By Staff
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1941 Fairmont 8-13 HP QBA 2 cycle engine mounted on tractor.
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1947 Maytag Model 72 DA Twin, just after starting. Note smoke at exhaust.
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1948 Maytag water-cooled Twin 2 cycle engine.
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Diagram A Crankcase Detail
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26 Mott Place, Rockaway Boro, New Jersey 07866, Foreword

I have written the following article for the GEM in response to
several remarks made by Mr. Wendel in the ‘Reflections’
column, in particular 23-11-8 and others, as well as having had
several discussions with my friends on the subject of 2 stroke
(cycle) engine oiling and operations. I, just like the next fellow
engine show enthusiast, do not enjoy being ‘gassed’ and
deafened by smoky and noisy 2 cycle engines at a show. However, I
realize why these engines run like they do and maybe this article
can give some insight and inspiration to both the readers and the
people who operate this unique style of engine.

For those of us in ‘engine land’ who have seen and sat
next to a noisy, smoking 2 cycle engine I can offer my sympathy and
some advice-don’t breathe too deep. All kidding aside, I
believe that some etiquette should be observed when running this
unique style of engine. Nobody, myself included, likes to listen to
a 2 cycle’s raspy bark, and smell the exhaust all day long.
Anybody who has been next to an open exhaust Fairmont with its 12
to 1 fuel ratio will get a massive dose of what I mean.

I believe in moderation for the operation of my
‘smokers’ and if more people would show the same
consideration a lot of shows would be more enjoyable, both to the
exhibitors and the visitors.

First is my choice of a set up area. If I know that it is going
to be a windy day, I try to pick a spot down wind from most of the
other exhibitors (especially if I run my ‘heavy oil
burners’ which include a 1950 Model 7 H Mall 2 man chain saw @
12:1, a 1941 Model QBA Fairmont 8 to 13 HP also @ 12:1, and my
Maytag Model 92’s @ 16:1). I’ll go into fuel-oil ratios
later in the article.

Second, I try to keep the running time down. Usually I’ll
only run them for about 5 or 10 minutes at a stretch. At a couple
of shows I attended I made up a sign with the time I would be
demonstrating a particular piece of equipment. This serves two
purposes: it keeps the air pollution (smoke) to a minimum, and
helps keep the noise level down. The noise made by an open exhaust
will drive me up a wall after about 5 minutes, how about you? With
the demonstration times listed, if someone wants to ‘hear it
run’, they can see and hear it go at the same time, and
everybody is happy. I also give the engine the once over before I
run it to make sure there are no loose items that could cause

This second item also applies to any engine I plan to run, and
you should do it too. I’ve saved more than one engine from
self-destruction with a close look over before starting up. As a
for-instance, I gave my Mall saw a going over at the Blue Mountain
Fall Show two years ago and discovered that vibration had worked
the governor set screw loose. If I had just started the engine it
would have run wild and blown up. I saved a lot of soul searching
by taking a few minutes of my time to check things out.

Third, if possible, I try to keep the noise down. I try to use
the original mufflers whenever possible, and almost never run an
‘oil burner’ with an open port exhaust. There are other
reasons besides the noise not to run a 2 cycle engine with no
exhaust pipe or muffler, but that too will come later. I like to
talk to people about the engines I am demonstrating, and with a
loud exhaust it is virtually impossible to hear anything but the
engine, much less the questions asked by an interested

Last but not least, I try to have a little variety in my
exhibit. I usually don’t take the same engines to all of the
shows I attend. The ones I take, I think, will be interesting to
the people who attend the show. For example, if last year’s
show had a dozen people exhibiting the Maytag twins or the Model
92’s, you can be sure that I won’t bring one this year
(unless it’s my Wico equipped twin which is sort of rare). I
also try to have my engines doing something besides just going
putt-putt-putt on the ground. I have one Model 72-D Maytag twin
that is belted up to an old G. M. alternator and regulator. It puts
out about 15 amps steadily and when it is hot it doesn’t smoke
too much. It makes for something interesting to show, and makes me
a few bucks charging other exhibitors dead batteries! (That’s a
treat, having fun and making money doing it!) An engine sitting on
its original equipment gives a visitor a better picture of what our
hobby is all about-the preservation of our antique engines and the
equipment they used to run.

This ends the showmanship part of my writing; in the next half
I’ll try to give you some information on 2 cycle engine
operations and the effects certain changes have on them.

The 2 cycle engine has come a long way since its conception.
Today’s 2 cycle engines can safely run on an extremely lean
fuel-oil ratio, and some of the new outboard engines use a 100 to 1
mix! (Using exotic materials, several engines have been run with no
oil in the fuel! However we won’t be seeing these in the near
future because of the cost). The most common ratio is approximately
50:1, that is 50 parts fuel to 1 part oil. All ratios are expressed
in this way today. Before the calculator days, as I call them, the
common way to express the ratio was parts of a pint to a gallon of
gas. For example: 8:1 was I pint to a gallon, 16:1 was ?-pint to a
gallon, 32:1 equals ?-pint, etc. 

Key to diagrams: 1) transfer port 2) exhaust
port 3) piston 4) crankcase 5) one-way valve (Reid) 6)carburetor 7)
cylinder (combustion chamber) 8) spark plug 9) head.- Direction of
flow- Direction of rotation  

Today’s engines can use the lean mix because of the superior
materials in use, such as chrome-lined steel cylinders,
molybdenum-coated rings, forged steel crankshafts with hardened
steel roller bearings and races, aircraft grade aluminum die cast
blocks, and a lot more. Another refinement is oil injection, in
which a constant flow of oil is metered to all the bearings and the
piston skirt. The oil injector serves three purposes. (1) To cut
back on the free oil in the crankcase of which about 80% was wasted
out the exhaust. (2) To insure direct oil delivery to where it is
needed most, at the wear surfaces. (3 ) To cool the bearings. In a
hot running engine, every little bit helps.

Not so the engines of days gone by! The most common materials
used were cast iron and brass, two fairly soft metals. These needed
a lot of lubrication and an 8:1 or 12:1 ratio was common for the
early engines. Usually a forgotten dose of oil meant at least a
seizure and at worst a melted bearing. However, most of the time
these metals were very forgiving. A lot of times when the engine
seized it was left to sit and cool down. Throw some oil on top of
the piston, yank on the flywheel a few times, and away it would go,
none the worse for wear till next time. Today’s engines
aren’t so forgiving. Some of the large bore engines used the
12:1 mix into the 1950’s although the smaller bores had gone to
a 16:1 mix as early as about 1915. This change doesn’t sound
like much but it did make a big difference. The 16:1 engines
didn’t foul their plugs as often, and didn’t need to have
the carbon removed from the head and ports as often, leading to
less down time for the engine. 

A word of caution here: If the owner’s manual says use a
certain fuel ratio to oil, USE IT. If you can contact the
manufacturer you can ask for technical data to see if you can lean
out the amount of oil in the mix.

When you are in doubt about the ratio to use in your engine, try
a 12:1 mixture to start. This is usually more than sufficient for
any 2 cycle engine. With a later small bore engine (under 2?’
bore) you can try a 16:1 ratio. A 12:1 ratio is ?-pint of oil in a
gallon of gas, 16:1 is ?-pint to a gallon. Some engines which were
designed to take a 12:1 mix will not have sufficient lubrication at
16:1. A case in point is my 1941 QBA Fairmont. The owner’s
manual calls for a 12:1 ratio of fuel to oil. I was not too happy
with the smoke that this engine generated (especially when it was
cold), so I reduced the ratio to 16:1. Although the engine seemed
to run just fine, about 2 tanks of fuel later the engine developed
a connecting rod knock. I took this to be from normal wear, but
after repairs the damage repeated itself. I then wrote a letter to
Fairmont and asked for some information on the proper mix to use in
my engine, and got this reply; ‘We do not recommend a change
from the specified 12:1 ratio in the operator’s manual, and we
also recommend that you do not use a synthetic oil in the QBA
Engine.’ (I’ll tell you more about the synthetics later.)
The 16:1 mix was too lean on oil to provide enough lubrication to
the connecting rod bearing, and caused its early failure. I
haven’t loaded this engine very hard either. It is important to
use the proper ratio when possible.

If you do not know the proper ratio to use it is better to
over-oil than to under-lube the engine. Too little means excess
wear and damage, and too much will mean the engine will smoke more,
run a little hotter (although the excess oil should prevent
damage), and the head and ports will have to be cleaned more often.
I for one would like to do a little more maintenance than a lot of

1)  Crankcase
2)  Crankshaft
3)  Carburetor
4)  Inlet passage and one-way valve
5) Transfer passage

On the subject of the new synthetic lubricants, I have this to
say: A synthetic 2 cycle lubricant is not an oil. It is a chemical
lubricant that is designed for the modern hard surfaced bearings in
today’s engines. In my experience it does not provide enough
lubrication for the older engines. It does not have enough
stickiness to stay on the bearings of the older slow turning
engines we deal with. The new lubes are designed for an engine that
averages between 10,000 and 15,000 rpm and a bore of about 1?’
in diameter as an average. A lot of fuel-oil vapor is passed
through the cases in these engines in a short amount of time. My
little 50cc chain saw will use a pint of fuel in less than 10
minutes at 14,000 rpm. The QBA Fairmont with about 600cc uses a
pint in about an hour at 1,500 rpm. I have used the new chain saw
lubricants in some of my Maytag engines with the following results:
in the Model 92 (FY-ED 4) @ a 16:1 ratio-no apparent ill effects,
perhaps as part of this engine’s normal function it coasts down
with no ignition allowing a raw fuel-oil spray to be passed out of
the engine, thus lubricating the top of the cylinder. So far my
92’s have had minimal wear on the inside. On the Model 72 DA
Twins it’s another story. On several I’ve had to
disassemble, I’ve found signs of scuffing on the pistons, and
when taking the engines apart the rods and pistons appear to be
dry. On one engine I also found some wearing of the big end bearing
on the connecting rod too. As a control I’ve used a Model 72 D
Twin using a 40 weight non-detergent oil instead of the saw lube.
Although there was more carbon in the ports and the manifold, the
interior of the 72-D had no appearance of scuffing, and all
surfaces were wet with oil. I used 40 wt. oil because the saw lube
said ’40-weight equivalent’ on the label. I also didn’t
see that much of a difference in the smoke output between the
engines I ran.

Whatever you do, do not use an engine lubricant marked ‘for
oil injected engines’ as a pre-mix oil. This is a special grade
of lubricant that is thinned at the factory to aid its dissipation
into the fuel vapor in the engine’s crankcase. It is way too
thin and is totally unsuitable as a pre-mix lubricant.

Up to this time I have assumed that the readers of this article
know how a 2 cycle engine operates. For the benefit of the readers
who do not, I’ll give a brief description. For the most part a
2 cycle engine uses the crank-case to hold the air-fuel-oil mixture
until it is ready to be forced into the cylinder (see diagram A).
While this mixture is in the case the oil in suspension settles on
all of the internal surfaces and some even gets on the bearings! As
the vapors swirl around in there, some of the ‘old oil’ is
washed off of the surface and back into suspension and at the same
time ‘new oil’ is deposited. In the older large bore
engines, not all washed-off lubricant was forced into the
combustion chamber, and it would settle to the bottom of the case.
This would not create a problem unless the engine was tipped, or if
the level of the oil reached the connecting rod. Some engines
actually depended on this excess oil for additional lubrication by
adding a dipper on the connecting rod (just like a 4 stroke engine
would use). However, eventually too much oil would remain and it
had to be removed manually. Examples are the Fairmont and early
Jacobsen engines. If the excess oil was not removed, eventually
liquid lubricant would be splashed into the combustion chamber,
resulting in a lot of smoke and excess carbon build up. Sometimes
the oil would foul the sparkplug too.

1) Piston dome-transfer deflector side
2)  Piston crown
3)  Piston dome-exhaust deflector side (note height of the
piston deck at edges A & B)
4)  Rings
5)  Wrist pin
6)  Piston body

Starting at bottom dead center, this is the operating sequence
of a-2 stroke engine (Diagram 1). The compression stroke starts as
the piston travels up the cylinder toward the head. The transfer
port is closed by the passing piston and a vacuum is created in the
crankcase by the receding piston. This draws the gas and oil (fuel)
into the case through the carburetor and either an intake port or a
one way valve. The type of valve varies between manufacturers.
Maytag uses a poppet valve on its Model 82 & 92 engines,
Jacobson uses a spring steel reed valve on its later engines and a
Piston Port arrangement on its early units. There are other methods
that are used but for the most part they are outside the scope of
our hobby. One notable exception is the Reid engine built in
Pennsylvania, which use a ‘charging cylinder’ and an
entirely different system of operation.

1924 Jacobsen 2 cycle upright engine. Note brass oiler in front
of carb; this supplies oil to the piston and bearings. Excess oil
drain is not visible. Pre-mix is 64:1. Directions read, ‘Use
1/8 pint of oil to 1 gallon of gas, adjust
oiler so a light grey smoke appears at all times.’ This engine
was purchased complete and running at a local salvage yard for
$3.00! Just needed a paint job and a spark plug.

As the fuel and air charge is drawn into the case, the former
charge is being compressed after the exhaust port is closed. As the
piston nears top center, the compressed charge is ignited. At the
same time the one way valves close, trapping the next charge in the
case. The engine is now in its power stroke (see Diagram 2). As the
ignited charge burns and expands, the piston is driven back down
the bore, thus turning the crankshaft and compressing the trapped
charge in the case.

When the piston nears the bottom of the cylinder it uncovers two
sets of ports in fairly rapid succession. First is the exhaust port
(see Diagram 3). As the piston passes and unblocks the port, the
hot burned gases are directed out the port into the manifold by the
shape of the dome on the piston’s top. As the piston recedes
further to the bottom of the stroke, the transfer port is opened
and the already compressed charge is released into the cylinder,
and is directed toward the top of the cylinder by the other side of
the dome on the piston (see Diagram 4 and piston detail). Then the
entire cycle is repeated. In the new saws all this is happening
about 15,000 times a minute, and it’s hard to imagine that that
is 250 times a second! In contrast, most of our old Smokers operate
at around 5 to 600 rpm and are topped out at 1500 (between 8 &
20 rps).

Many things influence how a 2 stroke engine operates, things
such as the timing of the ports, their size, the back pressure on
the exhaust. . . Oops! I almost forgot! After the spark timing and
the oil-fuel ratio, the exhaust is the next most important detail
on the 2 cycle engine. If carbon builds up in the exhaust port it
will change the timing of the port. Excess carbon buildup in the
muffler causes too much back pressure and both will lead to poor
performance and overheating. I used to own a late 1940’s
vintage Jacobsen rotary lawn mower. It used an 8:1 ratio mix for
fuel. The man who gave it to me told me it was worn out, all it
would do was idle and get very hot. I brought it home (to my
mom’s dismay) and decided to try it myself. I did and it did
just what the old man said. I noticed how quiet the exhaust was,
(you heard pffft, pffft, pffft) and I wanted to see what kind of
muffler it had, as I had another similar machine that was pretty
loud. This machine didn’t have a conventional blade on it. It
was a 2′ diameter 3/16 thick steel disc with 4 triangular
blades and cup shaped vanes mounted on it. I didn’t know what
the vanes were for but I found out later. After fighting a stubborn
bolt for ? an hour I finally got the monster off. I then removed
the muffler cover and couldn’t believe what I saw.

Apparently the old man had never had the engine serviced from
the time he bought it to the day he gave it to me. This engine had
4 exhaust ports; the only opening to the piston I could see was in
1 port, and that was only the size of a pencil lead! No wonder the
engine would only idle! I was surprised that it even could do that.
I removed the head and scraped all the carbon off it, and at the
same time cleaned out the 4 ports. The muffler was also packed
nearly solid with carbon and that had to be cleaned too. It took
about 4 hours to clean up the mess, three on the engine and one on
the driveway. Mom’s quote was: ‘and don’t come into the
house until it’s SPOTLESS!!!’ I reassembled the mower and
tried to start it. When it finally started the smoke was so thick
that my mom could not see the garage from the house, about 20 feet,
and she thought I had started a fire! After about three minutes the
smoke cleared a little and the mower was idling nicely, thank you.
I then opened up the throttle and started another smoke-out. This
cleared up quickly and the engine continued to pick up speed. At
this time the old man walked up the driveway and said, ‘It
hasn’t run that fast since I bought it!’ Meanwhile the
thing was still accelerating! Old John said, ‘I saw smoke from
my backyard (2 blocks away!), and I figured you got ‘er
runnin’.’ Meanwhile, I was just about to reach for the
throttle when the governor kicked in and stopped the rising howl
and turned it into a steady constant roar (so much for a nice quiet
muffler). I waited a few minutes and then closed the throttle. It
took the massive disc about two minutes to coast down to idle speed
again. Old John told me, ‘Don’t leave ‘er set in one
.spot runnin’ too long, it’ll suck the rocks right outer
yer drive! It’s the vanes ya see, they make ‘er act like a
big Hoover!’ And he was right! With a bag on, the machine would
pick up anything that wasn’t bolted down. I used it for two
years and then sold it to another friend (also named John!). John
made the mistake of leaving the engine run at full steam in one of
his customers’ front yard while he emptied the catch bag (John
did landscaping, you see). When he came back he saw dirt thrown
across the yard, off to one side of the mower, but he didn’t
think much of it until he moved the machine. It had pulled all the
grass under the deck out by the roots and made a hole in the poor
man’s yard about an inch deep!

Old John later told me that originally the mower only had 2 of
the curved vanes on it, and he had added the other 2 to help get
rid of the many leaves on his property (His yard was surrounded by
maple trees). Needless to say, that did not endear old John to his
neighbors! He used the machine with no bag to blow the leaves into
the street! A man who used to live across the street said that the
old mower had no problem blowing a 3 foot wall of dry leaves into
the street or a neighbor’s yard (‘After all, they ain’t
my trees!’).

Getting back to my original point, the ports must be cleared
once in a while to keep the engine operating efficiently. By the
same token a 2 cycle engine should not be run with an open exhaust.
If it is run with no muffler, serious damage can result. A 2 cycle
engine has to have some back pressure on the exhaust port for
several reasons. They are: 1) It helps the engine retain the new
intake charge in the cylinder, otherwise part of the charge would
be wasted out the exhaust. 2) It stops the backflow of air into the
cylinder which would cause the engine to run lean. 3) It slows the
initial surge of exhaust out of the exhaust port. If the flow is
not slowed it could lead to a melted piston (I know, I melted two
myself), or it could lead to burned ports and loss of compression.
In racing motorcycles, if the exhaust system develops a leak it
could lead to a complete piston meltdown in as little as 5 seconds!
4) A muffler does what it says, it muffles the exhaust pulse to a
sound that is much more tolerable, and quieter. I had a 1963 Sears
Allstate 175cc motorcycle that I learned to ride on. This engine
had a unique design, in that it had two pistons, but a common
connecting rod throw on the crank and a common combustion chamber!
If this engine was run with the baffles removed from the mufflers,
they acted like megaphones and directed the sound to the rear of
the bike. I only rode the bike twice with the baffles out for two
reasons: 1)I was too young to have a license and the police sort of
frowned on us for riding on an unfinished U.S. Rte. 280. The
machine could be heard by the cops (and the whole town for that
matter) for over 2 miles! My friend John’s mom could tell right
where we went: ‘I told you boys to stay out of the sand
pit.’ And 2) Both times I took it out I melted the front piston
top right out the exhaust ports! So keep ’em quiet.

I have one last point of information about 2 cycle engine
operations. Do not run your engines too lean; although it’s
alright to have the engine fire at every stroke at idle, at full
speed with no load the engine should ‘burble’ a little bit.
That is, it should actually miss or double stroke (fire every other
time) at top speed. At top speed with no load the fuel charge
isn’t completely burned, therefore the engine will sputter a
bit. Under a full load the fuel is burned, as the charge is held
longer in the cylinder. If you lean the mixture out so the engine
‘sings like a bee’, then the engine will be running too
lean, which could lead to a meltdown of the exhaust side of the

I hope that this article helps my fellow readers to understand a
little bit about the 2 cycle engines-the ones we call

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