85 tri z with newer yz250 engine. What will it take?

[86tri-zrider]

Hey everybody, ive searched for what seems like weeks now for someone that has or knows something about how hard it would be to swap a newer yz 250 (2001+) engine into a tri z. Yes i know the 80s yz engine are direct bolt in but thats not what i want. If anyone has an idea of what all it would take to get a newer yz motor in the tri z chassis please let me know!

[86tri-zrider]

Does anyone have any ideas on this subject?, id like to hear any and all opinions on things ill run into with doing this. Ive found an 03 yz250 all complete running for $500 it needs a clutch pushrod. I plan on using the wiring harness, carb, and twist throttle assembly from the bike along with the engine. Hopefully will have the bike this weekend to start tearing into this project. Again any feedback is helpful thanks

[sledcrazyinCT]

Good luck with the swap....hope someone chimes in. Make sure you post pics of the build!

[onformula1]

I don't know why the guys are not chiming in, my best guess is you only have two posts, we don't have a idea of your skill set, you are in the new member section and are a newby...but, I am jumping in on what I would do, thoughts and ideas as always we me everything is IMHO.

I have built some nice Tri-Z's and some fast YZ's, but never a Tri-Z with a modern YZ engine and have never seen nor heard of one. That doesn't mean it can't be sweet.

Possible problem areas-

The YZ engine is a vertical cylinder design meaning the cylinder sets back and straight up so the head may interfere and the exhaust area on the cylinder is different and uses a different size diameter, the power valve may also interfere.

I know the engine is smaller in size so that's good, but it was also designed to have the pipe on the throttle side so a custom pipe will be needed no matter which side you decide to route it. Could a Tri-Z pipe be modified to work, yes anything is possible, but it will not run correctly and you will lose a lot of the power gained.

I would drop kick the stock fuel tank and get a jeswinehart top mounted tank (Excellent, talented forum member here) now you will have some room for the canted YZ intake manifold and larger 38mm carb, I would build a custom airbox that uses the YZ airbox boot. The Modern MX bikes are designed from the airbox to the tip of the silencer to work together, a pod type filter will lose power you are gaining from a modern engine. I would use larger upgraded Tri-Z or the YZ radiators to keep it cool a MX bike has the cooling advantage of a skinny front tire, huge shrouds and are designed to get air in, cool the radiators and also get the hot air out these bikes are even wind tunnel tested. You never see a radiator coolant recovery tank on a MX bike

Forget the forward kick starter, that will be gone, so cut fenders or a flip-up will be needed. They have no lighting coil without mods so forget the lights.

Using a 9-10 oz plus flywheel weight will make the engine more ridable in a trike and will have a bit less vibration.

Fabbed engine mounts will be needed and the swing arm pivot bolt will be larger, so a machined sleeve through the cases are needed, build a head stay as well.

A wider axle, plus 3" swing arm, modified shock and forks to at least be stiffer and have more rebound would be very helpful with all the added HP.

I would also run a modified the YZ silencer (The stock YZ silencers are very good) for more fun chop the can down to 7-8" and pack it very, very tight. I would not mess with trying to make a Tri-Z silencer work.

The shifter will need to be lengthened or replaced

That's where I would start, I am here to help if you have questions, now post some pics!

[86tri-zrider]

First off i want to thank you for all of the useful info and your opinions on the subject. Most of the "issues" that youve pointed out i have thought about but there are i few that i did not. You say the yz engine sits at more of a vertical than the triz, how much so? Is it a huge difference between the 2 or minor? As far as the engine mounts i had already planned on having to make them custom, by no means did i think it was just gonna set in and bolt right up! Although that would be nice, by question is on the rear engine/swingarm mount. Is the yz the same as the z? Other than the size bolt that will be needed will the rear yz mount slide into the opening in the swingarm? And then will the chain come close to lining up? That was the part that i was hoping would be close. As far as the other mounts im not worried they can easily be fabbed up.

[86tri-zrider]

the chassis im starting with is an 85, after many years of neglect sitting in a buddys barnyard with the topend missing i finally talked him into parting with it. Being that the crankcase was left open to the weather i didnt have much to start with here which is what lead me to wanting to run the yz engine in the first place

[freewheeler]

A modern yz engine is in no way a bolt in to your tri-z.

[86tri-zrider]

A modern yz engine is in no way a bolt in to your tri-z.

Oh really? I thought it would fly right in and bolt itself down.

[onformula1]

Here are some pictures so you can see the vertical YZ engine in comparison. I am not saying it is a huge amount but when 1" on a Tecate KX500 means the difference between running a spark plug or not, it doesn't take much...LOL

Again I don't have both these engines in my shop, but modern engines are narrower, most of the time that includes between the swing arm which is good you will need spacers but that will allow you to offset the engine to align the sprockets.

Sit on a 1985 YZ for a half hour, then sit on a 2005 YZ it will feel like a tooth pick top to bottom. The frame is about the same thickness but the engine is narrower, which allows the designer to use a thin tank, air box, seat, ETC.

[86tri-zrider]

Yes i deffinatly see the difference when looking at them side by side in the pics, one good thing though is the size of the triz's engine bay, theres quite a bit of room for deviation from the original engine design.
The bike that i will hopefully be picking up this weekend is an 03 that suposedly runs very well but needs a clutch pushrod, or at least thats what the seller says. How big of a project is that pushrod to replace? The seller says the end is sheared off? Is that a somewhat common occurence in the yz or does that sound fishy? The pushrod itself looking it up online sells for about 15 bucks but ive never had a clutch on a bike apart before and dont really know what to think of this issue.

[onformula1]

The replacement is not tough, but get yourself a shop manual, you will at least need the specs.

Always plan on anything a used bike seller says is sketchy, play it safe.

That issue happens, usually from the gearbox oil not being replaced often, or the wrong weight oil, or a improperly adjusted clutch lever.

[86tri-zrider]

Alright thanks for the input, ill let you know more in a few days and post some more pics

[Tri-Z 250]

It can be done but your trans for the YZ250 has mod options as well. No doubt a full mod Athena 285cc motor might be an option but think 5speed. 426YZf's gears will drop into your YZ 250 cases with the talents of a good shop. It's basically todays 250YZX out for 2016 off-road market

[3 Wheel Drive]

Hey everybody, ive searched for what seems like weeks now for someone that has or knows something about how hard it would be to swap a newer yz 250 (2001+) engine into a tri z. Yes i know the 80s yz engine are direct bolt in but thats not what i want. If anyone has an idea of what all it would take to get a newer yz motor in the tri z chassis please let me know!

The forums have been pretty slow for a while but there is a lot of guys here who've done similar projects on the Tri Z'z:

http://www.3wheelerworld.com/showthr...ower+valve+tri

Try different Z searches there's lots of pics & info on this site.

[3 Wheel Drive]

If you decide not to go with a yz engine, Klemm Research offers a 350cc Tri Z kit. Raffa is the only one I know who has got one running but he does not post here anymore. There's vids on YouTube with his 350Z, I think the kit us north of 1k and requires case mods.

http://trikeracing.com/discussion/6/...-raw-meat-2/p1


More yz specific info:

http://www.3wheelerworld.com/archive...hp/t-7015.html
http://www.3wheelerworld.com/archive...p/t-58910.html