View Full Version : Tri-z Piston Failure
Just-Tri-It
03-24-2011, 10:05 PM
Well my Z quit running. Thought it was a carb. problem at first. When it showed no compression while kicking it I pulled the plug and covered the plug hole with my finger. Engaged the kicker and nothing. Not even a burp. So I pulled the cylinder and 'say it ain't so!' Found this hole. I checked the water pump and sure enough it was failing. But is water pump failure enough to cause a hole to be burnt in the cylinder. The piston was .030 over. On its second bore. I had ridden the bike only twice before the failure with about an hour total time. But only about 15 minutes on the next day at the time of the failure. Anyone else ever have this happen?
Thanks
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code200k
03-24-2011, 10:10 PM
to me that doesnt look like the pump failure caused that,which would be heat seaize no?to me that looks like a plug/detanation issue.PLus not enough for the bike to over heat
EDIT: got any pics of the plug?
younganreckless
03-24-2011, 10:19 PM
^ yes tht is exactly what I was thinking, my friends tri z did the same thing but it wasn't the water pump it was plug detenation
Just-Tri-It
03-24-2011, 10:27 PM
to me that doesnt look like the pump failure caused that,which would be heat seaize no?to me that looks like a plug/detanation issue.PLus not enough for the bike to over heat
EDIT: got any pics of the plug?
The plug was not damaged. It was medium brown and a fairly new plug. I had put a new one in when I got the bike and chopped it a few time. At time of failure it was med. brown and no damage. I'll try to get a pic.
Just-Tri-It
03-24-2011, 10:28 PM
^ yes tht is exactly what I was thinking, my friends tri z did the same thing but it wasn't the water pump it was plug detenation
What would cause that? Bad gas. It was 92 with 4 ounces to a gallon oil.
I believe they use to race the bike some. But it had sat up about 4 years before I bought it.
code200k
03-24-2011, 10:30 PM
What would cause that? Bad gas. It was 92 with 4 ounces to a gallon oil.
I believe they use to race the bike some. But it had sat up about 4 years before I bought it.
allot of this new gas has so much octane it that it kills these great two stroke motors from all the octane.a snowmobile mag explained it all in a good way
fabiodriven
03-24-2011, 10:38 PM
allot of this new gas has so much octane it that it kills these great two stroke motors from all the octane.
That doesn't sound like it would make sense. I'd like to see that article.
thestud25
03-24-2011, 10:48 PM
Plug is way to hot. Ie, running a NGK b6 or 7es instead of a b8 or b9es. What plug were you running?
Looks to me like a Tad to much compression and To low an octane fuel... I.E pre- ignition..that sucker got hot in a hurry...
Just-Tri-It
03-24-2011, 10:54 PM
Plug is way to hot. Ie, running a NGK b6 or 7es instead of a b8 or b9es. What plug were you running?
Running an NGK 8. The standard. It may have been a hotter one in it before I got it or when I first got it. I don't remember what it was. I put a new one in it to do the chops. It may have been about ready to go when I got it.
Dirtcrasher
03-24-2011, 10:56 PM
allot of this new gas has so much octane it that it kills these great two stroke motors from all the octane.a snowmobile mag explained it all in a good way
I've read ethanol affecting 2 strokes but not octane..........
New gas, more octane??
TECATEMATT
03-25-2011, 03:53 AM
8s aren't that hot of a plug? What kinda gas mixture are you running maybe a little to lean? Look on the bright side it could be worse, this is what I did to my old man's piston few years back on his tecate.
http://i154.photobucket.com/albums/s272/tecatematt/l_21f206540d1eea78413021d12adf3c36.jpg
Chazz of Blades
03-25-2011, 04:23 AM
Well, when you think about it pre-det is like striking the piston with a small hammer.
Octane lengthens the burn time of course, making the fuel harder for the engine to burn, thus lengthening the burn. Low octane gas equals more, and faster, bang than higher octanes. I always run 89 octane in everything, and if it runs fine, with no pre-det, or anything, it's fine with that octane. Higher octanes are really for higher compression motors, which would explain the "harder to burn" thing.
Overall I'd say you were SOOL my friend.
Just-Tri-It
03-25-2011, 07:55 AM
What about an air leak around a crank seal? The plug was not whitish though. Medium brown. Or if the previous owner was using racing fuel or additives?
Billy Golightly
03-25-2011, 08:25 AM
Closeup macro picture of the plug (With the threads removed if posible?)
Just-Tri-It
03-25-2011, 08:49 AM
Closeup macro picture of the plug (With the threads removed if posible?)
Best I can get of the plug.
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Dirtcrasher
03-25-2011, 09:27 AM
He wants to see the lower portion of the porcelain...............
Just-Tri-It
03-25-2011, 11:25 AM
He wants to see the lower portion of the porcelain...............
I don't know how to remove it without destroying it.
Billy Golightly
03-25-2011, 11:29 AM
Put the plug in a vise, take a hacksaw about a 3/8 half inch from the end (where the ground strap is) back towards the top, and hacksaw down until you hit the porcelian (You'll know when you hit, the blade will get really "slick feeling" rotate till you've cut all the way around it and the threads+groundstrap fall off. Take another pic for me :)
Its hard to tell in the blurry picture but it looks like youve mistaken the gray from melted aluminum for a black rich condition.
Just-Tri-It
03-25-2011, 11:50 AM
It'll takes some time but I'll get it.
Would leaking crank seals contribute to this or cause it?
Billy Golightly
03-25-2011, 12:41 PM
It could cause a lean out condition, yes.
tri-Z ripper
03-25-2011, 02:05 PM
welcome to the club, did you have your cylinder honed before installing new top end? http://i66.photobucket.com/albums/h265/german0024/3fa00761.jpg
http://i66.photobucket.com/albums/h265/german0024/d0adb31d.jpg
i got lucky and shot the piston pieces out the exhaust.
Just-Tri-It
03-25-2011, 03:34 PM
Actually I had just got the Z. I bought it from a guy who said he bought it and it was way too fast for him and he just let it set up 4 or 5 years. I got it and I changed the plug, gas and fluids but forgot to check the water pump. After the chops seemed to be ok I took it down a 5 mile trail never getting over 3/4 throttle. It quit on me and I thought the float was sticking as it just died in the road. After a minute it started back up and I came in. Next day I warmed it up and got about a mile down the road and it fell flat on its face again and wouldn't start. I noticed that it had no real compression as I kicked it over. Pulled it back and let it cool a little before doing any further inspection. Cleaned the carb again and found that the left back vent hose was stopped up but the other two were fine. Reinstalled the carb but no good. Pulled the plug and covered the hole and no compression on finger at all. So I pulled the cylinder and this is what I found. The first owners used to race it some I was told. Maybe the mixtures they were using began the process and the seals were weakened from sitting so many years and the water pump beginning to fail all conspired against it at the same time and caused it.
If I replace the crank seals while it's down would I have to split the cases?
Thanks
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k00leo
03-25-2011, 03:42 PM
well damn, at least you got the west coast swingarm going for yah.
Very nice looking tri-z
Chazz of Blades
03-25-2011, 04:00 PM
Quickly man! That Z needs a heart transplant!
But as billy said, lean condition *could* cause an overheating like that, but without further info I don't know.
tri-Z ripper
03-25-2011, 04:03 PM
well read on how to pin your water pump impeller as i dont think there is any billet ones left around, if it is that bad i would consider replacing the crank bearings and seals as well as new rod with a top end. certainly not cheap, but will keep it reliable for the rest of the time you own the bike! Yes seals require splitting cases! Then to reseal with yamabond. Don't be afraid to ask with help here.
WilliamJ
03-25-2011, 04:36 PM
It would have to be really lean. Much more likely it was a bad combination of too much ignition timing / low octane / high compression. Poor cooling would not help. Likewise a hot day can also contribute but that's not the case at this time of year. Scuffing is probably piston clearance going too small as it overheats from the detonation.
It is classic detonation. You can burn through a piston in no time at all when detonation starts. You cannot wreck it running too high an octane. It won't help power but it certainly will not hole a piston. You need to work out what CR you are running and you need to check your ignition timing. If in doubt retard the timing at least 5 degrees and see what effect it has. If you are not sure about the mixture then richen it up a little. Use the best gas you can find if you are running high compression.
Ethanol laden gas is bad stuff - authorities in Europe have just released a report slamming the 10% Ethanol as damaging to car engines as young as 6 or 7 years old. There is a date for this to be introduced but for the time being we are getting 5%.
Bill
code200k
03-25-2011, 05:02 PM
I've read ethanol affecting 2 strokes but not octane..........
New gas, more octane??
yes i meant ethanol sorry guys..long and tireing night
Just-Tri-It
03-29-2011, 10:03 AM
Is there a manual besides the oem service manual that gives a detailed step by step process of disassembling and reassembling the engine for a total rebuild?
Thanks.
Is there a manual besides the oem service manual that gives a detailed step by step process of disassembling and reassembling the engine for a total rebuild?
Thanks.
No. But here is a link to a good video series I posted, that used with the Z manual should walk you right through the process. It is a newer Yz 250 engine, but all steps are about the same.
NOTE!!! On a Z engine, the Input shaft end gear on the left side of the case (by the clutch arm) can be installed eiter way. One way is right, the other is wrong. Pay VERY close attention to the gear as you split the case and keep it oriented in its correct posistion
http://www.3wheelerworld.com/showthread.php?96672-A-pretty-good-tutorial-on-Engine-rebuilding.Videos-included.&highlight=
Just-Tri-It
03-29-2011, 04:02 PM
Can you go to this page of diagrams and give the one you are referring to. Thanks
http://www.boats.net/parts/search/Yamaha/All%20Terrain%20Vehicle/1985/YTZ250N%20-%20TRI-Z/parts.html
Gear #8 in this diagram. It can fall right off the shaft. There is no retainer clip. So pay attention to it.
http://www.boats.net/parts/search/Yamaha/All%20Terrain%20Vehicle/1985/YTZ250N%20-%20TRI-Z/TRANSMISSION/parts.html
Just-Tri-It
03-29-2011, 04:32 PM
I noticed on the inside of a spare case I have that there is a set of needle bearings right next to the clutch push lever assembly. Is number 10 that bearing the the same shaft carrying the number 8 gear rides on? The bearing has lost a couple needles in it and if the other one is like that I will need to replace that bearing as well.
Thanks
jmax857
03-29-2011, 04:33 PM
Gear #8 in this diagram. It can fall right off the shaft. There is no retainer clip. So pay attention to it.
http://www.boats.net/parts/search/Yamaha/All%20Terrain%20Vehicle/1985/YTZ250N%20-%20TRI-Z/TRANSMISSION/parts.html
when you put it in backwards, the transmission wont spin freely when the cases are "mated" together. i did this when rebuilding mine, i put the halves together and the tranny wouldnt move. i had to split it again and swap that gear around. its pretty obvious if you did it wrong.
I noticed on the inside of a spare case I have that there is a set of needle bearings right next to the clutch push lever assembly. Is number 10 that bearing the the same shaft carrying the number 8 gear rides on? The bearing has lost a couple needles in it and if the other one is like that I will need to replace that bearing as well.
ThanksYes that is correct. Number 10 is the input shaft main bearing.
when you put it in backwards, the transmission wont spin freely when the cases are "mated" together. i did this when rebuilding mine, i put the halves together and the tranny wouldnt move. i had to split it again and swap that gear around. its pretty obvious if you did it wrong.
Exactly. That is why I mentioned this issue. A) Guys will let it run that way. I actually took a Z engine apart that toasted that thrust washer and bearing becuase they ran it wrong.
B) Having to resplit a case after you have all the bolts in and a new layer of Yamabond on them sucks. So now, it can be done right the first time.
That #8 gear has a bevel on one side and a flush side with no bevel.That is why you want to pay attention to it when you split the case. The manual does NOT dictate which way it goes.
You should be splitting the case from the stator side (Left case coming up off the right case), so the gear should remain oriented in its correct location since the trans shaft will stay in the right side case as you pull the left case.
Just-Tri-It
03-29-2011, 06:57 PM
No. But here is a link to a good video series I posted, that used with the Z manual should walk you right through the process. It is a newer Yz 250 engine, but all steps are about the same.
NOTE!!! On a Z engine, the Input shaft end gear on the left side of the case (by the clutch arm) can be installed eiter way. One way is right, the other is wrong. Pay VERY close attention to the gear as you split the case and keep it oriented in its correct posistion
http://www.3wheelerworld.com/showthread.php?96672-A-pretty-good-tutorial-on-Engine-rebuilding.Videos-included.&highlight=
Is the video in the World Class help section?
Thanks
Is the video in the World Class help section?
Thanks
Click here.
http://www.3wheelerworld.com/showthread.php?96672-A-pretty-good-tutorial-on-Engine-rebuilding.Videos-included.&highlight=
There is 3 parts I posted in order. In that thread^^^
Click each youtube vid to see them.
I did not make the vids. I only posted them here.
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