- Getting Started
I hope to make this an interesting article, especially
for Blaster owners, but these engine building procedures
are not only useful when working on that engine - much of
this translates well to all 2 stroke engines. There's
going to be a huge amount of data associated with this
project and a lot of pictures so it is necessary to post
it in parts. This allows me to write it in logical,
progressive steps and lets me get the information out
sooner. It is my intention to make this piece readable by
everyone who has the desire to follow it. If something is
unclear I would appreciate a comment from you about it so
that I may find a way to more clearly explain the
concept.
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Respect
- Two stroke engine builders may be able to gain more
respect from their customers when they learn to not keep
as many secrets about what it is they do. The customers
who sit on the fence for a long time before choosing to
modify or not do so because they can not justify the
associated costs - they have nothing to judge them
against. It is very unlikely that every person the engine
builder tells his tuning strategy to will have the
ability to perform, skill to achieve, money for tooling,
patience to learn or the mechanical aptitude to carry out
the given tasks which are necessary to over ride them in
order to do the work themselves. In fact the reverse may
well be true. It is possible that once a person
understands what is involved in the two stroke power
building process they may be more willing to trust the
engine builder and offer less resistance when it comes to
buying more products or services because they have been
educated about the processes. Many people want to
understand what's being done to their favorite ride so
they can tell their riding friends more than the dollar
amount associated with the new found speed they're
experiencing.
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- When the sporting enthusiast can speak about some
porting specs, the uncorrected compression ratio or the
maximum squish velocity they will have become empowered
enough to feel confident in the ability to speak the two
stroke language. This can be a door opening experience
for some because it gives them more to think about and a
new way to speak of their engine. By understanding the
terminology used to describe two-stroke engines they now
have the proper tools to use to teach it to each other
and it's one more thing to add to the stack of life's
mysteries that have been handled enough to be considered
conquered. Any person that takes their knowledge to the
next level has decided to expand what was previously
known and add to it more of that which can feed the
cause. If one riding buddy tells another of his ability
to 'decode the two stroke mystery' the second buddy may
become more interested in being two stroke aware as well
- so they can speak the same language. It is a continual
process which can be healthier and more productive for
everyone.
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- I was tired of hearing stories about two strokes
being unreliable, temperamental and archaic a long time
ago. It seems that the mighty two stroke may well be on
its way to a second coming. This time it will be armed
with some serious artillery to keep it quiet, smooth,
clean burning, economical and above all powerful. Better
days are coming.
Rick - we can more easily understand what it is we're
working with when the complexity of its nature has been
broken down into smaller pieces that can more easily be
ingested and contemplated upon. It then becomes easy to
define and refine. macdizzy@macdizzy.com
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- What Happened
Since the crankshaft big end (B.E.) bearing went out
during its last outing - the time has come to open up
this motor and start replacing parts. It is my belief
that this engine was old/tired enough that a singular
trip to the over rev range by virtue of missing a gear
shift made it spill its guts. It would be more common for
a 2 stroke piston to seize than the B.E. bearing fail
during such an incident. Otherwise everyone would be
replacing crankshafts or rods every time they missed a
gear, hit a false neutral, the real neutral by accident
or simply over-revved the engine by a significant
amount.
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- What I'll Do
This project, a complete engine rebuild using the
Yamaha Blaster engine is coming together and there are a
couple of surprises. I asked every 2 stroke software
manufacturer to let me test their engine design software
on this engine. Of those I contacted, I am only waiting
to hear from one. Everyone else responded quickly and
positively. As it stands there should be at least 4
different manufacturers involved and a total of about 50
to 60 different programs to evaluate. I have a full
fledged manufacturer vs. manufacturer product evaluation
to write as well as the rebuilding of the engine itself.
I will design this engine 4 different ways, and publish
the results here.
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- Since I don't have several engines at my disposal
which would be required to individually test each
software package, I will be rating the software products
against criteria I invented. I will show the final output
parameters of the test engine from each software program
and include my thoughts and comments about it. I will be
rating the product in the following areas, in an effort
to spread the word about 2 stroke engine design
software.
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- 1) Installation
- a) Which operating system versions are
supported.
- b) How long it takes to get it up and running.
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- 2) Instructions
- a) Can the terminology be understood?
- b) Are they complete?
- c) Is there company support?
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- 3) Design Parameters
- a) Data entry - the requirements.
- b) What can be designed?
- c) What can't be designed?
- d) Is there adequate input to design the engine?
-
- I will include information about as many design
features as possible. This means every aspect of the
engine from the target operating RPM to the final output.
This article will have information about fuel and
lubrication, tuned inlet and exhaust, port timing -
including time area and vertical and horizontal port wall
considerations. There will also be information about the
reed valve, squish velocity and combustion chamber
design. I will be able to test this engine on a
dynamometer when its done.
-
- This is a very technical 2 stroke specific, moderate
to high output engine build. Though the actual engine
will be made to run 92 octane pump gas I will be able to
include information about making the power band and
performance quite different. I will show all the
necessary data to make a Yamaha Blaster engine fit the
following design parameters.
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- 1) Stock output using any octane pump gas - 125 PSI
compression - stock compression ratio
- a) Remove cylinder casting flaws
- b) Create a port map to discover the port timing.
Discover the horizontal and vertical port walls
- c) Index the port timing
- d) Discover the actual compression ratio (full
stroke)
- e) Calculate the area of the reed cage
- f) Establish jetting with stock carburetor
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-
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- 2) Moderate output - 92 octane - more compression
<-This will be the actual build specs of the test
engine.
- a) Remove cylinder casting flaws
- b) Create a port map to discover the port timing.
Discover the horizontal and vertical port walls
- c) Modify the port time area for increased midrange
power. Cut auxiliary boost ports
- d) Discover the actual compression ratio (full
stroke) - higher compression ratio
- e) Calculate the area of the reed cage and modify if
necessary
- f) Design a head using MSV technology (maximum squish
velocity)
- g) Establish jetting with stock carburetor
- h) Design and manufacture a tuned exhaust pipe
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-
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- 3) High output - 100 octane 50/50 pump/race - higher
compression
- a) Remove cylinder casting flaws
- b) Create a port map to discover the port timing.
Discover the horizontal and vertical port walls
- c) Modify the port time area for increased
upper/midrange power. Cut auxiliary boost ports
- d) Discover the actual compression ratio (full
stroke) - higher compression ratio
- e) Calculate the area of the reed cage and modify if
necessary
- f) Design a head using MSV technology (maximum squish
velocity)
- g) Establish jetting with 34 mm Keihin PJ
carburetor
- h) Design and manufacture a tuned exhaust pipe
- i) Change to premix
- j) Port the cases
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- 4) High output - 110 octane race gas only - maximum
compression
- a) Remove cylinder casting flaws
- b) Create a port map to discover the port timing.
Discover the horizontal and vertical port walls
- c) Modify the port time area for increased high RPM
power. Cut auxiliary boost ports
- d) Discover the actual compression ratio (full
stroke) - higher compression ratio
- e) Calculate the area of the reed cage and modify if
necessary
- f) Design a head using MSV technology (maximum squish
velocity)
- g) Establish jetting with 34 mm Keihin PJ
carburetor
- h) Design and manufacture a tuned exhaust pipe
- i) Change to premix
- j) Port the cases
- k) Increase displacement to maximum overbore using
stock liner (2 mm Wiseco)
- l) Use Banshee (long rod) and base plate
(compensating) spacer
- m) Deck or mill barrel as necessary to set port
timing
- n) Design engine parameters using a thermo-syphon
type water cooled head
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- What Is Known
-
- The stock Blaster engine has a bore and stroke of 66
mm x 57 mm for a displacement of 195 cm^3. It is fitted
with a 26 mm Mikuni carburetor and receives its intake
mixture through a reed valve. It is air cooled and oil
injected. Its connecting rod is 110 mm center to center.
It uses a copper head gasket which is .80 mm thick and
has a pyramid shaped combustion chamber. The output from
this engine is 17 HP at the rear wheels. Yamaha lists the
output as 15.2 ft.- lb. torque at 7000 RPM.
-
- The cylinder bore of this test engine is already at
66.5 mm (197.97 cm^3) and this was not damaged during the
crank failure. The cylinder was honed for new rings and
piston to cylinder clearance was found to be .0024". This
engine is fitted with a tuned after market exhaust pipe
of unknown origin. The exhaust port is fitted with a
flanged exhaust manifold which has an inside diameter of
35 mm and a length of 30 mm. The distance from the face
of the piston to the outside of the barrel is 57 mm (this
does not include the manifold). All engine components
will be investigated during this build. The following
replacement parts are being used in this project.
-
- Wiseco Piston kit #573P2 - ProLite
- Pro-X connecting rod kit #04963 - includes upper and
lower bearings
- Pro-X main bearings (same manufacturer as stock parts
- Koyo) # 83A915 ignition side, # 6305RI drive side
- Cometic head, base and reed cage gasket - kit #
C7093
- Pro-X crank seals Kit # 94963
- Yamaha gaskets (the rest of the engine)
- Yamaha seals (the rest of the engine seals)
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- Because the crank B.E. bearing failed - and the fact
that when the rod spun around in the cases (before the
crank stopped) it hit the case hard enough to create an
air leak at the junction of the case halves on the bottom
of the engine, it is necessary to lap the center cases
flat to prevent further problems. At this time all the
parts that can be lapped flat will be (head, barrel upper
deck, Intake area of barrel, block deck, center cases). I
will have information and pictures about how this is
done.
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- The Target
- This 92 octane pump gas engine will be designed
toward the following target. The RPM chosen for peak
power is 8000 - this is only 1000 RPM higher than the
output of the stock engine but 8 HP more - it is being
designed to produce 25 HP (to the ground) at its
peak.
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