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02 Sep 2019
Your admin has not been on the site much as of late as my main computer apparently seized up :( I have had limited access, but will be back soon. Thanks. Mako
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TOPIC: RT1MX head cylinder identification

RT1MX head cylinder identification 21 Apr 2019 03:01 #1

  • yamayeeha
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Hi everybody - new to this forum - tried an introduction but it didn't submit?

Anyway as a fan of all things AT1, CT1, DT1 and RT1 I thought joining was a good idea.
I have been collecting parts for a decade but with young kids, house renovations and work - builds are on hold. I hope to be able to share one soon .......but time will tell.

Anyway I have a cylinder and head combination that I want to share and maybe someone can shed some light. I have only seen one other like it.
Both look like RT1MX but have some major differences.
Things to note

  • No decompressor
    Extra fin on head and width of cylinder on oil tank side.(same as RT2)
    Porting map is different than RT2
    Cutaways appear factory same as RT1MX as you will see in the photos

  • I have added photos of mine as well as one of the cylinder from ebay - there is an original RT1MX head in my photos for comparison.
    Thanks
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    RT1MX head cylinder identification 21 Apr 2019 04:20 #2

    • RT325
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    Welcome from down under in NZ. Wow that's interesting. It's RT2 or RT3 due to reed inlet of course. I was thinking RT2MX initially but they're an over the top pipe,--i had one New anyway--new bike that is, not cylinder. Got me stuffed--& now i just Have to know lol, just when i thought i knew everything. If you flip the head over is it high comp compared to original head, as the reduce volume should be obvious to see. Thanks & hangin out to find out. Just wondering if there was a GYT Kit for an RT2 to turn it into a Monster. We never had kits & waited till the RT2MX came out later in the year. They had full fins on the cylinder plus taller fins on the head & by memory the fins were set oround the front so that the exhaust pipe was recessed where it bolted to the cylinder, sort of a half moon shape around the flange area. Anyway--just reminiscing. Take me back to the "70's.

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    Last Edit: by RT325.

    RT1MX head cylinder identification 21 Apr 2019 04:42 #3

    • yamayeeha
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    High compression - same as the Rt1mx
    photo attached.
    I have a RT2MX cylinder and head - porting map different again chamber in head different shape.
    I initially wondered if someone had hacked something up(RT2 or even YZ) to make the cylinder until i saw the second one on ebay. Also the head been wider by one fin has me stumped.
    Some kind of missing link between the RT1MX and the RT2MX?

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    RT1MX head cylinder identification 21 Apr 2019 09:25 #4

    • Bigdog302
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    The 1970 RT1M and the 1971 RT1 MX used the same cylinder and head and they are piston port engines.

    The 1972 RT2 MX was a 1 year only bike basically, this one has a Reed valve.

    the 1973-74 MX360 is a all new design and not at all related with the Old RT series 360.

    1970 RT1M
    www.google.com/search?client=firefox-b-1...imgrc=j5e97bp76XJgcM :

    1971 RT1 MX
    www.earlyyearsofmx.com/index.php/2018/07/13/yamaha-rt1-mx-1971/

    1972 RT2 MX
    www.mecum.com/lots/LV0117-262766/1972-yamaha-rt2-mx-360/
    The following user(s) Liked this Post: Snglsmkr, Super90

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    2 1968 DT1s,1970 RT1M,1970 DT1C,1971 RT1B,1971 Honda Z50K2,1974 DT100A,1974 Honda MT250,2 1975 DT400Bs,1975 Honda CR250M1,1978 DT175E,1979 Honda CR250R.
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    RT1MX head cylinder identification 21 Apr 2019 15:57 #5

    • yamayeeha
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    Thanks mate.
    I have both Rt1mx and Rt2mx cylinders and heads in the shed.

    The question I am asking is what is the cylinder and head in the photo.
    NOTE: If you count the fins on both heads on the oil tank side you will see what the problem is. Also the above cylinder is none of the 3 you have mentioned. It is also neither RT1 or RT2. Like RT325 said, it is like a GYT cylinder for an RT2 but we all understand there is no such thing.....?

    Regards

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    RT1MX head cylinder identification 21 Apr 2019 19:02 #6

    • Enduronut
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    yamayeeha wrote: .
    Anyway I have a cylinder and head combination that I want to share and maybe someone can shed some light.
    .

    .


    That mysterious cylinder & head in question, are from a 1971 Domestic Japanese RT1MX model.
    Yes .... "71" . . . They had the reed valve engines a year before the rest of us!



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    Last Edit: by Enduronut.

    RT1MX head cylinder identification 22 Apr 2019 01:25 #7

    • yamayeeha
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    Thanks for the identification, I had never heard about that before.
    Was that for any of the other cc bikes or just the 360?
    I bought both together with only the knowledge that I had purchased a NOS RT1MX head but suspected that the cylinder was still of some interest due to the lack of decompressor.
    Luck would have it that both are NOS.
    Funny thing was I thought I had a standard RT1MX head and somebody had probably shaved the side of the cylinder to fit the RT1 size. It was't until I pulled it out to photograph that I noticed the extra fin. When I saw the one on ebay recently I could see it was RT2 width and had the question - what head fits on that? All along I had the answer in my shed.

    Thanks again for clearing that up for me and am really happy that it is RT1 as it fits well in my bunch of stuff.

    Long shot - do you know if there is any articles or pamphlets that were made to show the reed valves.

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    RT1MX head cylinder identification 22 Apr 2019 03:39 #8

    • RT325
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    Very interesting reading Enduronut's answer. It had to be something like that but had me scratching!!. New Old Stock too. It doesn't come much better than that. I see the extra fin on the head.

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    RT1MX head cylinder identification 22 Apr 2019 04:39 #9

    • yamayeeha
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    Yes - it doesn't get much better than that - i feel very lucky.
    Somehow found its way down here to aus.
    Now I kind of wish I had bought the other cylinder on ebay - but was going to cost over $400AUS to get landed. Probably the only chance to get another, let alone one that was also NOS.

    I did happen to come across an opportunity to buy a couple of NOS RT1MX carbs if anyone needs one, but they were very expensive - out of my league as I am not building concourse bikes.

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