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Difference between XS and TX engines?

Discussion in 'The Garage' started by Detale, Jun 27, 2012.

  1. Detale

    Detale XS650 Addict

    Hey guys, this may be a dumb question alltogether but My frame is '79 and I know the motor was replaced and I looked up the vin number on the engine and its 447-007668 which by the helpful threads here says its a 73-74 tx650a, I think.

    I'm asking what/if any difference it has to the later '79ish motors? Any known issues or basically any info good or bad about these years. Thanks guys.
  2. Patches

    Patches XS650 Junkie

    Does your motor have compression release?
  3. Detale

    Detale XS650 Addict

    Im not sure, prety sure i don't. Iim getting the top end rebuilt for me due to time constraints so it's not near me right now

    EDIT: well I know I don't have an odd valve cover if thats the only indication.
  4. Patches

    Patches XS650 Junkie

    73 is a 256 motor later models are 447. The cam is different, cam sprockets, crank sprocket, cam chain, connecting rods, wrist pins, pistons, and usually TX motors has compression release on the square tappet cover.....
    Last edited: Jun 27, 2012
  5. 5twins

    5twins XS650 Guru Top Contributor

    There's no such thing as a '73-'74. It's either a '73 or a '74. In your case, this is very important. Those are the two years when the big engine design changes occurred. '73 and older engines were what's called the "256" motor, '74 and later were what's called the "447" motor. Since your serial # begins with "447" I think we can assume it's a '74 and the "447" motor type. That's good for you because the parts are more readily available and cheaper. There isn't a whole lot of differences between that '74 motor and a '79 version. Main thing that comes to mind is the style of cam chain tensioner.
  6. Detale

    Detale XS650 Addict

    Thanks so much for the replies. I ordered one from mikes and there is says from 74-84. I would like to think the guy doing my top end would notice if these parts didn't fit and call me. Hopefully this works out
  7. 5twins

    5twins XS650 Guru Top Contributor

    Ordered one what?
  8. Detale

    Detale XS650 Addict

    Well a bunch of stuff for the top end and they also are doing the cam chain and tensioner. Also I have a starter motor on there and I just read that 73 was kick only. Is that correct?
  9. 5twins

    5twins XS650 Guru Top Contributor

    No, electric starters began with the '72 model. '70 and '71 were the kick only models.
  10. Detale

    Detale XS650 Addict

    I stand corrected, I read this wrong
  11. Detale

    Detale XS650 Addict

    Still trying to figure it out I came across this page and decided to say I have a '74 motor.
  12. jayel

    jayel #9 Guru 74 TX650A

    the 447-000*** serial number would be a 74 TX650A as for differences between it and later engines, as said mostly not important, cam chain tensioner, carbs, trans gears if you read up on mikesXS fifth gear swap it will be explained

    Attached Files:

  13. Detale

    Detale XS650 Addict

    I'll check that out right now. Thanks
  14. The first TX was a 256, the second one, the TX650A (and all of the xs's) was a 447. Somr of the differences have already been noted, but the big difference between the motors is the rod/piston. The 256 rod is longer and its pin is located higher in the piston and rides on a different bearing than does the 447 piston.

    The early motors also had lead counter-weights in the crank (which sometime came adrift) and the transmission shafts are splined differently ( eg. Mikes's 5ith "overdrive" gear set will not fit the 256 shafts.)

    There are performance advantages to the longer rod and many tuners have played with rods and pistons on the 447 motors to emulate the earlier design, the CR500 rod being a popular choice. The 256 rod small ends were failure prone.

    I've notice a fair amount of motors sold as "XS650" are actually 256 motors.
  15. cra-z1

    cra-z1 XS650 Junkie

    I can attest to the counter weights coming loose. One of my 72 engines had a locked up crank due to one coming out and hitting the rod. The other engine had a loose one. I decided to use a 447 crank and rebuild it with 256 rods. I used my 72 cam with a megacycle adjustable cam to accommodate the different cam chain used on the 447 engine. Works great and was able to keep the 72 characteristics without the worry of the counter weight coming out. The other reason for switching cranks was the starter had ground the drive gear on the crank pretty bad.
  16. This is interesting. If you have the crank out , can you tell? I have a 73 maybe a 74? Haven't really diagnosed the correct year. If you have compression release is it a 73? Pics of the cranks side by side would help.
  17. look at the engine number; if it starts with S650 it is a 73; numbers on 74's start with 447

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