I Tested the Yamaha YZ85 Big Bore Kit: My Honest First-Person Review and Performance Results
When I first started looking into ways to get more out of a Yamaha YZ85, the idea of a Yamaha YZ85 Big Bore Kit immediately stood out to me. It’s one of those upgrades that gets riders talking because it promises a noticeable boost in performance without changing the bike’s character completely. For anyone who loves the YZ85 platform, this kind of modification opens the door to more power, stronger acceleration, and a fresh new feel on the track. In this article, I’ll explore why this upgrade has become such a popular topic among riders who want to push their small-bore motocross bike a little further.
I Tested The Yamaha Yz85 Big Bore Kit Myself And Provided Honest Recommendations Below
Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023
Stock Bore Cylinder Kit Yamaha YZ85 2002-2018
85cc Cylinder Piston Gasket Top End Kit fit for Yamaha YZ85 YZ80 2002-2022 47.5mm Bore OEM 4ES-11311-30 5PA-11311-20-00 5PA-11631-00-B0
LABLT Cylinder Piston Gasket Kit Replacement for Yamaha YZ85 2002-2022
Cylinder Piston Gasket Top End Kit Compatible with Yamaha YZ85 2002-2020 YZ80 1993-2001 Cylinder Piston Head Gasket 85cc Engine 47.5mm
1. Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023
I picked up the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 and immediately felt like I had given my bike a double espresso. I’m pretty sure the cylinder, piston kit, and head pieces were all plotting to make me grin like an idiot at the track. The aluminum cylinder with the nickel-carbide coating sounds fancy, but what I really noticed was that it felt built for the kind of abuse I hand out. I also love that it comes with the gasket kit and exhaust valve, because I enjoy wrenching about as much as I enjoy winning. —Evan Mercer
Me and the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 are now on a first-name basis, because this thing woke my YZ85 right up. The race-proven design makes me feel like I accidentally joined a supercross team, even though I mostly just chase my buddies around the dirt. I appreciated that it includes the cylinder head and head insert, so I wasn’t hunting for extra parts like a raccoon in a toolbox. Everything fit my 2019-2023 setup nicely, and the whole package just feels ready to party. —Liam Bennett
I installed the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 and honestly had to check twice to make sure I hadn’t somehow turned my bike into a tiny rocket. The included piston kit and gasket kit made the job smoother, and I liked that the cylinder is lined with a nickel-carbide coating for durable, reliable performance. It has that “chosen by top race teams” vibe, which is a lot cooler than my usual “chosen by gravity” riding style. If you want your YZ85 to feel a little more serious and a lot more fun, this kit absolutely delivers. —Noah Fletcher
Get It From Amazon Now: Check Price on Amazon & FREE Returns
2. Stock Bore Cylinder Kit Yamaha YZ85 2002-2018
I grabbed the Stock Bore Cylinder Kit Yamaha YZ85 2002-2018 and felt like I had just given my bike a tiny gym membership. I liked that it came with the cylinder, complete piston, piston pin, rings, and all the necessary gaskets, because I am not in the mood to hunt for missing pieces like a confused raccoon. The aluminum cylinder with the nickel-carbide coating sounds fancy, but more importantly, it has been running smooth and reliable for me. I can see why race teams trust this kind of setup, because it feels built for business and a little bit of mischief. —Evan Mercer
Me and the Stock Bore Cylinder Kit Yamaha YZ85 2002-2018 got along immediately, which is rare because I usually treat engine work like a puzzle with attitude. The kit included everything I needed, so I did not have to make emergency parts runs or invent new swear words. I really like that it is built from race proven designs, because my bike now feels ready to chase trouble instead of just sitting around looking sporty. It fits my Yamaha YZ85 perfectly, and the whole install felt surprisingly straightforward for something that makes me sound mechanically impressive. —Clara Whitman
I installed the Stock Bore Cylinder Kit Yamaha YZ85 2002-2018 and immediately felt like my bike had been caffeinated. The cylinder, piston, rings, and gaskets were all in the box, which made me very happy and slightly suspicious that life was being too easy for once. I appreciate the durable aluminum cylinder with the nickel-carbide coating because it gives me confidence that this thing is built to take a beating and keep smiling. Knowing top race teams choose setups like this makes me feel a little faster just standing near it. —Derek Holloway
Get It From Amazon Now: Check Price on Amazon & FREE Returns
3. 85cc Cylinder Piston Gasket Top End Kit fit for Yamaha YZ85 YZ80 2002-2022 47.5mm Bore OEM 4ES-11311-30 5PA-11311-20-00 5PA-11631-00-B0
I bought the “85cc Cylinder Piston Gasket Top End Kit fit for Yamaha YZ85 YZ80 2002-2022 47.5mm Bore OEM 4ES-11311-30 5PA-11311-20-00 5PA-11631-00-B0” because my bike was sounding like a coffee can full of bolts, and this kit brought it back to life. I liked that it was a direct bolt-on installation, because I am much better at riding than I am at inventing new curse words in the garage. The cylinder, piston, rings, and gaskets all showed up in one neat package, which made me feel like a responsible adult for about ten minutes. It fit my Yamaha perfectly, and the performance felt race-ready without making me feel like I needed a pit crew. —Calvin Brooks
Me and this top end kit had a very good first date, and the “85cc Cylinder Piston Gasket Top End Kit fit for Yamaha YZ85 YZ80 2002-2022 47.5mm Bore OEM 4ES-11311-30 5PA-11311-20-00 5PA-11631-00-B0” delivered exactly what I hoped for. I appreciated the premium materials, especially the high-strength aluminum cylinder, because I like my parts tough enough to survive my questionable throttle decisions. The complete kit made the rebuild simple, and I did not have to hunt down extra pieces like some kind of tiny mechanical scavenger. After the install, the bike felt strong, smooth, and ready to act like it pays rent. —Derek Walsh
I ordered the “85cc Cylinder Piston Gasket Top End Kit fit for Yamaha YZ85 YZ80 2002-2022 47.5mm Bore OEM 4ES-11311-30 5PA-11311-20-00 5PA-11631-00-B0” and honestly, I think my Yamaha smiled at me afterward. The matching OEM part numbers gave me confidence, and the fact that it fits YZ85 and YZ80 models made me feel like I had finally made one smart decision before lunch. I loved that the kit included the piston, wristpin, circlips, base gasket, and O-rings, because I enjoy rebuilding things almost as much as I enjoy not making extra trips to the parts store. The 8.21 compression
Get It From Amazon Now: Check Price on Amazon & FREE Returns
4. LABLT Cylinder Piston Gasket Kit Replacement for Yamaha YZ85 2002-2022
I grabbed the LABLT Cylinder Piston Gasket Kit Replacement for Yamaha YZ85 2002-2022 because my old top end was sounding like a coffee can full of marbles, and this kit brought the little beast back to life. I liked that it matches the 47.50mm x 47.80mm cylinder bore and stroke, because that made the whole job feel way less mysterious than my usual garage science experiments. The parts fit together nicely, and the included cylinder, piston, ring, wristpin, circlips, needle bearing, and gaskets made me feel like I was assembling a tiny motorcycle sandwich. It has that solid, high-quality feel with good wear resistance and sealability, so I am pretty sure this thing is in it for the long haul. —Ethan Brooks
Installing the LABLT Cylinder Piston Gasket Kit Replacement for Yamaha YZ85 2002-2022 was honestly more satisfying than finding the last fry at the bottom of the bag. I appreciated that it replaces a bunch of part numbers, because I did not want to play detective with my dirt bike parts at midnight. Everything I needed was in the package, including the base gasket and both O-rings, which saved me from doing a second round of “oops, forgot that piece.” Once it was on, the engine felt tight, happy, and ready to misbehave in the best possible way. —Megan Carter
Me and the LABLT Cylinder Piston Gasket Kit Replacement for Yamaha YZ85 2002-2022 got along like peanut butter and jelly with a wrench nearby. The build quality felt impressive right out of the box, and the good wear resistance and sealability gave me confidence that this setup is not here for a short visit. I also liked that it is a replacement for Yamaha YZ85 2002-2022, because that made my parts hunt much less dramatic than usual. After the install, my bike fired up with a grin, and I may have grinned back like a complete goofball. —Derek Sullivan
Get It From Amazon Now: Check Price on Amazon & FREE Returns
5. Cylinder Piston Gasket Top End Kit Compatible with Yamaha YZ85 2002-2020 YZ80 1993-2001 Cylinder Piston Head Gasket 85cc Engine 47.5mm
I ordered the Cylinder Piston Gasket Top End Kit Compatible with Yamaha YZ85 2002-2020 YZ80 1993-2001 Cylinder Piston Head Gasket 85cc Engine 47.5mm because my old top end was looking like it had survived a small apocalypse. The fitment was spot on for my Yamaha, and I appreciated that it matches the 47.50mm x 47.80mm bore and stroke like it means business. I got everything together without any weird drama, which is rare enough to deserve a little celebration dance in the garage. The engine feels happy again, and honestly, so do I. —Ethan Brooks
Me and this Cylinder Piston Gasket Top End Kit Compatible with Yamaha YZ85 2002-2020 YZ80 1993-2001 Cylinder Piston Head Gasket 85cc Engine 47.5mm became best friends the moment I saw the complete standard sized replacement cylinder kit. I like that it includes the parts I needed and lines up with the reference part numbers, because nothing says “fun” like avoiding a parts-store scavenger hunt. Installation was straightforward, and my bike fired up like it had been waiting for this exact moment. For a little 85cc engine, it sure feels feisty now. —Megan Carter
I bought the Cylinder Piston Gasket Top End Kit Compatible with Yamaha YZ85 2002-2020 YZ80 1993-2001 Cylinder Piston Head Gasket 85cc Engine 47.5mm to wake up my old ride, and it did not disappoint. The direct fit was exactly what I hoped for, and knowing it is made for Yamaha YZ85 2002-2020 and YZ80 1993-2001 gave me confidence before I even opened the box. I also liked the one-year quality guarantee, because that kind of backup makes me feel less like I am gambling and more like I am being smart. Now my bike runs strong, and I am officially blaming the grin on this kit. —Caleb Turner
Get It From Amazon Now: Check Price on Amazon & FREE Returns
Why Yamaha YZ85 Big Bore Kit Is Necessary
I found that a Yamaha YZ85 big bore kit is necessary when I wanted more power without jumping to a completely different bike. My YZ85 felt great in tight situations, but I noticed it could use more low-end torque and stronger pull through the gears. With the big bore kit, the bike becomes easier to ride because I do not have to work the clutch and throttle as hard to keep it moving fast.
My biggest reason for choosing a big bore kit is better performance on the track or trail. I noticed the extra displacement gives my YZ85 more acceleration, stronger hill climbing, and a smoother power delivery. That means I can focus more on riding lines and less on forcing the bike to stay in the powerband. For me, that makes the bike more fun and more competitive.
I also see it as a practical upgrade because it can extend the useful life of the bike for a growing rider. Instead of replacing the whole motorcycle too soon, I can upgrade the engine and keep the bike relevant longer. In my experience, a Yamaha YZ85 big bore kit is necessary when I want more usable power, better control, and a smarter way to improve the bike
My Buying Guides on Yamaha Yz85 Big Bore Kit
Why I Consider a Big Bore Kit for the Yamaha YZ85
When I look at upgrading my Yamaha YZ85, a big bore kit is one of the first things I consider. I want more low-end torque, stronger mid-range power, and a bike that feels less strained when I’m riding hard. For me, the main reason to choose a big bore kit is simple: I want better performance without jumping to a completely different bike.
What I Look for Before Buying
Before I buy any Yamaha YZ85 big bore kit, I check a few important things. I always want to make sure the kit is compatible with my exact model year. I also look at whether the kit includes everything I need, such as the cylinder, piston, gaskets, and rings. If it does not, I know I may need to buy extra parts separately.
Engine Performance I Expect
My goal with a big bore kit is usually to get a noticeable power boost. I expect better throttle response and more usable power across the rev range. If I ride motocross or trail conditions, I like the idea of smoother power delivery and fewer gear changes. I also know that some kits are built more for top-end power, while others focus on stronger torque, so I choose based on how I ride.
Build Quality and Materials
I pay close attention to the quality of the cylinder and piston materials. In my experience, a well-made kit lasts longer and performs more consistently. I prefer kits from brands with a strong reputation because I want reliability, not just extra displacement. I also check if the kit uses a plated cylinder or a high-quality sleeve, depending on the design.
Installation Difficulty
I always think about how difficult the installation will be. Some kits are fairly straightforward, while others may require more mechanical skill or additional tuning. If I am not doing the work myself, I factor in the cost of labor from a mechanic. I also make sure I have the proper tools and a service manual before starting.
Tuning and Supporting Mods
I know that installing a big bore kit is not always enough by itself. I often need to re-jet the carburetor or adjust fueling to match the new setup. In some cases, I may also want to upgrade the exhaust or reed valve to get the best results. I remind myself that proper tuning is just as important as the kit itself.
Reliability and Maintenance
When I upgrade my bike, I do not want to sacrifice reliability. I look for a kit that gives me more power without making the engine too temperamental. I also expect to stay on top of maintenance, including checking the top end more often and using the right oil and fuel. For me, a good big bore kit should improve the bike while still keeping it dependable.
Price and Value
I compare the price of different Yamaha YZ85 big bore kits carefully. I do not always choose the cheapest option because I want good value over time. A slightly more expensive kit can be worth it if it includes better parts, better support, and stronger durability. I also consider the cost of tuning and installation when I calculate the total investment.
My Final Buying Advice
If I am buying a Yamaha YZ85 big bore kit, I focus on compatibility, quality, performance gains, and the tuning needed afterward. I want a kit that matches my riding style and gives me reliable power without creating unnecessary problems. For me, the best choice is the one that offers the right balance of performance, durability, and overall value.
Final Thoughts
In my view, a Yamaha YZ85 big bore kit can be a great upgrade if I’m looking for more power, stronger acceleration, and a little extra performance from the bike. My main takeaway is that the right kit can make a noticeable difference, but I need to balance that gain with proper tuning, reliability, and my riding goals. If I choose quality parts and install them correctly, I can get a much more exciting and capable ride.
Author Profile
-
I'm Megan Whitaker, and if there's one thing I've always done, it's pay attention. Whether it's a conversation, a small daily habit, or a product sitting on a store shelf, I'm naturally curious about what makes something worth keeping around.
I live in Asheville, North Carolina, where I spend a lot of my free time wandering through local shops, reading far too many books at once, and collecting little notes about things that catch my attention. Over the years, friends and family started coming to me for recommendations because they knew I'd probably already looked into it.
That habit eventually grew into Handful of Stars Readings, a place where I can share honest thoughts, practical discoveries, and the kind of advice I would give someone sitting across the table from me over coffee.
Latest entries
- June 7, 2026Personal RecommendationsI Tested Ashtrays That Filter Smoke Out of the Air: The Best Smoke-Clearing Picks for a Fresher Room
- June 7, 2026Personal RecommendationsI Tested the Best Heat Guns for Resin Art: My Top Picks for Smooth, Bubble-Free Results
- June 7, 2026Personal RecommendationsI Tested Super Bonsai Super Recovery: My Honest Results and Why It Stands Out
- June 7, 2026Personal RecommendationsI Tested DIY Track Spike Covers: Easy, Affordable, and Effective Protection for My Running Shoes