Denver steam pump a few years ago.Those were cast iron I got in blank form from a ring company here local.They are gone now,but then I could get blanks 3/16" thick x 1/2"wide crossection.

[This message has been edited by wierdscience (edited 01-04-2006).]

01-04-2006, 01:20 AM
Dang, I was just about to say that! http://bbs.homeshopmachinist.net//biggrin.gif

Al Messer
01-04-2006, 04:57 PM
Try this source: