how much more stress does a hc pistion and ex cam put on the motor?


12 replies to this topic
  • Slinkyman16

Posted February 23, 2009 - 12:43 PM

#1

How much more stress would i be putting on the motor if i went with a high compression piston and exhaust cam? motor is starting to gather some hours and i want to start to invest in some motor work.

just want to know weather or not im making the right choice.


Thanks guys.

  • mxracer206

Posted February 23, 2009 - 01:35 PM

#2

The bottom end of the motor is tough but the piston pin and top of the rod is where a lot of wear occurs. I have had a top piston pin break, I know Wiseco has better pins that can be ordered for their h/c pistons. As far as the cams there are a lot of options, some require different valve springs. Have not done a lot of cams on 450's but the 250-Fs seem to wear on the cam and cam caps on the side opposite the lobe due to the extra lift on some cams.

  • KJ790

Posted February 23, 2009 - 01:44 PM

#3

The difference in force applied to the wristpin, rod, and crank is negligible compared to the forces these parts experience just changing the direction of the piston.

  • mxracer206

Posted February 23, 2009 - 06:24 PM

#4

The difference in force applied to the wristpin, rod, and crank is negligible compared to the forces these parts experience just changing the direction of the piston.


True but without bashing anyone I know for sure Wiseco offers a better pin for their 13.5 piston a lot of people use.

  • grayracer513

Posted February 23, 2009 - 08:48 PM

#5

True but without bashing anyone I know for sure Wiseco offers a better pin for their 13.5 piston a lot of people use.

Your point?

  • husqy360

Posted February 24, 2009 - 07:03 AM

#6

wisco pins are so bad, they want to catch up with the rest so they make a desent option for the hc piston ?:worthy: :lol:

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  • Slinkyman16

Posted February 24, 2009 - 02:19 PM

#7

the hc and cam i was going for comes from crowerperformance as a kit. cam is made to work with the stock valvetrain. i just want to make sure before i get this kit that it will at least be half way reliable as the oem stuff is.. i dont want to have to change out a pistion every other month.

  • mxracer206

Posted February 24, 2009 - 05:54 PM

#8

Your point?


Only that I have seen piston pin failures on the YZF-450 and YFZ-450 and the only way I would run a Wiseco h/c piston is to order the better pin.

  • harrperf

Posted February 24, 2009 - 08:20 PM

#9

Only that I have seen piston pin failures on the YZF-450 and YFZ-450 and the only way I would run a Wiseco h/c piston is to order the better pin.


the 09 pin is updated I believe.

  • grayracer513

Posted February 24, 2009 - 08:22 PM

#10

That's more understandable without the missing facts. Wiseco has had some problems with pins breaking. If they have an HD version, I'd recommend it.

  • Brad_Aus

Posted February 24, 2009 - 08:35 PM

#11

Theres a lot greater forces going on than some might expect..

Consider that at 13500rpm on a yz250f, the piston is peak accelerating at a mind boggling 8000g's. So therefore, small weight differences are amplified massively. The 210g of thereabouts for a piston assy is loading the conrod with about 1700kg worth of force....

Luckily, this peak load lasts for a period of only 0.00007 seconds. The load is completely reversed every 0.002 seconds....

Every gram counts, we can all see how conrods fail from fatigue, when they live that sort of life

  • grayracer513

Posted February 24, 2009 - 09:06 PM

#12

Theres a lot greater forces going on than some might expect..

Consider that at 13500rpm on a yz250f, the piston is peak accelerating at a mind boggling 8000g's. So therefore, small weight differences are amplified massively. The 210g of thereabouts for a piston assy is loading the conrod with about 1700kg worth of force....

Luckily, this peak load lasts for a period of only 0.00007 seconds. The load is completely reversed every 0.002 seconds....

Every gram counts, we can all see how conrods fail from fatigue, when they live that sort of life

All that's true, at least in principle, and it's something like what KJ said. But the question is whether there is significant additional stress resulting from the hop up parts.

If the piston is heavier, or if you rev it higher, then there is some additional strain. If it produces more power, there is more strain as well, but only while the additional power is being made/used.

OTOH, cams with higher lift and more aggressive profiles are tougher on the whole valve train when they are just operating.

Whether any of this exceeds the design strengths of a YZF in this case is the question, but I don't think it's anything to loose too much sleep over.

  • Slinkyman16

Posted February 24, 2009 - 10:57 PM

#13

All that's true, at least in principle, and it's something like what KJ said. But the question is whether there is significant additional stress resulting from the hop up parts.

If the piston is heavier, or if you rev it higher, then there is some additional strain. If it produces more power, there is more strain as well, but only while the additional power is being made/used.

OTOH, cams with higher lift and more aggressive profiles are tougher on the whole valve train when they are just operating.

Whether any of this exceeds the design strengths of a YZF in this case is the question, but I don't think it's anything to loose too much sleep over.


so i shouldnt really worry about it and just freakin order the thing?? lol..





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