Athena Big Bore Kit

Athena Big Bore Kit
Athena Big Bore Kit

$250.99 - $1108.99
14% Off - Save up to $187.00

  • Description
  • 23 Reviews
  • 135 Questions
  • Fitment
Item #ATH0004

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.

The Athena Big Bore kit is the missing source for increasing your motorcycles raw power.

  • The included cylinder is constructed out of aluminum with a nickel-carbide coating to increase durability.
  • The water jets have been widened for a higher flow rate, keeping the cylinder cool.
  • Athena built a reliable cast piston that has been molybdenum-coated for high performance use and extended wear life.
  • Includes a specially designed gasket kit to accommodate the big bore features.
  • Each kit also includes easy-to-follow step-by-step installation instructions.
  • Notes: Some kits will require case boring. Kits for 4-stroke applications do NOT include cylinder head. Image is for display purposes ONLY and may not represent actual product.

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23 Reviews
4.4 out of 5 stars
5 Star   16 4 Star   2 3 Star   2 2 Star   0 1 Star   3
Verified Purchaser
Durability   Ease of Installation   Performance   Power   Style  
Save your money

Get your cylinder machined rather than buy this mass produced one. I dont think the quality is there. I would probably just take a stock 125 and do other mods to it. Not enough gain for the money imo.

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.

Verified Purchaser
Missouri, USA
Durability   Ease of Installation   Performance   Power   Style  
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!!

Athena Big Bore Kit
Athena Big Bore Kit
Verified Purchaser
Richlands, NC
Durability   Ease of Installation   Performance   Power   Style  
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.

San Diego, CA USA
Durability   Ease of Installation   Performance   Power   Style  
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.

Verified Purchaser
Moorpark Ca
Durability   Ease of Installation   Performance   Power   Style  
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.

waipu New Zealand
Durability   Ease of Installation   Performance   Power   Style  
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!!!!!

Verified Purchaser
Pomona NY

milford, nj
Durability   Performance   Power   Style  
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.

Durability   Ease of Installation   Performance   Power   Style  
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..

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.

eastford ct
Makes big power

bigbore kit complete and made my bike haule

Battle Ground, WA
Durability   Ease of Installation   Performance   Power   Style  

i got this for my 06 yz 125 and it was definetly a waist of my money...i had to do a top end every 2 races...and then it ended up being a bottom end...i would not reccomend this to anyone...big waist of time and 134 big bore has alot more power.

Hartfeild, VA
Durability   Ease of Installation   Performance   Power   Style  
Very good

This kit adds huge power. Gave my lacking engine the snap and extra power i needed, it also made it sound better. It costs a little much but i would recommend it to any higher skilled or heavier rider looking for that extra power to rocket out of corners and launch over jumps you normally couldnt make.

Durability   Ease of Installation   Performance   Power  

The Athena big bore kit is an excellent bolt on for power. However.....givin the high end cost for the kit, athena has chosen to provide piston pin clips that are sub standard at best. Do your self a favor and replace the piston pin clips with factory yamaha clips instead. They fit great and will not come out. If you use the Athena clips, run a chance of those coming out and they will.

New Carlisle, IN
Durability   Ease of Installation   Performance   Power   Style  
Very nice

this was a rlly easy instaling it. the performance is rlly nice

vernal, utah
Durability   Ease of Installation   Performance   Power   Style  
Great purchase

the product is it has plenty of power. i installed this kit with hotrods stroker crank. loads of power i can now keep up with 450s off the line then naturally they stomp it in the end. but the weight to power on the trails is so much better dont get worked as bad anymore. the only down fall to the big bore is the heat it now gets so hot u cant leave it idleing for very long. if i had a second chance to increase power again i would go with stage 2 cams and a high compression piston also with the stroker crank. big bore kits arent always the way to go. hope this helps with some future ideas anyone has.

Rio Rancho, NM
Durability   Ease of Installation   Performance   Power   Style  

This kit is amazing! I have it on my TRX450R and I would NEVER go back! Given then only thing stock on mine is the frame, this made the biggest improvement to my bike! I love it! So, if you are looking for MAJOR power gain, this is the way to go!

Athena Big Bore Kit
Top 1000 Contributor
Bettendorf, Ia
Durability   Ease of Installation   Performance   Power   Style  
A Must Have

This kit is a must have. Fast bolt on kit, only about an hour and half. Started first kick. I have over 200 hours on the piston with very little wear. The power increase is amazing.

Yamaha YZ 144

I have a 2006 YZ 125 I installed the 144 kit with no problems just a bit of grinding and the rest is a breeze. No case splitting. This bike is a blast

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135 Questions
Answered:   134
Not Yet:   1
Location: Puyallup, WA, USA
Q: I have a 2009 rmz 250 im looking at the 290 kit?
26 days ago
will my stock head work? do I need to do any case shaving of case? and what would be the best jetting
Location: Florida, USA
Q: Re-program ecu for Kxf 450 ?
3 months 15 days ago
Hi, i have a Kxf 450 2011, do I need correct the fuel injection with this kit? Or come with your own electric ecu extension?
MotoSport Staff Expert
3 months 15 days ago
A: Yes you would need to re-program your bike after installing the Athena Big Bore Kit.
Location: Maine, USA
Q: Can I buy just the piston and rings? my cylinder is fine but need new piston and rings as it has low compression?
3 months 19 days ago
2003 Yamaha YZ 85
Expert MotoSport Staff
3 months 19 days ago
A: The Athena big bore piston can be found below. If the big bore rings are available through one of our suppliers for your bike, we would be happy to order it for you. Please contact one of our sales professionals to inquire about special orders and availability.
Dirt Bike: 1-888-676-8853
Location: Indiana, USA
Q: What size jets do i need to install?
4 months 10 days ago
i have put in a big bor kit athena 163.5 in my sons bike honda 150r 2007 do i need to rejet and what do you sugest i start with thanks mark
MotoSport Staff Expert
4 months 7 days ago
A: There is not a specific setting I could give you for jetting your bike. It would really depend on your location (altitude/temperature) and how your bike is running with the current jetting. Jetting can be very tricky, there isn't one setting that will work everywhere with every bike. I would recommend taking your bike to a local motorcycle dealership’s service department to have your bike properly jetted.
Q: Do I need a new cylinder head?
4 months 22 days ago
Stock cylinder head and case for 04 trx450r work with this kit? And will 93 fuel work?
Expert MotoSport Staff
4 months 4 days ago
A: No, the Athena Big Bore Kit would work with the stock head on your 2004 Honda TRX450R.
Q: Can you run 93 octane gas in this big bore kit for an 03 kx125?
Over 5 months ago
MotoSport Staff Expert
Over 5 months ago
A: High octane race gas would be recommended for the best performance.
Location: California
Q: Do you make a big bore kit for a 2003 KX 100 bike?
Over 5 months ago
I have a 2003 Kx100 that I would like to improve the performance on, but it looks like they make a kit for every bike except mine. I would like to see 125cc or 120cc instead of the 99cc I currently get with mine. But I don't want to go up in size on the frame (as you would get with any 125 bike). Any suggestions would be helpful, thank you...
Expert MotoSport Staff
Over 5 months ago
A: If there is a big bore kit available through one of our suppliers for your bike, we would be happy to order it for you. Please contact one of our sales professionals to inquire about special orders and availability.
Dirt Bike: 1-888-676-8853
Location: Lephalale, South Africa
Q: Looking at getting one for '09 KLX450R.?
Over 6 months ago
I'm from South Africa and will be in the States in February next year. Need to know if everything is included in kit as I'm 3 hours from the closes big town. Bike got hot the other day and now is using water every time I ride. Need some more performance out of it as well. Don't want to break the bank please. Will buy in States because the exchange rate is terrible.
MotoSport Staff Expert
Over 6 months ago
A: The Athena Big Bore Kit for your 2009 Kawasaki KLX 450R includes: Cylinder, piston kit, gaskets, rings, and piston pin.
Also, feel free to give us a call at 888-676-8853 and we would be happy to help you out with your order.
Q: Would any case modification be needed on a 2009 Suzuki RMZ 450?
Over 7 months ago
Expert MotoSport Staff
Over 7 months ago
A: No machining would be needed on your 2009 Suzuki RMZ450. See instructions here:
Q: 2004 YZ 125?
Over 7 months ago
Does this kit come with power valves, gaskets, and everything I would need to rebuild an entire top end?
MotoSport Staff Expert
Over 7 months ago
A: Yes the Athena Big Bore Kit for your 2004 Yamaha YZ125 would include:
- Aluminium cylinder with nickel-carbide coating, designed with wider water jackets;
- Specially designed high performance, hard anodised power valves (will not fit stock cylinder);
- Specially designed high performance cast-lite flat top piston kit;
- Athena performance top end gasket kit, including required seals and hardware
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