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Wiseco Piston Kit

Fits Your MachineDisplaying parts for your 2004 YAMAHA YZ250
Wiseco Piston Kit Pro-Lite Standard (66.4 mm)
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Wiseco Piston Kit Pro-Lite Standard (66.4 mm)

Fits: 2004 YAMAHA YZ250

Part# 1038400193 | Mfg Part# 804M06640

Our Price: $99.95

MSRP: $129.00 - You save $29.05 (23% off)

Get $2.00 in Quick Cash

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5+ In-Stock

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Additional Videos

How To - Rebuild A Top End

How To - Check Piston Ring End Gap

How To - Four-Stroke Top End Rebuild (Part 2)

How To - Rebuild Motorcycle or ATV Top End (Part 2)

How To - Hone A Cylinder

How To - Rebuild Motorcycle or ATV Top End (Part 1)

How To Measure Your Dirt Bike's Piston To Cylinder Wall Clearance

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Details

  • Lightweight forging for instant throttle response and maximum torque .
  • Computer engineered piston skirt profiles provide minimal cylinder wall friction .
  • Piston kit includes piston, rings, wristpin and circlips.
WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov

Wiseco Piston Kit Reviews

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4.8 / 5.0
514 Reviews
5 Stars
4 Stars
3 Stars
2 Stars
1 Star
451
51
6
4
2
Value
4.8 / 5
Durability
4.8 / 5
Fitment
4.9 / 5
Performance
4.9 / 5
Recommend it?
Yes (221)
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
2 stroke rebuild. great option
This is the third time i have used this piston on a rebuild. None of these have failed to perform. Each was replaced before it was needed. Great choice for replacing the OEM product.

-m-2004 SUZUKI RM250--
May 11, 2020
OP , FL, US
Age: 45-64
Gender:
Male
Weight:
191 - 220 lbs.
Height:
5'10 - 6'0
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
Great replacement for OEM
The Wiseco piston was a great replacement to the OEM. The piston was fairly priced, the installation instructions were thorough and fit was spot on. Additionally, the Wiseco piston was quieter than previous OEM replacement. I highly recommend.

-m-2012 KAWASAKI KX450F--
April 22, 2020
Kechi, KS, US
Age: 45-64
Purchased
1 month ago
Gender:
Male
Weight:
161 - 190 lbs.
Height:
5'7 - 5'9
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
Brap brap
Most reliable piston you can get

-m-2002 YAMAHA YZ250--
April 16, 2020
Coarsegold, CA, US
Age: 15-24
Purchased
1 month ago
Gender:
Male
Weight:
161 - 190 lbs.
Height:
6'1 - 6'3
Fitment
5 / 5
Recommend it?
Yes
great service!
Perfect fit. Fast delivery. Bike sounds great!

-m-1999 YAMAHA YZ125--
April 15, 2020
Millinocket, ME, US
Age: 45-64
Purchased
2 months ago
Gender:
Male
Weight:
191 - 220 lbs.
Height:
5'10 - 6'0
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
2008 CRF450R
My first piston swap. Follow instructions, get the right tools, and you'll be right as rain. The piston seems to be of good quality and everything works as expected after getting the bike back together. Very happy with the purchase and happy I decided to swap it out.

-m-2008 HONDA CRF450R--
User submitted image
Added Apr 11, 2020
April 11, 2020
Chattaroy, WA, US
Purchased
2 months ago
Good product
Would think a new pistom kit would come with a new wrist pin bearing. Other than that, good product.
April 10, 2020
Kerwood, ON, CA
Purchased
1 month ago
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
Installed, broke in and no problems!
This is the first rebuild I've done to a 4 stroke and other than getting everything in time and moving the head out of the way it wasn't that hard. Everything fit just fine and assembled no problem. Bike has noticeably higher compression when kicking and sounds a little deeper (probably because the old rings were pretty worn. I heat cycled once for around 3 mins. then shutoff and restarted rode lightly around the block in 2nd not really getting on it hard, then let it cool. Then took it for another light 2nd gear ride and let it cool completely. After that rode as usual and everything seems very good. I recommend taking your time with this measuring your cylinder and making sure your valves are good and you shouldn't have any problems and this in my opinion is not as hard as people make it out to be. Also I used Rocky Mountain's rebuild video and the actual service manual and it had everything covered and no questions unanswered. Overall I'm happy with the product and would recommend to anyone rebuilding their bike.

-m-2005 HONDA CRF450R--
User submitted image
User submitted image
April 6, 2020
Cincinnati, OH, US
Age: 25-44
Purchased
2 months ago
Gender:
Male
Weight:
191 - 220 lbs.
Height:
5'10 - 6'0
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
GREAT PRODUCT
Excellent product totally worth the price and long lasting. Would definitely recommend it
April 4, 2020
Fayetteville, NC, US
Purchased
4 months ago
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
High Performance, with peace of mind
I have used Wiseco pistons in many powersport toys, I have also ran them in small block ford builds many times. The forged pistons work great and I have thrown everything at them with no failures. I have ran high compression NA builds, no problems. I have ran lower compression, high boost (20+ psi) and again no problems. I have also ran them in high compression N2O builds while spraying the bags off them and you guessed it, not a single hitch. It does help however to know how much timing to run with said power adder or compression ratio, but they have always been solid performers for me. Dished, Flat top, or Domes versions have always just flat out performed, if your looking for a quality, durable, and performing piston choose wiseco, they just flat out work!!

-m-2012 POLARIS RANGER RZR XP 900--
April 2, 2020
Salyersville, KY, US
Age: 25-44
Gender:
Male
Weight:
191 - 220 lbs.
Height:
5'10 - 6'0
Value
5 / 5
Durability
5 / 5
Fitment
5 / 5
Performance
5 / 5
Recommend it?
Yes
Happy
Always buy wiseco pistons. They are a good product and have never let me down
-m-2005 KTM 125 SX--
March 21, 2020
Lapeer , MI, US
Age: 25-44
Purchased
3 months ago
Gender:
Male
Show more
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Browse 83 questions Browse 83 questions and 176 answers
Does this kit include all the gaskets needed as well as the piston?
Brandon P on Mar 26, 2017
BEST ANSWER: Just piston, rings and circlips. You will need to buy a separate gasket kit. I would recommend ordering and replacing the wrist pin also while it's tore down.
Does this kit come with all the gaskets for the rebuild?
A shopper on Mar 29, 2019
BEST ANSWER: No gaskets at all. You’ll even need to buy the top end bearing with this or any piston kit.
Wiseco Pro Lite piston kits have been the most durable for me and vibrate MUCH less late in the season.
From my experience, the Cometic steel/fiber complete gasket kits are the best by far. The steel layer prevents tearing if you ever need to remove a cover or head. They’ve cost just a little more and you’re life will be easier ...really.

Hope this helps.

Best,
John
Does this kit also come with the piston pin bearing?
A shopper on Dec 4, 2017
BEST ANSWER: No, it doesn't. The Pro-X bearing is Japanese made, good price. I always use them.
why doesn't the top of this piston have the 4 circles?
Rudy P on Sep 13, 2017
BEST ANSWER: Rudy,
It is just Weisco's design. Other manufacturers try different things to make their product different or better. It's a great piston. Weisco teflon Coates their pistons for extra protection. I have never had one not make it to the next overhaul.
So it doesn’t come with a wristpin? It says its included in the details
Tyler B on Jun 19, 2018
BEST ANSWER: Yes..Wiseco piston kits include wrist pin, wrist pin clips and ring set.
I have a yz450f 2006 will I have to run higher than 91 octane or will that work?
A shopper on Mar 5, 2020
BEST ANSWER: may need to make some jetting refinements. biggest thing is going to be making sure it is up to temp before opening it up... i've had good luck with mine on a kx500
Can this be used in an AMA stock class race?
A shopper on May 7, 2018
BEST ANSWER: Yes as long as you don’t change the displacement or stroke of engine you are in compliance.
My Piston only has one clip , and this one has two clips, is there any difference between one clip and two clips?
Sebastian C on Apr 4, 2018
BEST ANSWER: Your piston should have a clip on both sides just like the piston you will receive. There is a little groove on each side of the piston and you have to remove one clip to get the wrist pin off of the rod. I always put one in the piston before I put the piston back on the rod so I only have to put one clip back in once the piston
is in the machine.
Do the piston rings come pre gapped or is it likely I'll have to file them?
ROY D on Mar 11, 2020
BEST ANSWER: You should always check ring gap. Most of time you will be okay. It’s important that you check services manual for specks.
My compression ratio is 12:0:1. This piston is 12:4:1 is this a higher compression piston?
AARON H on Nov 13, 2018
BEST ANSWER: Yes, it is slightly higher but, not outrageously higher. You will need to use higher octane fuel but it will give you better performance overall. If you are already using the highest octane fuel you can buy you should be OK with no change. Your bike should run great. Higher compression in a two stroke is generally a good thing.
just to make sure I'm getting the right piston for my cylinder , when the description states "standard " (xx.xmm) does that mean the piston is that size or thats the piston for that bore? i caliperd my bore and its 66.4mm
Michael guillen on Jan 19, 2018
BEST ANSWER: It means it is for that bore or it is a standard size cylinder hasn’t been touched it is stock
If you have re sleeved the cylinder with a steel sleeve will the rings work?
SAMUEL M on Dec 24, 2017
BEST ANSWER: I apologize, I don’t have an answer to that. I assume so as long as the bore is correct.
Is this piston a single ring or double ring! The picture shows single, but the manufacturer number is a double ring. So what did you get when you bought this?
A shopper on May 12, 2020
BEST ANSWER: I received a single ring which was proper for my bike.
How much will this increase my compression by. Installing it on 2000 KTM 125SX?
Gerald B on May 2, 2020
BEST ANSWER: It will just depend on how low you’re compression is from worn out rings. It’s not a high compression piston it should be around stock compression from the factory with this installed
Will this fit A cylinders?
Anthony W on Apr 22, 2020
BEST ANSWER: I would be happy to look into this for you. What is the year, make and model for your machine?
Do the rings come pre gapped??
Anthony W on Apr 17, 2020
BEST ANSWER: Basically, yes, it should work out of the box. It IS ALWAYS a good idea to double check before completing the build.
For chrome plated cylinder?
A shopper on May 24, 2019
BEST ANSWER: yes for all cylinders all my dirt bikes have chrome plated cylinders and i use this piston.
Is the actually bore of this piston 54mm or is it 53.xx?
Tyler B on Jun 21, 2018
BEST ANSWER: Check wiseco website for available sizes.They make a standard size and sometimes up to 3 or 4 oversized pistons.Measure bore in 4 places with Inside micrometer or telesopic gauges first and then check for available sizes.
ordering it for my 16 rmz 250 is this the high compression piston ?
chris t on Jun 2, 2018
BEST ANSWER: The one I ordered was the wiseco but it was for my son's cr85 which was the high compression..if this is the same but different size I would assume it is high compression.
How often should i replace a piston?
A shopper on Apr 5, 2018
BEST ANSWER: it really depends on how the bike is being used; small bore with a fast kid racing 8hrs +/-, 250 race mode 25hrs,250 old slow guy 50-100hrs.
If the piston in my cr125 was 53.94mm and i'm putting in a wiseco 54mm, will it still work in the cylinder?
James L on Feb 26, 2018
BEST ANSWER: Where did you're measurement come from?53.94m.and yes it would b .06 mm different which is super close run it
89 YZ 250 - Bought new Wiseco piston - Prolite .020 (68.5MM), for 1989 YZ250WR. Bike has original bore (68mm - cast iron sleeve) - no score marks. Ring end gap was excessive on old rings, but no blow by on stock piston. Had 170 compression. Bike was getting hard to start. Was told to bore to next size up so that is why bought this piston. Took to machine shop today with new piston. Also brought cylinder head with me and they said that they do not need the cylinder head? I thought that the inside radius of the cylinder head needed to be opened up to accommodate the new piston/bore size? Also asked if they would champher/round edges on all ports inside cylinder after bore? They said no need to? Also wondering if power valve will need to be shaved? Anyone have any answers? Any suggestions?
Brian W on Jan 2, 2018
BEST ANSWER: Your machine shop is correct, the piston does not protrud the top of the cylinder. Also correct on rounding the edges, no need to. As far as the power valve goes I would check on reassembly.
will this fit a 2001 cr80? stock bore
james b on Sep 14, 2017
BEST ANSWER: Yes, the standard 47mm pro-lite piston is meant as a stock bore replacement with unmatched reliability from wiseco's race proven pistons
I have a 89 yz 80 the cylinder is 49mm what size piston will fit. The 48.5mm or no?
Chris T on Sep 5, 2017
BEST ANSWER: As long as its a standard bore and hasnt been altered by replating or sleeving the piston that wiseco reccomends will be the correct size.
I have a 2016 yz250 x

I want to rebuild top end over the winter. I want to go bigger.

Where do I see a chart of sizes which are available so I can see how big I can go?
A shopper on Sep 5, 2017
BEST ANSWER: On a 2016 the only way to go bigger is to buy the big bore kit. You can't bore the factory cylinder without putting a sleeve in it which would cost the same as the big bore kit with a new cylinder
it's for 2 times?
A shopper on Jun 20, 2017
BEST ANSWER: That's a vague question at best. But it is the second oversize bore from the stock piston if that's what u mean
Does this piston come coated or plain? Does it come with a TiN coated ring or plain ring?
Alexander H on Jun 15, 2017
BEST ANSWER: Mine was plain got it for my 2001 kx 125.
For a 2007 Yamaha yz 125 there are 4 different piston sizes to choose from. This piston only has one size when I enter my bike. Will it work or should I order OE?
Charles B on Jun 10, 2017
BEST ANSWER: You should alway check the piston size that came out of you machine to insure proper fit although most bikes have the metric size it is easy to figure out if it is a 65mm piston and you want it .020 over then it is 65.5 or to make it 66mm then it’s .040 over std size
Will this fit my 04 trx450 bored to a 96mm.?
armando s on Apr 4, 2017
BEST ANSWER: Select the correct size of piston upon checkout. Be aware must hone cylinder before installation of this piston.
Will this work good for 08 kfx450r rebuild? Any boring needed to be done?
Michael F on Mar 14, 2017
BEST ANSWER: As long as the cylinder is standard bore and the plating is good, this piston will work great in your bike. Always do a light hone to the cylinder whenever doing a piston replacement. It helps the rings seat and wear correctly. These pistons are one of the best on the market. I hope this helps.
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