Shopping CartCLOSE
  • Your cart is empty.
Athena Big Bore Kit
Athena Big Bore Kit

$252.99 - $1123.99
15% Off - Save up to $197.96

Description See Also: 7 Reviews 89 Questions Fitment Part Numbers
Item #ATH0004

Read More
7 Reviews
4.4 out of 5 stars
5 Star   6 4 Star   0 3 Star   0 2 Star   0 1 Star   1
Write a Review

Write your review and you'll automatically be entered in our monthly drawing. Include an image or video to DOUBLE your chances to win!

Write Your Review Write a review to win $500
All Reviews
Verified Purchaser
Tri cities Washington
Durability 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5
Awesome kit

Great kit really easy to install, I put it on my 07 CRF250R along wth a complete lower end rebuild, and stage 2 hotcam and it rips! Took some of the top end speed out so you’ll need a rear sprocket with less teeth good kit so far and seems high quality

Verified Purchaser
Santa Rosa, Ca.
Durability 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5

Fun to install and what an incredible change in performance!!!! The sound of the engine is a much deeper tone. Great for someone who doesn't necessarily know alot about engines. Follow the instructions and feel like you own your engine and its capability. It's very enpowering.

Verified Purchaser
Murphysboro, IL
Ease of Installation 5/5 Performance 5/5 Power 5/5
More power

I have recently installed the BBK and the stage 2 intake and exhaust cams. The power gain is amazing. My ‘08 DRZ 400sm had 33,000 miles on it. Instead of reringing it I dropped some coin and went with BBK and cams. I’m so happy I did. Installation was easy, I have almost 500 miles on the kit so far with no problems. I just recieved my fcr 39 and will be installing it tomorrow. This thing has really come alive with BBK and cams, can’t wait to see what the fcr does

South Carolina, USA
Durability 5/5 Ease of Installation 5/5 Performance 5/5 Power 5/5 Style 5/5

This kit absolutely made my bike stomp all competition track and trail once paired with a ported racing cylinder head and the correct jets. This is money well spent. The last test the bike was clocked at 128mph on stock sprockets. Kudos to Athens and a list of other upgrades

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.


Awesome part. Gave me alot more horsepower and a definately noticable difference in the corners. Overall worth every penny.

89 Questions
Answered:   83
Not Yet:   6
Q: What's the recommended way to deglaze this cylinder when doing a new piston
26 days ago
Top 10
26 days ago
A: For standard engine break in procedures, it is best to consult your owner's manual and go with the manufacturer recommendations.
Count Craigula
Q: 2018 yz125, Does the kit come with jetting recommendations? Don't want to burn it up right off the bat.
1 month 22 days ago
Top 10
1 month 22 days ago
A: It does not come with reccomendations in the kit, however Athena does have a guide available on their website that may help you out!
Q: This will bolt on to a 2017 yz 250?
1 month 28 days ago
Top 10
1 month 28 days ago
A: I am showing if you profile your machine correctly, yes, we do offer this for the 2017 YZ250.
Q: If i were too put this on a 13 KX450F do i have too run special gas or pump gas? 
2 months 10 days ago
Top 10
2 months 10 days ago
A: You can use Premium pump gas.
Q: Does it fit to suzuki gixxer 155?
2 months 26 days ago
Top 10
2 months 26 days ago
A: This is not sold for that model of suzuki
Q: Do you have to install a stroker kit? 
3 months 16 days ago
Top 10
3 months 16 days ago
A: It is not always necessary. However I would recommend inspecting the crankshaft bearings for any play on your connecting rod arm. If you need any other technical help you can chat, email or call Motosport at 1-888-676-8853
Q: Do you have a kit for a cr85r
3 months 18 days ago
Top 10
3 months 18 days ago
A: We may or may not have a kit for your CR85, it depends on the year of the bike as well. Be sure to profile your bike into the page correctly, to show parts that fit your machine specifically.
Q: The big bore kit for yz250 2 stroke work good for yz250 X, or i am going to have a yz290 for MX. thanks
3 months 26 days ago
Top 10
3 months 26 days ago
A: Yes this will work for the YZ250X model. Since you are only changing the piston size the rest of the bikes settings will still be for the X model.
Q: On a 2006 YZ125, will there need to be any case boring, or is this kit going to be a bolt up and go?
4 months 10 days ago
Top 25
4 months 10 days ago
A: Some kits will require case boring it depends on your machine
Smoke me mx
Q: Do you have a 2003 RM 144 kit?
4 months 23 days ago
Top 10
4 months 23 days ago
A: At this time I am currently not showing that I have anything of that sort for you.
1 - 10 of 89
See all bikes that this part fits...
See Fitments
# Part Numbers
Product Variant Manufacturer Part #
164cc P400210100023
280cc P400210100033
280cc P400210100009
490cc P400210100030
490cc P400210100001
490cc P400210100021
130cc N/A
280cc P400270100004
280cc P400270100007
80cc P400270100002
144cc P400250100011
80cc P400250100007
290cc P400250100013
290cc P400250100018
490cc P400250100003
490cc P400250100015
490cc P400510100008
435cc P400510100002
290cc P400510100004
290cc P400510100010
290cc P400510100020
490cc P400510100006
490cc P400510100012
490cc P400510100016
480cc P400210100007
490cc P400210100017
290cc P400485100032
478cc P400485100016
144cc P400485100030
144cc P400485100029
293cc P400485100042
105cc P400485100038
290cc P400485100026
290cc P400485100012
478cc P400485100021
478cc P400485100014