Best Couplings for Log Splitters Engine-to-Pump Coupling Guide
Table of Contents
Most gas-engine log splitters connect the engine to the hydraulic pump with a jaw-type coupling, and it’s usually the first thing to fail after the pump seals. Here’s what to look for in a replacement and which sizes fit the most common splitter builds.
Why Log Splitters Use Jaw Couplings
The engine and hydraulic pump on a log splitter rarely sit in perfect alignment, and the pump load pulses hard every time the splitter wedge bites into a log. A jaw coupling’s flexible spider insert absorbs that shock loading and tolerates the minor misalignment between engine crankshaft and pump shaft — a rigid coupling would transmit every shock load straight into the pump shaft and bearings, shortening pump life significantly.
It also means when the spider wears out (the usual failure point, not the metal hubs), you replace a $15–30 part in a few minutes instead of pulling the whole pump.
Sizing a Replacement Coupling
Log splitter engine-to-pump couplings are almost always in the smaller end of the jaw coupling range, since splitter engines typically run 6.5–15 HP. Before ordering a replacement:
1. Measure both bores. The engine-side hub bore matches your engine’s crankshaft diameter (commonly 1 in or 25.4 mm on Predator- and Honda-clone engines). The pump-side hub bore matches your pump shaft.
2. Check the keyway. Most small engines use a standard keyway size for their shaft diameter — measure it rather than assuming, since aftermarket engines vary.
3. Match or upgrade the spider material. Standard Hytrel (orange) spiders handle most splitter duty fine. If you’re splitting in cold weather regularly, note that Hytrel stays flexible down to about -40°F, so it’s rarely the limiting factor.
Common Log Splitter Coupling Sizes
Splitter engine and pump shaft diameters vary by manufacturer, but many DIY and replacement builds land in the L090–L099 range. Always confirm against your engine and pump spec before ordering — a coupling that’s undersized for the bore won’t seat, and oversized won’t grip.
Installation Tips
Leave a small gap (per the manufacturer’s spec, typically 1/8 in) between the two hubs so the spider isn’t compressed axially at rest. Tighten hub set screws onto the keyway, not onto bare shaft, and recheck torque after the first few hours of use once everything’s seated.
Shop Log Splitter Coupling Parts
For engine-to-pump connections, the Lovejoy L090 jaw coupling hub and Lovejoy L095 jaw coupling hub cover the most common splitter bore sizes. If your splitter uses a PTO-driven pump instead of a direct engine mount, see our Lovejoy universal joint options instead.
Browse the full coupling catalog to find the exact bore and keyway you need.