Free 3-Day Express Shipping on Orders Over $99*

Shopping for Parts? Select Your Bike: Manage Saved Bikes Manage Saved Bikes Dirt Bike Dirt Bike Sport ATV Utility ATV Sportbike Cruiser Make Year Model

Athena Big Bore Kit

Retail: $291.99 - $1,295.99
$269.99 - $1169.99
Please Select a Bike:
Dirt Bike Dirt Bike Sport ATV Make Year Model
 
It appears you may have cookies turned off in your web browser, or are using a browser that does not support cookies. You must accept cookies to use our site. For questions call us at 1-888-676-8853.

You may also like

Athena Big Bore Piston - Athena Big Bore Kit
$79.99 - $228.99

Hotcams Camshaft - Stage 2 - Athena Big Bore Kit
$53.77 - $259.99

Athena Big Bore Gaskets - Athena Big Bore Kit
$18.99 - $112.99

Athena Big Bore Kit

Product Description

Athena offers a wide range of cylinder kits for scooters and motorcycles with diameters and portings completely re-designed as original spare parts and / or specific boost to be used on tracks. In particular, racing kits consist of lighter pistons with a flat head, special portings, exhaust bridge, and a new cylinder head designed to increase the compression ratio and improve internal combustion. For some models Athena also supplies special long stroke racing kits complete with crankshafts and reinforced connecting rods.

  • Increase to 280 cc.
  • Suitable for off-road.
  • Includes: Aluminum cylinder, 79.97 mm piston kit, full gasket kit, and piston rings.
  • Customer Reviews
  • Ask an Expert
  • Also Offered For
(22)
4.6 out of 5 stars
5 star   16
4 star   2
3 star   2
2 star 0
1 star   2
1-10 of 22
Overall
Great Bark

I have 2 2004 CRFs, one stock and one big bore. Big difference in power and really aggressive bark. Much more torque on hand. You have to have intake valves on spec to start the extra displacement. I may go for kibblewhite valves to keep the compression over time.

Overall
Durability
Ease of Installation
Performance
Power
Style
Verified Purchaser
Location: Missouri, USA
Great item!..check your gaskets..

installed 4 of these kits. last kit on kx450. finished install. warmed up. cooled down. warm up. engine was quite and responsive. then I see that my engine oil is milky.. tear down. not fun the second time!! found small piece of gasket flash cut from coolant passage in center of the 3 piece head gasket. in the area between oil galley hole and coolant. see pics. contacted motosport and they helped me out and sent a replacment gasket set at no charge!!!. great customer service. replaced head gasket and ready to go!!! so check you gasket. the head gasket is a 3 piece riveted assy. just pull it open and inspect before installing.. thanks motosport!!

Overall
Durability
Ease of Installation
Performance
Power
Style
Verified Purchaser
Location: Richlands, NC
Awesome Big Bore Kit

This was a good price and excellent investment. Put it in a CRF150RB, the power range was increased all the way around, low, mid and high. Be aware that you will need to run at least 96 octane fuel with the big bore kit.

Overall
Durability
Ease of Installation
Performance
Power
Style
Location: San Diego, CA USA
Use circa clips provided

Installed on a YZ250F. Loads of power. Was able to keep up with 450s. Easy to install. Use the circa clips provided by Athena. I made the dumb mistake by listening to a earlier review by using stock circa clips but they came out and ruined my cylinder and piston. Use Athena's. They do extensive R&D with their products to include their clips. Wasn't Athena's fault at all. All my own. Got the new (discounted) kit in there and I'm back to full power. Of course do a valve adjustment with the swap for optimal power. Now I do have hot cams so my power is extensive.

Overall
Durability
Ease of Installation
Performance
Power
Style
Verified Purchaser
Location: Moorpark Ca
Gear head

I have used the Athena kit before. The quality is the best. It does require machining of the engine case to work properly. To do it right you must split the engine cases. The performance and reliability is great. To get the most performance from the kit I used an FMF Fatty pipe and powercore 2 silencer. Jetting the carb a lot richer is a must for reliability. Installation by a qualified experienced mechanic or gear head is a must for good results.

Overall
Durability
Ease of Installation
Performance
Power
Style
Location: waipu New Zealand
For experinced rider!

the athena 144 kit is great! adds heaps of mid range 2 the bike and still pulls up top. However good mechanical knowledge is needed for the installation and if you cant keep your 125 on the pipe dont bother. Time with your butt in the saddle will give you far beter advantage over your competion than this kit! cheers!!!!!

Overall
Verified Purchaser
Location: Pomona NY

Overall
Durability
Performance
Power
Style
Location: milford, nj
Awesome power

this kit is great i have it on my 07kx250f it gives you tons of power. you may need to do a few other things so the bike runs right though, i had to jet mine, a bigger bowl on the carb, loudmouth intake and some fine adjustments to keep up with it. drd exhaust helped too. but once you iron out any kinks it is unreal, my friend as a 490 kit in his rmz450 and i stick with him on starts. it also runs really hot i had to get a boyesen high flow water pump to keep it cooler. best if you dont let it idle or get too hot if you stall it it will be a rough time kicking it over again.

Overall
Durability
Ease of Installation
Performance
Power
Style
Location: Florida
Athena Kit...

Bought the Athena kit as a base to start a stroker build on my '07 LTZ 400. The Athena kits are really high quality, and have been around a long time. You will not be disappointed..

Overall
Location: Troutdale, OR
Athena 290cc Big Bore Kit

Nothing but problems with my new bike since installing the big bore kit. MotoSport doesn't tell you, but when purchasing this kit, you must also then spend an additional $500 in purchasing a new black box, as the stock one isn't compatible with the 290cc kit. Had I known this, I wouldn't have purchased the BigBore Kit.

1-10 of 22
Total Questions (88)
Questions with answers:
  87
Questions without answers:
  1
1-10 of 88
RYDEL2262 6 days 8 hours ago Location: Canada
Stock CDI work with kit?
2006 KTM250sxf with the 280cc Athena big bore kit installed, and proper carburetor tuning, will the stock CDI be efficient to run the bike properly ? (proper ignition, etc)
Expert MotoSport Staff
6 days ago Location: Portland, OR, USA
You should not have any issues running your stock CDI box with this Athena Big Bore kit. Going with an upgraded CDI box would not be a bad idea but it is not required for this kit specifically.
LeoDaltin 9 days 12 hours ago Location: Brazil
I have here in Brazil, a YZ 125 of 1999. Want to know if this kit fits this bike?
Expert MotoSport Staff
3 days 1 hour ago Location: Portland, OR, USA
Yes, the Athena Big Bore Kit is made to fit your 1999 Yamaha YZ125. Just be sure to correctly select the Year/Make/Model of your bike before ordering so we can be sure to send you the correct big bore kit for your bike.
Rafi 25 days ago Location: ISRAEL
GasGas EC 125 piston kit required?
Looking for an Athena piston kit for a GasGas EC 125 2013 model. Also am interested in a Big Bore complete kit for the same bike. Thanks
Expert MotoSport Staff
25 days ago Location: Portland, OR, USA
This kit is specific for the Yamaha YZ125 or the Kawasaki KX125. Unfortunately, we do not carry any pistons for GasGas Motorcycles.
Jordan 1 month 12 days ago Location: Lemont
What else needs to be done to a 2012 yz250f for this big bore to run correctly?
Like do you need to run a higher octane? New cams? bigger intake?
Expert MotoSport Staff
1 month 9 days ago Location: Portland, OR, USA
Athena doesn't specify that any extra items are required of that you would need to run a higher octane fuel with this big bore kit. It should be able to be installed on a stock engine and be ready to go! Here is a link to the Athena Technical Document on this kit for your Yamaha YZ250F: http://www.athenaparts.com/files/pdfs/P400485100026_EN.pdf
madbiker1414 1 month 18 days ago Location: Pottstown, PA, USA
Jeting?
I just bought the 105 kit for my yz85 and just bought the Boyesen Rad Valve. But I was wondering what jet to use because they both call for different jets.? Thanks Connor.
Expert MotoSport Staff
1 month 11 days ago Location: Portland, OR, USA
I would not have a specific jet number I could give you as it would depend mainly on your location (altitude and temperature). It's would be nearly impossible for me to correctly give you jetting specs without knowing what your current jetting specs are and how your bike is running with those settings. Jetting can be very technical and tricky. If you have not had much experience with it I would recommend finding a mechanic to help you properly tune your carburetor.
Geo626 2 months 20 days ago
Can u run gas from the gas station or do we need that racing gas ???
Expert MotoSport Staff
2 months 20 days ago Location: Portland, OR, USA
Athena's Technical Data on this Big Bore Kit does not specify that you are required to run race gas with this big bore kit. I would not recommend running any less that 92 octane pump gas in your bike with this kit though. ( Athena Technical Data: http://www.athenaparts.com/files/pdfs/P400485100030.pdf )
madbiker1414 2 months 21 days ago Location: Pottstown, PA, USA
Horsepower?
My yz85 pulls about 18 horsepower after I put this on what will it pull.
Expert MotoSport Staff
2 months 20 days ago Location: Portland, OR, USA
According to Athena's Specifications on this kit the horsepower at the Rear Wheel with the 105cc kit (OEM exhaust installed) would be approximately 22 Horsepower. With an aftermarket exhaust you will likely have 24 horsepower at the rear wheel.
quadracer 2 months 29 days ago
What is the compression on this kit?
06 yfz450
Expert MotoSport Staff
2 months 28 days ago Location: Portland, OR, USA
According to Athena's technical information on this the compression would be 12,4:1 [ http://www.athenaparts.com/files/pdfs/P400485100021.pdf ] [ http://www.athenaparts.com/eng/kits/view/7494/cylinder-kit-o-98 ]
jimmy 3 months 14 days ago
What accessories go with it?
Expert MotoSport Staff
3 months 5 days ago Location: Portland, OR, USA
This kit would come with everything you need to turn your 2002 Kawasaki KX65 into an 80cc big bore. I might recommend looking into an aftermarket pipe and silencer set up for addition increase in performance with this kit.
mxgarrett 4 months 26 days ago Location: springfield, va
Stock CDI?
I have a 2012 kx 250f. Will this kit work with a stock CDI?
MotoSport Staff
4 months 26 days ago Location: Portland, OR, USA
For the bike to run properly the fuel system will need to be re-mapped. If the fuel mapping is stock you will need to purchase a tuner to correct the EFI mapping.
1-10 of 88

Dirt Bike


Honda

Honda CRF150R
Honda CRF150R Big Wheel
Honda CRF250R

Honda CRF250X
Honda CRF450R

Honda CRF450X

Kawasaki

Kawasaki KLX110
Kawasaki KLX400R
Kawasaki KLX400SR
Kawasaki KLX450R
Kawasaki KX125

Kawasaki KX250F
Kawasaki KX450F

Kawasaki KX65

KTM

KTM 250SXF
KTM 250XCF

KTM 250XCFW
KTM 65SX

KTM 65XC

Suzuki

Suzuki DRZ110
Suzuki DRZ400E
Suzuki DRZ400S

Suzuki DRZ400SM
Suzuki RMZ250

Suzuki RMZ450

Yamaha

Yamaha WR250F
Yamaha WR250R (DUAL SPORT)
Yamaha WR250X (SUPERMOTO)
Yamaha WR450F
Yamaha YZ125

Yamaha YZ250
Yamaha YZ250F

Yamaha YZ450F
Yamaha YZ85

ATV


Arctic Cat

Arctic Cat DVX400

Honda

Honda TRX450R (ELECTRIC START)

Honda TRX450R (KICK START)

Kawasaki

Kawasaki KFX400

Suzuki

Suzuki LT-R450
Suzuki LTZ400

Yamaha

Yamaha YFZ450

Be Informed

Be Confident

Part of the Backcountry Family:
Copyright © 2004 - 2014 MotoSport, Inc. All Rights Reserved. Selected content copyright and trademark respective companies, used with permission.