Posts
67
Joined
4/18/2017
Location
Napoleonville, LA
US
Rocket164
2/10/2020 5:58pm
2/10/2020 5:58pm
Edited Date/Time
2/11/2020 7:53pm
Let me start off by saying I’ve been riding dirt bikes for 30 years and personally maintaining them to the highest of standards for 20 of those.
Recently my YZ125 cylinder plating started to flake around the exhaust port so I decided to send it to Millennium for a replate. Sent them the cylinder along with a new Vertex “B” piston so they could properly size the cylinder. A few weeks later I received the cylinder from Millennium and it looked fantastic to me and the customer service/process was without issue. I was bragging to my friends how great my experience was.
Assembled the engine and performed 5 minute break-in/heat cycle in my yard. Then an easy 5 lap break-in process at the track. Went out for my second Moto and on the second lap the bike seized going up to a fourth gear tabletop. Luckily I was able to clutch the bike and coast over the takeoff without injury.
I have been riding YZ125’s for the last 6 years with basically the same mods, fuel, jetting, etc and never had any cylinder/piston failure. When I pulled the cylinder off it showed that the piston seized on the exhaust side of the cylinder. This was discouraging to say the least for a bike that had 15 minutes of run time. I contacted Millennium customer service and sent them the piston, head, cylinder, and spark plug at their request.
In the meantime I purchased a new OEM cylinder, head, and piston because I did not want to go without riding any longer than I already had. With no other changes besides new cylinder, piston, and head the bike ran phenomenal. Same jetting (440, 40, 43-74 needle 3rd clip), fuel (C12 straight), premix (Motul 800 28-1), same outside temperature (60 degrees), and even same motocross track. I pulled the exhaust off to have a look after 5 hard Moto’s and just as I suspected it looked good as new with no marks on the piston skirt. See below.
Millennium contacted me once they received my damaged parts and said that they would cut me a deal and fix my cylinder for an additional $208. Said that my bike was detonating, running in a lean condition due to cold weather, and that i should have been running a 480 main jet.
The below pics speak for themselves. None of my parts show any signs of detonation, running hot, or lean. No material loss on head or piston, no hot spot on piston underside, and no carbon buildup on top of piston because bike was running rich and being ridden at a moderate pace.
Choose your cylinder plater wisely folks...... The issue is they did not clearance above and below the exhaust port like Yamaha does from the factory. I now understand why the OEM cylinders are stepped back in this area. My millennium replate did not show these signs as a stock cylinder does.
I have been told that there’s two sides to every story, I assure you there is only one side to this story..... Millennium did not properly relieve the exhaust port area on my cylinder and when it failed they did not make it right.
Recently my YZ125 cylinder plating started to flake around the exhaust port so I decided to send it to Millennium for a replate. Sent them the cylinder along with a new Vertex “B” piston so they could properly size the cylinder. A few weeks later I received the cylinder from Millennium and it looked fantastic to me and the customer service/process was without issue. I was bragging to my friends how great my experience was.
Assembled the engine and performed 5 minute break-in/heat cycle in my yard. Then an easy 5 lap break-in process at the track. Went out for my second Moto and on the second lap the bike seized going up to a fourth gear tabletop. Luckily I was able to clutch the bike and coast over the takeoff without injury.
I have been riding YZ125’s for the last 6 years with basically the same mods, fuel, jetting, etc and never had any cylinder/piston failure. When I pulled the cylinder off it showed that the piston seized on the exhaust side of the cylinder. This was discouraging to say the least for a bike that had 15 minutes of run time. I contacted Millennium customer service and sent them the piston, head, cylinder, and spark plug at their request.
In the meantime I purchased a new OEM cylinder, head, and piston because I did not want to go without riding any longer than I already had. With no other changes besides new cylinder, piston, and head the bike ran phenomenal. Same jetting (440, 40, 43-74 needle 3rd clip), fuel (C12 straight), premix (Motul 800 28-1), same outside temperature (60 degrees), and even same motocross track. I pulled the exhaust off to have a look after 5 hard Moto’s and just as I suspected it looked good as new with no marks on the piston skirt. See below.
Millennium contacted me once they received my damaged parts and said that they would cut me a deal and fix my cylinder for an additional $208. Said that my bike was detonating, running in a lean condition due to cold weather, and that i should have been running a 480 main jet.
The below pics speak for themselves. None of my parts show any signs of detonation, running hot, or lean. No material loss on head or piston, no hot spot on piston underside, and no carbon buildup on top of piston because bike was running rich and being ridden at a moderate pace.
Choose your cylinder plater wisely folks...... The issue is they did not clearance above and below the exhaust port like Yamaha does from the factory. I now understand why the OEM cylinders are stepped back in this area. My millennium replate did not show these signs as a stock cylinder does.
I have been told that there’s two sides to every story, I assure you there is only one side to this story..... Millennium did not properly relieve the exhaust port area on my cylinder and when it failed they did not make it right.
Paw Paw
The Shop
Millennium’s guide
This was not an overall clearance issue, It was a clearance issue at the exhaust port.
Man, crazy . . . because I literally just got an Athena YZ144 cylinder back today. (My nephew's bike)
Upon looking into the barrel, I notice the bridge over the exhaust port looked like it was relieved. I was guessing
it was to allow for more heat expansion. And I was just about to start a thread wondering same and saw your post.
So this is how it is supposed to look?
Again, sorry about your dilemma.
Usually the exhaust bridges are relieved (ground down after plating using a sanding drum) around .001"- .0015" and possibly a little larger on larger displacement engines. Honda used to relieve their exhaust bridges on the HPP 125 engines and the RC valve smokers as well.
If the exhaust bridge in NOT relieved, there is a good chance it will swell into the cylinder and cause a failure like the OP's issue.
My experience with Millennium is I gave them a dirt stained aluminum cyl with sieze marks,flaked coating and a 1/4" gouge in the wall .
I got it back shiny and clean and the cylinder looked like a piece of jewelry.
Unacceptable.
Call Millenium again and explain that you've consulted with other experienced YZ125 owners, confirmed the exhaust port relieving feature again, and that this really isn't your cost to bear.
If they are a reasonable shop, they will just fix the problem without charging you and chalk it up to operational improvements, check their production procedures to ensure this is covered (if not, fix it), and then address the mistake with the employee who did the work. Stuff happens, we're all human, but to put this on you is UNACCEPTABLE.
I had a similar situation with ********* on a CRF450R engine years back when they performed ISF treatment on my transmission. They didn't clean out all the abrasive media from the treated parts when finished, the engine was reassembled, and at first startup it made some of the weirdest dang noises I've ever heard. HAUNTING! I contacted them, they told me I'd have to send the engine back to them on my dime to have it assessed, I said "so it can get damaged in transit and then that's what you'll claim was the issue? No way. I'll let the MX forums decide with extensive pictures of all of the abrasive media THROUGHOUT THE ENGINE. Why would I even have a handful of this stuff? It's proprietary AND it shouldn't be inside all of the part cavities." Upon hearing that, I received a check in the mail for all parts damaged in the startup sequence (it was nearly $1000). I still had to rebuild the engine myself which took a lot of time, but they resolved the problem quickly to my satisfaction given the situation ... and again, mistakes happen.
If Millennium doesn't want to play nice - I won't be going to them anymore.
As most have said, they've had good experiences - and so have I. Please let us know if you get supported or they continue to hold the line that it was your fault.
If it's the latter, I will need to find a replater, too.
A $200 dispute is a silly amount to lose multiple customers over.
Good luck and keep us posted.
In my world cleaning is done before build up and is 100% the assembling mechanics responsibility.
Bridge relieving and port chamfering is the cylinder replaters job.
I bet that invoice had some sort of cleaning listed in the price break down
Actually, cleaning was one aspect of the ISF process selling points in that the parts are returned to you in new, ready-to-install form. I do think there was a line item for post-process cleaning & supplies, too. Can't fully remember.
I'm pretty meticulous when performing rebuilds, but I definitely might have been able to prevent some of the damage had I known the ISF process better and the potential for leftover media to be present and lodged into cavities. I blew all cavities out with compressed air multiple times, but the media has a way of lodging in yet allowing airflow. It was the vibratory aspect of the running engine that we believe enabled the abrasive to dislodge and come out. That was a learning experience for me, for sure, as well as Yoshimura. Yoshimura's Operations Manager at the time was very clear that this should have never happened and worked with me.
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