Friday, April 20, 2007

Rainy Friday

Gravity is silent. The stately tick-tock of the pendulum clock is the only sound in the shop, the lathes and mills lurking beneath their shrouds as I try to reason with Mr. Ohaus. Unlike the clock, which is made of wood, Mr. Ohaus is a man of metal but both are powered by gravity. A spate of rain sweeps over us, loud on the metal roof out behind the shop and for a moment I hope it will somehow change Mr. Ohaus’ mind but he is stubbornly insistent: the connecting rod weighs 605.9 grams.

Deep sigh.

I take the rod out back where the narrow belt of the polishing sander whisks away another film of metal, first on one side, then the other. Then follows a careful cleaning and back to the scale: 605.7, less a tad. I repeat the ritual as more rain blows in, a regular shower this time. I give the belt-sander two-potatoes less than before, clean the rod, weigh the thing: 605.5, plus a tad.

Big Smile. Because 605.5 grams is what I’ve been chasing for the last half hour, hiking back & forth between the sander - - a ‘dirty’ tool not allowed to associate with lathes and the like - - and the Ohaus triple-beam balance, trapped in its varnished cedar box over in the corner with other Precision Stuff.

A stock VW con-rod is about 5.4" c-t-c. Forged from mild steel, its weight may range from 505 to 550 grams. They are sold in sets graduated by weight with a 10 gram variation across the set of four. But for a good engine you want them to all weigh the same, or close to it. The rods I’m working on today aren’t stock. They are 5.6" c-t-c, intended for use on a crankshaft having a throw of 84mm (stock is 69).

This is the fourth set of rods I’ve ordered for this engine. The first three sets had been tampered with, probably by the clerks who shipped them, so that the weight difference across the set of four was as much as 16 grams. Since you can only remove about seven grams from an H-beam rod, it renders them unusable in a properly built engine. Which gets you a massive shrug from the people selling such junk.

This particular set of rods was ordered on 15 March from a retailer less than a hundred miles away (G.Serrano in Torrance). After several phone calls the rods finally arrived on 20 April. Fortunately, the set proved usable but even then, the carton had been opened and one of the rods removed from its protective wrapping. Had the set NOT been usable it would probably have taken another month to obtain replacements or a refund, which will help you understand why it has taken five months and three different retailers to obtain a suitable set of rods for this engine. In one case I was forced to pay a ‘re-stocking fee’ even though the parts were not to spec. Air-cooled Volkswagens are a vanishing breed and most of the remaining retailers simply shrug; take it or leave it, we’re only here for the money.

(So what to do? Buy your parts from Steve Bennett at Great Plains Aircraft Company. He builds his engines differently from the way I build mine but he’s an honest person and you will benefit from obtaining everything from a single source.)

- - - - - - - - - - - - - - - - - - - - - - -

In the mid-1950's the Ford Motor Company published (in the SAE Journal) the results of a decade-long test comparing the wear of engines fitted with a full-flow oil filtration system to other maintenance strategies, including frequent oil changes, by-pass filtering and so on. Full-flow oil filtration was the hands-down winner, reducing some types of wear by as much as 60%. Which is why all modern engines are equipped with full-flow oil filtration.

All of the VW engines I’ve built since the late 1960's have been fitted with a full-flow oil filtration system. This is accomplished by blocking the normal output of the oil pump and installing a new pump cover having a threaded fitting. The full output of the pump is plumbed to a filter canister then returned to the engine via a threaded fitting installed in the main oil gallery.

The VW oil pump can produce up to 300psi and a basic rule of engineering is that the first thing ‘seen’ by the output of such a pump should be a pressure relief valve, so as to protect the system from excessive pressure. The full-flow installation in the typical VW engine violates this rule since the filter canister is the first thing seen by the pressurized oil. Since the typical oil filter bursts at about 100 psi, starting a VW on a cold morning can be one hell of a mess.

(Yeah, they make high-pressure canisters... which typically cost $10 and up, when you can find them.)

In comparison to the connecting rods, finding a suitable oil pump cover is a slam-dunk. I called Dee Berg, widow of Gene, chatted for a few minutes and had a pair of suitable pump covers in my hands about eighteen hours later. (Gene Berg Enterprises is even farther from my shop than the outfit selling the con-rods :-)


Gene made his pump covers out of high-density cast iron that wears even better than the stock VW pump cover. He also offered a cover fitted with a ball-type pressure relief valve (GB-239x) that pops-off at about 90 psi that has become the standard for all serious engine builders. It costs significantly more than the bubble-pak’d cast aluminum crap but it’s money well spent. Not only will you recover the cost by about the fifth oil change, the cover will last in excess of 100,000 miles if treated with WSX (ie, tungsten disulfide dry lubricant). By comparison, even when hard anodized an aluminum cover will wear beyond spec in about 10,000 miles and show a steady decline in pressure thereafter.

Ed.Note: A reader suggested I define '...significantly more..' When I ordered the GB-239 pump cover in April of 2007 the price was about $50.

On the back-side of the GB-239 cover you can see the large hole for the normal outlet and the small hole for the over-pressured oil to feedback to the inlet-side of the pump.


Before using the GB-239 I take it apart, clean it good and break all the edges with a file. The socket-head screw securing the pressure spring goes into the jig and gets drilled for safety wire. The sharp edges of the outlet port are polished smooth then the Blanchard-ground surface is burnished on a surface plate using #600 W&D flooded with WD-40. After a careful cleaning the valve is re-assembled and the flatted surface treated with WSX (ie, a Tech-Line product).

- - - - - - - - - - - - - - - - - - - - - - - - - - -

The rain has turned into a steady drizzle, a welcome background for the tick-tocking clock. The day has gone gray as I lock Mr. Ohaus into his shiny wooden box, wipe down my tools and put things away. I stopped building engines for sale years ago, devoting more time to horology, itty-bitty steam engines and black-powder, which makes it kinda hard to explain why there’s so damn many engines in the shop. Probably because it’s good fun - - plus, you get to go flying now & then.

The coffee is hot in the house and there’s a screen-full of mail to be dealt with plus a pride of indignant cats pointing out that water is falling out of the sky and wanting to know what I plan to do about it. Guess I’d better get busy...

-R.S.Hoover
最新高清无码专区在线视频_一日本道不卡高清a无码_狠狠躁天天躁中文字幕