I will write a quick Technical Paper dealing with the finish on an RC Nitro Engine Liner to obtain optimum performance and fit longevity. I have been doing this to my own engines for 20+ years and have not told many people about it. This is a performance edge that you can now take advantage of. Have you looked at an rc nitro engine liner than has been run for a while and is really running well? What you will see is a finish on the top section of the liner where it gets tight on the piston that has a mirror finish. That is the optimum finish for performance. The Nova Rossi is a great example of the long break-in period to get a great running engine. They use very high silicon content pistons that are HARD and last a long time. It does take a lot of time to get the shine on the liner and still retain a little bit of bump.

I have an easier and much better way to break in an engine quickly to get to the mirror finish and great performance?

There are a few things that you should know about this process. This will apply for ANY RC Nitro Engine with a chrome liner finish. Even the OS Engines with the Nickel finish will benefit and be treated the same way. The nickel is a little softer so it doesn’t take as long to break in as the chrome liner.

History:

20 years ago, one of the foremost RC Engine Tuners (John Ackerman) obtained a Sunnen Hone to finish liners of his own engines and some of his closest friends. This tool cost about $500 at that time and was a superb tool to get a very round liner configuration. Many liners at that time were less than round and trying to get a round piston to fit perfectly in them was impossible. This tool made that easily possible. We could now hone our liners perfectly round.

John, in talking to the people at Sunnen, found that they had a product called “Cork Bond” that they said would be perfect for putting a mirror finish on the liner. Sunnen told John that the Corkbond didn’t take off hardly anything; it just shined up the liner. Thinking about this, he knew that this would probably eliminate most of the break-in required. John got some Cork Bond stones for the Sunnen Hone and as they say “The Rest is History”. We did find that the engines did not require ANY break in at all. They were ready to run at maximum right after “Cork Bonding”. John and I were working together on projects at that time and I started Cork Bonding all my engines. I never had to break an engine in again. Performance was much better too. John provided that service on all engines that he modified and people were super happy with the results. John has not been modifying engines for several years now and the service has not been available.

What does Cork Bond do to a Liner?

If you can imagine a liner under extreme magnification, the liner is like a metal file that has been coated with chrome. There are machine marks that are exactly like the cutting marks on a file. Imagine the piston working on this surface! Either the piston will wear out or the liner will become polished. Actually, both happen. The piston material gets scuffed off by the marks and the liner eventually becomes like a mirror. At that point, the engine will run at its optimum, but many times the “bump” is gone. If you would replace the piston at that time to tighten it up, that would probably be the optimum. With Cork Bond in a Sunnen Hone, all of this is unnecessary. You can just run the hone in the liner to make it like a mirror and you are ready to run at maximum performance.

Roundness of the Liner and Piston:

Any of you that have used one of Brad Christy’s Pistons, know that he offers to fit the piston to your liner for a small additional fee. Brad started using Cork Bond a couple years ago. Now he will “Cork Bond” your liner at the time he fits your liner with one of his new pistons. He is enough of a machinist that he made his own hone holder for the Cork Bond Stones. Our Sunnen Hone is slightly different though. Ours has a built-in taper to it, which closely adheres to the liner taper. Stu Barr also bought a Sunnen Hone a couple years ago and uses it on his own engines. I understand that he also provides the service to some of his customers. The setup that Ackerman had is slightly different than either Brad or Stu in that is has been modified to build in the taper that is found in all liners. This took a Master Machinist to do the taper modification for him.

Helical Lap:

Another question often asked: OK, now the liner is perfectly round after honing, how about the piston roundness? Another of the tools that John Ackerman used all the time to get the perfect piston/liner fit is called a Helical Lap. It is constructed so that you can lap a piston PERFECTLY round so that it will really seal perfectly to the liner. Most current pistons are manufactured on very good equipment and do not require this lapping treatment. However, we now have the ability and equipment to complete the lapping process in addition to the honing process.

There is now an alternative….. I recently obtained all of John Ackerman’s tools, supplies, machines, engine parts, etc. The hone was part of it. I am going to place the hone in the hands of Norm Doerr to provide the service of “Cork Bonding” to the boating and rc car racers, in addition to his Propeller Heat Treating Service. I could just keep this important tool to myself, but that is not the way that I operate. I personally don’t have the time to provide the service, but Norm can and will provide the service. John misplaced the small .21 sized hone and I am in the process of obtaining that adapter. I will set up a small website to allow ordering of this service sometime in the future, but for the present, if you need to contact Norm do so at: norm@hobbyheattreating.com or call him at: 727-452-5395 (Cell).

CONCLUSION:

I hope that this discussion will be helpful to you in getting the maximum performance out of your RC Nitro Engine. I can guarantee you that this finish on a liner, will provide maximum performance over the longest period of time. You will have a liner that has a super mirror finish and will hold a good fit (“bump”) for the longest time.