ENGINE - "THE FIT" Technotes (2/95) "The Engine Analysis Program" How to Measure the Seal of the Liner & Piston:(" The Fit") 20 years ago, a very accomplished model boater told me of a way he tested his engines to determine "The Fit". (Will Discuss Later in the Paper) THE LINER: There are many items which go into the engine with a perfect or near perfect fit. The taper of the liner from above the exhaust port to the top of the liner. You are in most cases stuck with the manufacturers specifications unless you have the liner honed and re-chromed. You can find a few people around the country who will do this. Henry Nelson is the most popular of these. Another item contributing greatly to fit is the roundness of the liner after the manufacturer hones or grinds the chrome. Many liners are not round and the only way to get them round is to have someone with a Sunnen Hone, hone and Corkbond the liner to force it to become round and with a nice finish. The finish of the chrome is also very important to "the fit". The chrome comes from most manufacturers with a slight swirl on the finish which is from the machining process. After an engine is run for a short period of time the area at the top of the liner where the fit is the tightest will become bright and shinny. This is sometimes easy to get after a short run-in period and sometimes it takes a long time. The taper and metallurgy of the piston determines this. As an example, the Nova Rossi 21 takes a great deal of time to break in and get this great seal. I have run several gallons of fuel through a 21 with little effect on breaking in the engine. When you get an engine like this, this is the best metallurgy you can find and is highly desirable. (Be Patient !) If you want to make the liner round and create this high polish finish I would suggest you find someone with a Sunnen Hone. He should use a very soft stone to make the liner round and then finish with "CorkBond" to create the polish. The only people I know who have this capability are John Ackerman, Steve O'Donnell, and Henry Nelson. Now the liner is round & with a polished finish. (You don't want to put a square piston in a round hole) NEXT TIME: The Piston