how close is the 85/86 yz250 engine to the tri z engine

[audioworks04]

it always seems easy when you start, but its never quite and easy and always takes atleast twice as long. Sounds easy enough though, Id try it, one thing to look out for is jetting unless you still have the yz carb also, and even then may have to rejet due to intake and exhaust. Also I know that most dirt bike motors are geared quite abit different than 3 and 4 wheeler trannys due to the rear tire size of the bike. I had this problem with my crf conversion, but not the end of the world just takes alittle getting used to. Good luck and lets see some pictures.

[Mosh]

You can run the YZ engine as a direct drop in with minimal mods. They do have a angled/larger intake assembly that will proabably give you problems mounting up the z intake system.
However, you will loose your lighting system, and there is no way to get around that other than swaping the Tri-Z crank into the YZ cases.( It is not in the wiring)
The flywheel on the dirbike is smaller, with a smaller stator, and the dirtbike crank journal is smaller, so you cant put a Z flywheel on the dirtbike crank. You can drop the Z crank in the dirtbike cases and swap the Z stator and flywheel over to the dirtbike engine to get you lights back.

Also, you can run the Z kicker cover and clutch cover and gears on the YZ engine and make it kick like the Z was intended to. Forward.
You will have to remove the power valve plug in the Z clutch cover to hook up the YZ power valve.
Honestly, I dont see where there is any gain by doing this conversion. They really do not give any advantage in performance other than quicker revving and a fuzz more on the top end.. Actually, you will be losing a little bottom end torque with the dirtbike engine.
if you were going all out drag trike, it may be worth it.

[stevensj13]

You can run the YZ engine as a direct drop in with minimal mods. They do have a angled/larger intake assembly that will proabably give you problems mounting up the z intake system.
However, you will loose your lighting system, and there is no way to get around that other than swaping the Tri-Z crank into the YZ cases.( It is not in the wiring)
The flywheel on the dirbike is smaller, with a smaller stator, and the dirtbike crank journal is smaller, so you cant put a Z flywheel on the dirtbike crank. You can drop the Z crank in the dirtbike cases and swap the Z stator and flywheel over to the dirtbike engine to get you lights back.

Also, you can run the Z kicker cover and clutch cover and gears on the YZ engine and make it kick like the Z was intended to. Forward.
You will have to remove the power valve plug in the Z clutch cover to hook up the YZ power valve.
Honestly, I dont see where there is any gain by doing this conversion. They really do not give any advantage in performance other than quicker revving and a fuzz more on the top end.. Actually, you will be losing a little bottom end torque with the dirtbike engine.
if you were going all out drag trike, it may be worth it.

I see your point. i thought it would be a simple drop and go thing, and while the headlight thing is not a big deal for me, if I am cracking open the Z clutch cover anyway then i might as well just replace the clutch plates and be done with it. This may be a project for another rainy day but I think it would be a wiser investment time wise to just finish up the Tri-Z engine. while the compression is low it does start and run (very rich might I add) so I think it would do fine this weekend for now. if this bike had a new seat and a new set of rear fenders it would look restored and I think I'll keep it original. thanks for the insight guys

[SawyerCustom]

I have both engines apart right now, as I have 2 tri-z's I am bringing back to life. A friend of mine gave me an 85YZ 250 engine and frame. I have the tri-z engine also.. Differences are: power valve linkage, jug, head, clutch cover has slot for linkage (need to close if not swapping to forward kick), gear ratio in tranny, stator is shaped different and has no lighting, flywheel is a lot smaller, KEY problem... Stator side crank is cut smaller than tri-z.. Flywheels will NOT swap. Need to replace crank if you want lights. I am currently in the process of cutting the flywheel rivets, swapping centers, and slug welding the YZ center into an old tri-z flywheel. I don't see why it wouldn't work. It takes the same puller, and is the same od. Those are what I found different.. Same cases, clutch, different internals, and top end.

[poolieZerUK]

is the inner and outer clutch basket the same?

[King Trikester]

If you do tackle it make a thread or add it to this one I'm interested in how it goes

[NeverLift]

http://www.3wheelerworld.com/showthr...i-z-PowerValve

Take a look at this. It should answer you questions.

[Mosh]

It has been a while since I have done anything with a Z. But the first one I built from the ground up was a hodge podge of Z engine parts and 86yz engine parts. With the exception of the 86 Z trans being a 6 speed....all.the research I have done suggest Yamaha used the same gears in all 83-87 YZ dirtbikes and the 85 tri-Z.
I spent some time on the OEM parts schematics crossing part numbers. The 5 speeds all appeared to.run the same gear ratios. I did not scour every number just did some quick checks so I may be wrong. But even going back to when I built a few all the gears were the same. Expecting a different ratio may not be realistic unless you run a 86 z six speed trans.

But please correct me if I am wrong.