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Compression release - Rare ?

Discussion in 'The Garage' started by Rotten Egg, Dec 29, 2012.

  1. Hey guys,
    I picked up a load of parts recently, and included was 2 compression releases.
    The guy told me they were Yamaha pieces (optional ?), and that they were pretty rare.

    One is complete with the valve cover, the other is missing the valve cover & cable

    So are they as rare as he said?
    What bikes did they come on?
    Anyone using them?

    Thanks for the help.
     

    Attached Files:

  2. DaveO

    DaveO XS650 Addict

    If I'm wrong I'm sure someone will jump in but the first XS I ever saw was my mates back in the 70s. It had electric start but a small battery. Turning over a 650 twin would have flattened the battery fairly quickly so yamaha organised a decompressor. A trigger on the handlebars activated the electric start and at the same time lifted one of the valves (the exhaust??). The bike had compression on only one cyclynder and was therefore easier to turn over. The other cylynder would fire and when the trigger was released the second would chime in. It could be possible that this is an item with potential to be retro-fitted but I can't see why you would want to.

    Later machines (I believe) have a bigger space for the battery and I can see reliabity of starting problems (if you had a weakness on the firing side). I thought it was pretty cool the way it sounded and maybe custom guys would want to do it "for the kicks". Of course someone who has an XS1 with these bits missing would want them too.

    Dave
     
  3. DaveO I think you're right. Check out this eBay XS, the picture looking at the left hand side close up, you can see the decompressor
     
  4. cra-z1

    cra-z1 XS650 Junkie

    790
    875
    93
    Idaho
    The compression release was only on the 72 XS2 which was the first year for the electric start. I believe they dropped it in 73. I had a new 73 in 73 but I don't remember it having the release at the valve just the lever under the controls for the electric start on the 73. Just looked at the only old photo of my 73 and I think I do see a cable going to the left side so maybe it did have the complete release.
     

    Attached Files:

    Last edited: Dec 29, 2012
  5. deadchef

    deadchef xsbobblehead

    holy hell that's a pretty engine!
     
  6. willyguzzi53

    willyguzzi53 XS650 Addict

    I know they came on the '73's cause I've had two of them and they both have them. I'm pretty sure they made the starter better in '74 and did away with them.
     
  7. willyguzzi53

    willyguzzi53 XS650 Addict

    Which prompts another question. I have several late starters and the starter on the 73 sounds pretty bad. Can I put a later starter on my 73 or do I need to rebuild the spring on the original starter and put it back on? Sorry, didn't mean to hyjack the thread. Seemed like a good time to ask.
     
  8. cra-z1

    cra-z1 XS650 Junkie

    790
    875
    93
    Idaho
    I agree. The release does no good without the early cam lever for the left side. So it's only value would be to someone with a 72 or 73 or someone with a early cam lever.
     
  9. Thanks for all the great info guys.
    Cra-z1 That Engine is beautiful ! Thanks for the info.
    Rick.
     
  10. If you had the rocker arm to go with them.They are great for a high compresion motor. Yamaha changed the cam profile on the newer motors from what I understand. They used the opening and closeing ramps as the compession release.
     
  11. jb_supermoto

    jb_supermoto XS650 Enthusiast

    Yeah as above, not really per se but only on the '72 and '73 I think. I have a '72. If you want to sell those I'd be interested for a spare or one to polish while mine is on the bike..

    JB
     

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