Bob Boyd wrote: > If I purchased a VW engine that is currently on a plane and appears > to have been flown in the past, how can I tell what size it is
Determining bore diameter from the outside is not something I could figure out, unless it's a nuance like "sharp-cornered" machining on the cylinders around the studs. But stroke isn't too tough...just remove a spark plug and insert a thin long screwdriver (or welding rod, etc) perpendicular to the piston. Rotate the engine to bottom dead center (piston all the way in) for that cylinder, and mark the screwdriver with a Sharpie or tape using some reference like the edge of a fin. Then, while holding the screwdriver steady, rotate the engine until the cylinder is at top dead center, and mark the screwdriver again. Measure the distance between the marks to see if it's closer to 69mm or 82mm. 69mm is stock, 82 is stroked. If it's stroked, it's likely bored as well (boring is cheap, stroking is expensive), and probably to 92mm. As Rob said though, you'll find out soon enough, but for planning purposes, at least you'll know what you've got, and can then decide how far you want to go if it involves a new stroker crank, boring the case for larger cylinders, and all that fun stuff. Also, check the hub and see what kind it is. If it's not a tapered hub like a Force One, it's probably not a stroker either (if you follow GPASC's recommendation. I would recommend a 2180cc engine if you have a heavy plane, plan to carry a passenger, or fly out of a high-altitude airport. Another variable is the cylinder head. Check the model numbers (such as 044) and compare to stock numbers. Non-stock is a sign of heads that are improved breathing (not that it'll make a big difference on an engine turning this slow). Big valves may not be so great...you won't get much performance gain, and the small area between the valve seats will crack in short order due to the large temperature differential. I am way overdue adding a narrative to this, but see http://www.n56ml.com/n891jf/2180/ for photos of a 2180cc engine buildup using a GPASC crank and Force One hub. This buildup is a little extreme, as this was a first time assembly, so rod and cam clearancing, among other things.... Mark Langford ML at N56ML.com http://www.n56ml.com
