Tri Z Engine Build

[El Camexican]

This engine only has about 6 hours on it, but I recently gave up on my aspirations to travel long distances over remote terrain on it, so I no longer see the point to keeping it trail worthy.

The engine came with a rough attempt at Phase II mods which I gingery tried to smooth over without adding to the loss of bottom end, but as much as I will defend its ability to be ridden in tight areas the fact is that it needs way too much clutching before attempting a jump to warp speed without notice. As much as I hate to admit it scares the bejesus out of me on anything but a long flat surface. I don’t know if it’s just the added traction, but it feels like it accelerates faster than my 300cc bike when it’s on the pipe.

So here goes. Below is what’s getting bolted on after the ports get another tweaking.


The Sprock head has a pump dome and that’s just fine with me, I don’t believe that 2 strokes like a lot of compression to start with. Thanks to off-Road Innovations for the head and Ricochet Off-Road for the dip in orange juice. More parts may end up there before this is over.


My manifold actually took the 38mm carb without a lot of fighting, but the boost bottle had to go, so a Sprock unit was picked up from Mrs. Mosh. I plan to use it with the stock cage, so it looks like some matching work and maybe even a little JB Weld will be needed.


The fly wheel was sent out to have 5 to 6 ounces lopped off. I’d promote the place that did it, but I’m not thrilled with the workmanship, so that ain’t happening.


The fuel Tee from SBDesigns here in the 3WW Store has been waiting to go on for a while now, as has the tether switch. The HD clutch springs are likely going to be needed at this point.

Also picked up a stock swing-arm from Manbearpig that will be lengthened, but how much is still to be determined.

You may have noticed some orange Yamaha decals in the photo. Still not sure about that. Input welcome.

[aramid]

.
hello el camexican, you probably know this but just in case, you can drop power by doing the following also.

6 mm thick reed cage spacer . . this will soften power and make it a little less pipey and lite switch like.

smaller carb

reduce the amount the reeds can open.

add weight to the flywheel . . removing weight makes them less tractable so the tires suddenly spin . . more weight will smooth out the power delivery a bit and make it harder for the bike to stall when applying the rear brakes . . you can get a ring made to press over the outside of the flywheel.

mill around .020" off the bottom of the cylinder to lower the ports, then run a thicker head gasket if your compression is still higher than you want but this increases the squish distance which can increase the potential for detonation in some cases even though it lowers the compression . . its a bit of trial and error.

retard your ignition timing around .015" on the timing plate.
.

[El Camexican]

Totally agree Aramid and if that was the goal I'd likely just put a stock cylinder and carb on it, but that's not the direction I want to go. For the amount of use it gets, it may as well just be a mild drag racer.

[Darius1502]

Having talked with Camexican I know this guy knows his STUFF!! ITs going to be an awesome motor!!

[cr480r]

Just curious if you have the timing specs of your current cylinder. Beyond phase 2? Have you put a wheel on it?

[El Camexican]

Having talked with Camexican I know this guy knows his STUFF!! ITs going to be an awesome motor!!

Darius, you're making me blush. I'll be happy if it just runs as fast as a stocker when I'm done with it.

[El Camexican]

Just curious if you have the timing specs of your current cylinder. Beyond phase 2? Have you put a wheel on it?

No sir, not yet, but that's the plan. Not sure what you mean by "Beyond phase 2?".

[onformula1]

I think he is talking about this part-

"The engine came with a rough attempt at Phase II mods which I gingery tried to smooth over without adding to the loss of bottom end"

[onformula1]

What reeds are you using? I would run Carbon Tech, carbon Fiber HI-Tension. Boyesen's work good as well, but I like something a bit stiffer, you could also make a reed stiffener.

You might want to run only 3 heavy duty clutch springs, especially after coming off a KTM hydraulic clutch. Maybe try that first, 6 HD's can kill your arm and are usually not needed.

[Mosh]

I dont know about tri z's...but I do know they like the timing retarded just a bit..
And they run the best with the v force 3's...and that pump dome aint a pump dome unless Sprock re worked them. If that is the old head design that is, unless it has been turned down. If Just a fyi..

[El Camexican]

I dont know about tri z's...

Yea, I heard that somewhere. If you had to pick a "random number" between 1 and 360 for that retarded timing # what would it be?

I've read many of your posts dating back to the inception of the Cool Head, great info. Compression will come up later, but for now I'm focused on the intake. You mentioned the V303A fitting the Tri-Z and that the 682m reeds are softer and work better, I assume that is for overall use more so that just top end? I'm a little leery of dropping the coin on the V-Force V303A's I see on ebay as there are multiple images, some with 6 mount holes! Can you confirm this fits the Z? and also if the angle of the block is any steeper than the stocker? http://www.ebay.com/itm/Moto-Tassina...f7240b&vxp=mtr

I couldn't find anything on the 682m reeds on the net yesterday, so for now I'm planning to work on mating the stock cage better to better suit the Sprock manifold. It looks to me like I can add a few mm of JB weld to the top and bottom of the manifold and then blend it into the cage. On the sides I plan to just widen the manifold and shape it much like the rubber tips on the stocker.

I've got a set of Boyesen's on it now and I think I'll start with them. I ordered a second cage with the stock stops still on it to experiment with as I "feel" like I'm getting some flutter up top (it has no stops at this time as per Boyesen's instruction). It may just be fat jetting, but I don't see how a set of stops will hurt anything if I just bend them open a couple mm.

Another thought is to get a manifold spacer and machine it into a wedge so that the carb is angled up a few degrees and keeping the pod filter off the frame. It could be done to the Sprock part, but I'd rather experiment with a cheap chunk of aluminum. I know for certain that the PWK works fine tipped up a bit.

Current compression with the modified stock head is 180# and no known detonation or overheating on pump gas, but then again I didn't try to climb a dune. It runs a lot hotter than my 300 KTM in the same conditions, but still cooler than I would have expected based on what I've read. I will measure and cc the stock head when I get it off to compare it to the Sprock dome. That should be a good indicator of what to worry about.

Lots to think about. Thanks for weighing in!

[El Camexican]

I think he is talking about this part-

"The engine came with a rough attempt at Phase II mods which I gingery tried to smooth over without adding to the loss of bottom end"

Ok, well if you've read the report you know what was suggested, so here's what I got:

- A second boost port made by punching various holes with a hand drill and then an attempt to blend them with what I assume was a tapered stone on the same drill
- No mods to the stock boost port
- Exhaust was raised, but only 1mm from where I took stock to have been
- The transition into the transfer ports looked like a combination of a terrible casting from Yamaha combined with more input from the hand drill. Good news is that not a lot of material was removed, so I smoothed them out a little and left them. This time around I plan to blend them properly and if need be JB Weld any gouges.

Boost ports after being cleaned up


I think the clutch uses 5 springs. I'm ok with a stiff clutch. What does a reed stiffener consist of?

[onformula1]

If you Goggle image- "yamaha tri-z 250 clutch hub" every picture shows 6 springs.

You can buy reed stiffeners of just cut down a old reed set & put them on top of the new reeds, you can go between 1/4 to 1/2 of the stock length reed. I always seem to land on 1/3, so cut 2/3 off the reed and clean up the ends with light sand paper, bevel the sharp points.

[3 Wheel Drive]

Ive got an extra HD Sprock Racing base gasket if want one pm me. All the info for the Vforce3 reeds is good on the Z they will come with 4 holes no worries. Here's a pic of the reeds & HD Z gaskets:



Its hard to believe after all the bling on your Z and time building that trailer, you don't have those fancy reeds yet?!

[El Camexican]

I've been staring at newer YZ engines looking for differences between my old 25-30 hp engine and newer 45-50hp engines. Here's what I see so far at a glance:

Tri-Z - Big OD head pipes and large wide exhaust ports
Newer YZ - Smaller head pips and ports (and of course power valves)

Tri-Z - Long, large intake tract with piston windows
Newer YZ - shorter intakes with no piston windows, but instead a port that starts in the intake floor and exits in the cases, so opens the reeds much sooner than the Tri-Z.

Tri-Z - Single slot shaped boost port
Newer YZ - Round, oval boost ports

Interesting...