by James Wonder
Hello again,
I cannot count on both hands how many times I was asked about engine
blueprinting this past weekend. It seems with a fairly large break everyone is
looking to do their motors over. It will be quite competitive at the next race
I am sure!
So, I am going to try to tell you what happens when you send your motor off and
pay all that money. It looks the same when it comes back, with a few extra
stickers! What did they really do?
My disclaimer goes here. I know some about the Comer K80 (cadet) and the
Rotax motors, but I would really like someone to talk about the Yamaha motors.
1) Most of the horsepower is in the carburetor. In the comer and Rotax, they
are as cast and the tuning is very fine to get the most out of the motor. Your
engine builder will tune the carb to their
specifications.
The Rotax motors are spec motors, and the carb is the
whole thing if they are sealed by a reputable engine builder.
2) In the comer motors they align the cases. Basically, the crank and the
piston is not at 90 degrees with each other perfectly.
They machine the case to make this happen. This is where the time spent doing this matters, and as far as I know there is only one man (I
forget his name) in the
3) They then go through a very lengthy process of reducing drag and friction
wherever they can. This is where a great deal of time is spent, making sure
everything is straight, true and runs without friction. Yes, .0005 of an inch
does matter and the really good engine builders spend a great deal of time
here. Bearings and low friction seals are just part of the game, and most will
not tell you everything they do at this step, but it is very time consuming if
done properly.
4) The good engine builders shape the head to tune the motor to the specific
performance you need, or for your local track. Changing the head cut can change
the horsepower and torque curves drastically.
5) Clutches get tuned and tested.
6) The motor then gets put on the dyno and tested.
The break-in occurs here mostly, and the builder is able to see if the engine
meets his expectations. Many times the motor gets pulled off the dyno and re-done or tweaked to make it right. The carb gets tuned during this stage as well. This takes time
to get right!
So, if anyone has anything to add please do! This is just a very simple and
straightforward list that I put together. I would love someone to fill in the
Yamaha stuff.