OzVMX Forum

Clubroom => Tech Talk => Topic started by: ChrisACT on April 04, 2009, 10:30:22 am

Title: Best piston for DT2
Post by: ChrisACT on April 04, 2009, 10:30:22 am

Howdy,

After reading this thread:
http://ozvmx.com/community/index.php?topic=4405.0
I think I know which is the correct original piston for my DT2.

But.....

Is there a better one?

1981 - 82 YZ250 has the same bore and seems to have a similar compression height as the DT2 reed pistons.  But they have a large cutaway on the inlet side of the piston skirt instead of the twin holes the older pistons have.  Plus they've done away with the Kettering ring and just run two strandard rings.

Which is better?  I also understand that the TS250 pistons fit (with a spacer under the barrel).

I'm planning to run relatively high compression, 12:1 so I want the get the piston up in the bore as high as possible anyway.

The barrel is 71.25 so I'll have to bore it up to 71.5mm to take a Wiseco piston.

The barrel is going to be significantly ported, so keeping it stock is not an issue.  Performance is the issue.

Any advice would be appreciated.

Thanks,
Chris

Title: Re: Best piston for DT2
Post by: cyclegod on April 04, 2009, 11:28:41 am

http://cgi.ebay.com/ebaymotors/WISECO-PISTON-KIT-76-79-YAMAHA-YZ250-DT2-3-MX-060_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ35595QQihZ002QQitemZ120034959116QQrdZ1QQsspagenameZWD1V

These pistons have the full cutaway on the intake side, not the two round holes like the stock piston.

Title: Re: Best piston for DT2
Post by: Lozza on April 04, 2009, 01:35:41 pm

If performance is the issue why use old shitter pistons  ???Change to a YZ 250 130mm rod and it wll open up to use modern KTM 300 pistons.

Title: Re: Best piston for DT2
Post by: ChrisACT on April 04, 2009, 05:00:41 pm

KTM300 STD bore is 72mm.

I'm not sure the liner that's in my barrel will take that.  It's going to be at the limit at 71.5mm.  It's pretty damn thin to my eye even at 71.25mm.

There does seem to be a "big bore" kit for modern YZ250's that starts at 71mm (YZ285).  That might be the shot if they do oversizes from there.

Title: Re: Best piston for DT2
Post by: ChrisACT on April 04, 2009, 09:19:38 pm

This one may be an option.

http://www.denniskirk.com/1/1/170716-wiseco-piston-assembly-431m07125.html (http://www.denniskirk.com/1/1/170716-wiseco-piston-assembly-431m07125.html)

71.25mm for the following engines:

1981 Honda ATC250R
1982 Honda ATC250R
1983 Honda ATC250R
1984 Honda ATC250R
1978 Honda CR250R Elsinore
1979 Honda CR250R Elsinore
1980 Honda CR250R Elsinore

It runs the exact same wrist pin and clips they ship with the DT/MX/YZ250 piston so it'll fit the SE bearing.

(http://www.denniskirk.com/denniskirk/b2c/product_images/d/k/4/600pix/dk431m07000.jpg)

Just a matter of working out what the compression height of it is and then chosing the right conrod.  By zooming into the pic and holding a ruler up to the screen I calculate the compression height to be about 23mm.  So I would probably have to machine a couple of mm off the barrel or run a longer rod and space the barrel.

Another option, anyway.