All Things Moto! Web Forums

Go Back   All Things Moto! Web Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums > 2-Stroke Dirt Bikes - Yamaha

     
Reply
 
LinkBack Thread Tools
  #1  
Old 08-09-2007, 08:24 PM
mbogosia's Avatar
Intermediate Class
 
Join Date: Aug 2007
Last Online: 01-21-2008 07:02 PM
Location: Nashville
Posts: 140
Default YZ 125 seized?

I recently installed a new top end. Went riding tonight and after a long time the rear tire froze up and the kick starter would not move.

After pushing the bike home I took her apart and the cylinder and piston are fine. However the rod will not move up and down anymore. Does anyone know what would cause this? Also, there were some metal shavings.
Reply With Quote
  #2  
Old 08-09-2007, 09:35 PM
crfjedi393's Avatar
Super Moderator
 
Join Date: Nov 2004
Last Online: Today 06:20 AM
Location: Duncan, OK
Posts: 13,544
Default Re: YZ 125 seized?

Could you have dropped something down in the crank while doing the top end? An old piston ring or something?
It may be a lower rod bearing that went out. Tough call. If you've got shavings, something got chewed up before it froze the crank.
Reply With Quote
  #3  
Old 08-09-2007, 10:30 PM
Intermediate Class
 
Join Date: Jul 2007
Last Online: 12-05-2009 11:05 AM
Location: South Dakota
Posts: 239
Default Re: YZ 125 seized?

I had something similar happen to me. It turned out to be the big end on the con rod. The shavings might be plastic and metal both from the con rod bearing. Time for a new crank probably.
Reply With Quote
  #4  
Old 08-09-2007, 10:39 PM
2000kx250's Avatar
Intermediate Class
 
Join Date: Apr 2006
Last Online: 02-23-2013 11:32 AM
Location: Central New York
Posts: 342
Default Re: YZ 125 seized?

And while you're down there, might as well replace both of the main crank bearings.
Reply With Quote
  #5  
Old 08-10-2007, 05:15 AM
mbogosia's Avatar
Intermediate Class
 
Join Date: Aug 2007
Last Online: 01-21-2008 07:02 PM
Location: Nashville
Posts: 140
Default Re: YZ 125 seized?

I am pretty sure I didn't drop anything. I still have the old piston and ring. Okay new crank and crank bearings sounds right to me. What would have caused this to happen? Could I have done something wrong on my piston install besides dropping something in there?

So this is what I need right? I assume I need the bearing on the right side of the page also. [Only registered and activated users can see links. ]

Last edited by mbogosia; 08-10-2007 at 05:23 AM.
Reply With Quote
  #6  
Old 08-10-2007, 07:46 AM
Intermediate Class
 
Join Date: Jul 2007
Last Online: 12-05-2009 11:05 AM
Location: South Dakota
Posts: 239
Default Re: YZ 125 seized?

The Yamaha crank uses plastic inserts for counter balance on the big end connection and this plastic will melt and flow into the bearing starving it for oil. A Hot Rods rep. told me that Yamaha designs their cranks to do this in the event of over heating to prevent it from coming apart and causing a lot more damage.
I see by the rockymountainatv link that you have a 98 yz125. This year is especially prone to doing this apparently. Mine is a 98 yz125 also. You problably did nothing wrong in the re-assembly of the engine. Just running it hard can do it.
Reply With Quote
  #7  
Old 08-10-2007, 08:16 AM
mbogosia's Avatar
Intermediate Class
 
Join Date: Aug 2007
Last Online: 01-21-2008 07:02 PM
Location: Nashville
Posts: 140
Default Re: YZ 125 seized?

Just dropped it off at the shop. He said that I probably didn't do anything wrong with the piston because the piston would have been messed up. He thinks the bearings got messed up and that in turn locked it up. The good thing is they are going to completely go through the engine while it is apart and it should be in great shape when I get it back. I am just worried about the cost of the repair.
Reply With Quote
  #8  
Old 08-10-2007, 09:46 AM
Intermediate Class
 
Join Date: Jul 2007
Last Online: 12-05-2009 11:05 AM
Location: South Dakota
Posts: 239
Default Re: YZ 125 seized?

A hotrods cam will cost you less than pressing that crank apart and puting in new bearing, pin and con rod. In mine I replaced all the ball bearing races in the bottom while I was there that was about $75 worth not counting the crank bearings and seals which was $42 at rockymountainatv and the crank for $142. So that comes to $259 I spent on mine in just parts. with labor
But a lot less than another bike.
Reply With Quote
  #9  
Old 08-10-2007, 10:03 AM
ATM! Pro Class
 
Join Date: Jan 2006
Last Online: 03-28-2010 04:02 PM
Location: anchorage alaska
Posts: 2,112
Default Re: YZ 125 seized?

I dont buy into the damage prevention story. I think someone was creative when he told it. The reason that Yamaha uses those is just to take up space. I have a 98 lower end in the cases sitting here. I also have a crank from one sitting here. The crank will balance "BETTER" without the inserts, which are there for increasing primary compression. The rod side of your crank is quite a bit heavier than the blank side. Find some straight edges and set it up on them and see if I am not right.

For years people have been "dremeling" that plastic away to get better oil access to the lower end bearing.

I doubt you did anything wrong either, other than like many of us just kept the crank too long. With a new top end developing power more like it was when new, it just sped the failure process up a little bit.
Reply With Quote
  #10  
Old 08-10-2007, 11:17 AM
The Baron's Avatar
ATM! Pro Class
 
Join Date: Jan 2007
Last Online: 07-18-2008 01:40 PM
Location: Arizona
Posts: 2,579
Default Re: YZ 125 seized?

Quote:
Originally Posted by AV8R View Post
The Yamaha crank uses plastic inserts for counter balance on the big end connection and this plastic will melt and flow into the bearing starving it for oil. A Hot Rods rep. told me that Yamaha designs their cranks to do this in the event of over heating to prevent it from coming apart and causing a lot more damage.
.
I'm going with Ossa on this one. The plastic is there to reduce crankcase volume and is used to keep the crank lighter than if their area were replaced with steel.
Reply With Quote
  #11  
Old 08-10-2007, 12:19 PM
Tdub's Avatar
ATM! Pro Class
 
Join Date: Dec 2002
Last Online: 04-20-2014 01:38 PM
Location: The OWB, Kentucky
Posts: 3,016
Default Re: YZ 125 seized?

AV8R, you sure have some misleading info.
"A hotrods crank will cost you less than pressing that crank apart and putting in new bearing, pin and con rod" Not true!

"The Yamaha crank uses plastic inserts for counter balance" Absolutely not true!

"This year is especially prone to doing this apparently." Where do you get your information????

It is fact...cranks will eventually fail in time. This being a '98, has the crank evern been replaced or rebuilt?? If not it has been on borrowed time for many years! Tdub
Reply With Quote
  #12  
Old 08-10-2007, 01:09 PM
ATM! Pro Class
 
Join Date: Jan 2006
Last Online: 03-28-2010 04:02 PM
Location: anchorage alaska
Posts: 2,112
Default Re: YZ 125 seized?

"If not, it has been on borrowed time,,,,"
My son is cleaning out my garage. He found two YZ cranks, 3 for a cr 250 of the 92-2001 variety, and two for a CR500. He said "Dad, they all seem good." I know, it is why I keep them. All used and chances of me using them again are slim to none (except for the CR500 cranks). They got replaced because "it was time". In the case of the ones for the XR500, XL350, XR600, XL600, XR650L and all the british and spanish stuff are things I will use again. Probably not the XR250 stuff though. Anyone need any?
Reply With Quote
  #13  
Old 08-10-2007, 01:15 PM
The Baron's Avatar
ATM! Pro Class
 
Join Date: Jan 2007
Last Online: 07-18-2008 01:40 PM
Location: Arizona
Posts: 2,579
Default Re: YZ 125 seized?

I'll trade you a used YZ front fender, a cut down YZ seat and an old pickle jar full of misc bolts, nuts and screws for one of the YZ cranks.
Reply With Quote
  #14  
Old 08-10-2007, 01:29 PM
ATM! Pro Class
 
Join Date: Jan 2006
Last Online: 03-28-2010 04:02 PM
Location: anchorage alaska
Posts: 2,112
Default Re: YZ 125 seized?

I could use the jar I supose.
Reply With Quote
  #15  
Old 08-10-2007, 02:04 PM
The Baron's Avatar
ATM! Pro Class
 
Join Date: Jan 2007
Last Online: 07-18-2008 01:40 PM
Location: Arizona
Posts: 2,579
Default Re: YZ 125 seized?

Quote:
Originally Posted by ossagp1 View Post
I could use the jar I supose.
Okay. Do you the misc. junk that's in it, too? If not I'll toss the contents out to save on shipping.
Reply With Quote
Sponsored Ads
  #16  
Old 08-10-2007, 03:07 PM
mbogosia's Avatar
Intermediate Class
 
Join Date: Aug 2007
Last Online: 01-21-2008 07:02 PM
Location: Nashville
Posts: 140
Default Re: YZ 125 seized?

Well, after talking to a friend I went and got my bike from the shop and we are going to do the job ourselves. He has done 2 bottom ends and has all the tools. The crank is the original on my 99 and hasn't been replaced. I ordered a hotrod crank assembly($142), Bearings($42), and complete gasket kit($34). I am also going to give my friend a $100 for helping me. Am I forgetting anything?
Reply With Quote
  #17  
Old 08-10-2007, 04:48 PM
mbogosia's Avatar
Intermediate Class
 
Join Date: Aug 2007
Last Online: 01-21-2008 07:02 PM
Location: Nashville
Posts: 140
Default Re: YZ 125 seized?

Got the motor pulled out. The bolt that held the front sprockett on was so loose I could take it off by hand. Thats not right is it? Also, it had a washer behind it with teeth that was mangled pretty bad. On top of that it looked like oil had been leaking right there too which I assume is from the loose nut.
Reply With Quote
  #18  
Old 08-11-2007, 09:18 PM
Intermediate Class
 
Join Date: Jul 2007
Last Online: 12-05-2009 11:05 AM
Location: South Dakota
Posts: 239
Default Re: YZ 125 seized?

FFracing11x,
In these parts it costs $50 to have a crank pressed apart then it cost $99 for new con rod pin and bearings total $149. To buy a hotrods crank on rockymountainatv.com it costs $142. Easy math for me plus a brand new crank.
As far as the information on the plastic slugs and their inherint "fault" that information comes from "Motocross and Off-Road Performance Handbook" Third edition written by Eric Gorr. published 2004.
The man has been a motorcycle mechanic since 1971. He is an inventor and performance engine builder. He has worked as contributing techinical writer for the biggest dirt bike magazines on three continents. His mail order company is Forward Motion. Etc,Etc. I believe him to be qualified as a pretty good source for motorcycle technical information.
Now risking copywrite infringment I will quote from his book concerning one of the faults of the 1997 -2004 Yamaha YZ125's.
"Another significant design error lies in the crankshaft. A two stroke crankshaft has less mass at the top near the pin hole to compensate the balance factor of the reciprocating mass of the connecting rod and piston assembly. Manufacturers use different designs to fill the void around the pin hole........Yamaha uses plastic slugs"
So it apears that in fact these plastic slugs are used to fiil the void and not counter balance. You are correct. Read on.
" The problem seems to be that the plastic slugs are fitted so closely around the pin hole that they shroud the big end bearing from getting enough lubrication" It goes on to describe how the slugs expand and eventually melt and flows into the bearing starving it for lubrication.
This is where I got my information.
My apologies for mis-stating that the plastic slugs are use for counterbalance.
Reply With Quote
  #19  
Old 08-11-2007, 09:47 PM
Intermediate Class
 
Join Date: Jul 2007
Last Online: 12-05-2009 11:05 AM
Location: South Dakota
Posts: 239
Default Re: YZ 125 seized?

Don't forget Yamabond or similar subtance. Not Yamabond 5 it hardens you want the semi-drying liquid gasket for the day when you or someone else needs to split the case again.
The Yamaha dealer here told me that Yamabond
is no longer in production that was my reaction but then they sold me this stuff that they use for a replacement called Threebond 1194. I did two cases with it and no problems.
The countershaft sprocket nut should be torqued to the spec in your manual it should not be loose.
That little bit of oil could be the seal or it could be chain lube. The nut has nothing to do with keeping the oil in the transmission.
As long as you have the cases open check all the other bearings in there for obvious noise or loosness or a rough feeling when being turned. particuarly the one just behind the front sprocket on the countershaft.
Reply With Quote
  #20  
Old 08-12-2007, 02:38 AM
ATM! Pro Class
 
Join Date: Jan 2006
Last Online: 03-28-2010 04:02 PM
Location: anchorage alaska
Posts: 2,112
Default Re: YZ 125 seized?

AV
I would bet if you had to buy the crank in your "parts" it, like the rod would be way more expensive. For the price online of a rod, it is attrative to most, as I am sure Tryce is getting at.

As far as Eric Gorr goes, no one has to tell FFR about him. If you call Eric and just use the first name "Tryce" Eric will be able to tell you a lot about the man who questioned your advice.

The passage in your diatribe on the YZ crank that I disagreed with was the part about how the plastic inserts were designed to melt and cause less damage than if they were made of a different material or were absent. I don't necessarily blame you for believing it. Again though, I can't believe any of it. The part about the inserts melting is true and well known, and that wasn't what Welch was disagreeing with. Since your (and mine too) 98 crank looks like my 95 and my 99 crank, as far as the inserts go, I am betting none of the years are any worse than the others. I was curious where you heard that the 98 was particularly bad in comparison to the other years. The part about them being there for balance is pretty reasonable to assume too. It just isn't correct. Mount the piston, pin, bearing, rings, and clips to your crank and see how much heavier that side of the crank is than the blank side. (The full weight of the piston is not usually considered in balancing a crank shaft.)

In short, after reading what you said Eric Gorr stated on that crank, you have to admit you were pretty far off.
Reply With Quote
Reply

  All Things Moto! Web Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums > 2-Stroke Dirt Bikes - Yamaha


Bookmarks

Thread Tools


Similar Threads for: YZ 125 seized?
Thread Thread Starter Forum Replies Last Post
YZ125 seized NEED HELP!!! scjeepsxj 2-Stroke Dirt Bikes - Yamaha 1 02-11-2009 07:39 PM
84 CR 250 Seized boom.... done 199q_cr 2-Stroke Dirt Bikes - Honda 2 08-12-2008 12:22 PM
Kickstarter seized Rossi_Mad46 2-Stroke Dirt Bikes - Yamaha 5 01-19-2008 07:20 PM
Rm 125 seized need help...... hoytproshooter 2-Stroke Dirt Bikes - Suzuki 5 12-15-2007 04:47 PM
Seized... SirFallsALot243 General Discussion 44 04-08-2004 08:29 PM


All times are GMT -6. The time now is 06:48 AM.

Portal Forums Photo Gallery Popular Tags RSS Feeds

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright ©2002-2014, JDub Consulting, Inc. All Right Reserved.