“Tribal Knowledge” is an unfinished work based on what I learned about tuning a TZ250 by racing a few of them in Hawaii and North America. It was my idea but I needed a writer. Jim Hubert wrote it based on a few long phone conversations. Michael Gougis helped with the editing. The knowledge herein is not mine, it is the shared knowledge of a community of racers and it is yours to use. By using this knowledge you are obligated to pay it forward.
Ed Sorbo 3/26/14
Please go to Ed's website to read the entire informative article.
Tribal Knowledge
(The Care and Feeding of a TZ250)
Copyright 2004, Jim Hubert
This article is the culmination of a series of conversations with
former 250cc GP front-runner, Ed Sorbo. For those of you who don’t
know Ed…
Best race of all time: Brainerd in ’99 Finished 6th. Started
from last on grid. 15 MPH slower than the guys racing with.
Announcer said he moved from paradise to live in a motorhome. That
is why! WRITE INTO A STORY
From the outset, Ed wanted it clear that although he might be the
one willing to sit still long enough for me to write it all down,
the information contained herein is not all his own discovery. Ed
feels indebted to a number of racers and tuners, especially his
racing partner — Bruce Lind. In fact, it was Bruce who coined the
phrase “tribal knowledge pool” when referring to the body of
information amassed by TZ racers. This article is a start at
disseminating that knowledge. Most of the information is hands-on
nutsy-boltsy stuff but there is a fair mix of theory for those of
you who want to know “why” instead of just “what.” Don’t be scared
off by this because, as Ed is fond of pointing out, “If you’re
smart enough to ride the motorcycle, you’re smart enough to work on
it.”
This article discusses the 50.7mm-stroke vees from model years 1991
to 1999. Those model years comprise the bulk of the machines
inexpensively available. If fact, Ed estimates there are probably
1000 such machines in the US today. The AMA’s opinion
notwithstanding, 250cc 2-strokes are not going away overnight.
Considering that most parts for the ’99 model are backward
compatible to the ’91 machine, and that Yamaha is obligated to
provide parts for 10 years for a given model year, racers should
have ready parts availability until at least 2009. Additionally,
Ed believes that if there is sufficient demand, aftermarket
suppliers could step in to fill the void.
In many ways, the short-stroke vee engine represents a good
compromise for the racer on a tight budget. For one thing, the
engine cases — which are based on the TZR250 street bike — are
pressure cast. This equates to a longer life span than the sand-
cast cases used on 2000+ models. Similarly, the short-stroke
engine should have a longer service life than the “square” motors
which are more heavily stressed.
Ease of Maintenance:
Ed says many racers get the wrong impression of how much effort is
required to keep a TZ in top condition. “They see us working on
our bikes all the time and figure it’s a bitch to keep them running
right.” Quite the opposite is true, “We work on the bikes because
it is so inviting. Ease of maintenance was high on the list of
priorities when the TZ was designed.” For example, an experienced
mechanic can remove and replace a TZ crank in an TWO HOURS, BRUCE AND I DID IN 1.5 ONCE hour at the
racetrack. The crankcases split vertically, so that the bulk of
the engine can remain in the frame for the procedure. If you
destroy the crankshaft in a 4-stroke, your weekend is over.
Full Disclosure:
Racers endorse products and services for a variety of reasons –
sponsorship, contingency money, perceived value, future
consideration, and friendship immediately come to mind. When we
mention a product or service by name, it is entirely possible that
an alternative, competing one, will work just as well, perhaps
better, for you. We have endeavored to be as objective as
possible. In some cases (Rino fender, for example), there is no
competing product. In others cases (Kawasaki wrist-pin trick), we
hope it is apparent that we don’t have an agenda to forward.
However, in the interest of full disclosure, we want you to know
that Ed was WAS AT DIFFERENT TIMES (IS?) sponsored by Silkolene, and received contingency
money from VP Fuels. OTHERS? BRIDGESTONE, EBC, SILKOLENE, TSUBAKI, RK, BARNETT, SPEED TUNE, VP
Please go to Ed's website to read the entire informative article.
Brought to you by:
Steven Aspland
