1985 Yamaha Tri-z 250 Rebuild Advice?!

[Tklehr96]

Hello, I am new to this site and have some questions. I just recently bought a 1985 Yamaha Tri-Z 250 (Red & Black) trike and haven't had it very long. Seemed to be running fine but tonight on a quick ride it stalled on me a couple times but kept firing back up. I limped it home and now it wont start at all. Started to tear into it too see what was up. Kinda had a bad feeling. Compression after 4 kicks shows 120psi. Pulled the exhaust off to have a quick look at piston and cylinder and from what I can see there's a lot of scoring on the piston and quite a bit on cylinder walls. That's as far as I am right now and am assuming the worst that it will need a complete top end rebuild kit. I have 3 Hondas and have worked on them some but am not as familiar with the Tri-Z. Does anyone have any information on good rebuild kits for this trike? As far as a new jug, piston, rings, gaskets ect. I cant find much and like I said am not familiar with good options. Is there any other direction I should be going? Not exactly sure what caused this but ive read that fuel pump failure is common on these and tends to lean them out? Anything else I should look into after rebuild? Any response is greatly appreciated and thank you so much in advance!!

[rmcollector]

I restored the 85.5 last year and have the 85 as well (yellow/black), good parts are definitely harder to come by with the Z. My compression runs about 172-178 or so on both. 120psi is obviously too low, but it is enough to get it started. Before breaking it down, did you run a leak down test?

[Tklehr96]

Probably should have but didn't as everything seemed to be running really well. Had tons of power and sounded right. Talked to a couple people today around my local area and they said I should have it bored. Might seem obvious to everyone else but like I said im quite new to the 2 stroke trike scene. I also have a 86 250R and parts seem easier yes. While I have motor pulled is there anything else to look for? Ive read that water pumps are also problematic on these. Noticed something as well, there's a small red light in the headlight assembly. I can only assume its a temp light? Is it suppose to come on when I start the machine for a bit and then turn off? Mine does nothing upon starting. Thanks for the reply!

[rmcollector]

Yeah I was asking because I would hate for you to freshen up the top end and there possibly be an air leak somewhere and it would just end up destroying your new top end if the air leak wasn't found in time. That's what im dealing with now, my 85 tore up the piston, head, and took a small chunk off the cylinder skirt last week. Finding it on the leak down, it has a hair line crack in the right case right below the crank. I never had any issues with the water pumps, but I guess it's hit or miss with these older bikes.

Yea the small red light is the high temp light in the headlight assembly, it should only come on for a second or so once started and then it should cut off. If it's not doing nothing then check connections first. Could just need a hone, but you said the cylinder and piston looked scored, so it will most likely need a bore if it looks like that when you get it apart.

[bobtdms]

If you are still running the stock airbox assembly, make sure that the nipple on the bottom of the intake tube is capped off. Both of the complete running tri-z's that I bought had the same problem. Previous owners left it open to suck in dirt. They ran great and started first kick, but the top end was worn out and needed a bore and piston.

[Tklehr96]

Thank you for this information, it does have the stock airbox and will definitely be looking into that intake nipple! This coming week I will be starting the tear down and referring to this thread for any questions. Im assuming a leak down test is something you do after the top end rebuild? Never done one before so any info on that would be helpful. Have to find a way to seal intake and exhaust ports on jug? Is it worth tearing into the bottom end for extra measures? Any other info you can think of would be greatly appreciated! Thanks!

[Tri-Z 250]

In your rebuild process pin the impeller to the shaft, of the water pump. Replace the rubber case seal as well on the pump for good measure. Talon makes a YZ490 clutch basket should yours be worn out.

[rmcollector]

Here is a leak down tester I built specially for the Tri-Z, the tester comes out the right sight of the engine once inserted into the intake boot. Of course you can make it go any way you want if the engine is out of the bike, but I found this to work both ways, being the gas tank, etc, is in the way if you are testing with the engine in. I have a shorter one for the 250R.

You will be using a doorman expansion plug 1-7/8 in. - 2 in. to seal off exhaust port. You can easily find this at the auto parts store, and the rest at Lowe's or Home Depot. You will be using a 1" pvc pipe for intake boot. Any bigger and you will tear the rubber boot apart. Make sure to use teflon when assembling all parts.




262088

[Tklehr96]

May have found a culprit. Built myself a leak down test today and immediately wouldn't hold pressure and could hear air hissing out of the reed block gaskets bad. Im guessing sucked air dirty air and ran lean? Sprayed rest of motor down with soap and water and didn't get any other bubbles showing that I could find. Opened trans plug and couldn't hear any hissing in there. Started taking motor out and didn't take long until I got too the swingarm bolt. That was a bear holy crap...Bushings look worn and since im this far im probably going to do a bushing kit from parts giant unless someone else sells a better kit? Thanks for replies!

[rmcollector]

Were you able to hold any air while spraying the other areas of the motor? The Tri-Z only calls for one gasket around the reed area, the oem is still available on Partszilla, etc.

Stick with oem gaskets if you can. If your taking the top end off, try to get the oem metal head gasket (38W-11181-00-00) off of eBay or something, not the cheap paper ones.

Let us know how that cylinder and piston look when you get it apart.

[Tklehr96]

I thought I seen 2 gaskets, one on intake boot and one on other side of reeds? Could be wrong I’ll post some pictures tonight when I’m home from work. I was able to hold about 8 psi steady but not with air valve closed. I suppose a more accurate test would be to replace The gasket/gaskets and then see if it holds. Thank you for heads up on top end gaskets was kinda wondering which route to go.

[Tklehr96]

Didn’t take any photos yet. Tore into it this week and things don’t look good. Piston is scored completely around. Walls don’t look too bad believe it can be bored but wrist pin was seized pretty good. Rod bearing looks and feels pretty loose to me. Having a mechanic look at the bottom end right now. If the top end didn’t get oil that only means the bottom didn’t either.