Greetings Dean, I?ve been trying to figure them out too and its remarkable how little info I?m pulling up - just goes to show that almost nothing actually existed before the internet.
Depends on what HAPI model you have. This give some specs of the different models: http://www.enginehistory.org/HOAE/HAPI.html <http://www.enginehistory.org/HOAE/HAPI.html> IMHO, most important update would be to replace or reinforce the alternator/stator/flywheel. The HAPI develops stress cracks between the lightning holes and separates. Replace with one from GP? From what I read almost everyone had a problem with that. Cost~$500? There are also reports of problems with the crank/prophub. If you are scarred off of the HAPI crank/prophub (which I may be), then it seems the best replacement would be the Revmaster. That involves sending Revmaster (or perhaps a machine shop?) the engine and having them machine both the nose and the #3 bearing? Then replacing crank and inserting #4 nose bearing. Cost is something around $1000-1200? Alternatively, you could replace with a crank and Force One prop hub from GP, also ~$1,000. We have one of the Magnum models. I?m hoping its the 82, since it had a 78mm stoke crank and the Revmaster crank is a 78mm. The 75 had a 69mm stoke crank. My son is going to pull a head this weekend and measure the stoke. If you have a Magnum with the SCAT split heads, they seem to have a problem with heating - leading to valve train issues. Fix would either be to replace heads (~$1,000) or have the piston tops, vale faces, exhaust port, and combustion chamber top coated with a ceramic thermal barrier coating (maybe by Swain ~$600). My son?s web page has a summary of what he?s leaned so far: http://hugheskr2s.yolasite.com/progress.php <http://hugheskr2s.yolasite.com/progress.php> Fixing everything that folks have mentioned may come close to the cost of buying an new engine. I?m more that a little discouraged by the VW and am considering a Lycoming. You can buy a used cont or lycoming for ~$3000 and spend another $3000 doing a very nice overhaul (if you do it yourself. Then you will never have to touch it again (except maintenance such as oil (25hr), timing (100-500hr), etc.). From what I read it seems VW are rebuilt every 200 - 500 hours. I know this is a touchy can of worms and seems to go against the entire idea of a KR. Cheers, Owen
