YZ125 Power Valve

b8res
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b8res
Edited Date/Time 7/16/2021 12:14pm
Any insight on what may have caused the power valve pin backing out and not catching the power valve spring??
27 hours since it was part for a new OEM piston.

I assume the press fit of the pin is now compromised and the entire power valve should be replaced??


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FGR01
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FGR01 10/25/2020 9:34pm
10/25/2020 9:34pm
They get sloppy. What year bike? Some guys will get a slightly larger pin machined and pressed in.
b8res
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b8res 10/25/2020 10:10pm
10/25/2020 10:10pm
FGR01 wrote:
They get sloppy. What year bike? Some guys will get a slightly larger pin machined and pressed in.
It's easier to just replace the power valve, I'm doing a topend so might as well replace it. It's not the first one I've had to replace.... their relatively inexpensive considering.

There must be just enough harmonics for that pin to vibrate out of position. It's not loose by any means or sloppy...


FGR01
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FGR01 10/25/2020 10:29pm
10/25/2020 10:29pm
b8res wrote:
It's easier to just replace the power valve, I'm doing a topend so might as well replace it. It's not the first one I've had to...
It's easier to just replace the power valve, I'm doing a topend so might as well replace it. It's not the first one I've had to replace.... their relatively inexpensive considering.

There must be just enough harmonics for that pin to vibrate out of position. It's not loose by any means or sloppy...


Easier, yes for sure. Relatively inexpensive? You are the first person I've met that thought that $160-$210 for a small piece of metal was inexpensive... haa! Powervalves are one of those weird, OEM-only overpriced parts.
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Paul_Pitzonka
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Paul_Pitzonka 10/25/2020 10:33pm
10/25/2020 10:33pm
Install Roll pins... definitely cheaper than a new power valve...
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Tuna
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Tuna 10/25/2020 10:55pm
10/25/2020 10:55pm
I used roll pins. Worked fine. It’s a known issue and fix.
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DynoDan22
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DynoDan22 10/26/2020 7:12am
10/26/2020 7:12am
This is a common issue with YZ125's after they get 80-100hrs on them. The PV pin boss fatigues and the press fit is lost. I take the PV's out and drill/tap a 4mm x .07mm hole for a set screw. I grind a small flat on the pin and I tighten the set screw to hold the pin in place.
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FWYT
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FWYT 10/26/2020 10:05pm
10/26/2020 10:05pm
Tuna wrote:
I used roll pins. Worked fine. It’s a known issue and fix.
Yep, this is what I did, too. A few bucks and good to go.
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FWYT 10/26/2020 10:07pm
10/26/2020 10:07pm
DynoDan22 wrote:
This is a common issue with YZ125's after they get 80-100hrs on them. The PV pin boss fatigues and the press fit is lost. I take...
This is a common issue with YZ125's after they get 80-100hrs on them. The PV pin boss fatigues and the press fit is lost. I take the PV's out and drill/tap a 4mm x .07mm hole for a set screw. I grind a small flat on the pin and I tighten the set screw to hold the pin in place.
Dyno Dan coming in with the sano set-up amongst all us roll pin fixers!!! Laughing Laughing Laughing
DynoDan22
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DynoDan22 10/27/2020 8:13am
10/27/2020 8:13am
It's not that hard to do and it's easier to replace the pins as the groove over time. It took me 20min when I had the PV's in hand. Yamaha should have known over time that the PV would lose its press fit to the pin and the pin would walk out. You can hear some YZ125's at the track that have lost the pins in The PV. They give a signature "buwaaap" when they land from a jump and the powervalve bounces shut because it's not functional. Hahahaha. Oh, and for the love of all that is holy, please Yamaha, please use better materials in your YZ250 tranny gears. Rant over.
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rucka356
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rucka356 7/11/2021 7:19pm
7/11/2021 7:19pm
This just happened to me. Anybody got the details on using the roller pins? I had one back out all the and the other one is about all the way out too.


garagedog 7/12/2021 5:45pm
7/12/2021 5:45pm Edited Date/Time 7/12/2021 5:45pm
rucka356 wrote:
This just happened to me. Anybody got the details on using the roller pins? I had one back out all the and the other one is...
This just happened to me. Anybody got the details on using the roller pins? I had one back out all the and the other one is about all the way out too.


https://www.harborfreight.com/315-piece-roll-pin-assortment-67682.html

I havent used this yet but here is a cheap way to try it.
rucka356
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rucka356 7/12/2021 10:34pm
7/12/2021 10:34pm
I went to ace and found some tonight that worked

3
Muscle-Milk-KTM 7/13/2021 8:04am
7/13/2021 8:04am
rucka356 wrote:
I went to ace and found some tonight that worked [img]https://p.vitalmx.com/photos/forums/2021/07/12/501499/s1200_20210712_220902.jpg[/img]
I went to ace and found some tonight that worked

What year is your YZ?
garagedog 7/15/2021 3:28pm
7/15/2021 3:28pm
rucka356 wrote:
I went to ace and found some tonight that worked [img]https://p.vitalmx.com/photos/forums/2021/07/12/501499/s1200_20210712_220902.jpg[/img]
I went to ace and found some tonight that worked

Is that left power valve plate aligned correctly?
rucka356
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rucka356 7/15/2021 5:37pm
7/15/2021 5:37pm
rucka356 wrote:
I went to ace and found some tonight that worked [img]https://p.vitalmx.com/photos/forums/2021/07/12/501499/s1200_20210712_220902.jpg[/img]
I went to ace and found some tonight that worked

garagedog wrote:
Is that left power valve plate aligned correctly?
No I just set them in there temporarily. waiting on a new shaft to come in and will align it all when I install. Which should be tomorrow, I love tinkering on these things. the shaft had some really bad wear spots

b8res
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b8res 7/15/2021 5:50pm
7/15/2021 5:50pm
I pressed out the bad pin, replaced it with a 5/32 roll pin. That lasted about 3 hours, and it was out of place. I even peened the end to try to prevent it from "walking", did work.

Ordered 2 update power valves from Yamaha, the new power valves have a shoulder on the pin to prevent them from "walking". At the same time I replaced the pin and another small part.

It's been a full topend cycle with 25 hrs and the new power valves show no signs of failure.
rucka356
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rucka356 7/15/2021 8:20pm
7/15/2021 8:20pm
b8res wrote:
I pressed out the bad pin, replaced it with a 5/32 roll pin. That lasted about 3 hours, and it was out of place. I even...
I pressed out the bad pin, replaced it with a 5/32 roll pin. That lasted about 3 hours, and it was out of place. I even peened the end to try to prevent it from "walking", did work.

Ordered 2 update power valves from Yamaha, the new power valves have a shoulder on the pin to prevent them from "walking". At the same time I replaced the pin and another small part.

It's been a full topend cycle with 25 hrs and the new power valves show no signs of failure.
Do u think some loctite squirted in there would hold it? I'm about to put mine back together, but dang i don't want to have to do this again after 3 hours. pulling the motor isn't fun

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b8res
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b8res 7/15/2021 8:40pm
7/15/2021 8:40pm
b8res wrote:
I pressed out the bad pin, replaced it with a 5/32 roll pin. That lasted about 3 hours, and it was out of place. I even...
I pressed out the bad pin, replaced it with a 5/32 roll pin. That lasted about 3 hours, and it was out of place. I even peened the end to try to prevent it from "walking", did work.

Ordered 2 update power valves from Yamaha, the new power valves have a shoulder on the pin to prevent them from "walking". At the same time I replaced the pin and another small part.

It's been a full topend cycle with 25 hrs and the new power valves show no signs of failure.
rucka356 wrote:
Do u think some loctite squirted in there would hold it? I'm about to put mine back together, but dang i don't want to have to...
Do u think some loctite squirted in there would hold it? I'm about to put mine back together, but dang i don't want to have to do this again after 3 hours. pulling the motor isn't fun
Hard telling, but there must be a ton of harmonics/ vibration on the pins. If you truly think about it, the power valves are responding to the throttle input and have to be under some forms of stress. I've had 2 broken power valves at the base... what causes that? Fresh clean breaks.

The Yamaha power valves on the 125 are prone to having failures, Yamaha has recognized the issue and has changed the design. $350.00 or so to replace both, I bite the bullet and replace them with the updated part. If they last 200 hours or 4 topends then so be it. It comes with the territory.
Muscle-Milk-KTM 7/16/2021 9:10am
7/16/2021 9:10am
b8res wrote:
Hard telling, but there must be a ton of harmonics/ vibration on the pins. If you truly think about it, the power valves are responding to...
Hard telling, but there must be a ton of harmonics/ vibration on the pins. If you truly think about it, the power valves are responding to the throttle input and have to be under some forms of stress. I've had 2 broken power valves at the base... what causes that? Fresh clean breaks.

The Yamaha power valves on the 125 are prone to having failures, Yamaha has recognized the issue and has changed the design. $350.00 or so to replace both, I bite the bullet and replace them with the updated part. If they last 200 hours or 4 topends then so be it. It comes with the territory.
What year did they update the part, I have an 18 YZ125?
b8res
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b8res 7/16/2021 12:14pm
7/16/2021 12:14pm
b8res wrote:
Hard telling, but there must be a ton of harmonics/ vibration on the pins. If you truly think about it, the power valves are responding to...
Hard telling, but there must be a ton of harmonics/ vibration on the pins. If you truly think about it, the power valves are responding to the throttle input and have to be under some forms of stress. I've had 2 broken power valves at the base... what causes that? Fresh clean breaks.

The Yamaha power valves on the 125 are prone to having failures, Yamaha has recognized the issue and has changed the design. $350.00 or so to replace both, I bite the bullet and replace them with the updated part. If they last 200 hours or 4 topends then so be it. It comes with the territory.
Muscle-Milk-KTM wrote:
What year did they update the part, I have an 18 YZ125?
Not sure, but when you order the power valves there is a superseded part number. The new valves are different with regards to the pin. In 07 or 08 they also updated the governor spring which I updated as well. It opens 1000 rpm sooner than the 05 spring.
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