John,
Here's the #1 thing you can do to free up a bunch of horsepower and 2000-3000 top end R.P.M. in these engines. Coincidently this will also add many hours of life to your engine as an added bonus.
Align the crankshaft and countershaft bearings the best you can.
From new, most of these engines have been assembled such that the bearings are so misaligned that the crankshaft and countershaft do not rotate freely.
The two shafts should float in the cases when properly assembled.
You will notice that the 2 case halves have a register, (alignment boss & groove), around the area that encloses the crankshaft. This is supposed to ensure that the bearings are aligned. Not only does this register rarely align the crank bearings...it provides no means to align the cases at the countershaft. With the cases pressed together by hand, you may not be able to shuffle them at the crank...but the cases can still be rotated independently which leaves no accurate means of aligning the countershaft.
Procedure:
Thoroughly clean both case halves ensuring that you have removed all traces of the old gasket.
Install the crankshaft, "only", into the case half with the boss. Place a new gasket on the case surface and slide the other case half onto the crank. If your crank had end-play shims, don't forget to install them.
Ideally you will have procured the correct length M6X1 socket head cap screws, a 1/4" drive (inch pound) torque wrench, a loose 5mm allen wrench, and an M5 short allen on a 1/4" drive adapter (allen socket). You can do it without this...but it is going to be a lot more trouble. If you decide to use the original philips head, or uni-head screws, you are going to have to get the "feel" for the uniform tighness of the screws in order to not distort the cases. This becomes especially tedious as you are going to have to assemble and disassemble the cases several times before you are finished.
Install the case screws and just tighten them lightly and uniformly, in a criss-cross pattern, with an allen wrench. There's no need for the torque wrench yet as the crank may already be in a bind.
Spin the crank and see how smooth it rotates. The crank should be completely free to spin. There should be a fair amount of crank end play, as the gasket has yet to be compressed. When torqued you want .004"-.008" end play.
If the crank does not freely rotate...if there are any tight spots what-so-ever...you are going to have to create a chamfer, or bevel, on the register boss so that you can essentially defeat the original mis-aligned register. You can do this with a file. Hold the file at a 45 degree angle and sweep around the boss evenly. I suppose you could do it with a dremel, but I would not recommend it as you will likely slip with the tool and end up with a mess.
If the crankshaft does float completely free; it is time to break out the torque wrench. Torque the case screws to 65-75 inch pounds in three even steps. Set the wrench for 25 inch pounds...tighten the screws in a criss-cross pattern...check the crank. Does it still spin freely? If yes, go to 50 inch pounds and check again...then 75 inch pounds.
At this point the crank is good to go...take it all back apart again. Yeah I know it's tedious, but if you want the gain you'll have to endure the pain.
Insert the sprocket side countershaft bearing...make sure it is bottomed. Slide the clutch side countershaft bearing onto the countershaft. Slide the contershaft into the sprocket side bearing. The countershaft should include the rod that the flower nut attaches too, the main spring with collars and cross pin...nothing else.
Coat the cases with permatex aircraft "300"...slide the crank in...lay the gasket on...and slide the two case halves together. Coat the threads of the case screws with just a bit of locktite blue.
Once again tighten the screws by hand at first with a loose allen wrench. The crank should spin freely. Check the countershaft...does it spin freely? If not, lightly tap one of the two cases near the countershaft end from the top until the countershaft spins completely free.
Torque the case bolts as above in three steps in a criss-cross pattern...each time checking both the crankshaft and countershaft. Each component should spin completely free after final torqueing. You should be able to hold the small end of the connecting rod and spin the crank with ease. A good snap of the fingers on the countershaft should set it free spinning for several revolutions before it stops.
Note:
On the many engines i've disassembled the center-to-center distance of the bearing receivers for each case has always been spot-on. The problem has always been that the two case halves are not aligned with each other.
Have fun,
Jim
