NAMBA March 2021 Web

PROPWASH March 2021 21 Allen Rod Hardening Fixture Assembled Allen Piston and Rod Jim tested a lot of rod and needle bearing designs before coming up with the final design. Tested Bearing Cages Tested Connecting Rods Another issue in mechanical design is the piston and liner. We discussed fits and port design previously. Now we need to cover how to hold everything in place at varying temperatures. The combination of a brass liner with a high silicon, aluminum piston has become standard in production engines. The brass liner has a similar thermal expansion to the high silicon, aluminum piston, maintaining the fit as temperatures rise. Both piston and liner need to remain round. Again, Jim tested a lot of different liners with many piston alloys. He found that a thick upper lip on the liner was the best way to hold the critical upper end of the liner round and in position. This area is where the piston seal really matters. The Allen 90 engine liner had a full diameter, .200” (5 mm) thick lip. That’s around one fifth of the piston travel. The lip also gives a large cooling area on the liner to hold expansion down. The liner is supported on its flange for machining. Allen 90 Piston and Liner