The original post with hyperlinks is at https://q-list.groups.io/g/main/message/54501


For reference, my engine is S/N A-2605 delivered on July 9, 1985 with all options, minus a turbo.

1) First and foremost, a major cause of issues with the original QAC Revmaster was a compression ratio (CR) that was far too high. My original booklet show this clearly, with listed CRs of 9.3 to 9.4 (9.35 to be exact).





At "some point" Revmaster did "some thing" to reduce the CR as shown in the latter manuals but I have no idea what.



The latest Sonex AeroVee 2.1 Assembly and Installation Manual and Great Plains manuals recommend 7.0 for mogas and 8.0 for 100LL for increased longevity. Your engine builder can help you with this. Combinations of various cylinders, heads, and shims can get you there using a calculator like this: CB Performance Engine Calculator

2) The original "75 HP" Revmaster heads just...aren't. To make matters even worse, you need to carefully check that the cooling passages aren't blocked off by casting flash. Highly recommend Mark Langford's page on the subject.

3) The magnesium engine case is now known to age harden and develop cracks. Various fixes such as "deep studding cylinder 3" and "welding in behind cylinder 3" do help at our high continuous power settings but the real issue is the age hardening. The ultimate solution is a new aluminum case that does not suffer from this problem. Unfortunately, the special machining for the Revmaster propeller hub means you can't just buy a stock VW case. If you decide to reuse the case (like I did) then expect a 250-400 hour TBO until it inevitably cracks. As John Monnett says, that's realistically a couple years (at least) of flying though. Note that a high(er)-aluminum content (AS21) magnesium case is different than an all-aluminum case.

Here are some additional videos/articles, in no particular order:
1) Engine Assembly Tips for the Type 1 VW with Steve Bennett (EAA Webinar)
2) Q-talk 117 - The Little Engine that Could
3) Q-Talk 163 - Revmaster Cracked Case Repair
4) Engine Rebuild in 2013 (Calvin Thorne's blog)
5) Q-talk 153 - Kuhlman & Dirks Q2
6) History of Prop Hubs (Bob Hoover's blog)
7) Aero VW Cooling Limitations (Bob Hoover's blog)
8) The VW Aircraft Engine for DragonFly/Q-Bird with Steve Bennett (YouTube)
9) AeroVee Engine History: SuperVee to AeroVee (YouTube)

Personally, I am proceeding with 92mm "thick wall" cylinders (92mm base / 94mm top) to help with cylinder to head sealing and 68cc Panchito heads which purport to have better cooling as documented on my build log. This should yield a bolt together, no shim CR of 7.38 while reusing my original case.