This article has been written to answer the many questions I get about running Norvel engines.  It is limited to discussing the Norvel .25 BB AME engine as that is what I have experience with.  Much of the information on break-in and fuel content can be found on other web sites.

The Norvel engine uses different metallurgy and design than we are used to with more convention engines like OS, Magnum, Irvine, Thunder Tiger, etc.  Not better, just different.  There are many things that are different on these engines than on others so it pays to know a lot about them to get the most performance from them.  All the information contained in this article has been learned through trial and error experience. It is hoped that in the next few paragraphs we can make your Norvel experience successful.

Break-in:

In the following paragraphs you are going to read about the best way to break in a Norvel engine.  You do not do it on an airplane.   You do it on a test stand.  If you do not have a test stand please invest in one now as it will last your lifetime and you will find it pays for itself countless times over.

Mount your engine to the test stand and fill your four-ounce tank up with the recommended fuel. A word about glow plugs might be wise here.  Our best experiences have been with OS R5 plugs.  These are “cold” plugs that are needed to hold up to the high rpm of the mousse cans we run.  The best common plugs we’ve found are the K&B HP plugs, which are more than satisfactory if you run good fuel and the stock Norvel muffler. The break in propeller is the same we use for flight the Master Airscrew 9X4.

Expected performance

With a MA 9X4 propeller, 15% nitro fuel, and the standard Norvel muffler you should achieve peak ground rpm readings of 16,400 to 16,600 after the first hour of running.

The Norvel engine will vibrate significantly from the increase rpm provided by the mousse can.  The engine will run between 18,500 and 19,200 rpm with a mousse can installed.  The increased vibration will cause the fuel to froth or “foam”.  This will cause the engine to go lean in flight or surge.  Either condition is very bad for the engine, and very frustrating for the pilot.

Another thing that causes excess vibration is using a hand drill to ream the prop open for the 6mm shaft to pass through.  A hand held drill is seldom if ever centered in the prop bore and will cause the hole to be off the prop center.  Purchase a good tapered reamer to keep this from happening.  The tapered reamer is guided into the center and assures that you will keep the bore centered.  Also it is important with high-speed engines to balance the propeller.

A Norvel BB AME .25 will consume almost 6 ounces of fuel when run with a mousse can during a normal combat match.

Problems and Fixes:

Carburetor: The carburetor of the ball bearing engine can seize up.  The carb of the plain bearing engine does not have this problem.   The bb carb barrel will freeze or lock in position and cannot be rotated.  This is a very common problem. Once it happens your best course of action is to immediately ship the carburetor back to SIG for replacement.  I have stripped several servos, as have many others when a carb locks up.  The cause is the idle stop screw.  It scrapes the carb barrel, which nicks the aluminum housing.  Some carbs have barrels that the bore is not cleaned up and they nick the aluminum.  If you are patient and are part masochist you can fix it yourself but a better course of action is to return it to SIG for replacement. Another carburetor problem is that the spring inside the carb that pushes against the throttle barrel can get lodged between the crankshaft and crankcase if the idle stop screw vibrates out.  This locks the engine in flight – the solution, send it to SIG for replacement under warranty

Unusual Running Characteristics:

1.     Fuel leakage at fuel nipple – Norvel originally used aluminum fuel nipples and has since changed to plastic.  There is no difference in performance between the two, they both leak.  It does not make any difference in how good or bad the engines run.  This design flaw may have been lifted from the pages of British Sports Car design manuals.  Some folks will exchange the Norvel needle valve, and spray bar from ones manufactured by OS.  The OS will thread into the same spray bar hole but it needs to shortened by about 1/8” to fit properly.  I have tried it and it works fine but the OS needle valve threads are coarser than Norvels and getting a good setting is more difficult.  I’ve decided to live with the fuel leakage just like I did on my old MGA 1600.

Good luck running your Norvels.

I strongly suggest you read the break in article written by Dubb Jett at his web site www.jettengineering.com or read the one published
in 2001 in Model Airplane News by Dave Gierke as they both contain a wealth of valuable information.

Background:  The Norvel engines are manufactured in Russia and distributed in the USA exclusively by Sig Manufacturing
(www.sigmfg.com). The engine repair work and two year warranty done by sig is performed by Justin VanDee who can be emailed by
writing justin@sigmfg.com you will find him to be extremely helpful.

The good things about the Norvel .25 BB AME engine are its low cost, light weight, high performance, and durability.  In over two years
we have yet to wear out a Norvel .25 BB AME after hundreds of rounds of combat, they are durable.  The bad things are that the
carburetors can be defective, the crank stud will break, it is a pain to put the motor bolts in the exhaust side and you have to have a
couple of special tools to work on them.

The metallurgy of the Norvel engines is primarily aluminum.  They have an aluminum cylinder and aluminum pistons.  Most other
brands of engines will use and Aluminum piston, brass cylinder sleeve plated with either chrome or nickel, and a cast crankcase.  
Norvel uses aluminum for lighter weight, better heat transfer and cooling.  To achieve the same performance as an engine with a
chrome or nickel-plated cylinder Norvel had to come up with a way to harden the cylinder walls.  This was done through a process that
Norvel calls aluminum-aluminum-oxide.  A hard “ceramic” like coating is applied to the parts to give them the running characteristics
desired.

A byproduct of this manufacturing and design process is that the engines will actually absorb oil into the pores of the aluminum over the
first hour of running time.  This is the reason that Norvel’s continue to improve during break-in for the first hour then reach their normal
performance level. The metals have wicked up enough oil to fill the porosity, and since they are fully coated with oil the friction is reduced
from metal to metal contact to liquid to liquid contact.

Break in of a Norvel is an extremely critical step and is much more important to the life of any new engine than the sport fliers at your
field will lead you to believe.

Before you begin the break-in of your Norvel there are two tools you need to either have or buy.  They are the Norvel head wrench and a
5mm socket.  The initial run of a Norvel engine normally causes the head to loosen slightly.  Tighten after the first run and it should hold
from then onwards.  If you do not tighten it your engine will be hard to start, run hot, and burn up the head gasket.  The 5mm socket is to
tighten the nut that holds the carburetor bar in place.  This nut is very thin and if you grab it with a pair of pliers you will round it off.  It
needs to be tightened firmly and you cannot do it without a 5mm socket wrench.

The fuel you should run in your engine should contain the same nitro content you expect to run when you fly.  Nitro makes the engine
hot.  Heat causes expansion of the piston and cylinder.  The piston and cylinder need to be hot to expand.  If the piston expands but not
the cylinder you will wear the surfaces of both.

The oil content of your fuel should be at least 18% (the bare minimum), and 20% -24% is preferred. The oil content should be at least
20% castor. We run Wildcat Premium which is 15% nitro and 18% oil then add four ounces of Klotz Synthetic oil to a gallon to bring it to
22+%.  In all testing done to date the Norvel engines run faster on 22% oil than 18%.  We like our engines to run fast and we like a lot of
oil in them to make them run a long time.

For break in we wire the carb throttle wide open.  We do not adjust the engine with the throttle at all until it is broken in.  Use of the
throttle has ruined more engines during break in than any other single thing.

The purpose of break in with either an ABC or AAO engine is to loosen the fit between the connecting rod and the crankshaft crankpin as
well as to get the piston and cylinder heated up enough to expand and fit to each other.  Little metal fitting is done during break-in with
piston and cylinder fit, instead we are heat cycling the metals to get them to relax.

Start your engine and immediately get it above its four cycle setting to a rich two cycle.  Let it run at a medium to fast two cycle for thirty
seconds.  If you have a tach check it after thirty seconds.  It should be running between 14,500 – 15,000 rpms at this time.  Let it run the
tank out but pinch the fuel tubing for five seconds at a time every thirty seconds.  This leaning out by pinching raises the temperature of
the engine but when it is released the engine will run cooler as it richens up.

You want to run six tanks of four ounces each through your engine gradually lengthening the time you peak the engine by about 5
seconds each tank.  By the sixth tank you should be hitting 16,400 with a Master Airscrew 9X4 and Norvel muffler.  When the engine will
hold a steady peak setting for 30 seconds or more it is ready for flight.  You may also adjust the carburetor and low speed needle setting
at this time.

The easiest way to increase the power of the Norvel is to install a Mac’s 2310 exhaust header and Kentucky Mousse can muffler
system.  Both are available from www.flyingzhobbies.com for roughly $28.  A lone mousse can completely ready to run is $8.  The
reason that the mousse can from Flying Z hobbies increases the performance of the engine is that it mimics the actions of a tuned-pipe
system.  The audio wave from the exhaust leaves the engine and travels the length of the mousse can.  Upon reaching the end of the
can it is bounced back toward the exhaust opening.  As it reaches the exhaust opening the piston has not yet moved below the exhaust
port so the wave bounces away again, this time it travels a short distance before the piston moves down and opens the exhaust port.  
The suction of the wave moving away from the port sucks exhaust out of the engine, and more importantly draws new fuel through the
intake ports into the cylinder.  In effect the tuning of the mousse can is supercharging the engine.  You will notice a significant increase
in fuel consumption once you install a mousse can because the increase power is made from more fuel going into the engine.

Some fliers have been successful in reducing fuel foaming by putting several drops of Armor All in a fresh gallon of fuel.  The high
silicone content of the Armor All reduces surface tension of the fuel.  Others have reduced fuel line bubbles by putting a large fuel filter to
act as an air trap between the tank and the carburetor.  Neither of these techniques has worked adequately for us.  We are running
tanks that are called “bubbleless” because they have bladders in them where the air is removed from the bladder prior to filling.  The
best commercial bubbleless tanks are available from www.jettengineering.com.  There are other sections of this web site where you
can examine the construction of a bladder tank if you wish to fabricate one for yourself.

Prop Stud breakage:  Norvel uses a threaded 6mm screw in prop stud.  It is threaded on each end but plain in the middle where the
prop sits.  This stud has broken for a number of fliers.  After lengthy discussions with Justin at SIG he is of the opinion that the threads
go into the shaft to far putting stress on the smooth part of the threaded stud.  This causes the stub to be under stresses and almost
all breaks occur where the threads meet the smooth part of the shaft.  This problem has become almost non-existent in 2002 as
Norvel changed processes.  If you wish you could purchase 6mm Allen bolts at the hardware store and grind off the head then cut
them to length.  We keep a couple of these in our flight box.

Connecting rod breakage: this is not something that happens to many fliers; normally those that really push their engines are most
susceptible to it.  The rod will break in engines that have not been properly broken in and run too hard too early.  That thirty-minute
break-in period assures the fit of the connecting rod to crankpin.  If you do not use enough oil in your fuel this will also happen.  The
connecting rod will either break on the crankpin or just above the crankpin.  SIG will warranty these failures and rebuild your engine for
you.  Send it to them if this happens to you.

2.     Fuel leakage from head – if the engine is very flooded and cranked with an electric starter you can actually see fuel blow out of the
head.  When you go to tighten the head you find it is already tight.  I guess I would rather the fuel blow out of the head than hydrolock the
piston and crank.  In any event the engine will run just fine, but you should replace the head gasket.  I flew three rounds at the 2002 Nats
with an engine that did this and it was my best engine at the contest.