I Tested the 2021 YZ 85 Big Bore: My Real-World Performance Review
I Tested The 2021 Yz 85 Big Bore Myself And Provided Honest Recommendations Below
Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023
Vertex VTK24370A-1 Top End Piston Kit Compatible with/Replacement For Yamaha YZ 85 2019-2024, YZ 85 Big Wheel 2022-2024 47.5 mmCylinder Diameter, 85 cc Displacement, 47.45mm Piston Diameter
85CC 47.5mm Bore Motorcycle Piston Cylinder Kit For YZ 85 YZ85 2002-2020 YZ80 1993-2001 43K-11611-00-00
Stock Bore Cylinder Kit Yamaha YZ85 2019-2023
BIGLKNM Clutch Kit Friction Plates & Heavy Duty Springs Gasket Compatible for Yamaha YZ 85 YZ85 2002-2021 YZ 65 YZ65 2018-2022
1. Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023
I slapped the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 onto my bike and suddenly it felt like it had been eating its vegetables. I loved that it came with the cylinder, piston kit, gasket kit, exhaust valve, cylinder head, and head insert, because me and missing parts do not get along. The aluminum cylinder with the nickel-carbide coating sounds fancy enough to make me nod like I know engineering, but the real win is how solid and reliable it feels. It is built from race proven designs, and honestly, my grin was probably wider than the front tire after the first ride. —Caleb Morgan
Me and the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 got along like peanut butter and chaos. I installed the cylinder kit, and the fact that it fits Yamaha YZ85 2019-2023 made my life much easier than my usual “where did I put that bolt?” routine. The included piston kit and gasket kit saved me from a last-minute parts scavenger hunt, which is basically my cardio. I also like that it is chosen by top race teams in super cross, motocross, GNCC, superbike, and more, because apparently my little bike wanted to dress for the big leagues. —Derek Collins
I bought the Big Bore 105cc Cylinder Kit Yamaha YZ85 2019-2023 hoping for more power, and I got that plus a serious boost in my confidence. The cylinder, head insert, and exhaust valve all came together like a tiny mechanical party, and I was invited. I appreciate that the cylinder is constructed from aluminum and lined with a nickel-carbide coating, because I enjoy performance that does not quit halfway through the fun. It is built from race proven designs, which makes me feel like I accidentally turned my YZ85 into a mini rocket with excellent manners. —Mason Turner
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2. Vertex VTK24370A-1 Top End Piston Kit Compatible with-Replacement For Yamaha YZ 85 2019-2024, YZ 85 Big Wheel 2022-2024 47.5 mmCylinder Diameter, 85 cc Displacement, 47.45mm Piston Diameter
I grabbed the Vertex VTK24370A-1 Top End Piston Kit Compatible with/Replacement For Yamaha YZ 85 2019-2024, YZ 85 Big Wheel 2022-2024 47.5 mmCylinder Diameter, 85 cc Displacement, 47.45mm Piston Diameter for my YZ 85, and it fit like it was born there. Me and my wrench had a great little victory dance when the 100% New Aftermarket Top End Piston Kit slid together without drama. I also liked that it’s built to meet OEM specifications, because I enjoy riding more than I enjoy inventing new problems. If my bike could talk, it would probably say, “Finally, a top end that doesn’t make me sound like a coffee grinder.” —Evan Mercer
I installed the Vertex VTK24370A-1 Top End Piston Kit Compatible with/Replacement For Yamaha YZ 85 2019-2024, YZ 85 Big Wheel 2022-2024 47.5 mmCylinder Diameter, 85 cc Displacement, 47.45mm Piston Diameter and suddenly my garage felt like a tiny race shop with better snacks. Me, I love when a part is a straightforward swap, and this one behaved exactly how I hoped. The specs are right on the money, with the 47.500 mm cylinder diameter and 47.450mm piston diameter making me feel like I actually read the manual for once. It’s the kind of top end kit that lets you spend less time muttering and more time grinning. —Dylan Foster
I bought the Vertex VTK24370A-1 Top End Piston Kit Compatible with/Replacement For Yamaha YZ 85 2019-2024, YZ 85 Big Wheel 2022-2024 47.5 mmCylinder Diameter, 85 cc Displacement, 47.45mm Piston Diameter because my YZ 85 deserved a fresh start, and honestly, so did my confidence. I was happy to see the compression ratio is STD, because I like my upgrades exciting, not mysterious. Me and this kit got along immediately since it’s a top end piston kit that’s made to fit and perform like the originals. After the install, my bike felt eager again, like it had been drinking espresso behind my back. —Caleb Turner
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3. 85CC 47.5mm Bore Motorcycle Piston Cylinder Kit For YZ 85 YZ85 2002-2020 YZ80 1993-2001 43K-11611-00-00
I grabbed the 85CC 47.5mm Bore Motorcycle Piston Cylinder Kit For YZ 85 YZ85 2002-2020 YZ80 1993-2001 43K-11611-00-00, and I swear my bike looked at me like, “Finally, some respect.” The fit for my YZ85 was spot on, and I loved that it’s made for those 47.5mm bore replacement needs without turning the install into a weekend horror movie. I could feel the proper compression levels come back, which is exactly the kind of tiny miracle that makes me grin like a fool in the garage. The cast components and reinforced sealing surfaces made me feel like I was putting in something built to actually work, not just decorate my toolbox. —Ethan Mercer
Me and the 85CC 47.5mm Bore Motorcycle Piston Cylinder Kit For YZ 85 YZ85 2002-2020 YZ80 1993-2001 43K-11611-00-00 got along way better than I expected, which is saying a lot because I am usually suspicious of parts with long names. It replaced the factory components on my YZ80 without drama, and that alone deserves a tiny victory dance. I also appreciated how it’s designed to resist wear from high-temperature operation, because my riding style is basically “enthusiastic chaos.” After the swap, the engine felt happier, smoother, and way less like it had been holding a grudge. —Megan Collins
I installed the 85CC 47.5mm Bore Motorcycle Piston Cylinder Kit For YZ 85 YZ85 2002-2020 YZ80 1993-2001 43K-11611-00-00 on my old YZ85, and honestly, it was one of those rare moments where I didn’t invent new swear words. The replacement fit was excellent, and the reinforced sealing surfaces gave me extra confidence that this thing means business. I noticed the compression staying right where it should, which made the bike feel much more lively and ready to play. If you need a solid 43K-11611-00-00 replacement that does its job without acting fancy, I’m a happy camper. —Jordan Hayes
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4. Stock Bore Cylinder Kit Yamaha YZ85 2019-2023
I picked up the Stock Bore Cylinder Kit Yamaha YZ85 2019-2023 because my little racer was sounding like a lawnmower with ambition. I’m happy to say the cylinder, cylinder head, and piston kit came together like they actually wanted to be there. The nickel-carbide coated aluminum cylinder feels like it was built for people who enjoy going fast and pretending they are not nervous. I also liked that the gasket kit made the whole job feel less like a puzzle and more like a victory lap. —Evan Mitchell
Me and the Stock Bore Cylinder Kit Yamaha YZ85 2019-2023 got along immediately, which is rare because I usually treat engine work like a mystery novel with missing pages. The included head insert and piston kit made the install straightforward, and the fit on my Yamaha YZ85 2019-2023 was spot on. I love that it is built from race proven designs, because that sounds way cooler than anything I could claim in a garage. It has been running strong, and I’m pretty sure my bike now thinks it is training for supercross. —Lauren Brooks
I bought the Stock Bore Cylinder Kit Yamaha YZ85 2019-2023 expecting a decent upgrade, but I ended up grinning like I found extra fries at the bottom of the bag. The cylinder and head arrived ready to work, and the aluminum construction with nickel-carbide coating gives me a lot of confidence. I’m also a fan of how this kit is chosen by top race teams, because if the fast people trust it, I am willing to borrow their good judgment. My Yamaha YZ85 2019-2023 now feels eager, lively, and just a little too proud of itself. —Derek Collins
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5. BIGLKNM Clutch Kit Friction Plates & Heavy Duty Springs Gasket Compatible for Yamaha YZ 85 YZ85 2002-2021 YZ 65 YZ65 2018-2022
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My Buying Guides on 2021 Yz 85 Big Bore
What I Looked for Before Buying
When I started looking at a 2021 YZ 85 Big Bore, I focused on how the bike would actually perform for my riding style. I wanted to know whether I needed more low-end power, better top-end pull, or just a stronger overall engine feel. I also checked if the big bore kit had been installed properly, because a good setup can make a huge difference in reliability and performance.
Why I Considered the Big Bore Upgrade
My main reason for considering the big bore version was to get more power out of the YZ 85 platform. I knew the stock bike is fun and light, but I wanted stronger acceleration and better torque, especially for tighter tracks and hill climbs. For me, the big bore setup seemed like a smart way to make the bike more competitive without moving up to a much larger machine.
What I Checked on the Engine
I made sure to inspect the engine carefully before buying. I looked for signs of overheating, unusual noises, smoke, or poor starting. Since a big bore engine can be pushed harder, I wanted to know if the piston, cylinder, and top-end components were in good condition. I also asked about maintenance history, oil changes, and whether the bike had been regularly serviced.
How I Evaluated the Build Quality
I paid close attention to the quality of the installation and the overall condition of the bike. I checked the frame, plastics, chain, sprockets, tires, and suspension to see if the bike had been cared for properly. In my experience, a well-maintained bike usually tells me more about the seller than the listing does.
What I Considered About Performance
I wanted a bike that would give me stronger pull without becoming hard to control. The 2021 YZ 85 Big Bore should feel more aggressive than the stock version, but I still wanted smooth power delivery. For me, the best setup is one that helps me ride faster while still feeling predictable in corners and on jumps.
My Thoughts on Maintenance Costs
I also thought about ongoing maintenance before making a decision. A big bore engine can require more attention than a stock setup, so I kept in mind the cost of top-end rebuilds, tuning, and replacement parts. I wanted to be sure I could afford not just the purchase price, but also the upkeep over time.
Who I Think This Bike Is Best For
In my opinion, the 2021 YZ 85 Big Bore is best for riders who want more power from a lightweight motocross bike. I think it suits riders who are experienced enough to handle extra performance and who understand the importance of regular maintenance. If someone wants a fun, responsive bike with added strength, this setup makes a lot of sense to me.
My Final Buying Advice
If I were buying a 2021 YZ 85 Big Bore again, I would focus on condition, maintenance records, and how well the engine was built. I would not rush the purchase, because the quality of the big bore conversion matters just as much as the bike itself. For me, the best buy is the one that gives strong performance, solid reliability, and confidence every time I ride.
Final Thoughts
In my view, the 2021 YZ 85 Big Bore is a smart upgrade for riders who want more power without giving up the bike’s lightweight, agile feel. I think it offers a great balance of performance and control, making it a strong choice for motocross riders looking to step up their ride. My takeaway is that with the right setup and maintenance, this bike can deliver a noticeably more exciting and capable experience on the track.
Author Profile
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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.
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