by sportsterpaul » Sat Jan 28, 2017 6:52 am
Yeah, I heard flat-track racers used to reduce the pinion shaft hole as well. The consensus seems to be early models have a little too much oil whipping around the bottom end, while 1977 and later cases have way too much oil in the bottom end, since the gearcase drains into the flywheel cavity.
When Vance Breese campaigned his road-race Sportster (in AFM I think it was,) he reduced the pinion hole, welded on a sump, and added an extra scavenge pump driven off the #2 Cam. All the experts told him he was crazy to do that, and double crazy to not run an oil cooler. They promised he would burn up the engine on the 5th lap. Thing is, without all that extra oil down there, he didn't need an oil cooler and told me his oil temps dropped 20 degrees. He never did have wear or oiling problems with the bike.
I worked with a guy, Dale Ransom, that was a tech at the GE electric motor plant in San Jose. He confirmed this "too much oil" theory, when he described a test he did on big roller bearing used in power plant generators. He said they would run hot dry, and a little bit of oil would cool them. Then more oil would cool them a tiny bit more. Then even more oil and they would run hotter again. All that oil gets whipped around and heated, and I wonder if too much oil does not make the bearing skate a bit as well.
I am surprised that you could block the piston oilers, if that is the same as a Sportster-- holes in the lower part of the cylinder to drain oil from the top end. Anybody that has pulled a timing plug while the engine runs know how much oil spray is flying around down there. I just assumed the factory was using crankcase vacuum to suck down the oil drain holes, but my 79 sure seemed to need the side oilers, as evidenced by the two scuffed pistons I got when there was no oil to the top end. I didn't see any horrid wear to the valve tips or guide or rocker arms, but the pistons seem to scuff in a hundred miles. Lesson learned was to fix any problem, even if it did not seem relevant. If I had investigated why oil was dripping out the breather tube I would have seen the blown gearcase gasket, maybe before either front piston scuffed.
BTW, I think the front cylinder and head runs hotter because the exhaust port is wrapped back with more surface area to transfer heat into the head. Other people say its because more oil gets whipped up into the back cylinder by the flywheel. Some people even say the rear runs cooler since the mixture to the back is richer. Curious as to your thoughts. I guess all I have to do is mount a rear head and cylinder on the front and see if it runs cooler. Hmmm, I am pretty sure people have done this already.