Aircraft Engine Overhaul – Poplar Grove Airmotive

What happens to your airplane engine once it’s shipped to a major engine overhaul shop? My engine is being overhauled at Poplar Grove Airmotive (C77), a well known aircraft engine overhaul shop and FAA certified repair station.

This video is about the process from the time the engine is dropped off until it’s ready to be returned to the owner.What most impressed me was the scale of the operation, thoroughness, and organized process by which each engine is handled. Poplar Grove overhauls Continental and Lycoming engines.

You can comment and find overhaul follow-up videos on my YouTube channel.


Dave: Good morning from Poplar Grove, Illinois. I’m here at Poplar Grove Airmotive and today we are going to walk through the engine overhaul shop where Steve Thomas and his crew overhaul over 200 engines per year.

Poplar Groves was started by Steve and his dad back in 70’s and really expanded in the 1990’s when they started a residential aviation community here on the field and today have the Engine Shop flight school a  budding avionics division and a museum, and also an EAA chapter that has built a Jenny which was a world war one ear biplane using a blueprints from scratch. Let’s go inside.

1:26 Airframe Shop & Receiving Engines
Steve: This is the airframe shop where we do annuals repairs everybody’s airplanes, engine removals, reinstallations, you know. There’s always a few airplanes here that uhm people fly in and have us do the removal the overhaul and the reinstallation. The challenges are finding a place to park them through, down time, you know.

Dave: Yeah

Steve: ‘Cause we always wanna keep the customer’s airplanes inside with the weather in this part of the country. These are engines waiting to get worked on. They come in from all over the country and this kind of our holding pen. Once the engine arrives, we received it, we’ll put a work order or book with all the serial numbers, all the data and the marching orders, what the engines here for repair prop strike, or overhaul and it all starts here.

And as we chew though this holding pen they go into the shop and we start working at them. It might be here, these days, couple three weeks before we can get them in the shop.

Dave: How many engines in the cue in these days?

Steve: I believe there’s a 120 engines, give or take in the shop now, including these.

Dave: Everytime we speak, it goes up

Steve: Yes it has and there’s more coming. I know there’s three or four engines en route right now.

2:18 Poplar Grove Engine Shop
Now this is the engine shop. These carts have someone’s engine. Each engine is assigned a cart. So when they are not being worked on, we cover them with plastics. So they will not accumulate any dust or foriegn materials.

Steve: This is your engine Dave, and this is your book and we got your name, and address, all the particulars, your engine and our marching orders, “repair engine for reported cam and lifter failures, stop and report at inspection”. So at that point, we’re gonna stop, and we’ll tell you what we found and we make our decisions then and what you’d like to deal with.

Dave: Ok

Steve: Because at that point, we can still repair and we’ll know what we got or issues and then we can continue on with some simple repairs and have a good engine for long haul or if there’s some serious issues maybe you’ll like to overhaul it while it’s here and then good for the long term.

Dave: This stuff, corrosion like that can, typically be cleaned up.

Steve: Yep, that’s not bad, that can be cleaned up.

Dave: And on the motor mounts?

Steve: I noticed up here, we talked about that, there’s, well, once we get it cleaned, we’ll know if there’s any pitting or damage done but it’s hard to tell right here but it’s an indicator, thats why we take a lot of pictures before we put a wrench on it. We take pictures of everything. So we can go back to it.

Dave: Ok

Steve: We’ll start on your engine, shortly.

4:20 Cleaning Disassembled Engine Parts
Steve: And everything gets cleaned in here. Your engine looks kinda nasty right now but by tomorrow afternoon, everything will be down to the bare metal and clean, all these parts will be cleaned. So we can  inspect them.

The crank case will be dye penetrate tested, all the aluminum castings, like he’s washing a crank case right now and they’ll check that for crafts and not just destructively testing  check for crafts that you can see in naked eye.

All the steel gets clean and will go for magna-fluxing which is a non-destructive way testing steel for crafts that you can’t see.

5:10 Cylinders
Steve: Now, we make our way to the cylinder shop. This is the cylinder shop, you can see, we got a lot of cylinders and the brand new cylinders received in the boxes as well as cylinders that have been removed or either repair for overhaul depends on customers wanted. In your case, your cylinders come here for inspection. Just like the rest of it.

Steve: These cylinders for  each job in the shop could be related into an engine in the cart or could be where shops just sends us individual cylinders, could be they low compression in an annual and can send you the cylinder that will be repaired. Whether it is refacing the valves and the seats or replacing the guides or just putting new rings, instance in.

Steve: Now, the end of it, inspection and rework area.

6:12 Reworking The Parts
Steve: Bryan, are you a reworking an engine or inspecting?

Bryan: Reworking this, I just checked part for this. [Banter]…I really need it out of here.

Steve: Yeah, yeah, yeah. It’s going to end up here anyway.

Bryan: Right, right, We need them out of our way.

Steve: This is where Bryan, when he is inspecting, he starts out and he is looking it, in every tooth and every gear measuring and every bushing, all the pieces that go into the engine.

Dave: To make sure that they make the tolerances required…

Steve: Yes and when they get in the rework, they’ll put the new bushing and rocker arms and they check the face on the rocker arm. This is really important to have perfectly true because this worn at a slight angle when it’s moving it that valve up and down it can be putting a side load on the value up and it will wear the guide, the valve guide.

Dave: I see.

Steve: So it’s really important to have this perfectly true. That’s a lot of things the folks do thru this inspection process.

This is more than the same. Here working more different engines.

7:44 Engine Assembly
Steve: And then we work our way around assembling. This looks like 360 Continental for someone and as we are building the engine we have pictures that we took earlier when the engine come in to make sure that we route the ignition harnesses the same way, fittings going at the back of the engine where we them pointed the right way so when they go install it, everything lines up the way it should.

If we didn’t have these we wouldn’t know if this fitting goes in this direction or this direction. We wanna give the same thing that they [his mechanics] got. So their mechanic installing it isn’t fighting something.

Dave: So this is just, this is almost finished right.

Steve: Yes

Dave: It looks like it is.

Steve: Yeah, probably by the end of the day. We’re gonna get mags, some other things on it.

Dave: Looks factory new; looks beautiful.

Steve: Yeah, it will be when it’s done.

8:35 Poplar Grove Team
Dave: All the technicians are A&Ps or most?

Steve: You don’t have to be. We’re a repair station. So that the repair station, the shop signs it off. Some are, probably half are, some are, have inspection authorization but a lot of times we can find some of our best technicians that aren’t aviation oriented but they are good with the calipers and wrench and they just have good judgment; good mechanical aptitudes is really important to start with.

Dave: How many folks you have working for you?

Steve: Uhm, I think they are about 60 total on board. 25 in this shop, in the engine shop, 2 in accessory shop, and 7 in the airframe shop and of course all important ladies in the part room.

[Entering the parts room] Dave: Hi

Steve: These are the four ladies in the part room that keep them all happy. Even though we sell parts over the counter, probably 95% of their customers go to our mechanics.

Dave: Ok

Steve: That’s the biggest customer, either that or customers that getting work done on own their airplanes.

Steve: Here’s an early [Continental] 470 out of a very early Debonaire and the customer wanted it custom painted so we honored his wishes and had his own paint colors of his choice put on it which we did. It’s kind of fun. It’s emotional thing for a lot of people.

Dave: Sure

Steve: It’s not just a piece of business, it’s kind a family. Aviation is a emotional thing. We love this.

10:21 Test Stand – Dynamometer
Steve: So from here, we go to the test stand and a we have a two different ways of testing engines. This is our dyno, we built it ourselves. We fabricated everything ourselves. I bought a M&W dyno from a farmer implement dealer that went out business and they used it in testing tractors, farm tractors. So we just modified it, to serve this purpose and it works great.

We tested hundred of engines here. We designed it ourselves. Everybody had a fun part in MacGyvering  how we’re gonna engineer this thing.

Dave: Yeah

Steve: But it works great.

Steve: We bolt this to the shop and this is the PTO shop from a dyno works down here. From this, the engine drives the dyno. Then we increase the load agains the dyno to measure the horse power.

The testing is quite a step-through routine, lower power settings shutdown, check for things, higher power setting longer period of time, and then a the last half hour once everything proven up good, we put preservative oil in it. Because we don’t know how long it might sit in the other area before it gets reinstalled. So we don’t want any corrosion taking place with everything fresh. So that’ll protect it a little bit.

11:48 Final Checks & Completed Engines
Steve: This is kinda what your engine look like. This is a [Lycoming] L2A 160 180 horsepower for a 172. It has new Superior [cylinders] because we couldn’t get Lycomings for it. That’s what yours look like.

Dave: So whether it’s IRAN or an overhaul. It will come out looking…

Steve: It will come out looking just like that, yup.

Steve: Now, this is a O-300 Continental for Cessna 172; earlier 172 with 145 horse power.

Steve: You find little things here and there. You can tidy up. so it’s 100%.

Steve: This is 6 cylinder Lycoming out of a Harmon Rocket.

This is a big Continental that’s going…a turbo charged Continental 520 that’s ready to ship.

I think we have another Lycoming 4-cylinder here, an E2D. A customer ordered at a flight school on the Chicago area and not just quite ready for it his needs in other week.

So maybe I get these guys going on your engine.

Steve: What will take to down to where you’re splitting the case? 2 to 3 hours? Couple of hours?

Ryan: couple of hours

Steve: Couple of hours? Then we’ll split it and see what’s inside. I think once we get this disassembled we’ll have Bryan from the cylinder shop inspect the cylinders and you can be a part of that.

Dave: Ok

Stave: And he can talk, speak to you about what he finds.

My Engine Teardown in 2 minutes

Magneto Test and Rebuild