YZ 125 2006 transmission oil check bolt

tomotorhead
Hey all - I'm having a 'discussion' with Yamaha as to why my lads 2006 YZ 125 has a serious transmission oil volume difference if we fill it a) by measuring jug volume and b) fill until oil starts to run out of oil check bolt hole in clutch casing cover as per manual ? Anyone else experienced this ? Apparently, no reported issues to Yamaha? So is it just me? Any advice appreciated
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tomotorhead 4/19/2017 1:29pm
4/19/2017 1:29pm Edited Date/Time 4/19/2017 1:35pm
Thanks for pointing me to this. Looks slightly inconclusive though - reason I ask is because we changed oil before first race of season and refilled using check bolt method - clutch plates goosed by second block - replaced plates and refilled oil using measuring jug and been ok since. Big difference in oil quantities though - surely it's not just down to having to wait for oil level to settle so it doesn't come out of check bolt too early ? Seems as though bolt hole is too low to me ?
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Paw Paw 271
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Paw Paw 271 4/19/2017 2:53pm
4/19/2017 2:53pm Edited Date/Time 4/19/2017 2:54pm
There are several bike on the market that will yield less than desire oil quantity when using the check bolt. Honda CRF450R's will be about 200cc low on quantity when filled using that method. Some of the Yamahas will also be low.
I really don't like that method as it is not accurate.

Paw Paw
tomotorhead 4/19/2017 3:01pm
4/19/2017 3:01pm
Phew - so I'm not going mad then? Pity the manufacturers don't acknowledge this - or is it a case of us being the small fish in a big pond and they reckon nobody will challenge ?
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Tuplavee
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Tuplavee 4/20/2025 12:05pm
4/20/2025 12:05pm

I seem to have same issue with 2022 YZ125? How is this possible?

Didnt measure the oil when drained but seemed to be quite small amount. 

Prepared 700ml as per manual, but it started flowing out of check bolt after 350ml. Checked 10minutes after and still started flowing.

Guess I'll add missing 350ml and call it good if theres no overflow from the hose noted

 

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Nairb#70
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Nairb#70 4/21/2025 4:31pm
4/21/2025 4:31pm

I've always used whatever volume is reccomended by the manufacturer. Never even removed the check bolt in my life.

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StankBooty 4/22/2025 12:32pm
4/22/2025 12:32pm
Tuplavee wrote:
I seem to have same issue with 2022 YZ125? How is this possible?Didnt measure the oil when drained but seemed to be quite small amount. Prepared 700ml...

I seem to have same issue with 2022 YZ125? How is this possible?

Didnt measure the oil when drained but seemed to be quite small amount. 

Prepared 700ml as per manual, but it started flowing out of check bolt after 350ml. Checked 10minutes after and still started flowing.

Guess I'll add missing 350ml and call it good if theres no overflow from the hose noted

 

Same happened to me a few years ago with my 2005 YZ125 (same motor from '05 through '21, probably not all that different from the '22+ as far as cases goes in the transmission/clutch cavity) when I randomly tried using the check bolt with a measured amount of oil poured in.

Once that happened, I remember googling around for info about it and saw some little snippet that someone posted from some service manual (maybe for a KDX?) that talked about basically this phenomenon, showing the oil level and the check bolt height in a little cross-section diagram of the transmission and clutch areas, and the passages between those 2 cavities.

I can't find it now, but I wanna say it was something to do with how the location of those passages made the 2 "chambers" fill up differently (unevenly) when pouring oil in.  Probably best to just stick with pouring in a measured amount.

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Rickyisms 4/22/2025 12:44pm
4/22/2025 12:44pm
Nairb#70 wrote:

I've always used whatever volume is reccomended by the manufacturer. Never even removed the check bolt in my life.

I’ve never understood why anyone would bother doing anything other than putting in exactly how much the manufacturer specifically tells you to put in. 

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Tuplavee
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Tuplavee 4/23/2025 9:36am
4/23/2025 9:36am
Nairb#70 wrote:

I've always used whatever volume is reccomended by the manufacturer. Never even removed the check bolt in my life.

Rickyisms wrote:

I’ve never understood why anyone would bother doing anything other than putting in exactly how much the manufacturer specifically tells you to put in. 

Manufacturer also specifically instructs to use check bolt. 

Rickyisms 4/23/2025 4:58pm
4/23/2025 4:58pm
Tuplavee wrote:

Manufacturer also specifically instructs to use check bolt. 

The manual for a 2006 YZ125 I have saved in my phone specifically implies you pour in the specified amount of oil, and then use the check bolt to verify the quantity is correct. If you have to rely on the check bolt after you just poured in the amount they told you to pour in, go for it. A check bolt is completely unnecessary. 

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Falcon
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Falcon 4/25/2025 1:07pm
4/25/2025 1:07pm
Nairb#70 wrote:

I've always used whatever volume is reccomended by the manufacturer. Never even removed the check bolt in my life.

Same. Drain out all the old, put in the amount it says on the case cover. (I believe it is 650cc on a YZ125.) 

SoCalMX70
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SoCalMX70 4/28/2025 9:40pm
4/28/2025 9:40pm
Nairb#70 wrote:

I've always used whatever volume is reccomended by the manufacturer. Never even removed the check bolt in my life.

This is the way.

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