OzVMX Forum

Marque Remarks => Yamaha => Topic started by: Woody on January 23, 2014, 10:45:33 pm

Title: Interesting Piston mods? - 250H
Post by: Woody on January 23, 2014, 10:45:33 pm: Here's a pic of the piston in the 250H roach bike that I've been toying with. Has some interesting holes drilled into it. Anyone seen one drilled like this before?

(http://i380.photobucket.com/albums/oo249/vmxwoody/YZ250H/DSC05705c.jpg)
Title: Re: Interesting Piston mods? - 250H
Post by: frostype400 on January 23, 2014, 11:59:17 pm: They must be speed holes that can't be a good idea making the piston weaker to remove a couple grams of material.
Title: Re: Interesting Piston mods? - 250H
Post by: topari on January 24, 2014, 12:36:07 am: Looks like a drill press was used and secured by way of hand. Not good.
Title: Re: Interesting Piston mods? - 250H
Post by: John Orchard on January 24, 2014, 09:28:47 am: The word 'butcher' comes to mind.
Title: Re: Interesting Piston mods? - 250H
Post by: crossedup2 on January 24, 2014, 12:50:21 pm: So do they line up with the exhaust port?

Didn't think that the H had a bridge in the exhaust port!!!!

I know, they are using the back pressure wave from the pipe to supercharge the crank case. ;) Drill the middle hole out to 15mm to take advantage of the pressure wave! ;D

Peter B
Title: Re: Interesting Piston mods? - 250H
Post by: Slakewell on January 24, 2014, 12:58:56 pm: Might explain whilst its slow, wrong side for holes.
Title: Re: Interesting Piston mods? - 250H
Post by: Maicoman on January 24, 2014, 08:33:30 pm: Quote from: Slakewell on January 24, 2014, 12:58:56 pm
Might explain whilst its slow, wrong side for holes.

Yep should be on the Inlet side. The standard IT pistons have the hole or window. Alot of guys drill the Wiseco pistons like that if they use them in IT's.
Title: Re: Interesting Piston mods? - 250H
Post by: crossedup2 on January 24, 2014, 10:19:38 pm: If you look at the other side of the piston it appears to be cut away like a YZ is. The pistons definitely the right way around, the bloke who drilled the holes should have been drilling his own skull to let out the pressure! Massive brain fart :o