OldSchoolin86
09-21-2004, 09:05 AM
This is an article from 3 & 4 wheel action in 85 that covers the Yamaha wrench report. It's a bit long but hopefuly you think it was a good read too.
PHASE I:
THE CYLINDER
All of the work done to the cylinder should be done by someone who's knowledgeable about two-stroke motors. The porting required is rather simple, but if it's done by the wrong person, the results could be catastrophic. You wouldn't want your Tri-Z to run like a blender, so take the time to find a savvy grinder. First, grind 1.5mm from the top of the exhaust port. The top of the port should measure 36.5mm from the top of the cylinder. Once it's ground, all the edges must be smoothed and contoured, with no abrupt changes in the shape of the port. All sharp edges or protrusions should be chamfered along the port edges.
With a hand drill and porting tool, duplicate the boost port (intake, sub-inlet port) on the right side of the cylinder. Both boost ports should be enlarged to 12mm wide and 24mm high. Make sure that the base of the holes matches the edge of the base gasket surface. Use caution in drilling so that the ports do not break into the cylinder stud holes-the results are major-league air leak time and a blown engine.
http://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/port.gifhttp://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/intake.gif
CYLINDER HEAD
The next step requires precise machining. Using a lathe or milling machine, cut approximately 0.5mm from the gasket surface of the head. With the head installed, the cranking pressure must be between 170 psi and 175 psi with the engine cold. Machining the head increases the compression and is critical to the Wrench Report gains in performance. There should be a minimum of 0.75mm of clearance between the piston and the head. If this squish band is less, you'll need to recut the head to meet the requirements.
EXHAUST PIPE
Next, a section of the header pipe on the exhaust system must be cut out. Take a hacksaw and slice out a 10mm section from the right side of the pipe while it's on the bike. The cut should be right at the U-shaped section that bulges as the header section leaves the cylinder. Tack weld the pipe together, then remove it from the machine and complete the weld. Again, use extreme caution, and preferably, have an expert do the welding.
http://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/pipe.gifhttp://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/adapter.gif
AIR FILTER
If water, mud and extreme dust are not factors, the stock air filter and intake system can get trashed. The high breather system stifles the air intake and hampers the power of the Tri-Z.
This intricate design is replaced by a K&N filter, #RC2000. If you look closely, it's the same filter used on Harley choppers. If you run this filter, the tool kit and coolant reservoir get the ax. Also, a section of the rear fender must be chopped away to allow room for the K&N unit. Leave the stock intake boot on the carb. An adapter must be made to connect the new filter to the carb boot. Check the photos to get the idea; it should measure 30mm long with a 74mm O.D. and be 2mm to 3mm thick.
REEDS, CARB AND MUFFLER
Take the stock reeds off and replace them with Boyesen fiber reeds. Only a small carburetion change is needed; change the main jet from a 470 to a 490. Last on the list is the silencer and spark arrester. Chuck the stock model and pop on an Answer Products unit.
AIR FILTER
If water, mud and extreme dust are not factors, the stock air filter and intake system can get trashed. The high breather system stifles the air intake and hampers the power of the Tri-Z.
This intricate design is replaced by a K&N filter, #RC2000. If you look closely, it's the same filter used on Harley choppers. If you run this filter, the tool kit and coolant reservoir get the ax. Also, a section of the rear fender must be chopped away to allow room for the K&N unit. Leave the stock intake boot on the carb. An adapter must be made to connect the new filter to the carb boot. Check the photos to get the idea; it should measure 30mm long with a 74mm O.D. and be 2mm to 3mm thick.
REEDS, CARB AND MUFFLER
Take the stock reeds off and replace them with Boyesen fiber reeds. Only a small carburetion change is needed; change the main jet from a 470 to a 490. Last on the list is the silencer and spark arrester. Chuck the stock model and pop on an Answer Products unit.
SOUNDS COMPLICATED, BUT HOW'S IT WORK?
Let's deal with Phase I first. With the minor porting, head work pipe mods, filter grafting, Boyesen reeds and Answer spark arrester, the docile, semi-hard-hitting Tri-Z comes alive. There's no power gain in the slim low-end delivery, but a substantial boost comes to the mid-range and upper hit. The power remains tractable like the stocker; it just slams harder, much harder, and revs out a good deal further than the showroom model. Had it come from the factory like this, we'd have been grinning like idiots.
There's no doubt that the mods make a considerable difference in the overall power delivery of the Yamaha. Phase II is completely berserk. Every particle of noticeable bottom-end grunting force completely vanishes. A riled, abrupt attack builds rapidly, slams through the usable mid-range, and surges directly into a walloping strike at the upper revs. Its Pro-like thrust requires delicate throttle and clutch coordination to stay on top of the hostile hit. Experienced pilots will scream in delight; less seasoned riders will
shiver and curl up at the explosive, light-switch-type acceleration.
SUSPENSION SONG:
FROM MEEK TO CONTROLLED
Our only complaint with the stock suspension action is that it's too soft for anything other than very casual riding. Yamaha's cure is very simple and effective. They offer heavier fork springs and a stiffer rear spring that firm up the action just right.
Up front the smallish 35mm forks get the heavy optional springs and a change of internal damping blood. Drain the standard oil and replace it with 15-weight fork oil. With the springs out and the forks collapsed, set the oil level at 150mm from the top of the tubes. Setting up the forks this way, by oil level rather than amount, will make for more consistent action. Both sides will have the identical level and, in turn, work better.
Out back, install the optional heavier rear spring, and set the length at 232mm. That's the compressed length of the spring, or the set length while the shock is off the machine. Set the compression damper at #9 and the rebound at the second click out.
One ride through any gnarlies will quickly show off the new-found virtues of the Tri-Z's suspension prowess. Rather than bottoming and wallowing over whoops, it reacts and holds a straight line. Jumps, sand dunes and mud holes can be attacked rather than cringed at.
SO...
Yamaha has come up with the technical knowledge and the parts needed to transform the Tri-Z from pleasant to exciting. All you have to do is find someone to do some of the labor, bolt on a few items, and you're set. The mods are definitely worth the time and money invested. Next month look for Phase III of the Tri-Z update. We're going to get rad with the engine and some of the running gear, and, attempt to make it into a race-winning missile. Stay tuned.
PHASE I:
THE CYLINDER
All of the work done to the cylinder should be done by someone who's knowledgeable about two-stroke motors. The porting required is rather simple, but if it's done by the wrong person, the results could be catastrophic. You wouldn't want your Tri-Z to run like a blender, so take the time to find a savvy grinder. First, grind 1.5mm from the top of the exhaust port. The top of the port should measure 36.5mm from the top of the cylinder. Once it's ground, all the edges must be smoothed and contoured, with no abrupt changes in the shape of the port. All sharp edges or protrusions should be chamfered along the port edges.
With a hand drill and porting tool, duplicate the boost port (intake, sub-inlet port) on the right side of the cylinder. Both boost ports should be enlarged to 12mm wide and 24mm high. Make sure that the base of the holes matches the edge of the base gasket surface. Use caution in drilling so that the ports do not break into the cylinder stud holes-the results are major-league air leak time and a blown engine.
http://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/port.gifhttp://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/intake.gif
CYLINDER HEAD
The next step requires precise machining. Using a lathe or milling machine, cut approximately 0.5mm from the gasket surface of the head. With the head installed, the cranking pressure must be between 170 psi and 175 psi with the engine cold. Machining the head increases the compression and is critical to the Wrench Report gains in performance. There should be a minimum of 0.75mm of clearance between the piston and the head. If this squish band is less, you'll need to recut the head to meet the requirements.
EXHAUST PIPE
Next, a section of the header pipe on the exhaust system must be cut out. Take a hacksaw and slice out a 10mm section from the right side of the pipe while it's on the bike. The cut should be right at the U-shaped section that bulges as the header section leaves the cylinder. Tack weld the pipe together, then remove it from the machine and complete the weld. Again, use extreme caution, and preferably, have an expert do the welding.
http://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/pipe.gifhttp://www.quadpit.com/images/mags/stories/1985/yamwrenrpt/adapter.gif
AIR FILTER
If water, mud and extreme dust are not factors, the stock air filter and intake system can get trashed. The high breather system stifles the air intake and hampers the power of the Tri-Z.
This intricate design is replaced by a K&N filter, #RC2000. If you look closely, it's the same filter used on Harley choppers. If you run this filter, the tool kit and coolant reservoir get the ax. Also, a section of the rear fender must be chopped away to allow room for the K&N unit. Leave the stock intake boot on the carb. An adapter must be made to connect the new filter to the carb boot. Check the photos to get the idea; it should measure 30mm long with a 74mm O.D. and be 2mm to 3mm thick.
REEDS, CARB AND MUFFLER
Take the stock reeds off and replace them with Boyesen fiber reeds. Only a small carburetion change is needed; change the main jet from a 470 to a 490. Last on the list is the silencer and spark arrester. Chuck the stock model and pop on an Answer Products unit.
AIR FILTER
If water, mud and extreme dust are not factors, the stock air filter and intake system can get trashed. The high breather system stifles the air intake and hampers the power of the Tri-Z.
This intricate design is replaced by a K&N filter, #RC2000. If you look closely, it's the same filter used on Harley choppers. If you run this filter, the tool kit and coolant reservoir get the ax. Also, a section of the rear fender must be chopped away to allow room for the K&N unit. Leave the stock intake boot on the carb. An adapter must be made to connect the new filter to the carb boot. Check the photos to get the idea; it should measure 30mm long with a 74mm O.D. and be 2mm to 3mm thick.
REEDS, CARB AND MUFFLER
Take the stock reeds off and replace them with Boyesen fiber reeds. Only a small carburetion change is needed; change the main jet from a 470 to a 490. Last on the list is the silencer and spark arrester. Chuck the stock model and pop on an Answer Products unit.
SOUNDS COMPLICATED, BUT HOW'S IT WORK?
Let's deal with Phase I first. With the minor porting, head work pipe mods, filter grafting, Boyesen reeds and Answer spark arrester, the docile, semi-hard-hitting Tri-Z comes alive. There's no power gain in the slim low-end delivery, but a substantial boost comes to the mid-range and upper hit. The power remains tractable like the stocker; it just slams harder, much harder, and revs out a good deal further than the showroom model. Had it come from the factory like this, we'd have been grinning like idiots.
There's no doubt that the mods make a considerable difference in the overall power delivery of the Yamaha. Phase II is completely berserk. Every particle of noticeable bottom-end grunting force completely vanishes. A riled, abrupt attack builds rapidly, slams through the usable mid-range, and surges directly into a walloping strike at the upper revs. Its Pro-like thrust requires delicate throttle and clutch coordination to stay on top of the hostile hit. Experienced pilots will scream in delight; less seasoned riders will
shiver and curl up at the explosive, light-switch-type acceleration.
SUSPENSION SONG:
FROM MEEK TO CONTROLLED
Our only complaint with the stock suspension action is that it's too soft for anything other than very casual riding. Yamaha's cure is very simple and effective. They offer heavier fork springs and a stiffer rear spring that firm up the action just right.
Up front the smallish 35mm forks get the heavy optional springs and a change of internal damping blood. Drain the standard oil and replace it with 15-weight fork oil. With the springs out and the forks collapsed, set the oil level at 150mm from the top of the tubes. Setting up the forks this way, by oil level rather than amount, will make for more consistent action. Both sides will have the identical level and, in turn, work better.
Out back, install the optional heavier rear spring, and set the length at 232mm. That's the compressed length of the spring, or the set length while the shock is off the machine. Set the compression damper at #9 and the rebound at the second click out.
One ride through any gnarlies will quickly show off the new-found virtues of the Tri-Z's suspension prowess. Rather than bottoming and wallowing over whoops, it reacts and holds a straight line. Jumps, sand dunes and mud holes can be attacked rather than cringed at.
SO...
Yamaha has come up with the technical knowledge and the parts needed to transform the Tri-Z from pleasant to exciting. All you have to do is find someone to do some of the labor, bolt on a few items, and you're set. The mods are definitely worth the time and money invested. Next month look for Phase III of the Tri-Z update. We're going to get rad with the engine and some of the running gear, and, attempt to make it into a race-winning missile. Stay tuned.