Jump to content
Sign in to follow this  

Drill or not drill free piston on 09 yz250f.

Recommended Posts

I'm changing oil in my forks, I weight 190#s w/o gear ride mx tracks, do I drill the piston as per Smart Performance or no.

Thanks

Share this post


Link to post
Share on other sites

the better question is why SHOULD you.

Is it better to have that rise in cartridge pressure near the end of the stroke or not...

Share this post


Link to post
Share on other sites
the better question is why SHOULD you.

Is it better to have that rise in cartridge pressure near the end of the stroke or not...

This is actually an interesting question because if you don't drill them, then the third chamber remains closed or isolated. The pressure build-up within that chamber is constant and rather minimal.

Open up the free piston and thereby remove the third chamber, you then expose the air pressure of the lower chamber onto the backside of the free piston, which by comparison, is a lot...and certainly a lot more force than the IC spring is producing at that point...assuming the lower oil level is within range to make a difference. However, in this scenario the real piston is the rod. :thumbsup:

But the issue with drilling the free piston is more about making sure you keep them from cracking. Yes, I know....drilled free pistons still crack, but not a new drilled free piston.

And the factory bikes run a vented piston, by the way.

Share this post


Link to post
Share on other sites

I'm seriously thinking on replacing my drilled free pistons and going it back to stock.

I didn't feel any performance gain with drilling them, if anything it may have added mid-stroke harshness and less bottom out control? I say that due to the oil volume change with the drilled pistons.

Only one way to find out, I'll be calling Dave and placing an order at some point.

Share this post


Link to post
Share on other sites
This is actually an interesting question because if you don't drill them, then the third chamber remains closed or isolated. The pressure build-up within that chamber is constant and rather minimal.

Open up the free piston and thereby remove the third chamber, you then expose the air pressure of the lower chamber onto the backside of the free piston, which by comparison, is a lot...and certainly a lot more force than the IC spring is producing at that point...assuming the lower oil level is within range to make a difference. However, in this scenario the real piston is the rod. :thumbsup:

But the issue with drilling the free piston is more about making sure you keep them from cracking. Yes, I know....drilled free pistons still crack, but not a new drilled free piston.

And the factory bikes run a vented piston, by the way.

eh...some do!

Honda and ktm??

doubt it.

Share this post


Link to post
Share on other sites

the new metal replacement pistons are vented.they also have no top o-ring anymore.

Share this post


Link to post
Share on other sites
eh...some do!

Honda and ktm??

doubt it.

I saw the inside of the forks on Chad's YZ, back in the day, and they were metal and they were drilled.

Not sure about the rest.

But if anyone hasn't noticed yet, the 2010 CRF250R forks, SHOWAs with KYB internals, have a bleed or vent screw for the back side of the free piston. So it would not surprise me if some of the works stuff has this chamber isolated.

Coming soon - free piston sub tanks! :thumbsup:

Share this post


Link to post
Share on other sites

Well they are drilled now, not sure if I ride fast enough to tell right now:ride: Not sure if I bled the first fork IC right or not. left the bleed hole open on the top cap due to motion pro bleeders and a lil shot of air weeped in while bleeding cartrige(in the early stage).

Thanks.

Share this post


Link to post
Share on other sites
I'm seriously thinking on replacing my drilled free pistons and going it back to stock.

I didn't feel any performance gain with drilling them, if anything it may have added mid-stroke harshness and less bottom out control? I say that due to the oil volume change with the drilled pistons.

Only one way to find out, I'll be calling Dave and placing an order at some point.

I would think it hard to get more harshness and less bottoming control at the same time, i think its all in your head :thumbsup:

I have drilled them and felt no real difference at all.....

Share this post


Link to post
Share on other sites
Well they are drilled now, not sure if I ride fast enough to tell right now:ride: Not sure if I bled the first fork IC right or not. left the bleed hole open on the top cap due to motion pro bleeders and a lil shot of air weeped in while bleeding cartrige(in the early stage).

Thanks.

The air bleed hole in the cap does not vent to the interior of the cartridge. The passage leads to the outer chamber only.

Share this post


Link to post
Share on other sites
I would think it hard to get more harshness and less bottoming control at the same time, i think its all in your head :ride:

I have drilled them and felt no real difference at all.....

Sure it can do both. By drilling you have effectively lowered your oil level volume from where it was before the drill. Then because it is no longer isolated you have the added outer chamber pressures and it's influence on the back side of the free piston during mid-stroke.

I'll test it so I dont have to guess.......:thumbsup:

Share this post


Link to post
Share on other sites
The air bleed hole in the cap does not vent to the interior of the cartridge. The passage leads to the outer chamber only.

sounds great!

thanks again:thumbsup:

Share this post


Link to post
Share on other sites

I have tested back to back with and without, the difference is marginal at most, 5cc of oil either way would throw out the feeling more IMO.I am not sure with a few small holes or one big one, pressure will transfer fast enough for it to matter even.

Like i said its theoretical not actual, or its all in your head not in your riding :thumbsup:

Share this post


Link to post
Share on other sites

strange as ross told me to drill them....

Share this post


Link to post
Share on other sites
strange as ross told me to drill them....

You should know by now to always listen to me!

:thumbsup:

Share this post


Link to post
Share on other sites
The Factory Connection and Technical Touch forks I have seen were not drilled. Just making a note:ride:

I know that ENZO drills there, and I'm almost certain that Factory Connection does.

In either case, I think we all know that they crack and I think we now know why they crack, so I can't think of why you would not want to drill (vent) them.

Share this post


Link to post
Share on other sites

Often I see ICS pistons with fluid trapped in them. These are pistons that have NOT been drilled yet.

Now obviously the seal is leaking to some extent.

That said, when this occurs, I think it's MORE likely that the piston gets filled enough such that it hydrolocks to an extent...and thus causes breakage.

Obviously drilling them "fixes" this.

But I still don't feel it is a performance improvement in any manner.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

  • Similar Content

    • By smokey9lives
      Hi,
      I have a 2003 DRZ (actually a KLX400) and the head tube bearings are shot.  I ordered a new set to install but I'm wondering if anyone has any recommendations on other parts I should replace while I have the front disassembled.  I was thinking about new rubber fork protectors, but are there other things that wear out on the DRZ front ends that you can only get to when disassambled?
      I also broke off a replacement key that I got for the steering lock.  I must have been made of cheap pot-metal.  Should I just remove the whole lock mechanism?
      Any tips or tricks for getting the old bearings out and the new ones in would be welcome!
      Thanks!
    • By hondahondo
      A few picks of my winter project.













    • By Luke Hufford
      Hey guys. I recently purchased a 16 yz250x and the first 2 rides i LOVED the suspension. Then the day before a race i reset all my clickers to stock and everything felt like crap. No plushness at all and deflected off everything. I now have a 5.4 shock spring for my 190 pound weight and dialed in sag. Any recommendations on where i should go from here? Right now the fork is 12 out on comp and 15 out on rebound. Shock is 1.75 turns out on hsc, 14 out on lsc, and 18 out on rebound. Any help would be appreciated!
    • By jake gu
      Today we’re going to be talking a little bit about automotive suspensions and how they work to smoothen the ride of your car. There are mainly three purposes of the automotive suspension system. First, they support the  weight of the vehicle. Second, they maintain accurate tire contact with the ground. And third, they absorb any shock that you get through the road when you hit a bump.
      Most modern vehicles come with an independent front suspension. Which means if one wheel hits a bump it does not disturb the other wheel. Nowadays, people use Coil Spring to support the majority of weight in the car. As it has a really good characteristics for absorbing any bumps as you go up and down on the road.
      However Springs aren’t very good at dissipating that energy. In fact that’s why you have the shock absorber. Which is there to smoothen out the ride and make sure the tire maintains contact with the road.
      In modern passenger vehicles the two most popular suspensions are McPherson strut and double wishbone style of suspension. The main advantage of the McPherson strut suspension is that it’s really cheap and simple that’s why a lot of manufacturers are moving towards this design. The double wishbone design allows the wheel to stay perpendicular to the body as it navigates a corner or as it goes over a bump. And that maintains good tire contact patch no matter where the wheel is situated. Another advantage of this design is that it can be made adjustable where you can control the position of upper control arms ball Joints.
      Click to Know More About Ball Joints and other Suspension Components
×