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Bottom End

Bottom End Engine Parts for Dirt Bikes & Motorcycles

If the top end is where power is made, the bottom end is where that power is held together. The crankshaft, connecting rod, main bearings, and cases form the foundation of every engine, and when those components wear out or fail the consequences are far more serious and far more expensive than a routine top end job. A spun bearing, a worn crank, or a damaged connecting rod left unaddressed will take out everything around it. Catching bottom end wear early and rebuilding with quality components is always cheaper than fishing for case fragments after a catastrophic failure on the trail or track.

Mad Lads Moto stocks bottom end engine parts for two-stroke and four-stroke dirt bikes, motocross bikes, enduro machines, and street motorcycles. Whether you are doing a full engine rebuild, replacing a worn crankshaft assembly, or refreshing the bottom end bearings and seals after a top end job, we have what you need. Here is what we carry:

  • Crankshaft Assemblies - Complete OEM-spec crankshaft assemblies ready to drop in, covering two-stroke and four-stroke applications across all major makes and models.
  • Connecting Rods & Rod Kits - Individual connecting rods and complete rod kits including the big end bearing, small end bearing, and all associated hardware for a clean rebuild.
  • Main Bearings & Crank Bearings - Precision main bearings, crank bearings, and bearing sets designed to restore proper clearances and eliminate play that causes noise and accelerated wear.
  • Cases & Case Covers - Replacement engine cases, case halves, and case covers for engines that have suffered damage beyond what a standard rebuild can address.
  • Bottom End Rebuild Kits - Complete bottom end kits that bundle the crankshaft, rod, bearings, and seals into one purchase, taking the guesswork out of parts sourcing for a full rebuild.
  • Oil Pumps & Lubrication Components - Oil pumps, oil pump gears, and lubrication system components that keep the bottom end fed with clean oil under all operating conditions.

Hot Rods is the go-to brand for bottom end rebuild kits and crankshaft assemblies, with a reputation built on OEM-spec fitment and reliability across hundreds of applications for Honda, Yamaha, Kawasaki, Suzuki, KTM, Husqvarna, Beta, and GasGas. Wiseco connecting rod kits are trusted by racers who put their engines through the kind of abuse that exposes weak components fast. For bearings and seals, quality matters more than price. Cheap bearings in a bottom end are a false economy that always costs more in the long run. Use our year, make, and model fitment tool to find parts confirmed to fit your specific machine before you order.

What are the signs that my dirt bike needs a bottom end rebuild?

Bottom end wear is often more subtle than top end wear until it becomes a serious problem. Early warning signs include a knocking or rattling noise from the lower engine that gets worse under load, excessive vibration that was not present before, metal particles in the oil during an oil change, and play or roughness when the crankshaft is rocked side to side with the engine out of the frame. On two-stroke engines, crank bearing wear often shows up as an inconsistent idle, difficulty starting, and a subtle but persistent knock that worsens as the engine warms up. If you are doing a top end rebuild and the engine has significant hours on it, inspecting the bottom end at the same time is always worth the effort. Finding a worn rod bearing during a planned rebuild is far better than finding it on the trail.

Can I rebuild just the bottom end without replacing the top end at the same time?

Yes, but if the engine has significant hours on it and both ends are due for attention, doing them together saves considerable labor time since the engine is already apart. If the top end is recently rebuilt and still within spec, there is no mechanical reason to replace it during a bottom end job. The decision comes down to hours, condition, and the cost of labor versus the cost of parts. For a home mechanic doing their own work, splitting the jobs is a reasonable approach. For someone paying shop labor rates, combining the rebuild into one teardown and reassembly almost always makes more financial sense.

What is included in a complete bottom end rebuild kit?

A complete bottom end rebuild kit typically includes a crankshaft assembly or connecting rod, main bearings, crank bearings, and all necessary seals and gaskets to properly seal the bottom end after reassembly. Some kits also include the transmission bearings depending on the application. Hot Rods bottom end kits are a popular choice because they bundle everything needed for a complete rebuild into one part number, eliminating the need to source individual components from multiple suppliers. Always verify what is included in a specific kit before ordering so you know exactly what additional parts, if any, you will need to complete the job.
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