Monday, June 11, 2007
I continue to receive questions about the lubrication mods described in 'HVX MODS' posted here on the 29th of May.
Several have asked for the dimensions of the drillings, which are included in the drawings. If you will double-click the drawing it should appear full-size.
A few voiced a reluctance to perform any modification that involves drilling holes in the crankcase.
Actually, we're merely deepening holes that are already there. In doing so we cause the holes to intersect and when that happens it causes the right-hand side of the engine to receive significantly more oil that it was getting before.
In the photos you can see how I've used a wrap of masking tape prevent drilling too far. I did not verify these lengths against the previously posted drawing, I simply used another -- already modified crankcase -- as a gauge. So it would be wise to verify the dimensions.
Some folks say they couldn't find a 7/32" aircraft drill. Which means they simply didn't look hard enough. But if all you have is 1/4" then use that.
For most, the tricky bit is drilling down through the #3 cam bearing saddle to intersect the extended tappet oil gallery. If you go too far you will have ruined the crankcase -- or at least make it rather difficult to repair. That means the safest method is to extend the horizontal oil gallery first and then drill cautiously down through the cam bearing saddle until you run into the new drilling.
After you do it a few times you won't even think about it; it is simply another step in preparing a new crankcase for use.
Finally, there were a few who suggested I was misleading homebuilders because such mods were clearly unnecessary, citing their own engine and years of experience as justification for their opinion. That opinion is fairly common among builders of recreational engines -- for dune buggies and the like; a toy to be taken out and played with for a few hours per year.
I don't think it serves any purpose to discuss why their present engine does not have these mods, any more than it does to argue the merit of the Model T over a modern-day vehicle. There's no question as to the value of these mods since their functional equivalent can be found in all modern-day engines including the Type IV Volkswagen.
Professional engine builders -- and I'm talking bucks-down racing where people pay up to ten grand for a race-winning engine -- have been using some or all of these mods for the last thirty years. In doing so they are merely retro-fitting modern-day engineering to a design that dates from the 1930's, not because of a whim or fad but as a means of improving the reliability of the engine.
The key point here is that you have to finish in order to win. The main purpose of the mods is to enhance the engine's durability. It seems only common sense to include them in a VW converted for flight, especially since they add no weight.