Saturday, December 3, 2011

Gonna get moving again!

Alright...Haven't done anything since...April? Yeah, it's been a while. It would appear that taking the engine to my buddy's house was a mistake. Not because anything bad happened, but because nothing happened at all!

He lives 10 minutes from where I work, but 40 minutes from my house. Finding the time to go to his house just hasn't happened, so we decided it would be best if I just took it home, worked on it when I can, and if I get stumped, to go to his place or ask on the forum for help.

So let the games continue!

Just like any engine, the Shovelhead needs a way to "breathe"--when the pistons move up and down, they create a vacuum/over pressure situation in the crankcase. Not a big deal if the pistons are moving opposite each other, but these move up and down at roughly the same time, so they don't balance each other out. To remedy this, the Shovelhead has a hollow tube with a steel screen on it that spins in a housing and is "timed" by the crankshaft so that the screen fits a window in the housing at just the right time.

What this does is allow over pressure to be blown out a relief tube that is attached to the engine. This tube is often run out over the final drive chain so that any oil mist that comes out of it will help lube the chain.

On the up stroke, this screen is opposite the window, which causes a vacuum in the case. This vacuum helps suck (or "sump") oil from the bottom of the crank case to the oil pump, removing excess oil from the crank. The Shovelhead is a "dry-sump" engine, which means it shouldn't store oil; oil should constantly be moving through it, but at no time should there be more than six ounces of oil in the crank case.

Here's the problem I'm going to fix: From the factory, the window cut for the screen is oval and rough. It was done cheaply and "good enough" for a stock engine. For a high-performance engine, a builder will actually split the crank case open, attach a timing wheel to the crank, and recut the window to match certain specs he has in mind. I'm not going to waste my time with that, as I'm just building a stock engine as close to factory spec as possible (with a few minor upgrades for engine longevity).

What I plan on doing is taping off the interior of the cam chest (the area I'm working on), plug the "deep end" of the breather housing with plastic and tape, draw a rectangle over the oval, and, using a Dremel tool, cut out a rectangle that matches the screen on the breather gear.

Here's the cam chest:

You can see the pinion shaft (out of focus). Above that is the cam bearing, and to the left of that is the breather gear and its window. See the rough casting and oval window?

Looking from above, down through the front tappet block hole:

Looking from above, through the rear tappet block hole for a different angle:

Here's the breather gear assembly. The screen is to catch anything larger than the holes in it INSIDE the breather gear, and has saved many an engine when a spring, washer, or spacer in the heads or rocker boxes has disintegrated (reaming a new hole and installing an over-sized breather is MUCH cheaper and easier than replacing, say, a crank):

I have finals coming up soon, so I'm hoping to get this done in the near future, but am not promising any particular time frame!

1 comment:

  1. He's back... good to see things moving again for you... i will keep in touch and check back to see how things are progressing... god's speed.