How to power valve your Tri-Z

[Derrick Adams]

Well, I thought i'll go ahead and start this thread for anyone that's curious.

I've started my engine assembly and i've been documenting it.

In case anyone wonders why you would do this, it has been said that this drastically improves overall performance of your engine, giving it more torque thru-out the powerband.

First your going to need to locate a complete 83-87 YZ250 engine. You can either use the whole YZ engine or just the components related to the power valve, which is what I did. It works the same either way.

The first part neccessary to swap is the crank gear, if you choose to use the Tri-Z lower engine. The gear off the YZ is a double gear used to operate the power valve governer.

Next you need to install a bearing in the Tri-Z case for the governer. These are still available from Yamaha for $11.00

[Derrick Adams]

Here's a couple shots of the YZ and Tri-Z cylinders beside each other. Notice the volume difference in the intake.

The intake is also angled slightly to the left, which is an issue we will deal with later.

[Derrick Adams]

Now we'll address the modifications neccessary to adapt the Tri-Z clutch cover for the power valve governer.

First a bearing needs to be installed in the clutch cover to support the governer. These are still available from Yamaha for $11.

Then you must knock out a punch plug from the Tri-Z cover. All of the casting and machining to accept the power valve equipment is done from the factory. You need to simply install it.

Once the plug is out you'll need a seal to replace it. This is still available from Yamaha for $6.00. Then just install the rod assembly and governer from the YZ engine and cover into the Tri-Z cover.

[twgranger]

This thread has been done before. Can't wait too see the finished product!!! Wish i had one.

[Derrick Adams]

That's where i'm at so far. I'll install the cylinder and finish it up later this week. Still waiting on the piston. I'll also cover how the install goes into the bike.

[CHAINSAW]

Very informative Derrick! Great thread!

[LonesomeTriZ]

I do not suppose you have a printable form of instruction sheet.

[Red Rider]

Looks much easier to adapt the YZ cylinder & governor to the Tri-Z, than it was to adapt the CR cylinder & governor to my ATC 250R. Now every Tri-Z's gonna be powervalved! Cool thread Derrick!

[LonesomeTriZ]

Which way does the stock YZ kicker go? Front or rear?

[Derrick Adams]

Kicks rear. When I do my other YZ engine, I'm going to do it the opposite way and use the YZ bottom end. So, i'll be switching the kicker gears. It will be a couple weeks before I get to that though. I'll add all that info to this thread as well.

[LonesomeTriZ]

So it is not neccassary to use the whole Tri Z side cover on a YZ bottom end?

[03 ORANGE SHEE]

the easiest thing to do ,like i did, was swap the whole top/ bottom in place, my intake is straight in, yours it at an angle..mmmm....great information for the ones with questions with this swap, next i think im going for the 426 or 450 thumper in one , problem is those engines cost way too much

[CHAINSAW]

What year motor you got Derrick? Mine is an 87 and its slanted to. I know 88 on up went back to 6 pedal reeds, and had a straight intake.

[Derrick Adams]

Both of mine are 87's.

[Jeb]

Good stuff Derrick! Now hurry and finish it!