Saturday, April 5, 2014

Rebuilding the Engine

This is one of the first things I started although I just finished it. The Hornet had matching numbers and I wanted to make sure the engine cases were good before spending a lot of time and money on the bike. After cleaning and soda blasting everything I measured all of the key components. The crankshaft journals and main bearing were worn out of spec while the connecting rod small ends looked good. The timing side camshaft bushings were also out of spec. The cylinder bores had .01 inch of taper in them too. Precision engine machining is an area I decided to let the experts tackle. I took the engine and its components to Expert Motorcycle Works in Hobart Indiana.  They had new cam bushings put in and honed to size. They did not do the breather end as this measured within spec. They bored the cylinder out .020, ground the crank and installed a new crank bushing which was honed to size. I also had them put new bearings on the crank and in the case.  The bike was left to sit for several months while I collected parts, saved money and worked on other things.

 The first thing I did after getting the engine back from Expert Motorcycle Works was to shim the crankshaft. This was not too difficult but took a lot of time as I had not done it before. I setup the crank with the original shims and it measured .005 in of float. BSA spec is .002 so I added a .003 shim and rechecked it. I had to purchase a bearing separator for the job which I found at Harbor Freight. It worked well.

Mike Brown’s “Building a Better BSA” DVD gave me a lot of pointers which I gladly followed. One was to install the countershaft sprocket before assembling the cases. This made the task much easier than I have found it to be in the past. I had to install high gear to accomplish this so I decided to go through the transmission at that time also. I will discuss this in a later post. Honda 4 gasket maker was used to seal the cased together and grease was used to hold the crankshaft thrust bushing in place. This went well and was uneventful. After sealing the case the end play was still at .002 in.

I elected to put the primary and transmission sides together before putting on the cylinder. Using this method I was able to put a rod through the piston small end bearings to torque engine nuts. This is much simpler than wrapping a chain around the drive sprocket. I purchased a set of motorcycle ring clamps to assemble the top end. Money well spent although big pipe clamps would probably work too. 


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