Lovejoy Coupling Replacement: A 7-Step Checklist for Getting Dimensions Right

I've been handling Lovejoy coupling replacement orders for about eight years. That sounds like I know what I'm doing. Some days I do. But the checklist I use now came from failures, and the biggest failure happened in September 2022.

That month, I approved a pump-drive replacement order. The old hubs were clearly marked L190, and the bores I selected matched the catalog. Everything looked right on paper. What I didn't check was the actual gap between the pump shaft and the motor shaft. When the parts arrived, the coupling assembly was physically too long for the space available. The cost was $1,267 in machined hubs, rush shipping, and wasted labor, plus a two-week delay for a customer who didn't deserve it.

This article is the checklist I built after that invoice. It is not a lecture, and it is not a full engineering course. If you have an old or worn Lovejoy coupling and you need to order a replacement with confidence, work through the seven steps below.

When This Checklist Is Useful

Use this checklist when the original drawing is missing, the part number is incomplete, or somebody just says it's a Lovejoy coupling without any other detail. You don't need all seven steps if you are replacing a complete coupling with an identical, current part number. You do need it when the only thing left to look at is a greasy hub and a motor nameplate.

The Checklist

Step 1: Record Every Marking Before You Clean or Remove Anything

Take photos first. I'm not talking about one photo; take several. Get the coupling from a few angles, and make sure the lighting lets you read any stamped numbers.

Write down every marking you can see on the hub, spider, or spacer. Look for the Lovejoy logo, an L-series size like L190, a spider color, and any torque or bore stamps. If the flexible element is still partly intact, note its color and shape. That matters because colors and durometers are not universal, but they help narrow down what you actually have.

Do not skip this step because you think the part number is obvious. In my first year doing this, I skipped it and ordered by memory. That mistake cost me about $480 in wrong parts and a very awkward phone call.

Step 2: Measure the Shafts, Not Just the Old Hub

This is the step most people ignore, and it is the one that caused my 2022 failure. The outer diameter of the old coupling hub does not tell you what bore you need. You need to measure the shafts that the coupling will sit on.

Use calipers, not a tape measure. Measure each shaft diameter in at least two spots, because shafts can be tapered or worn. You should also measure:

- The usable shaft extension length on each side.
- The keyway width and depth.
- The distance between the two shaft ends when the machine is in its normal running position.

That last number is the one I missed. The catalog told me the hub dimensions were fine, but the physical space on the machine was not. Always measure the shaft gap before you approve a quote.

Step 3: Confirm Which Lovejoy Family You Are Dealing With

Lovejoy makes several different coupling styles. A Jaw coupling with a spider is the most common, but there are also S-Flex couplings, gear couplings, and disc couplings. The replacement process is different for each one.

If the hub is marked with an L and the flexible element is a star-shaped spider, you're almost certainly dealing with an L-type jaw coupling. If the flexible element looks like a rubber tire with teeth, it's probably an S-Flex. If you're not sure, send a photo to a local distributor and ask before you start ordering.

I say this because people use the phrase Lovejoy coupling to mean all of these. But the L190 Lovejoy coupling dimensions that someone asks about are not the same as the dimensions for an S-Flex or gear coupling. The wrong match is a $400 mistake plus downtime.

Step 4: Note Everything Else Sharing the Machine

Take a photo of the motor nameplate. If the motor is a single phase ac motor, write that on the job sheet too. It might feel too basic, but it is exactly the kind of detail that gets lost later in a conversation.

If there is a brake on the motor, record the brake model. An electromagnetic disc brake that drags can add heat and repeated shock to the drivetrain, which makes a coupling look undersized even though the dimensions are correct. That is a common trap. Replace the coupling if the old one is worn, but don't try to fix a brake problem by installing a heavier coupling.

You should also record whether the coupling sits between a motor and gearbox, or between a gearbox and the driven machine. Torque is different on each side of a reducer, and the coupling has to be selected for the actual location.

Step 5: Find the Current Size Chart, Not a Random Image

Look for the official Lovejoy coupling size chart PDF from the manufacturer or an authorized distributor. Try to get the current version of the catalog, not a photocopy from 2011 that someone uploaded to a parts forum. Dimensions and part numbers change over time.

Once you have the PDF, search it for the exact notation on your hub. If you search for L190 Lovejoy coupling dimensions, you should land on a table that shows max bore, hub length, and torque ratings. Write down those numbers, but do not order yet. Compare them with the shaft measurements from Step 2.

This is where I have to be honest about my own limits. I'm not a design engineer, and I don't trust my memory for catalog numbers. I have quoted a max bore from memory before, and I was wrong. The PDF exists for a reason. Use it.

Step 6: Size for the Real Application, Not Just the Motor Nameplate

A motor's nameplate tells you nominal output torque. For example, a 5 HP motor running at 1750 RPM produces roughly 15 ft-lb of torque, before you add service factors. That seems small, which is why people undersize couplings.

But the nameplate number is not the whole story. Starting torque, shock loads, reversing duty, and brake torque all matter. The coupling catalogs handle this with service factors. If you don't know how to apply them, call a distributor and describe the application honestly: what is the driver, what is the driven load, how often does it start, and does it reverse?

This is also where my opinion about pricing shows up. I do not think the most expensive option is always the right one. But I have learned that the lowest quote is not the same as the lowest total cost. Since 2021, I have tracked 21 urgent replacement orders where I picked the cheapest quote without checking the technical details properly. Thirteen of those 21 orders had some kind of problem: a tolerance issue, a missed delivery date, or missing paperwork. The price was lower. The total cost was not.

Step 7: Verify the New Parts Before You Shut Down the Machine

When the replacement arrives, do not wait until the millwright is standing there with tools. Open the box, check the part numbers, and dry-test the bore on the shaft if you can. It takes ten minutes and it has saved me multiple times.

In 2024, this checklist caught 47 potential errors before they became downtime. Some of those were small things like a wrong keyway. Others were bigger. The point is that the verification step is not optional, especially when you are working with a custom bore or a rush order.

Mistakes I Keep Writing Down

A few other warnings from my own logbook:

Do not trust the color of an old spider. Colors fade with heat and grease, and different manufacturers use different color codes. Do not assume a metric shaft is exactly the same as an inch shaft. A 28 mm shaft is not a 1-1/8 inch shaft, even though they look similar at a glance. And do not lubricate a jaw coupling spider unless the catalog tells you to. Grease attracts dust and it does not make the coupling stronger.

One more note about a search that lands here from time to time. A few visitors ask what happened to Pete Jackson gear drives. That is outside my area, and I don't have a sourced answer I am confident enough to put in writing. What I can tell you from the parts side is this: when any legacy power transmission product disappears, the same rules apply. The old part number stops being reliable, and you have to identify what is actually in front of you before you order a replacement. That is true for an old Lovejoy coupling, and it is true for any other discontinued drivetrain component.