Casting flaws

10 replies to this topic
  • BoffoRider

Posted July 30, 2004 - 02:52 AM


I have a buddy who is crazy with a dremel. He has ported and polished his 250 2 stroke and insists that there are many casting flaws left behind in all bikes. He claims that by cleaning up the casting flaws there would be a significant performance increase. He has already taken another guy's 426 and cleaned up the flaws and they both claim it would now easily match the power of my 450. Not that I necessarily believe them, but my questions are whether cleaning up these casting flaws would deliver a noticeable increase in power and are there really that many flaws left behind in these bikes? Any insight would be greatly appreciated.

Thanking you in advance,

  • CRFThumper

Posted July 30, 2004 - 03:27 AM


ABSOLUTELY! Will it help yes!Will it turn it into a fire breathing monster no!But every little bit helps right?But be careful be very careful a little boo boo and there goes
some $$$$$

  • BoffoRider

Posted July 30, 2004 - 11:33 AM


Is there anyone that has done this to their bike? What in particular should I be watching out for?

  • yz426onNOS

Posted July 30, 2004 - 08:54 PM


Go to a pro. If you micro polish it has to be done on a machine. You cant do it by hand.

  • Jeffro426

Posted July 30, 2004 - 09:42 PM


If all he wants to do is remove the casting flaws thats fine, but dont let him do much more unless he has years of experience in this area...engine porting is a very delicate opperation that requires a professionals touch to make it perform properly. And for what its worth...the 426 does make just as much power as the 450...the 450 however, makes it a little more smoother and the bike is substantialy lighter.

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  • Hamish

Posted July 31, 2004 - 12:59 AM


It will make a slight difference. Just make sure that he doesn't 'polish' the inlet ports. They need to remain rough.

  • sirthumpalot

Posted July 31, 2004 - 08:54 AM


It will make a slight difference. Just make sure that he doesn't 'polish' the inlet ports. They need to remain rough.

Ditto, my understanding is that polishing the intake side might help with the very high top end, but not much good for anything else inbetween. The rough surface helps to mix the fuel and air. Now if you have some passages that just don't line up between bolt together pieces then that's a different story.

  • jespertheil

Posted August 01, 2004 - 10:31 PM


Don´t let him play with your top!!!!!! :thumbsup:
You can´t do any porting without a flowbench. You will need that to mesure the vacum i the top. If wrong you will loose power instead of gaining.. As said earlier, you will need a pro to do it..

  • wrx_stud56

Posted August 02, 2004 - 10:26 AM


another good point being is that if your friend messed it up ? whos payin for it ? and when a pro does it, atleast you know it will be done 100% right .. and with 100% percision

  • felony

Posted August 02, 2004 - 10:58 AM


i have a buddy who happens to be Casey Johnsons mechanic(#121 national)and even though casey rides a kx250,he has also worked on michael brandes 250 4 stroke.he told me that actually they dont touch the exhaust ports,they only massage the intake ports.believe it or not they try to make the opening smaller to increase velocity for increased throttle response and low to mid.when i tear mine down ill let him have at my head. :thumbsup:

  • Hamish

Posted August 03, 2004 - 02:07 AM


believe it or not they try to make the opening smaller to increase velocity for increased throttle response and low to mid.

This is true if the head design allows it. On some heads (426 for example) building up the port floor kills the flow at full valve lift, in which case you end up with a compramise. The 450 is much more suited to this procedure. You end up with higher port velocity for torque with no loss in flow. I've never heard of this being done on the exhaust port.... :thumbsup: normally you'd just use a stepped header pipe to get that effect.

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