Posted Friday, May 30, 2008 @ 10:34 AM
The stock 1300/1500/1600 crankcase (ie, 69mm throws) fits the 1200 crankcase. New, VW crank is presently about $125 in southern California. I don't know of any new 64mm cranks being available here; possibly in Europe, where the 1200 remained an option into the late 1970's (VOA, the importer of VW vehicles to the USA stopped importing vehicles fitted with the 1200 engine about 1965.)
A stock, after-market 69mm crank (Bruck) has a street price of about $90. Quite a few of these tucked away at the back of various shelves.
The fact the crank fits the 40-horse case doesn't mean it's a bolt-up. The big-end of forty-horse rods is 1mm wider than later rods, meaning you'll want to run them through the surface-grinder. If the rods are 401's you can take the meat off one side but for the later 401A's you'll want to take half from each side, since the center-line of the little-end is off-set on 401A's. Jack Riddle's shop in Santa Ana is probably your best option for such work. Jack is no longer with us but Riddle Machine Company (aka 'RIMCO') remains the largest and most experienced shop for work on air-cooled VW engines.
Since the 40-hp case is about 3/4" narrower than the later crankcase, you'll need to add a spacer under the barrels and re-set your valve-train geometry, relatively trivial chores. With .010" barrel spacers the CR will be about 8:1. If you'd like to drop it, see any of the numerous articles on adjusting compression ratio. (There's one in my blog.) The added 5mm of stroke results in an engine having a displacement of about 1286cc (ie, the same as the 1300 engine).
Forty-horse rods also use a smaller piston-pin, 20mm vs the later 22mm. They are also 7mm shorter than later rods. This argues against using later rods & jugs unless you're willing to bear the necessary expense. As it is, the 130mm center-to-center length of 40hp rods puts them right at the limit for a 69mm crank (ie, as defined by the Ricardo Rule).
Should you wish to punch it out to accept larger jugs, RIMCO is probably your best choice. They will try to discourage you from doing so with a 40hp case since it's not as strong as the later crankcase. In a similar vein, the increased displacement will only improve your PEAK output, which you may enjoy for about four minutes during take-off. After that, the engine's sustainable output is determined by the surface area of the fins on the heads, which is typically between 35 hp and 45 hp REGARDLESS of displacement. (Variation reflects the local atmosphere. For Standard Day conditions, maximum sustainable output is about 40bhp.)
-R.S.Hoover
