Wednesday, July 18, 2007
Crank Basics - V
Bagged and swaddled, the crank shown in Fig 1 gets laid gently in the back of my 1965 VW bus and we putter off toward Escondido. Traffic on Highway 78 is moderate so the eleven mile trip takes only twenty minutes with just two sessions of stop-&-go. The old bus has no trouble keeping up with the 300hp punkin seeds darting from lane to lane looking for what doesn't exist. Highway 78 is a linear parking lot about twelve hours out of 24, virtually empty the other twelve.
Don at HDS looks the crank over, we discuss the job, he writes me out a ticket and I'm free to return to the six-lane insanity. Barely an hour after leaving the house, I'm back.
As you can see from the photo the crank was delivered fully mantled save for the bearings. On one end of the crankshaft is the propeller flange and spool from Great Planes, on the other is the Harley Davidson permanent magnet dynamo, installed on a hub of my own design and manufacture. Drawings of the rotor hub and the stator mount will be posted to the Chuggers Group when I get around to it but previous posts will give you a hint as to what it looks like.
No one answers the phone in southern California any more. We live in what has become an up-scale ZIP code, targeted by politicians, telemarketers and evangelists to the tune of two dozen calls a day. We spin through the messages every evening and after a couple of days HDS leaves a message saying the crank is ready for pick-up.
This time I take surface streets. It's a few miles farther but takes less time.
The job-ticket is translated into a bill which I take to the office for payment. The yellow receipt is the crank's Ticket of Leave and Don haul's it out to the bus for me because it's kinda oily and I'm wearing a spiffy Hawaiian shirt. We chat for a bit, discussing the rattle from the spacer and the fact the assemblage was relatively clean, meaning he didn't have to do much work to remove the wobble. In fact, on the first run-up it was within spec for a stock VW crankshaft (8 gm/cm ) which he reduced to about .1 gm/cm. Once it's mounted in the airframe I'll go through the same procedure with the prop. No one ever believes how much this benefits the power-plant until they actually do it.
"Nice shirt," he sez, pretending to go blind. I've known him about twenty years; have three more crankshafts coming his way. I'll wear one of my really gaudy ones next time.
Back home via Stagecoach Road and Twin Oaks Valley, I lug the crank into the shop and start writing on it. The crank has survived its Rite of Passage. It is no longer just a crankshaft, it is part of an engine, serial number HVX0381, which I scribe onto one of the flanges with a carbide burr. I get one of the little red Engine Logs from the cupboard and start filling in the blanks. The log book will go into a big zip-loc along with the other documentation. Now I get to take the sucker apart for the second time, the first having been to trial-fit the main bearings, during which I also clocked the case to determine what size cam-gear I'll need. Fitting the cam-gears is one of those unimportant details the shade-tree types like to ignore.
Due to normal tool wear and tolerances, the distance (and sometimes the alignment) between the crankshaft and the camshaft varies slightly. The difference is small but significant, since it involves a gear-train. To accommodate the differences Volkswagen used nine different sizes of cam gears, from a -4 thru zero to a +4. They started out with just four sizes; -1, 0, +1 and +2. But factory-overhauled engines often required align-boring, which lead to the other sizes. The markings are on the inner face of the cam gear so as not be confused with the o used for the timing alignment.
The Factory Manual will tell you what checks to perform to see if you've got the proper cam gear. Or you can read all about in my two-part article "Dialing in Your Cam" that appeared in the 2001 October and November issues of 'VW Trends' magazine. (Sure to be a collector's item :-)
But right now I was busy taking the crank apart and writing, etching or stamping '0381' on all the bits & pieces. Well.... most of them, anyway.
In Fig 2 you can see how little metal Don had to remove to achieve zero wobble. (There's a matching patch on the opposite end of the crank, on the other side.) Grinding away that amount of metal meant the crankshaft had to be fully dismantled, all the plugs pulled then cleaned to within an inch of its life. Or whatever. I used lacquer thinner in a wash-bottle as my solvent, plus a variety of brushes, one of which you see in the photo.
After being scrubbed and scoured the crank gets blown dry then undergoes a visual inspection, where you poke a grain-of-wheat lamp on a wand into this hole here whilst peering down that hole there to make sure there's nothing in the hole but hole.
Then you get to put it back together again, only this time with bearings.
Since this crankshaft is counterweighted it has about four more pounds of flanges than a stock crank. When balancing a flywheel or stock crankshaft the usual method of removing metal is to drill it out. That isn't always possible with a counterweighted crankshaft because the outer portion of the flanges is fairly thin, which is why the metal is removed by grinding instead of drilling. Figures 3 is the 1/3 flange of a new stock 69mm crankshaft that has been factory balanced, (Meaning it's 'way the hell out of balance by modern-day standards.) Fig 4 is the 2/4 flange on the opposite side. Such divots are the balancer's spoor, telling you that particular component has been balanced to... some standard or other. The stock crank is destined for a 1968 bug. It will be presented to the balancer wearing a flywheel & clutch cover on one end, all of its gears, and a stock steel fan-belt pulley on the other. It will then be balanced as a complete assembly and to modern-day standards. In return, the engine will typically produce about 10% more power for the same amount of fuel.
This article marks the end of the series on crankshafts. I'll probably cover installation of the rods using a different engine. Right now, I want to complete work on the crankcase and start prepping the jugs. And there's still a pair of heads waiting to be prepped. (Good thing I got all this time on my hands :-)