Construction details for a reliable high performance connecting rod

[Jack ODonnell]

Mr. Miller. Hi Lohring; Looking at the crankshaft, looks like you may have a problem with the inter race of the ball bearings sliding on the crankshaft. J.

 

[Jim Allen]

Definitely agree!! A small but very important detail that is overlooked in any split crankshaft single cylinder engine that is presently manufactured. A crankshaft that is not pressed into the inner races of the bearings on at least one side or a crankshaft that is not mechanically fastened to the inner races of the bearings on at least one side will cause unwanted axial movement at high engine RPM's. Roller bearing assemblies were never designed to accept axial loads!!

Jim Allen

 

[Jim Allen]

Another very important detail that is overlooked by most engine modifyers & engine builders is the SQUARENESS of the cylinder bore to the crankshaft bore. If the two are not square to one another, all types of unsolvable mechanical problems will show up, such as; the connecting rod walking on the crankpin; cocking of the piston in its bore; poor wear characteristics in a bushed or roller rod; high wear in the piston boss holes; unnecessary high radial clearance amounts in the upper & lower connecting rod roller assemblies; high friction & heat in associated parts.

Jim Allen

 

[Jim Allen]

The squareness of the cylinder's axis to the crankshaft's axis in any miniature size engine is critical!! Therefore, any fixture used to hold the crankcase for boring of the cylinder bore & the crankshaft bore MUST be square within + or - .0001" over 6.000". The photos show a fixture that can be mounted to a precision face plate (using a draw bar) & a rotary table (using 3/8-16 bolts). Both mountings are located with 3/8' dowel pins.

Jim Allen