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Balancing a Warner 165 Engine

I've been overhauling my Ryan SC-W's Warner 165 engine this winter and one of the last steps before final assembly of the bottom end is balancing the crankshaft. If you are not entirely sure of the operational and overhaul history of your engine it is worth doing at least a static balance, since Warner 165s have been assembled with different piston and counterweight configurations. Performing a balance ensures that your engine will be smooth-running.

The master rod of a Warner 165 prepared for weighing

With the help of Mike Connors, Harman Dickerson, and Al Holloway I've been able to distill this set of instructions. Any errors are entirely my own. Since the engine overhaul manual is not helpful when it comes to balance (e.g. "Send the crankshaft back to the factory"), education is the first order of business: The idea of balancing is to try to zero out the forces acting on the crankshaft of the reciprocating pistons and rods, and the rotating masses of the master rod assembly and the crank throw. Balancing for small radial engines such as the Warner 165 is done with fixed counterweights, no fancy moving higher-order vibration dampers are typically used on small radials.

There are two papers written in the late 1970s by W.B. Richards that outline research into the balancing formula for the Warner 165 engine: Balancing Radial Engines Part 1 and Matching Pistons and Crankshafts for Warner 165 Engines. Based on these papers and practical experience of experts I used the following procedure:

To have a balancer static and dynamically balance the crankshaft you need to determine the "bob weight" mass. The bob weight is a weight temporarily bolted to the crankpin which should exactly offset the final counterweight mass, and result in a balanced, smooth-running engine. The key formula from Richards' papers is Wc = Wrot + .510 Wrecip where Wc is the bob weight mass, Wrot is the rotating mass, and Wrecip is the reciprocating mass.

To determine the rotating and reciprocating mass you can either send your entire rotating assembly off to the balance shop, or weight the parts yourself and send only the crankshaft. Weighing yourself is not difficult but does require a fixture and a scale. Electronic scales are cheap, and a fixture is fairly easy to make if you can't borrow or don't want to buy one.

Determining the reciprocating mass for the pistons, piston pins, piston pin plugs and rings is easy: just put them all on a scale. A 1000g scale with 0.1g precision is adequate for this task and for all of the Warner 165 other than the master rod weights. Total the weights of all of the above.

Piston on scale. Notice the articulated, adjustable rod end support on the weighing fixture for weighing rods.

The master rod and link rod weights must be split into rotating, or crankshaft end weights, and reciprocating, or piston end weights. The rods should be prepared with all bushings finished, bearings inserted, rod cap bolted up, lock pins, nuts, and cotter keys temporarily inserted into bolts, so that the weight is identical to the finished weight. You should also insert the knuckle pins into the master rod, since they are rotating mass, which on the Warner 165 means inserting them before the bearing shell inserts are installed!

The rod weighing fixture is designed to weight a rod around its CG and isolate each end's weight. The fixture uses a low friction roller pin and movable arm to relieve side loads on the rod end. Some fixtures also suspend the rod end not on the scale using a trapeze like arrangement. One end of the rod is on the scale stand and the other end suspended. The rod must be level when it is on the fixture by adjusting the height of the suspended end. You can find several videos on YouTube such as this one which show the weighing process, although unlike automotive parts we will not be equalizing rod weights using a grinder! Once you get the weights of each rod end, add them together and check against the weight of the entire rod on the scale alone. The two end weights should equal the total weight of the rod within a gram or two, or else you've done something wrong.

Link rod on scale. Rod has been leveled and piston end weight, or reciprocating portion of the rod weight, is shown on scale

I had purchased a balancing stand from Summit Racing which worked well enough except for the master rod. The master rod in a Warner weighs approximately 3.8kg and has a 3" wide big end, which means it falls off the automotive-sized fixture. The fix is to modify the fixture with a larger roller (3" long screw, wider spacer, and support roller) and to modify the scale stand to be taller. To handle the mass of a fully assembled Warner 165 master rod you need a scale with a 4kg or greater capacity. 1g precision should be sufficient for the master rod. There are "gold" scales available with a 4 to 6 kg weight range and 0.1 gram precision for a reasonable cost that do the job well.

Modified weigh fixture stand for master rod big end: wider roller and support bearings, and taller scale stand.

Once the weights are recorded and the bob weight value calculated, send the crank off to a balance shop. Since the crank should be in final configuration the sludge plug and cotter key should already be installed prior to balancing. As of 2013 the balance shop recommendation is Electronic Balancing Company near Long Beach, CA. They will perform a dynamic balance of the crankshaft using a dynamic balancing machine, and add or remove weight from the counterweights as needed. Electronic Balancing is experienced with aircraft parts and has done Warner 165 cranks before.

Alternatively a static balance alone is probably just fine, but requires access to a balance stand, plus the machine tools to build weights for the crankshaft if necessary. Weight can be added using slightly tapered plugs driven into the holes in the counterweights, then punch the end of the holes to keep the weights from backing out.

When assembling the engine, you will see that there is some variance in the reciprocating parts. Attempt to balance out these differences by mixing the pistons + rings, piston pins and piston plugs to find the nearest you can get to equal weights for each cylinder. If there are large variances on the pistons you have a problem but you can do limited material removal on the pistons to balance them (prior to calculating bob weight values). With Warner pistons you shouldn't need to adjust them much.

The master rod being weighed, with modified Summit Racing weighing fixture able to accommodate width of the Warner master rod

All of the link rods and master rod ready for weighing