The Homebuilt Engine, Part 1

On Sep 20, 2:59*pm, Copperhead wrote:
On Sep 20, 4:45*pm, "Morgans" wrote:

"Copperhead" wrote

and a VW aircraft engine in the 70-80 HP range rund in the 5-6+ grand

A 70 HP VW engine does not exist. *Not if you want it to run more than 30
hours or so.
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Harbor Freight is offering a Leak-Down Tester for $30 ( Item
#94190-3RBH, on page 7 in catalog 768-D)

If you operate your engine with a SUSTAINED output level equal to
70hp, the odds are it would fail to pass your leak-down test at 25
hours. What you chose to do with it at that point is up to you but a
surprising percentage of flying VW owners simply keep on flying the
thing... until they suffer a catastrophic valve failure, which can
cost them a new engine.

If your goal is to always operate your engine at high levels of output
the wiser course is to have FOUR heads, two installed on the engine
and a freshly overhauled pair on the shelf ready for use. But at high
levels of output don't be surprised if your TBO is 25 hours or less.

The T4 engine does a bit better, thanks to its greater fin area.

For maximum TBO you'll have to operate your engine BELOW its point of
Maximum Sustained Output, which for the Type 1 is between 35 and 45
hp, depending on the local atmosphere. At that level of output you
can expect to see about 200 hours before the exhaust valves fail the
leak-down test. At that point you should pull the heads and do the
wiggle test. If the heads pass the wiggle test (ie, the valve & guide
are still within spec), you may elect to simply lap the exhaust
valves. But when the head fails the wiggle test it's time to replace
the exhaust valves and their guides, a relatively simple task if
you're tooled up for it. (See any of several articles that address
this chore.) Here again, the wiser course (in my opinion) is to
maintain a spare SET of heads. This allows you to simply swap heads,
giving you up to 200 flying hours to overhaul the removed set.

What sets my ass on fire is the guys who say their engine puts out
80hp... and in the next breath tell all the newbies it only burns 3
gallons per hour... without bothering to explain that the first figure
has NOTHING TO DO with the second. (Three gallons per hour is about
36 horsepower.)

-Bob Hoover