How to Break-In an Engine

The big problem here is that air cooled engines are different from
water cooled engines, and while we can find lots of good information
of breaking-in a newly assembled engine, it turns out that 99% of it
has to do with WATER COOLED engines. Which turns out to be Bum Dope
when you're talking about Flying Volkswagens.

How an air cooled engine is broken in has a lot to do with how long
it lasts. I've already written quite a bit on the subject of
breaking in an engine and won't bore you with it again but the key is
to keep things cool. The first run is never more than two or three
minutes and that charge of oil is then discarded. I consider this to
be the last step in the ASSEMBLY procedure rather than the first step
in wearingin since it serves as a kind of Emergency Flush of the
finished engine.

The wear-in cycle is the hardest part of your engine's life.
Machined surfaces are NOT all that smooth; there is considerable
metal-to-metal contact and that produces some enormous heat loads.
So you run the engine just a few minutes at a time then allow it to
cool. This is unique to air cooled engines; with a waterpumper you
simply size the radiator accordingly... or add cold coolant when it
beings to boil. With an air cooled engine the key factor in the
cooling equation is TIME.

To make matters worse, VW's having larger than stock displacements
experience even more wearin heating than the stock engine. And if
it's for an airplane, being cooled by the blast from a propeller, the
task of wearing it in properly becomes even more difficult. I have
spent as long as two weeks (!) accumulating five or six hours on a
newly built flying Volkswagen. Although half that amount is more the
norm, it is the ENGINE which decides, not some manual devoted to
cars.

Allowing the engine to cool to the point where you can place your
hand on the heads takes about half an hour in cool weather but can
take twice that long on a hot day. Then too, the other purpose of
wearingin the engine is to detect problems and there will always be
a few. The timing and valve lash will change slightly from run to
run, reflecting the vastly accelerated wear rate during breakin and
those things must be attended to. Unless you are using a knowngood
carb that has run on other engines and you know to properly adjusted,
then there is the ohsocautious tweaking of the mix. You want it
rich during wearin. But not too rich. (I use an oxygen sensor.)

After the engine has accumulated an hour or so of run time, which may
have taken six or even eight runs over a span of three or four hours,
it will become obvious that the temperatures are rising more slowly
and not going quite so high. The oil pressure will also be up. In
effect, the engine is telling you it is ready to do a bit more work.
Now the runs can become longer. But in no case should you run the
thing more than twenty minutes or so, and NEVER at a constant speed.
It drives the neighbors crazy (and the guys at the airport too) but
you have to sit right there, protected by your ear muffs and cycle
the throttle slowly up and down across a range of 500 rpm or
thereabouts. (It is the decelleration involved here that is the
other half of properly seating the rings.)

Somewhere around three hours of running the engine gets a new charge
of oil and a new filter.

During the wearin cycle the engine should be fitted with 'bat wing'
air scoops and a club optimized for pumping them full of air. You
should have fitted the largest oil cooler you have available,
positioned perpendicular to the air blast. (As the wearin proceeds
you'll probably cover some portion of the cooler to keep your oil
temperature above 170.) You actually wearin the engine according to
what it tells you in the way of temperatures and pressures, including
manifold pressure.

After five or six hours, the engine SINGS. It starts at a flip, has
a lovely, throaty idle, accelerates smoothly and once at full
throttle (about 26" on the manifold) it will sit there and roar.

THEN you can start paying attention to the torqueometer.

For me, building engines is more fun than building airplanes. The
engines talk to me, not only when they are running but laying there
on the bench in pieces. Not talktalk of course. But pick up the
cam and you can hear what it's saying. It comes through your hands
and the way the thing snuggles into its bearing shells. You KNOW
when it's comfortable, when it's looking forward to doing its job.
All of the parts are like that. A gang of guys brought together to
form a team.

It takes... as long as it takes to assemble an engine. Most go
together after three or four trial assemblies, some insist on more.
The goal is harmony, for want of a better word. The parts have to
learn to live and work together. It's difficult to describe exactly
how that happens; what transformation takes place between a set of
lifters from Brazil and a cam from Los Angeles and jugs from Japan
under heads cast in Spain... but you know when things are good. The
engine tells you so.

R.S.Hoover

Veeduber wrote:
The big problem here is that air cooled engines are different from
water cooled engines, and while we can find lots of good information
of breaking-in a newly assembled engine, it turns out that 99% of it
has to do with WATER COOLED engines. Which turns out to be Bum Dope
when you're talking about Flying Volkswagens.

now there is one we can fully agree on.