YZ125 cylinder casting numbers

RyanLester761
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7/26/2014 10:57am Edited Date/Time 7/30/2014 6:31pm
I recently picked up a 1994 yz125 and I am pretty happy with it, besides looking for more power. I bought a used '96 yz125 cylinder off ebay to put on, hopefully to make it run a little stronger. I am trying to ensure the cylinder is in-fact from a 1996...

I have an MXA magazine with the '96 YZ125 test and photos. The cylinder in the magazine has a casting number 45500 124cm3 Y-2. The cylinder I just purchased has a casting number 45500 124cm3 Y-1. Could the '96 YZ125 come with two (or more) different casting numbers on the cylinder? I don't believe this is a 1995 cylinder because I have another magazine with the '95 cylinder and that number is 4PE00 124cm3 Y-2. Where can I find the casting number/year designation information for these cylinders?

Any help???

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RyanLester761
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7/27/2014 5:25pm Edited Date/Time 7/27/2014 5:28pm
Hey thanks for the info DJFXpro. A lot of helpful stuff there. I thought the y-1/y-2 might designate the A or B bore also. But, I'm pretty sure they bore and plate after the cast (with numbers) is already made. So, I kinda ruled that out.

I work at a medical implant company and our knee implant component castings will often have a number batch on the raw casting. Maybe the y-1 came from the -1 mold and the y-2 just came from a different mold but still the same design. If that makes sense.


It's good to know your '98 cylinder's first 5 numbers are way different, so I can assume each year cylinder would be a lot different number sequence.

I have a friend that works for Yamaha. I might contact her. Maybe she can ask an engineer there.
RyanLester761
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7/30/2014 1:26pm
I just realized it looks like the "45500" is actually "4SS00" and the 4SS is the first numbers in the part#. I'm confused on the following two digits though. And I'm still not sure on the Y-1/Y-2 differences. I emailed my friend who works for Yamaha.

Here are part #s of the following cylinders, if anyone cares.



4PE-11310-00-00 1994
4PE-11310-00-00 1995
4SS-11311-20-00 1996/1997
4SS-11311-30-00 1998
5ET-11311-10-00 1999
5HD-11311-11-00 2000

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