Lovejoy Coupling Replacement Checklist: Spider Sizes, Gear Coupling Catalogue PDFs, and Mistakes I Made

I didn't set out to become the person who keeps the coupling replacement checklist. In my first plant job, I ordered a replacement by pointing at a worn-out insert and saying, “like this one.” The result was predictable: wrong material, wrong size, and a machine down for four extra days. That was back in 2018. Since then, I've handled power transmission and Lovejoy coupling orders for about six years, and I've personally documented 11 order mistakes totaling roughly $4,800 in wasted parts and expedited freight. This is the checklist I now use for every Lovejoy coupling replacement.

This checklist is for standard motor-to-pump, motor-to-gearbox, and small conveyor drives. It is not for highly dynamic servo axes or large high-speed compressors. My experience is based mostly on mid-size equipment with jaw and gear couplings up to about 4-inch bores. If your machine is much bigger, take this as a starting point, not a final answer.

Before you start: prepare the machine for measuring

Lock out the drive. Remove the guard. Clean the coupling area. You need to see the hub markings and the flex element before ordering anything. I have tried to identify a coupling from memory using only a shaft diameter, and that is not a no-brainer. When someone asks for “a coupling for a 5 hp motor” without a part number, that is a red flag to slow down.

Step 1: Know which Lovejoy family you are dealing with

The first question is not “what size is the motor?” It is “what style of coupling is on the shaft?” There are two families I see most often:

• Lovejoy jaw coupling spider: you can see a flexible spider with arms between two hubs. The hubs have curved jaws, and the insert is usually a rubber or polyurethane-looking part.
• Lovejoy gear coupling: there is usually a metal sleeve over hubs with external gear teeth. It may be grease-covered and requires a different part numbering system.

I ordered a jaw spider for a coupling that turned out to be a gear coupling. In my defense, the guard was still installed when I measured it. Now I don't quote anything until I look at the actual coupling, or at least get a clear photo sent to me.

If the insert is missing or broken, remove the hubs and look for Lovejoy or a hub size code on the outside flange. Many hub markings are stamped into the hub but hidden under paint and dirt. Clean first, then measure.

Step 2: Download the right catalogue before calling a distributor

This sounds basic, but I still get it wrong when I rush. Download a current Lovejoy gear coupling catalogue PDF if you have a gear coupling. Download a jaw-type catalogue if you have a jaw coupling. The manufacturer's literature section has both, usually free on the Timken/Lovejoy site. As of 2025, that is still the fastest way to get current dimensions.

Older third-party PDFs are risky. I used a cached copy once and missed an updated bore limit. The wrong part arrived, and the machine sat for two extra days. Now I check the catalogue date and only use the current PDF.

Step 3: Identify the Lovejoy jaw coupling spider by hub code, not shaft size

The most common spider mistake on our floor is matching to the motor shaft only. A 1-inch shaft does not automatically mean L095, L110, or anything else. That shaft size can appear in different hub sizes depending on torque and the coupling series.

What has saved me:

• Look for the hub size code, like L095, L110, or L150. Write it down on the work order before someone cleans the flange.
• Match the Lovejoy jaw coupling spider to that hub code. If you don't have the code, match the hub's major dimensions, not just the spider's outside diameter.
• Note the material if the old spider is intact. If the old part was brittle, don't assume a harder spider is better. A stronger-looking spider can change vibration and actually make the machine noisier.
• Take a photo of the motor identification tag too. It helps me confirm shaft details later.

I write “Lovejoy jaw coupling spider L___” with the code filled in on every order. If the hub isn't stamped, I say so and provide dimensions. Generic “jaw spider, fits 1-inch motor shaft” descriptions cause phone tag and wrong shipments.

Step 4: Check the motor type before assuming it works like a normal AC motor

Motor type matters for load behavior, but not for basic bore sizing. In my plant, many small blowers and conveyors use a single phase induction motor. With those, a standard jaw coupling and a standard spider are usually fine if the shaft and hub match.

Servo motors are different. If you are repairing an industrial servo axis, do not pull up a hobby servo spec sheet for an “mg996r servo motor” and expect to connect it to a Lovejoy L-series coupling. The MG996R is a hobby-class servo with a small output spline, not an industrial servomotor. A standard industrial jaw coupling normally won't fit that spline. For real servo applications, you need to check torsional stiffness, misalignment, and system inertia before choosing a coupling. Hobby servos use small servo arms, horns, or bellows-type connectors instead.

Step 5: Figure out why the old coupling failed

If the Lovejoy jaw coupling spider is shredded, you can replace it and be running in twenty minutes. But if a soft foot or misaligned shaft caused the failure, the new spider will die early. I replaced the same spider three times on one motor before someone checked the base. Looking back, I should have checked the soft foot after the first premature failure. At the time, it was easier to blame the part.

Check parallel offset, angular misalignment, and the gap between hubs before you install. This probably takes 20 minutes. It will save the cost of a second part and another service call.

Misalignment can also explain odd damage on a gear coupling. A Lovejoy gear coupling is reasonably tolerant up to its catalogue limits, but if the coupling has been running outside those limits for a while, the teeth will show it.

Step 6: Put the useful details on the purchase order

Don't email your distributor with “one Lovejoy coupling, asap.” I have written that sentence and regretted it. Instead, write what matters:

• Coupling family and series code, for example Lovejoy gear coupling or jaw coupling with the hub code from Step 1.
• Bore sizes and keyway sizes on both sides.
• Hub material if you can confirm it, such as cast iron, aluminum, or steel.
• Spider material and durometer if you need a jaw replacement.
• Current catalogue part number if you are confident it matches the code.

If a bore size in the catalogue is smaller than the existing shaft, do not bore out the hub beyond the maximum. I tried that on an order in 2022. The hub cracked within a few weeks. That mistake cost around $890 in replacement material plus a day of downtime. Mental note: never exceed the maximum bore in the current catalogue PDF.

A quick answer for the LM8LUU search

One phrase that seems to land in this article is “what size is lm8luu linear bearing.” Short answer: LM8LUU is a standard metric linear bushing with an 8 mm bore, a 15 mm outside diameter, and a 24 mm length. It is not a Lovejoy coupling part. I include this because someone building a linear actuator often ends up looking at couplings and bearings in the same session, and the two parts use completely different sizing rules.

Where this checklist has limits

My experience is mostly with standard industrial motor drives, not every power transmission problem. If you're working on a large high-speed coupling or a custom engineered gear set, do not rely on this checklist alone. The catalogue ratings and application constraints should be reviewed by someone with the full machine data.

Also, this article does not tell you which Lovejoy coupling is “the best.” There is no best coupling. There is a coupling that fits your bore, handles your torque, and works with your misalignment. If your only goal is to make a worn part match the old one, like-for-like is usually the right move.

Bottom line: the extra 15 minutes of measuring and catalogue checking has caught 13 potential shipment mistakes on our team's orders in the last 18 months. Most of those would have meant a few hundred dollars in rework plus a delay. There is something satisfying about opening a box and seeing the exact Lovejoy part number that you expected. After my first few years of learning the hard way, I don't trust my memory until it's written down on a checklist.