Using 1984 YZ 250 Clynder on Tri Z....Anyone done it?????

[Darius1502]

There is an 84 YZ engine on ebay....damn if the thing looks just like the Tri Z engine. Actually this is no surprise to me....but I have heard that the 84 YZ was a beast which made about 43 hp...way ahead of the times.

Has anyone done this mod?

Here is the link:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=34284&item=2442210285

[Darius1502]

FYI....they did it here:

http://www.3wheeler.org/3wheeling/12-84~pg38.html

Z seems to be a monster on top but no bottom with the mods.

[Tri-Z Pilot]

You need to make a hole for the powervalve actuator.

[Jeb]

Here's a link to an older post with a pic.



http://www.3wheelerworldforums.com/viewtopic.php?t=14333&highlight=doubts

[krizo88]

theres the answer to your problem slippy4

[TRI-Zbrian]

ive got an 85 yz 250 cylinder that soem one did away with the power valve on by putting a plug on each side of the cylinder to make it work with out the power valve in it i might bore it to a fresh bore and throw it on to see how well it does it should still make a decent power incrase being the reed housing is so much bigger all that much extra air flow in and out you would think it would be better then the tri z cylinder.

[slippy4]

so it justs bolts right on? what is the powervalve anyway? can you still use the tri-z head?

[TRI-Zbrian]

the power valve tunes the exaust and yes the head from the tri z will bolt right on to the yz cylinder also.

[slippy4]

is it necisarry to have the powervalve or is it just a performance thing? will the intake from the z bolt right in also?

[Tri-Z Pilot]

No, you'll need a yz250 intake, but it's bigger so you get more flow< probably better response too.

[denn]

I did this a while back with an 85 cylinder. It ran like a bat outta hell. You don't have to drill a hole for the powervale rod. If you look at your clutch cover above and your water pump cover about 2 inches back there is a flat spot about 1 inch high. There is a plug in there that you knock out from the inside so you can put the rod through. Yamaha never changed that part of the casting on the clutch cover, they just made room for the extra kickstart gear. The is also a rubber seal you will have to get to fit in there. It is a YZ part number. The problem is the head. The cooling inlet on the head is on an angle and kind stops the hose from going on by hitting the radiator. I took my tri-z head and the YZ head and had the tri-z head machined to match the CC's Of the yz head to keep compression the same. I would also recommend getting a gas tank where the airbox is. This will eliminate drilling a hole in the cylinder for the fuel pump. This is a pain in the ass cause the tri-z has a flat spot machined for it and the YZ dosen't. You will have to use the Yz intake, carb and boot. I don't know about the 84 but the 85 intake boot is on an angle which makes it hard to hook up to the stock tri-z set up. Which is another reason to get a gravity feed gas tank so you can put a clamp on filter. Other than that you have to get a few misc bearings and a stuff which are all stock YZ. You can go on parts fish or something like that and see excatly what you are missing. I don't think you can use anything higher than an 85 cause 86 and 87 had bigger heads so you cant put a triz head on it therefore you will probally have to mod the radiator.( I have an 86 YZ cylinder but haven't done to much with it). 88 and 89 would work great cause the head dosen't have the cooling inlet, it goes through the case but then you are stuck cutting you fenders so you can kick it cause you cant use the tri-z clutch cover. I am in the process of building and 86 tri-z 6 speed tranny with the yz cylinder and crankshaft. I can't imagine how fast that will be with an extra cog. And the throttle response and mid on an 85 yz is amazing. If I ever get done I will post pics. Sorry for the long post but I hope this helps some people.

Thanks Denn

[Jeb]

Awesome Stuff... Denn! :-D

[TRI-Zbrian]

im also re doing an 85 cylinder to do the same ive got the intake carb and reed cage with reeds all i need to do is bore the cylinder out to a fresh bore.