Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread:

  1. #1
    Noobie
    Join Date
    Jul 2018
    Location
    dover nh
    Posts
    10
  2. Default increasing the Stroke

    Hey guys Im Curious If anyone know how much you can increase the stroke on the blast engine. I dont want to put my bike down just to figure it out. thanks
    Come to the darkside we have a blast

  3. #2
    The Boss
    (Admin)
    Jet-Lee's Avatar
    Join Date
    Mar 2012
    Location
    Oakley, CA
    Posts
    6,755
  4. Default

    You have to swap the crank to increase the stroke. You can go with a XB12 crank, but then you need custom connecting rods and the whole assembly re-balanced.

    Custom con-rod because the Blast has a taller case deck than the XB's. The Blast rod will be way too long, XB9 rod a little too long and XB12 rod a little too short. You could also get the jug decked and use the XB12 con-rod to bring your rod:stroke ratio back down, but I think the taller ratio would be better to prevent rocking/slapping the piston against the cylinder walls.

    You also need to check on bearing types in use. XB's use a lot of newer-style bearings that the Blast doesn't, so a fair bit of machining will be required.
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

    Click here to enlarge
    Left to Right:
    2003 Blast (Blue), 2001 XBlast (Rex), 2007 XB9R Firebolt (Bolt)

    Do you like the forum? Do you appreciate the input and community support? Consider donating to help keep us alive and growing! Click here to donate!
    Like us on Facebook!

  5. #3
    Noobie
    Join Date
    Jul 2018
    Location
    dover nh
    Posts
    10
  6. Default

    I was Thinking of having The blast crank pulled apart and re machined. This way I dont have to have custom con arms or bearing seats. Im more curious about how much room I have to play with. Do I have enough room for a 3.5 in stroke?
    Come to the darkside we have a blast

  7. #4
    The Boss
    (Admin)
    Jet-Lee's Avatar
    Join Date
    Mar 2012
    Location
    Oakley, CA
    Posts
    6,755
  8. Default

    You have two methods of modifying the crank for more stroke...
    1. Move the crank pin further from the center; this requires new machining on the opposite side of the current location and still have to re-balance.
    2. Machine the crank pin smaller and offset; still requires re-balance.

    Either way you go, you need to shorten the connecting rod. You have about .05" (being generous here) between your piston and head. ANY stroke increase will require a shorter con-rod.

    Unless you are the machinist or know someone who works for free, you will spend more money on machining than if you were to buy a new crank built to the spec you want. I've priced it, I know this for fact.
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

    Click here to enlarge
    Left to Right:
    2003 Blast (Blue), 2001 XBlast (Rex), 2007 XB9R Firebolt (Bolt)

    Do you like the forum? Do you appreciate the input and community support? Consider donating to help keep us alive and growing! Click here to donate!
    Like us on Facebook!

  9. #5
    The Boss
    (Admin)
    Jet-Lee's Avatar
    Join Date
    Mar 2012
    Location
    Oakley, CA
    Posts
    6,755
  10. Default

    Increasing the stroke moves the piston closer to the head at the top of its travel. You currently have 3.125" stroke and ~.05" space (require no less than .03"). That means you can go to 3.165" stroke...or buy thinner base/head gasket to achieve the same result.

    If you want to go to 3.5" stroke, you need a con-rod that is .1875" shorter, none of the factory options work perfectly.

    Blast half-stroke is 1.5625", plus the con-rod (7.438") give a crank-center-to-piston-pin-center of 9.0005".

    If you increase that half-stroke to 1.75", plus an XB9 con-rod (7.27"), that gives you a crank-center-to-piston-pin-center of 9.02".

    You need to clay the piston beforehand to make sure you do indeed have at least .05" between piston and head. Then you have to use stock .020"/.040" base/head gaskets. If you have more than .05" clearance before the stroke increase, you can make it up with thinner gaskets to bring your end result to .03" after stroke increase. If you have less than .05" to start with, you need to change your stroke target because any larger than stock gaskets is likely to leak/blow.
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

    Click here to enlarge
    Left to Right:
    2003 Blast (Blue), 2001 XBlast (Rex), 2007 XB9R Firebolt (Bolt)

    Do you like the forum? Do you appreciate the input and community support? Consider donating to help keep us alive and growing! Click here to donate!
    Like us on Facebook!

  11. #6
    The Boss
    (Admin)
    Jet-Lee's Avatar
    Join Date
    Mar 2012
    Location
    Oakley, CA
    Posts
    6,755
  12. Default

    Wish Mik, Piratius and maybe just_some_dude could get in on this as well.
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

    Click here to enlarge
    Left to Right:
    2003 Blast (Blue), 2001 XBlast (Rex), 2007 XB9R Firebolt (Bolt)

    Do you like the forum? Do you appreciate the input and community support? Consider donating to help keep us alive and growing! Click here to donate!
    Like us on Facebook!

  13. #7

    Default

    Quote Originally Posted by Jet-Lee View Post
    Increasing the stroke moves the piston closer to the head at the top of its travel. You currently have 3.125" stroke and ~.05" space (require no less than .03"). That means you can go to 3.165" stroke...or buy thinner base/head gasket to achieve the same result.

    If you want to go to 3.5" stroke, you need a con-rod that is .1875" shorter, none of the factory options work perfectly.

    Blast half-stroke is 1.5625", plus the con-rod (7.438") give a crank-center-to-piston-pin-center of 9.0005".

    If you increase that half-stroke to 1.75", plus an XB9 con-rod (7.27"), that gives you a crank-center-to-piston-pin-center of 9.02".

    You need to clay the piston beforehand to make sure you do indeed have at least .05" between piston and head. Then you have to use stock .020"/.040" base/head gaskets. If you have more than .05" clearance before the stroke increase, you can make it up with thinner gaskets to bring your end result to .03" after stroke increase. If you have less than .05" to start with, you need to change your stroke target because any larger than stock gaskets is likely to leak/blow.
    Yup you are right and i think you have great experience in riding and have a great knowledge about the bike

  14. #8
    Noobie
    Join Date
    Jul 2018
    Location
    dover nh
    Posts
    10
  15. Default

    wow That is amazing Info thank you for the input. Where would you purchase a modified XB Crank and con rod. So with a XB setup What would the total stroke be I have a goal of 720cc. This may not be achievable in this engine but I keep seeing the "44 magnum" Blast but see no other way to achieve this.
    Come to the darkside we have a blast

  16. #9
    The Boss
    (Admin)
    Jet-Lee's Avatar
    Join Date
    Mar 2012
    Location
    Oakley, CA
    Posts
    6,755
  17. Default

    You need a 1200 crank re-balanced for a single cylinder, this will get you to 601cc. You then need a 3-13/16" bore, this requires boring the case larger for the oversized jug and piston skirt. That will get you to 721cc. After that, you need to address fueling and ignition timing for the almost 50% gain in displacement.

    Here's a few photos:

    3-13/16" piston


    3 pistons; 3-13/16" (left), 89mm 12:1 c/r for XBlast only (right), Stock Blast (back)


    50 lbs/hr injectors (stock XB were 30):
    "It is impossible, until some crazy son of a bitch has the audacity to believe that no matter what the expert says, I can still do that shit." - C.T. Fletcher

    Click here to enlarge
    Left to Right:
    2003 Blast (Blue), 2001 XBlast (Rex), 2007 XB9R Firebolt (Bolt)

    Do you like the forum? Do you appreciate the input and community support? Consider donating to help keep us alive and growing! Click here to donate!
    Like us on Facebook!

  18. #10
    Noobie
    Join Date
    Jul 2018
    Location
    dover nh
    Posts
    10
  19. Default

    Is it easier to modify the xb intake or to find another fuel injection system that only has one intake. Also Back to the con rods should I get one custom made or use a XB one
    Come to the darkside we have a blast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •