Athena Big Bore Kit

Athena Big Bore Kit
Athena Big Bore Kit

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

Description See Also: 23 Reviews 142 Questions Fitment
Item #ATH0004

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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
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All Reviews
Twistedthrottlegarage Verified Purchaser
Durability 1/5 Ease of Installation 1/5 Performance 3/5 Power 3/5 Style 3/5
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.

rmz490 Verified Purchaser
Missouri, USA
Durability 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5
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
NC762 Verified Purchaser
Richlands, NC
Durability 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5
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 4/5 Ease of Installation 4/5 Performance 5/5 Power 5/5 Style 4/5
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.

JMReeves Verified Purchaser
Moorpark Ca
Durability 5/5 Ease of Installation 4/5 Performance 3/5 Power 3/5 Style 5/5
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 4/5 Ease of Installation 3/5 Performance 5/5 Power 5/5 Style 4/5
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!!!!!

carpenter197 Verified Purchaser
Pomona NY

milford, nj
Durability 4/5 Performance 4/5 Power 5/5 Style 5/5
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 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5
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 1/5 Ease of Installation 2/5 Performance 1/5 Power 1/5 Style 1/5

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 5/5 Ease of Installation 4/5 Performance 5/5 Power 5/5 Style 5/5
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 3/5 Ease of Installation 5/5 Performance 5/5 Power 5/5

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 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5
Very nice

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

vernal, utah
Durability 4/5 Ease of Installation 3/5 Performance 4/5 Power 5/5 Style 3/5
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 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5

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
yamanick14 Top 1000 Contributor
Bettendorf, Ia
Durability 5/5 Ease of Installation 4/5 Performance 5/5 Power 5/5 Style 4/5
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

See 3 More Reviews
142 Questions
Answered:   136
Not Yet:   6
Location: Ohio, USA
Q: Will the athena 290cc big bore kit make a noticeable difference and is there any thing you have to change to make it run correctly?
19 days ago
Location: Western Massachusetts
Q: Is case boring required on a 2014 crf450r?
1 month 4 days ago
Top 250 Contributor
12 days ago
A: case boring should not be required
Location: OK
Q: Would case boring be required for installation in a 2004 KX65?
1 month 8 days ago
Location: Australia
Q: Hi i was wondering can you get a big boar kit for a 2014 ktm sxf?
1 month 11 days ago
Q: Would i need to beef up the lower any to handle the extra power?
1 month 20 days ago
Wondering if its a good idea for someone who rides hard to put this on a stock lower end. 2006 kx450f
Location: Minnesota
Q: Hi I have a 2012 kx250f and I am planing to get a Athena 290cc big bore kit?
1 month 28 days ago
I was wondering if I would have to buy a new efi or will the stock one work and how would I be able to tune it with out a dyno and also I'm used to carbs I'm not used to efi yet when it comes to tuning? One other thing I am also thinking about getting the pro circuit ti6 full system will this work well with the 290 big bore ?
Location: Kirkland, WA, USA
Q: Athena Big bore Kit on 08 wr250r?
4 months 8 days ago
is there any aditional parts or components needed to make this kit workl on my WR250R? like a ECU or something? I have a PC5 already a FMF can and Powerbomb header.
Location: Perth WA 6000, Australia
Q: With the 144cc kit for yz 125 . does it come with jetting for carby . is there a recommended jetting setting for this kit i?
Over 10 months ago
We are in australia operating at sea level approx atmospheric pressure 101.1 KPA
MotoSport Staff Expert
Over 9 months ago
A: No it would not include jets. 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.
Location: Florida, USA
Q: Re-program ecu for Kxf 450 ?
1 year 1 month 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?
Expert MotoSport Staff
1 year 1 month 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?
1 year 1 month ago
2003 Yamaha YZ 85
MotoSport Staff Expert
1 year 1 month 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
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