1974 Honda MT125 Elsinore VMX Racer Refresh.

Discussion in '2 smokers' started by RustyStuff, Sep 14, 2015.

  1. Scootern29

    Scootern29 Long timer

    Joined:
    Sep 4, 2012
    Oddometer:
    1,075
    Location:
    In the hot, hot, dezert
    Hopefully the spring rate won't be too much for your bike. The 76's were a forward mount shock set up which has stiffer springs. Be careful on the first big hit you take on it.
    #21
  2. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    I'll keep it in mind/
    I've read the spring weight was 131lbs vs 100~lbs for the 74-75 bikes. I'm actually hoping they are stiff enough, I'm 6ft and 195lbs. Most of these 125's were sprung for little guys around 140lbs based on the magazine tests I've found.. :D
    #22
  3. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Pulled the head this morning.
    One very oily engine. No wonder it fouls plugs.
    [​IMG]
    [​IMG]
    [​IMG]

    Normal Squish band head/
    [​IMG]

    look at how rough that casting is and how small those ports are.
    [​IMG]



    Head gasket comparo-

    Stock MT head gasket is a fiber spacer with a copper sealing ring right on the cylinder. Stock CR gasket is a sheet of soft copper.

    [​IMG]
    .043" thick if I'm reading the indicator correctly.
    [​IMG]
    VS . .013"
    [​IMG]

    My understanding is that the dimensions of all parts on the MT/CR are the same regarding piston/rod/crank/deck height. The biggest difference, and the reason the CR has a 7.9CR while the MT was around 7.0cr is the head gasket thickness. I'm going to take some squish measurements to be sure, but I've talked to people who have successfully done this. Should give a marked increase in torque.
    #23
    Gamequeazy likes this.
  4. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Long overdue update, The points were replaced by a proper CR CDI ignition system and I've got a Freshly rebored CR125M cylinder on the way. Only things left are new OS Piston, new CR style seat and chain/sprockets and a bunch of tuneing.

    Can't wait to race the Pomeroy memorial 125 cup series my local club puts on this spring. The spring rates actually not that bad though I was never able to get it running well enough with the points to really romp on it.
    #24
    Euromad likes this.
  5. Euromad

    Euromad Been here awhile

    Joined:
    Feb 16, 2010
    Oddometer:
    605
    Location:
    Lower Slobbovia
    Great project! I had a 74 CR125- my first race bike. Looking forward to a race report in the future. :thumbup
    #25
  6. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    I now have a seat, 3rd world manufacturing techniques win again!

    The old seat was JUNK! The cover was rotted, foam eroded and pan rusted out.
    [​IMG]

    A real CR125 seat is not cheap, so I went digging though my junk seat stash to find my old GS450L choppa seat.
    Trim the pan, add and move rubber bumpers.
    [​IMG]
    [​IMG]
    Perfect length.
    [​IMG]

    Whallah...

    [​IMG]

    Ugly but functional.

    Now to make a decent cover.
    #26
  7. Euromad

    Euromad Been here awhile

    Joined:
    Feb 16, 2010
    Oddometer:
    605
    Location:
    Lower Slobbovia
    A Moto-Cafe. You sir, have invented a new style :clap
    Fun to watch your thread. I've done a bit of similar engineering. A bike needs to be ridden.
    #27
  8. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Thanks, I'm glad others are enjoying this project as much as I am. This is my favorite way of building things, find the best deals on parts and make them work.

    New cylinder is here today, Freshly re bored to 57mm and blasted/powder coated by the looks of it. Though like everything, nothing is perfect. Going to need to heliCoil the exhaust spigot bolts, stripped out.


    The biggest difference between the MT and CR porting is the Size and location of the crankcase intake port and exaust port.

    [​IMG]
    [​IMG]
    MT enduro-Single small rectangular port.
    [​IMG]
    [​IMG]

    CR exaust ports are taller and wider with extra cutouts at the top.
    [​IMG]
    [​IMG]
    [​IMG]

    MT intake-
    [​IMG]
    CR Intake-
    [​IMG]
    [​IMG]

    And a great discovery, The rod is in immaculate condition. Side play is in spec and there is no up and down play at all and no rust or damage.
    [​IMG]

    I also just found a Wiseco 57mm piston kit for a fantastic price. So we may not be far off from the test firing!.
    The current list of parts is-
    '75 MT125 frame/Steel tank/Forks( 15W oil in forks to increase damping),wheels and fenders.
    '80 GS450L seat base and foam.
    '76 CR125 "bottle" shocks, taller and stiffer than stock.
    '75 CR125 expansion chamber( the one that mag writer's called "obnoxious and excessive" :D
    CR125m CDI igntion
    28mm Kiehin round slide off a '74 CR125,
    Cylinder from a 74-76 CR125, CR125 copper head gasket mated to a 75 MT125 dual plug head.
    75 MT125 bottom end and 5spd semi-close ratio trans.
    The rear brake system is part 74 CR250m and Honda 90 3wheeler....
    #28
  9. JCool

    JCool Long timer

    Joined:
    Oct 15, 2016
    Oddometer:
    3,686
    That's not a dual plug head. The side hole came plugged. It was to add a compression release.
    #29
  10. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Interesting, every one of them I've seen has a 2nd plug in the hole.
    A compression release on this bike seems pretty funny really.
    #30
  11. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Joined:
    Oct 29, 2007
    Oddometer:
    13,892
    Location:
    Omicron Persei 8
    It may seem funny now, but a compression release was very common in the early to mid 70's. Yes, they really didn't stop you very well and they did suck dirt into the motor but they were common. Its what we did.
    #31
    turnsleft likes this.
  12. JCool

    JCool Long timer

    Joined:
    Oct 15, 2016
    Oddometer:
    3,686
    A second plug won't be worth a crap anyway after a couple hundred miles of carbon builds up on it from never firing. I used to pull the CR with the throttle held open while slowing down. When you're read to accelerate again , you just let go of the CR and your gone. The same works with a kill switch.
    #32
  13. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Very interesting, Never would have though of using a compression release like that. I can imagine it would trash a top end fast in the volcanic dusty soil we have here.

    What's interesting me the most is I'm pretty sure the CR125 head was lacking in the hole, while the MT enduro head has it.
    #33
  14. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    No project is complete without trials and tribulations.
    First I discover that the exhaust spigot mounting bolts had been stripped out on my new cylinder. While looking it over I find that they have been somewhat poorly retapped to 1/4"x20... Well I'll run with it. Not much material so I don't really want to drill it out for a m8.

    My "New weisco 57mm CR125m" piston showed up today. It's not new, it's not a 57mm, and it's missing the clips for the wrist pin. Ebay Seller better do a refund because this is crap.
    #34
  15. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Joined:
    Oct 29, 2007
    Oddometer:
    13,892
    Location:
    Omicron Persei 8
    Just my personal opinion, but installing a used piston, rings, wrist pin & clips from some other bike is a very bad idea. Especially if you can get brand new from Wiseco.
    #35
    JCool likes this.
  16. JCool

    JCool Long timer

    Joined:
    Oct 15, 2016
    Oddometer:
    3,686
    $128. Wiseco says the MT and CR125M pistons are one and the same.
    #36
  17. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    It was listed and advertised as a "NEW" in box weisco piston.


    Seller gave me a refund so whatever. First time I've had a problem on there.
    #37
    turnsleft likes this.
  18. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Joined:
    Oct 29, 2007
    Oddometer:
    13,892
    Location:
    Omicron Persei 8
    OK that's good, but around these parts there are a lot of really cheep bastards (aka: KLR owners) so for us on the other end of the conversation we don't always know.
    #38
  19. RustyStuff

    RustyStuff Long timer Supporter

    Joined:
    Jan 14, 2012
    Oddometer:
    13,223
    Location:
    Crakima,Wa
    Yeah I understood why you asked,it irks me that someone would sell something without confirming what is actually in the (slightly beat up)sealed box.
    #39
  20. kenny robert

    kenny robert Long timer

    Joined:
    Aug 21, 2015
    Oddometer:
    1,652
    Location:
    south orygun
    awesome it will smoke and smell soon eh ?
    git ya some blendzall additive green or gold label all you need is a couple oz per gallon to harken back the smell of a saterday nite at the shortrack
    i have an mr175 seat the cover was pro made custom
    lightly usede no =rust no holes in cover
    you can have it for the shipping and a couple cups of, spendy , drive thru coffe
    #40