[2005bully]

I need "L" section piston rings for a highly stressed air cooled 2 stroke race kart engine. I have searched the world over with NO LUCK finding one that is of high enough quality in the size range required. (56.5mm bore) So I set out to manufacture a few of them myself....... I thought that the hard part would be creating the proper ring profile. But that seems to be very doable. The problem is selecting a material that will retain its spring tension at temp. From information found on line I am advised to look for a material with about 18%cr with substantial amounts of Nickel and or cobalt. That criteria falls into the "super alloys"... The first "super alloy" I tried was "nitronic 60". It was chosen with the hope that it could be used without heatreating. But after a short run time the rings lose to much of their free gap (spring tension). The next consideration is stainless 330, alloy 25 or inconol 625. I can only find these materials in round bar which makes the pricing rather steep using it for piston rings. Hoping someone here can point me in the right direction before I get in a lot of material I can't use. The cylinder liner is centrifugally cast steel. And if the ring material chosen is not compatible with the liner, I can have the face of it hard chrome plated. Thanks for any input.......2005bully

[RICHARD ZASTROW]

"L" rings aka Dykes rings were used on Rotax engines.

Try Franks Rings, they may already be in stock. If not, he probably is set up to make them.

Dick Z

[2005bully]

I am aware of Bowman the ringmaster. Passed on him earlier, under the impression that he only made rings out of cast iron for very small rc motors. Rotax did make some snowmobile engines with 57mm bores that used L rings. OEM they were a full Keystone, some of the aftermarket replacements still available are 1/2 keystone, And nowadays all of the new aftermarket pistons have gone to rail rings. Original plans were to use the Rotax rings in-fact I have tested several sets.. But the rings radial force created by the angle of the keystone, together with their narrow radial width created to low of a thermal limit. Thanks for the suggestion. I'll contact Frank and see what he has to offer.... 2005bully

[RICHARD ZASTROW]

Our Rotax race engines worked fine with the Dykes (L) rings. We kept our exhaust temps @ 1100 deg.f and didn't melt pistons. 440cc gave us 167 hp., 340 115 hp. all on 100 octane gas with 60:1 oil mix.

These were snowmobile engines in cold air. Nice dense air with plenty available oxygen.LOL

Just remember, they run best just before they melt or blow up.!!!!!!!

Dick Z

[2005bully]

When it comes to engineering 2 stroke engines Rotax has proven they are at the top of the game. The race engine project here however has somewhat different requirements than a "production" Rotax snowmobile. In this case the engines are air cooled running on "loaded" fuel. They displace 150cc with a usable power band width of 11,000 to 18,000 rpm's, and make 60 plus bhp. The expected life span of the piston ring assy only needs to be in the range of 2 hours. The piston crown temp is the limiting factor in power production, and the "L" ring design is key to keeping the piston crown temp under control. The Rotax "L" rings are well engineered. They seal well, resist carbon build-up, last a long time in their intended environment. But when used in this application they create excessive drag and don't dissipate enough heat out of the piston crown. We need a ring with more radial width, non keystone ring lands, and constructed of a material capable of withstanding very hi temps. Machining such a ring with the profile we require is handled. Just hoping to find some guidance in the choice of materials. 2005bully

[Dougal]

What temperatures do your rings actually run at? Have you measured cylinder wall temp as that will be reasonably close.
You won't get anywhere near exhaust temps so superalloys aren't needed.

[2005bully]

Thank you for the reply....
As far as actual internal cylinder wall temps...I don't know a really good way to measure while the engine is operating. The head temp at the spark plug will run 320 to 360f under normal operating conditions. 400f is the absolute max CHT. Exhaust temps measured 2 inches from the piston will run 600 to 800 degrees under normal conditions, with melt down usually occurring right around 1000 degrees. These engines are air cooled and the the temp of the cylinder varies greatly around the circumference of the bore. I ran some tests with the CHT near max. Then used an infa-red thermometer to measure the external cylinder temperatures in-between the cooling fins. The intake side reads in the range of 260 to 310f. Close to the exhaust port temps would flash as high as 450 degrees. Not really sure if that test is representative enough of internal wall temps. Another clue that might better represent ring temps is the discoloration of the ring itself. On smaller bore engines where quality L rings are available, when near max temps the bottom side of the ring will discolor to straw color to slight blue. The color at the bottom of the ring land tends to be rubbed away rather quickly unless the engine is shut down immediately after such a hi temp is reached. I attached a photo that shows the bottom side of a ring shut down right after max temp was seen. Not knowing the alloy of the existing rings, this might not be usefull information either. Thanks for any input..... 2005bully

[Dougal]

Some heat-treating colour charts will give you a good idea of how hot that particular ring got. I used to know some of that, but have since forgotten.

My watercooled diesel engines run exhaust temperatures up to (and sometimes higher than) 750C, but the cylinders and head do benefit from the water cooling.
I have friends involved heavily in kart racing, but I've never been involved myself.

[packrat]

In your first post on this, you said your cylinder liner was cast steel. If you are using steel for the rings it makes it, steel against steel. This years ago was a no-no, never put like materials in a sliding movement. The use of like materials was said to cause "micro-welding"

Have you tried Ductile Iron for the rings?

[2005bully]

Most of the rings are hard chrome plated at the wear face. Tried Ductile iron rings. They break with-in the first 2 or 3 dyno pulls. Again there are no issues with any part of fabricating the ring except the choice of an affordable material that will withstand the temperatures involved with out losing tension. Nitronic 60 worked very well except that the free gap starts to close up with exhaust temps even as low as 700 degrees. I know Waspalloy and some of the Inconel alloys will hold up. But can not find any small qty's of these alloys in tube. That means making the rings from Solid bar stock which is very expensive. 2005 bully

[packrat]

Have you tried contacting some one like; Inconel 600®- UNS N06600 - Sheet, Plate, Bar, Wire Pipe, Tube (tubing), Forgings, Flanges, Fittings- Magellan Industrial Trading Company, Inc Some times it works better to call and talk directly with people, rather than sending a E-mail. Harder to say no talking direct

Here's a whole page of companies to try if they say no; inconel pipe suppliers - Google Search

Before calling look at a pipe size chart; Ansi Standard Steel Pipe Chart and see what size comes close (if any) to what you can make the rings from. Ask if they have any "drops", short left over pieces from orders other people bought.

Hope this helps, cary

[Dougal]

I figured with any custom machining job like this, material cost is only going to be a fraction of the final price.
Pipe vs machining from bar/plate would be the least of my concerns, there's probably only $20 in it. If you were making 100 then that $20 would be a concern.

[packrat]

I figured with any custom machining job like this, material cost is only going to be a fraction of the final price.
Pipe vs machining from bar/plate would be the least of my concerns, there's probably only $20 in it. If you were making 100 then that $20 would be a concern.

I take it you haven't priced Inconel. When I served my apprenticeship we worked a lot with Inconel and had to account for all the scrap and return chips and bad parts back to customer.

[Dougal]

I take it you haven't priced Inconel. When I served my apprenticeship we worked a lot with Inconel and had to account for all the scrap and return chips and bad parts back to customer.

I'm 99.9% sure he won't need inconel.

[nateacox]

420SS - Stress relieve at 1150F, Gas Nitride afterwards. CrN coating on the Face would help as well for reduced friction. This is what type of ring we currently sell for Nitro and Alcohol blown engines.

What type of ring gap are you targetting?

Nathan Cox
Hastings Piston Rings
Hastings Piston Rings...Since 1915

[packrat]

I'm 99.9% sure he won't need inconel.

O/P's first post asked about Inconel

[2005bully]

nateacox......Thanks a million. That is just exactly the type of information I was trying to come up with. In the past on comparable engines with "production steel/chrome faced rings" I have set end gaps in the range of .008" to .014". With a ring land clearance of .001" to .002". How essential is the CrN coating to the face? Can I get by at least for testing running the 420ss directly against the liner? Again thanks for taking the time!!!!

[2005bully]

Nateacox... For reference here is the process being followed to make these rings. The 420ss is cold rolled round bar stock that in a V.M.C is machined leaving .004" over size on the final O.D. Next the ring is compressed around a fixture that registers to the I.D. of the ring. This fixture clamps the ring in tight from the sides and while held between centers the od of the work piece is ground to rid its face of any machine marks. Next the ring is removed and while in its free shape is clamped between flat plates and "stress relieved".
Is this the right track so far?
If it is then next is Nitriding and plating. I checked with our usual heat treater and they do not offer gas nitriding. Plus they were not aware of anyone in the area that does. Looking on line there appears to be about as many proprietary Gas nitriding processes as there are business's that offer the service. What do I need to know to make an informed choice for this next step? 2005bully

[2005bully]

Recently my Son (Chris Buller) won the IKF (international karting federation) open class national championship using a piston ring that information from this forum allowed me to construct. I still have a ways to go with improving my fabrication methods. But the performance these rings offer in severe working conditions is beyond expectations. A special thank-you goes to Nate Cox. As well as the others that contributed.......

2005bully Kermit Buller


Link to the IKF web page results....


http://www.ikfkarting.com/OfficePage...peedway&SM.pdf