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73 125 mx cylinder identification

  • zestycj7
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73 125 mx cylinder identification was created by zestycj7

Hey everyone. I just picked up a 73 125 mx and need some help indentifing the cylinder that is on it.I was told the enduro cylinders have no part number and the mx does,
26 Jan 2023 12:10 #1

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Replied by MarkT on topic 73 125 mx cylinder identification

What numbers did you find?

If I remember correctly both Enduro and MX reed cylinders have displacement (123cc) cast in on lower edge by transfers and I think both have a "code" cast in someplace... lower edge again or often around the intake area... that identifies the model.

Maybe something like 318 or 31800?
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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26 Jan 2023 13:46 #2

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Replied by Ht1kid on topic 73 125 mx cylinder identification

Greetings from Tennessee. 

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26 Jan 2023 15:56 #3

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Replied by RTD2 on topic 73 125 mx cylinder identification

I have a NOS MX Cylinder on my 73 125 MX, I will go check.

Mike
68 DT1, 70 DT1C MX, 70 Husqvarna 250 Cross; 71 CT1C, 71 RT1B, 71 DT1E MX, 73 AT3MX, 73 MX360, 76 Honda Elsinore; 2021 KTM 500 EXC-W; 2001 Honda XR400R; 2007 Harley Davidson Sportster 1200
26 Jan 2023 17:06 #4

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Replied by RTD2 on topic 73 125 mx cylinder identification

I see nothing stamped on the cylinder except 123cc.  I will try to dig out my original cylinder and see if there is anything visible on that.  

Mike
68 DT1, 70 DT1C MX, 70 Husqvarna 250 Cross; 71 CT1C, 71 RT1B, 71 DT1E MX, 73 AT3MX, 73 MX360, 76 Honda Elsinore; 2021 KTM 500 EXC-W; 2001 Honda XR400R; 2007 Harley Davidson Sportster 1200
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26 Jan 2023 17:16 #5

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Replied by MarkT on topic 73 125 mx cylinder identification

It's possible there are no markings... not sure exactly when Yamaha started adding model numbers to casting.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
26 Jan 2023 18:46 #6

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Replied by RTD2 on topic 73 125 mx cylinder identification

Mark, I will dig out the original cylinder tomorrow and look. It is so damn cold here right now, that I didn't want to dig into my parts tonight. I will turn on the heater in my shop tomorrow morning and look. I will have a definitive answer, the cylinder I took off was the original.

Mike
68 DT1, 70 DT1C MX, 70 Husqvarna 250 Cross; 71 CT1C, 71 RT1B, 71 DT1E MX, 73 AT3MX, 73 MX360, 76 Honda Elsinore; 2021 KTM 500 EXC-W; 2001 Honda XR400R; 2007 Harley Davidson Sportster 1200
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26 Jan 2023 19:01 #7

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Replied by RTD2 on topic 73 125 mx cylinder identification

All, I dug out the original cylinder from my 73 AT3MX and the only stamping is the 123cc on the base. It does have a huge intake port BTW!

Mike
68 DT1, 70 DT1C MX, 70 Husqvarna 250 Cross; 71 CT1C, 71 RT1B, 71 DT1E MX, 73 AT3MX, 73 MX360, 76 Honda Elsinore; 2021 KTM 500 EXC-W; 2001 Honda XR400R; 2007 Harley Davidson Sportster 1200
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27 Jan 2023 10:01 #8

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Replied by zestycj7 on topic 73 125 mx cylinder identification

Mike, thanks for digging the cylinder out. Sorry about not posting sooner. Life got real busy.
I got a cylinder off a guy that told me it was for an MX, it has a number cast into the bottom of the cylinder, it is #31602. The stock GYT cylinder that came on my bike has no numbers other than the  123cc. I have the porting layout for the Enduro and MX and checked both cylinders. The GYT cylinder ports match the dimentions for the MX and the other matches the Enduro dimentions. The GYT cylinder also has the fins cut back so the expantion chamber is tucked up close to the engine. I put the #31602 cylinder on the bike and the pipe will not fit without hitting the cylinder.
I also noticed the the #31602 cylinder has no hole in the side of the intake for the oil injection line but on the GYT cylinder there is a hole for the banjo bolt.
This whole thing has given me a headache...LOL
I just need to find some where that might have a part number listed for the #31602 cylinder.
24 Jun 2023 08:21 #9

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Replied by MarkT on topic 73 125 mx cylinder identification

My best guess since you said the cylinder has:
-31602
-no oil injection port drilled at base
-enduro porting
-fins not cut for pipe

is that you have a 1976 DT125C cylinder
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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Last edit: 24 Jun 2023 11:40 by MarkT.
24 Jun 2023 08:43 #10

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