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Thread: Bigger exhaust valve?

  1. #1

    Bigger exhaust valve?

    My exhaust valve tip has a crack= time to replace. Any Point in a bigger valve with 630cc volume with 49mm intake valve? Experiences? Any ideas where to find?

    Dudas

  2. #2
    Fitted a 49 to the Salt Racer...worked well and will fit with a standard sized seat from memory...with performance cams make sure to check the valve to valve clearance on the overlap as well as valve to piston...we ran stock sized exhausts...and bronze K Liners in the guides.

    SR
    ...'Any unnecessary items on the bike, that it doesn't really need, shouldn't be there!'. (Café racers creed). SR..

  3. #3
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    I fitted a lot of oversize valves over the years (so far up to 51) to all sort of sr/xt configurations.
    Depends on the cam you have that it would make sense. Anything bigger than 90bore and bout 13ish lift with short (otherwise you might end up with a pipey engine) duration makes a lot of sense!
    On non early (45!!) xt heads you ll end up with enough meat on the rings.
    With such valves stay away from 62-x18grind even though there might be enough clearance with stock valve. I run 49/41 with 180 and it works excellent.

    Kind regards

    Christian
    Last edited by Hudriwudri; 07-22-2017 at 11:45 AM.

  4. #4
    Thank you both.

    I'm Sporting a 49mm intake valve with a webcam grind 88 (12.75mm lift, 279 duration intake and 252 exhaust) at 98mm bore and 630cc. Valve to valve clearance was - if I remember correct - around 3mm.

    Where did you find the 41mm exhaust valve?

    Mikael
    Last edited by Dudas; 07-26-2017 at 01:20 PM.

  5. #5
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    Hi mikael,

    I would recommend the intake valve of a XS650 its about 2mm's longer which you should be able tocompensate but check for safeties sake!
    Which such engine specs and to satisfy the gulp factor of the engine i'd recommend you besides a serious appropriate porting a cam like the MC180 (15mm lift) or J2 (14mm lift) which both have reasonable not exagerated overlap and steep short ramps.
    You would be amazed how that engine will pull if not throttled

    All the best and

    Kind regards

    Christian

  6. #6
    Cheers mate,

    Will give the XS650 valve a go.

    My head is ported as well and she ran great prior to cracking the cylinder. Will put your cam suggestions on hold as a potental winter excersise.

    Mikael
    Last edited by Dudas; 07-30-2017 at 12:58 PM.

  7. #7
    IMO, the exhaust valve is adequate for much higher cc's than stock, and too big for stock size engines. Save the space for a larger intake valve instead.

    Bob

  8. #8
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    &hoffmann: 98mm bore!

  9. #9
    Quote Originally Posted by Hudriwudri View Post
    &hoffmann: 98mm bore!
    Needs all the intake valve it can get!

  10. #10
    Got a 49mm intake since before. The XS650 41mm intake valve fitted just fine as exhaust - thank you Christian for the tip! Now awaiting a bore and nikasilcoating job from a shop in Stockholm on the sand cast cylinder I picked up from EGU during summer, then she'll get back together again.
    Last edited by Dudas; 09-24-2017 at 06:58 AM.

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