‘THE TWIN’ FOUND AT LAST!
In part one, collector Andrew Mackey described the roots behind his love of Jacobsen engines. After a 20-year search, Andrew was the owner of not one, but two, Jacobsen Twins. While evaluating the near-running engine’s condition, he began the tear-down. He removed the magneto, starter, tinwork, flywheels and ended with the lower shroud.
The next step was to split the crankcase. To do this, I had to remove the engine base from the wooden mount. I then found where the mystery nut came from. Two of the four engine mount bolts were missing, and one of the other two, still in place, was missing a nut. How it got inside the flywheel housing the world may never know. Next came the removal of the upper block from the lower crankcase mounting bolts. There are four bolts that are threaded into the engine block lower section, at the center bearing location. There are also 12 nut and bolt assemblies that go around the perimeter of the block. Once all the bolts and nuts were removed, the exhaust stacks were removed and the engine was placed upside down, resting on the heads after the broken spark plugs were removed. I split the case by gently tapping on the crank with a plastic hammer. There seemed to be no gasket between the upper and lower case halves, just a tightly machined fit. After reading a manual for “The Twin,” it was explained. No gasket exists. Expert machining of the crankcase halves and the bearings make for an air-tight, metal-to-metal fit. The bearings are clamped between the case halves. The center bearing is split and is anchored by a 1/4-inch dowel placed in the upper case half. The two outer bearing mains are solid and must be slipped onto the crank. They are pinned in place by 1/4-inch dowel pins, located in the upper block as well. All bearings are grooved internally to help circulate oil. The crankshaft seals needed repaired.
Once I had the case split, I found quite a few things that needed attention. The lower case half was full of crud. Gummed up oil and rusty debris filled the engine sumps. Next, the connection rod big end caps were reversed. Stamped in location marks did not line up. Someone had been inside before and sullied the alignment. Besides that, the conrod big end retaining
