Conversion - T3 Taylor

Rev - Nov 17, 2017

 By - Rex Taylor (EAA 87893)
Edited - Jan Zumwalt (EAA #66327)


There aren't any miracles,  there aren't any secrets;  all
the answers exist in tried and true methods.  Our task
is to sort out the simplest, most effective, most reliable
means of converting the VW engine to aircraft service.

See Also

Taylor 10 articles appeared in EAA's "Sport Aviation", 12/1979 thru 9/1980, 45 pages (15mb): Taylor - What about Volkswagen conversions.pdf   (includes HAPI design)

Taylor VW engineers' manual (3.1mb, 75 pages): Taylor - How to Build a Reliable Aero Engine.pdf   (includes HAPI design)

Robert Hoover VW manual (1mb, 119 page):  Hoover - VW aircraft engine building.pdf

Rex Taylor leads the reader through the development of the HAPI conversion research. Most information is applicable to Type 2/3 with some specific information regarding Type 3. Be sure to download and read the entire 44 page pdf manual. So that we can provide a small glimpse into the depth of Mr Talor's knowledge we now present a sample of his 10 part series on the VW engine.


Taylor Manual Contents
Part 01 - Pros & Cons of the VW Engine
Part 02 - Choosing the Right Engine
Part 03 - Balancing Cranks & Pistons
Part 04 - Tools & Techniques
Part 05 - Design Considerations
Part 06 - Assembling Crank & Case
Part 07 - Power Options & Compression
Part 08 - Heads & Cylinders
Part 09 - Carburetor & Induction
Part 10 - Mounting, Oil, Props


The very first thing we must understand and deal with is the definition of the word "conversion". When applied to aircraft engines, I would define it this way: "To take an engine designed and perfected over many years of service to do the specific job of powering an automobile and adapt that engine (convert it) to do a job it was not designed, engineered or developed for; specifically, to power an aircraft with a practical degree of reliability."

The primary reason [racing] goodies don't work is that they are designed to increase rpm and allow the engine to breathe at high speed. Big valves, porting and polishing, multiple carburetors, and big cams are all designed to allow the engine to turn faster, and produce more power at the top end. Great . . . but not very useful to us [beacuse we need power at the low end]... unless we are using a reduction unit. - Rex Talor

Any successful conversion is still a conversion. None have every part engineered from the drawing board for aircraft needs, consequently, conversions have many features that are less than ideal and some inherent weaknesses that we must attempt to overcome or at least minimize to the degree that reliability and safety can be achieved. Just how reliable are these conversions? How difficult is it for the average guy to build his own engine as well as the airframe? There are many ways of converting various parts of the engine, but which is the best? And why? Where can this potential engine builder get the parts and information, the machine shop services, and how much should it cost? How much honest power and service life can you expect out of your conversion?

Questions Answered

What about the use of "hop up" parts to get more power? This article will try to answer some of those questions, 

  • Selecting an engine for conversion — new or used?
  • Inspection procedures
  • Engine tolerances
  • Engine assembly
  • Torque tables
  • Engine installation in the aircraft
  • Engine cooling and baffling
  • Carburetion and ignition (single and dual magnetos)
  • Engine tuning
  • Accessories: starters, alternators, vacuum pumps, etc.
  • Operating limitations
  • Turbo charging, is it for you?

Please note this article is based on the VW type 3 engine case and recommends it as the "best" engine case. A type 3 case has a few minor advantages for an aircraft engine but since this article's initial printing in 1979 the type 2 is now generaly considered the "best" case due to better after market support and pricing (a type 2 engine is about 1/3 the cost of a type 3). However, the information presented is generaly identical to rebuilding a type 2 case laugh


Fig-1: VW Type 3 universal case ready for a rebuild.


The plain fact is that Volkswagen has done a pretty fair job of designing everything just as it is. Ideally, if we want to increase the power, we want to increase it at low rpm's, say the 2000 to 3500 range. A Volkswagen engine in a Microbus is in that power band and its camming, porting and timing are about as optimum as you can get. We should not forget VW has spent millions in testing, and has billions of miles of history in use trying always to get more power in this RPM range.

Problem Areas

As a VW engine runs there is wear generated on the outer side of the bearing insert and in the bearing support saddle itself. This results in the wear condition seen here and may only be returned to serviceable limits by boring the saddles ("align boring") to restore the proper crush on the bearing.

Fig-2: The pencil indicates the number 4 main bearing.
Note the small size of the bearing which greatly limits
the loads we can subject it to.

Another wear problem that you may encounter is a damaged thrust surface on the rear side of the #1 bearing. The number 1 insert is flanged on both sides and the thrust load is taken up on the flywheel side of the bearing. Often this bearing has been worn until it looses its crush then starts to move in the saddle, wearing down the rear face of the saddle. This results in wear reducing the bearing saddle thickness of .867 thousandths to something less.

If you simply put a new insert in, the flange would now be unsupported and a thrust failure might well occur, particularly in our aircraft conversions where this flange is taking all the thrust load.

The fix for this type of damage is to machine the thrust surface to cleanup, then purchase a set of bearing inserts specifying "recut thrust", then the #1 insert is cut to whatever is the new saddle width. This must be fitted to +.001 -.000 to be right.

The cam bearings in the late cases are also inserted bearings. Some of the earlier cases had no inserts — the camshaft ran directly in the case itself. Cam bearing damage is not frequent but does occur, and align boring is necessary to restore serviceability.

Other problems to be found commonly in used cases are stripped cylinder stud holes in the case, cracked cases and center mains that have seized for lack of oil. Be sure to download and read the entire 45 page pdf manual. We also recomend reading Robert Hovers 119 page manual VW aircraft engine building.