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Athena Big Bore Kit
Athena Big Bore Kit

$268.99 - $1070.99
19% Off - Save up to $250.96
Rating: 4.3 out of 5 stars

Quantity

Item #ATH0004

11 Reviews

4.3 out of 5 stars
  •   9 reviews
  •   0 reviews
  •   0 reviews
  •   0 reviews
  •   2 reviews

All Reviews

yankee

Verified Purchaser
Over 6 months ago lexington sc
5 out of 5 stars
Durability
5/5
Ease of Installation
5/5
Performance
5/5
Power
5/5
Style
5/5
Easy install

Working on jetting, but it's running strong

TODD

Verified Purchaser
Over 7 months ago Slidell, La
5 out of 5 stars
Durability
5/5
Ease of Installation
5/5
Performance
5/5
Power
5/5
Style
5/5
Improved power

I installed the 290cc big bore kit on my YZ250F along with the hot cams stage1 cams. Nice improvement in the low to mid range power with no loss on top end. Allows me to be even lazier in the trails with plenty of roll on torque, LOL. Some tuning advise after installing this kit you will need to go down in jet size or it will be too rich. Yeah I know just the opposite of what you would think.

Markh

Verified Purchaser
Over 10 months ago
1 out of 5 stars
Durability
1/5
Ease of Installation
3/5
Performance
2/5
Power
3/5
Style
3/5
Sheared piston pin clip

Installed this after 5 hours the pin found it's way out the side of the piston destroying the piston and cylinder. Faulty hardware

Andy

Verified Purchaser
1 year ago Norcal
5 out of 5 stars
Durability
5/5
Ease of Installation
5/5
Performance
5/5
Power
5/5
Style
5/5
Perfect improvement!

My son needed just a little extra out of his yz85, so 3 years ago I upgraded his top end to the 105cc big bore, and just like that he was back in the game, keeping up with the bigger bikes. Didn’t have a single problem with installation and even picked up extra set of rings and it lasted almost 3 seasons. Also no machining required.

Roger21

Verified Purchaser
1 year 8 months ago Tri cities Washington
5 out of 5 stars
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

Jerbo

Verified Purchaser
1 year 9 months ago Santa Rosa, Ca.
5 out of 5 stars
Durability
5/5
Ease of Installation
5/5
Performance
5/5
Power
5/5
Style
5/5
Awesome

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.

Ler1

Verified Purchaser
1 year 9 months ago Murphysboro, IL
5 out of 5 stars
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

TeeO

2 years 11 months ago South Carolina, USA
5 out of 5 stars
Durability
5/5
Ease of Installation
5/5
Performance
5/5
Power
5/5
Style
5/5
Perfect

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

Twistedthrottlegarage

Verified Purchaser
Over 3 years ago
1 out of 5 stars
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.

edgrrr

Over 6 years ago
5 out of 5 stars
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.

118 Questions

  • Answered:   110
  • Not Yet:   7

Question asked by Puff

Question: Where Can i purchase a replacement piston for my 2015 yz Athena 105 bigbore kit?
Question asked 5 days 5 hours ago

Question asked by Walker

Question: I have a 2015 Yamaha 250f. Will I have to bore the case halfs?
Question asked 1 month 24 days ago
Question answered by Paul
User's contributor status: Top 1
Question answered 1 month 24 days ago
Answer: The Athena Big Bore Kit does not require modifications to the cases.
The Athena Big Bore Kit is model-specific. To help us to provide accurate information, we will need to know if your 250F is the Honda, Husqvarna, Kawasaki, KTM, Suzuki, or Yamaha.

Question asked by kmod42

User's contributor status: Verified Purchaser
Question: I have a @009 Kawasaki KX250f. Does anyone know if the cases will need to modified for the 290cc kit???
Question asked 1 month 25 days ago
Question answered by Paul
User's contributor status: Top 1
Question answered 1 month 25 days ago
Answer: The Athena Big Bore Kit is available for your 2009 Kawasaki KX250F. The kit includes the oversized cylinder, piston and all necessary seals and gaskets. This kit does not require modifying the cases.

Question asked by Jhf2005

Question: Will the stock head fit onto the kx65 big bore kit?
Question asked 2 months 13 days ago
Question answered by robert
User's contributor status: Top 10
Question answered 2 months 13 days ago
Answer: No the kit will include an matching head.

Question asked by Semaj

Question: What piston come in the kit for a 05 trx450r
Question asked 4 months 16 days ago
Question answered by robert
User's contributor status: Top 10
Question answered 4 months 16 days ago
Answer: The kit will include a 97mm Athena piston.

Question asked by Josh780

Question: Got a 2003 yz250 2 stroke   Blew my top end up looking to replace. With the Athena big bore for this bike and if so is there any mods I need to do ? 
Question asked Over 9 months ago
Question answered by CodyGearhead
User's contributor status: Top 25
Question answered Over 9 months ago
Answer: Some kits require case boring and it will specify in the instructions. Otherwise this kit should bolt right up without any other parts.

Question asked by bgsgaming

Question: I was wondering something about the kit. It will fit my bike, yes. But will I need to do anything to crank,etc. will I only need to adjust things like values, and carb? Is there anything else Ill need to do to the bike when installed or installing
Question asked Over 9 months ago

Question asked by Jason

Question: Will I need to buy anything else to install this on a 2017 Yamaha WR250R like a fuel pack or something? 
Question asked Over 10 months ago
Question answered by robert
User's contributor status: Top 10
Question answered Over 10 months ago
Answer: The bike will need to be tuned to the bigbore kit, a fuel injection tuner like the one from jd jetting may be a good option to look in to. This will insure the bike is running at peak conditions.

Question asked by Locster

Question: Will I have to bore the cases rmz450 with athena big bore kit 100 mm
Question asked Over 10 months ago
Question answered by Trevor Gearhead
User's contributor status: Top 10
Question answered Over 10 months ago
Answer: It doesn't look like that's needed on an RMZ450.

Question asked by StangBang2647

Question: With this kit on a 2019 YZ125, will I need to bore the case or is this a bolt-n-go kit?
Question asked Over 11 months ago
Question answered by DaveGearhead
User's contributor status: Top 10
Question answered Over 11 months ago
Answer: You will need to bore the cases for that bike. Here are the notes from Athena's site:

ATTENTION! To assemble the cylinder kit P400485100030 Ø 58 you need to make the boring of the engine crankcase.All ATHENA products, which are manufactured with higher displacement and power than those permitted by law of the country where the end user lives, are intended solely for competition-sports usage. Use on public roads as well as in aeronautics and marine is prohibited. ATHENA is not responsible for any different usage.The customer takes full responsibility that the distribution of the articles purchased from Athena is in line with the current regulations of his country and therefore frees Athena from whatever responsability in this matter.
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Fitment

See all bikes that this part fits...

# Part Numbers

Product Variant Manufacturer Part #
105cc P400485100038
130cc P400250100005
144cc P400250100011, P400485100030, P400485100029
164cc P400210100023
276cc P400270100015, P400270100017, P400270100021
280cc P400210100033, P400210100009, P400270100007
290cc P400250100013, P400250100018, P400510100004, P400510100010, P400510100020, P400485100032, P400485100026, P400485100012, P400250100019
293cc P400485100042
300cc P400220100002, P400220100004
365cc P400270100005
435cc P400510100002
478cc P400485100016, P400485100021, P400485100014
480cc P400210100007
490cc P400210100030, P400210100001, P400210100021, P400250100003, P400510100008, P400510100006, P400510100012, P400510100016, P400210100017, P400250100010, P400250100023
80cc P400270100002, P400250100007

California Proposition 65

WARNING: This product contains chemicals known to the State of California to cause cancer, and birth defects or other reproductive harm. Wash hands after handling. For more information, go to www.P65Warnings.ca.gov.