Pistons

General forum on engines, transmissions, gearing and modifications to each

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Dubsey
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Pistons

#1 Post by Dubsey » Tue Nov 07, 2017 7:06 pm

What pistons are people using/available

Going to be hard track use
Mediocrity is a sin !

Stinke
Posts: 85
Joined: Fri Nov 30, 2007 5:07 am
Location: Sweden, Borgeby

Re: Pistons

#2 Post by Stinke » Wed Nov 08, 2017 5:41 pm

Hi, running the Yambits Mitaka. Rebuilded my engine 2 years ago, on standard bore with fresh hone and 4 new pistons.
It has mild porting, milled heads, Jollymotos, Keihin 28, zeeltronic don't drive much, but hard.
Very happy with the pistons and the price is good I think.

/ Stinke
2 x rd 500 -84
Rd 350 ypvs -84
Rd 250 -74
Kh400, t20

The best of swedish metal: https://youtu.be/gkBt7yLXyDk" onclick="window.open(this.href);return false;

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WVWRZ500N
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Re: Pistons

#3 Post by WVWRZ500N » Wed Nov 08, 2017 6:42 pm

This is an old post I made several years ago about Wiseco piston choices. I use the 236 pistons. You may find it useful. There are other brands of piston available besides these. Depends on final use and they all require a good machinist to set them up. And don't let the arched opening bother you in using them on the upper cylinders, no adverse effects at all.

Good questions. You have three choices from Wiseco, if you are over the bore limit for factory replacement pistons.

1. Piston 236MOXXXX Yamaha AT,IT,MX,DT and YT125s (Arch intake Opening)
Pros: Durable and two rings for better longevity in compression, also a good match to the stock squishband for street riding performance, head re-work required to match for good race performance.
Cons: HEAVY, 152gr in standard size and up to 172gr in .080" oversize, approximately +5gr per oversize needed, needs serious lightening.

2. Piston 679MOXXXX Yamaha DTR,TDR125s (Minor Arch Intake Opening)
Pros: Durable and two rings for better longevity in compression, taller from wrist pin to crown edge by .005" which can be beneficial when acquiring proper squish clearance.
Cons: Still a bit on the heavy side even as a Prolite, 143gr in the standard size and up to 167gr in the .080" oversize. Approximately +6gr per oversize needed. Arch not well suited to the upper cylinders.

3. Piston 521MOXXXX 1985 YZ125 (Arch Intake Opening)
Pros: Lightest of the three although not a Prolite, 131gr in standard up to 156.5gr for the .080" oversize, approximately +6.5gr per oversize needed. Shorter skirt by about 8mm, still well suited for the 500 and widely used by many rebuilders and perf. tuners as a replacement.
Cons: Single ring, worst example for compression loss, Wiseco factory ring pin limits the modification of boost and sub ports due to location.
So with that you have some choices, there are other manufactures as well of which I am not at all familiar, it really comes down to what you are trying to do with the bike. If your handy or have a real good machinest you could choose any of them and modify them to suite or just go with the one you find most appealing to your application.

Remember, whoever you have do the bore and hone must follow Wiseco's clearance specs or you WILL sieze them. Wiseco has a bad rap from this very thing as the rebuilders set the tolerances for the OEM pistons instead and it always leads to failure.

Good luck, drop me an email and let me know what you plan to do.
Regards,
Bill Wilson
Wilson Performance
Lee's Summit, MO
http://www.wilsonperformance.net
Member RZ500 Owners Group #573
816-377-3185
WVWRZ500N@aol.com

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