On 6/2/2023 9:31 AM, dee david via KRnet wrote: 1. Where is top dead center? Is there a marking for it? 2. How do I adjust the mag to fire in the compression at 28 degrees BTDC. 3. Talked to a mechanic - he said he needed a procedure or timing marks.4. Is there a Hapi manual out there that is electronic that someone can share?
--------------- David,
For the purpose of adjusting valves, you can just insert a screwdriver into the cylinder horizontally, and rotate the crankshaft until the screwdriver extends the maximum distance (indicating the the piston is at top dead center). And again, on the compression stroke, not the exhaust stroke. This is close enough for adjusting valves....and like I said earlier, adjust the valves for each cylinder at TDC once you've found it.
As for determining exactly where TDC is, , you need a "piston stop", which are available on Amazon (see https://www.google.com/search?q=piston+stop+amazon&rlz=1C1SQJL_enUS946US946&oq=piston+stop+amazon&aqs=chrome..69i57j33i160l2.4534j0j7&sourceid=chrome&ie=UTF-8 ). You can make your own, but buying one from Amazon is far easier. Make sure you buy one that matches your spark plug thread size, likely 14mm, but could be 10mm. Then keep adjusting the stop to narrow down the range around TDC, then mark the outer edge of the prop hub at the vertical seam of the crankcase as center, if you don't have a spinner yet) to define exactly where TDC is....centered between the two limits of piston travel.
Next, for purposed of checking timing advance, you'll need a "degree wheel". I've enclosed one in this email. This assumes you have a timing light and know how to check timing on a running engine. I made this degree wheel for the engine I built for N891JF, so it has some cam specs for my particular cam, but for the purpose of adding degree marks to a prop hub or spinner back plate, that stuff doesn't matter. This particular degree wheel is made to fit a Great Plains Aircraft prop hub. Glue it to a piece of cereal box, cut out the center hold and outer ring, and glue or tape it to the prop hub....and you'll need a prop hub or something like it to do this with any accuracy.
As for timing mags, you just twist them in the hole just like a distributor, in order to change the timing.
See a bunch of photos of the rebuild of the 2180cc engine in N891JF, at http://www.n56ml.com/n891jf/2180/ , although it will likely just confuse you more. Sorry, I didn't bother adding text to it yet. Maybe someday....
See enclosed degree wheel. Mark Langford m...@n56ml.com http://www.n56ml.com Huntsville, AL
degree_wheel-vw.pdf
Description: Adobe PDF document
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