Propwash April 2019 web.pub

or an AAC type engine because there is no piston ring to be seated. Taper masters are used to grinding the needed taper on the liner and pistons. They are used to cut taper amounts that vary by .001" (.02 mm) over a distance of .100" (2.5 mm) on pistons. The piston's circumference at its top is tapered for use in tapered cylinders. The pieces are machined 20X longer in length to make setting of the compound accurate. For a .001" (.02 mm) taper per side, the diameter at both ends varies by .020" .5 mm) over a distance of 2.000" (50 mm). The top pieces in the photo are used to cut or grind tapers in cylinders. They are 2X the actual length of the 1.635" (42mm) length needed. The diameters at both ends vary by .001" (.02 mm) but over a distance of 3.270" (83 mm). They are machined with a length that is at least 2X the actual length required, but sometimes 20X the actual length required. Each taper master can be reset while being held in a precision grade collet and indicated at both ends for concentricity. A .00005" indicator is used for this operation and for the setting the compound's angle. A Themac tool post grinder, turning at 26,000 RPM, is mounted to the compound to grind the cylinder's ID taper. The grinder’s stone is diamond dressed after mounting. The fixture, mounted in a collet, allows for precise centering of the cylinder by indicating the cylinder's OD. Grinding gives a superior finish to the chrome that cannot be achieved with honing, even if the cylinder is finished honed with 95 grit stones. The 4032 aluminum sleeves used in all the Nelson Q-40 pylon racing engines are chromed in the same way. The process involves several different chemicals with the same type brass fixture, PVC holding fixture and CrO3, H2SO4 bath. The chrome plated on aluminum is as hard (approximately 1100 Vickers) as any plated on a steel or a brass piece. The only real difference is in the cleaning and etching processes involved. Many engine manufacturers have given up on chroming aluminum cylinders because of this. The information below is for brass liners. The mixing of all chemicals should be done with a protective rubber apron, rubber gloves and a face splash shield. All chemicals are mixed by volumes in their particular ratios. 1. Mix hydrofluoric acid and nitric acid in a 1 to 3 ratio by volume. 2. Mix nitric acid and water in a 1 to 1 ratio by volume 3. Mix zincate and water in a 2 to 1 ratio by volume. The procedures are as follows: 1.With rubber gloves on, clean the cylinder's ID twice with Dawn dish washing soap and hot water. Use a nylon bottle brush to scrub the cylinder's ID. While holding the cylinder on only its outside with a formed aluminum wire, place the cylinder and aluminum wire holder in the hydrofluoric and nitric acid solution for 30 seconds. Agitate the piece and solution together. Remove and rinse in hot water. 2. Place the cylinder with formed wire in the zincate and water solution for 60 seconds. Agitate the piece and solution together. Remove and rinse in hot water. 3. Place the cylinder with formed wire in the nitric acid and water solution for 5 seconds. Remove and rinse in hot water. 4. Place the cylinder with formed wire in the zincate and water solution for 90 seconds. Agitate the piece and the solution together. Remove and rinse in hot water. 5. Place the cylinder, with its brass holding fixture, in the preheated chrome tank after attaching the anode (positive) and the cathode (negative) contacts. All connections MUST be solid connections. With the power turned on, place the entire fixture in the chrome tank. The current should immediately begin to read. Use the half current amount for approximately 8 to 10 minutes and then the full current amount for 90 minutes. The full current amount is calculated from the total area of the cylinder and it's brass holding fixture, divided by the current to give 3 amps/ sq in. With a lead antimony anode of 1/4" clearance, the tank should be able to put on .001" to .0015" of chrome/ side. Improper cleaning, etching or bad contacts will result in blistering, pitting or poor deposit thickness. If done properly, with a bath temperature of 125* to 130* F, a current density of 3 amps/ sq in, the plating should be approximately 950 to 1,025 Vickers hardness. This means the plating cannot be cut with any type of carbide tooling! The next step is finishing the chromed liner and matching pistons. This can be done with a Themac tool post grinder in a lathe if both are in excellent condition. Jim uses a sulfur based grinding oil, Sunnen #MB 30-5, which has been used to previously grind chrome. I make the 1” (25 mm) dia X .750 (19mm) wide (100 grit) wheels, and grind at 26,000 rpm to get the proper finish. The compound can be set accurately and quickly with taper masters shown in the photos below. The typical amount of chrome to be removed will be less than .0005" (.01 mm) per side. To make all the cylinders being ground a particular size, a tapered, hardened steel gauge is used to measure the ID. It's depth in the cylinder determines what size is being ground. No cross hatch pattern is used in an ABC PROPWASH April 2019 27 Taper Masters Liner in Grinding Fixture