Sunday, June 3, 2007

Crank Basics - I

When you build an engine from scratch you must round-up all the ancillary parts. In a previous article describing how to prepare the crankcase I’ve mentioned various kits of parts meant to ease this task. Unfortunately, such kits may not be as convenient as they appear.

The same situation applies to your crankshaft in that it requires a number of additional parts to make it usable. Here again, retailers offer kits but the odds are you’ll run into the same problems as with case-kits or hardware-kits.

A typical crankshaft kit contains a pair of Woodruff keys, the cam gear, spacer, distributor scroll gear, distributor pinion gear, two end-play shims, the oil slinger and a snap-ring. Typical price (April 2007) is about $50. Unfortunately, the kit is not complete, lacking a very critical spring. And it may not be complete with regard to your specific crankcase. Nor do they mention that some of the parts in the kit are liable to be used. (Note the wear marks on that pinion gear!)

The biggest potential problem is that such kits are liable to contain a cam gear from a 36hp engine. Such mix-ups don’t happen very often but like a mid-air collision, once is enough. (The two gears on the left are okay; the one on the right is for the earlier engine.)

Here is a kit of guaranteed-used parts I salvaged from junked engines at the cost of tearing them down. (Note the 'unimportant' little spring... that plays a critical role in reducing wear.)

The salvaged pinion (on the right) not only has less wear than the pinion from the after-market kit, I've treated it with a baked-on, dry film lubricant (Tech-Line Coatings DFL-1).

After failing to include the required spring I suppose it’s no surprise to see the notorious Racer Spacer included in such kits. The stock spacer ring has been known to fail on the drag-strip and on engines that regularly turn above 5000rpm. That makes the ten dollar Racer Spacer an absolute necessity... according to the ‘experts’ :-)

In fact, the stock spacer works perfectly well on flying Volkswagens, costs about six-bits and weighs less than the Racer Spacer.

External snap-ring pliers are one of the tools you'll need to assemble and disassemble the crankshaft. The jack-knife gives you some idea as to their size.

The jaws should look like this. Get a good pair. If they let the snap-ring slip it can bugger the #4 bearing journal. (The pair shown are Craftsman [brand name], about 30 years old. They've done a few engines :-)

You're also going to need an hydraulic press with a press-plate to match the cam gear, or a VW-specific gear-puller as shown below. Do not try to use a regular gear-puller for this task. You'll simply bugger the teeth of the cam gear, a very common problem on amateur-built engines. VW gear pullers are commonly available but they don't come cheap.

This one is kinda tatty-looking. I've had it for a while; had to repair it once or twice. Still works okay but I generally use an hydraulic press.

If you have access to a lathe and welding equipment you can make your own VW-gear puller for much less than the cost of buying one. The critical dimension here is the lip that supports the gear-teeth.

And along about here someone always says, "I won't need this becuz I'm only assembling the engine."

Dead wrong.

One of the most critical parts of engine assembly is balancing all of the rotating components. In the case of the crankshaft, it must be balanced in its fully assembled state (less any reciprocating components, such as the connecting rods). That means everything that attaches to the crankshaft and which rotates on the same axis must be installed at the time the assemblage is balanced. Everything... Gears, prop-hub, magneto drive, coaxial dynamo or what-ever. (Just another of those 'unimportant' little details :-)

(See the picture? The complete crankshaft assembly, from fan-pulley to flywheel, is being dynamically balanced.)

Then you take it all apart again for cleaning, installation of the #3 bearing and so forth. So you do need the gear-puller... if you want to build a good engine.


No comments: