Lycoming engine code minutia

[Kiddo's Driver]

Piper Warriors (IIs?), (PA-28-161) come with one of two engines: O-320-D2A or O-320-D3G. The difference between the two is, as far as I can tell, simply which brand of magneto's are installed.
D2As us Bendix.
D3Gs us Slick.
That said, MY O-320-D2A in my Socata Tampico has Slick magnetos.
What FAA rule, policy, whatever, allows you to swap from Bendix to Slick or from Slick to Bendix without having to change the official engine suffix/Dash Number?

O-320-D2A160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as D1A but with fixed-pitch propeller provisions and 3/8 inch attaching bolts.
O-320-D2G160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1. Same as the D2A except with Slick instead of Bendix magnetos and 7/16 inch instead of 3/8 inch propeller flange bolts.
O-320-D3G160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1. Same as the D2G but with 3/8 inch propeller attaching bolts.

 

[Bell206]

What FAA rule, policy, whatever, allows you to swap from Bendix to Slick or from Slick to Bendix without having to change the official engine suffix/Dash Number?

Unless Lycoming has a bulletin or other engineering document for that swap, it will be a major alternation as it changes models numbers. I'd call Lycoming to see.

 

[Kiddo's Driver]

Unless Lycoming has a bulletin or other engineering document for that swap, it will be a major alternation as it changes models numbers. I'd call Lycoming to see.

I’ve got the 337 CD for my plane from the FAA. I’ll check that.

 

[Bell206]

I’ve got the 337 CD for my plane from the FAA. I’ll check that.

Try this:
Lycoming SI 1443

 

[Kiddo's Driver]

Try this:
Lycoming SI 1443

Ah, I’ve seen this before. It was when I was comparing D2A & D1A.
So the SI is what allows installing Slick on a D2A, essentially making it a D3G but retaining the D2A markings.

 

[Kiddo's Driver]

Interesting.
Different left mags.
That means D2A with Slick mags != D3G.

 

[Bell206]

So the SI is what allows installing Slick on a D2A, essentially making it a D3G but retaining the D2A markings.

One of the benefits of being the TC holder is one can easily modify/upgrade the aircraft specification or type design in house which allows you to simply install the upgrade as a minor alteration. This process also stated in the definition of a major alteration which exempts aircraft spec changes.

That means D2A with Slick mags != D3G.

Not technically. If you needed a stamped D3G you couldnt put Slicks on a D2A and install it. Some OEMs simply list changes similiar to this in the parts manual as an alternate part, however, I believe with engines, since that part does change the model number that method is not is not available like on a Cessna.

 

[Kiddo's Driver]

One of the benefits of being the TC holder is one can easily modify/upgrade the aircraft specification or type design in house which allows you to simply install the upgrade as a minor alteration. This process also stated in the definition of a major alteration which exempts aircraft spec changes.


Not technically. If you needed a stamped D3G you couldnt put Slicks on a D2A and install it. Some OEMs simply list changes similiar to this in the parts manual as an alternate part, however, I believe with engines, since that part does change the model number that method is not is not available like on a Cessna.

I did not do a good job of writing what I was trying to say.
Because the left mag for a D2A, 4373, and the left mag for a D3G, 4371, are different, just changing the Bendix mags out on a D2A to the SI-approved 4373 does NOT make it a D3G.

The real funny part about this is that I have been saying in another thread that all I had to do to change my D1A into a D2A was to change the position of the plug inside the hollow crankshaft and change the propeller flange bushings from 7/16" to 3/8". It turns out there is a third requirement that I was following, but not mentioning/acknowledging; I needed to change the left mag from a 4371 to a 4373. This was/is easy to accomplish since I have a suitable 4373 coming off of my current installed engine, but it IS a requirement.

Oh, and I don't need a D3G. I just find these minor changes being the driver of the suffix interesting. Previously, I thought of those numbers as written in stone.

 

[Bell206]

Previously, I thought of those numbers as written in stone.

It depends on who is carving those numbers. For you, it is closer to written stone; for the OEM it's closer to written on a dry erase board.

 

[Kiddo's Driver]

It depends on who is carving those numbers. For you, it is closer to written stone; for the OEM it's closer to written on a dry erase board.

You really just have to understand the differences between the engines & have, or BE, an A&P/IA that is comfortable doing 337s.
I can take my O-320-D2A and, if my 4373 goes bad, install my spare 4371 on it, converting it to an O-320-D3G. All it takes is a logbook entry and a 337. The PA28-161 can use either engine.

 

[Bell206]

You really just have to understand the differences between the engines & have, or BE, an A&P/IA that is comfortable doing 337s.

And have the approved data to complete the 337. Without that, nothing happens.

I can take my O-320-D2A and, if my 4373 goes bad, install my spare 4371 on it, converting it to an O-320-D3G.

As I noted above, you'll have a D2A with a 4371 mag installed and not a D3G. For it to be legally a D3G, it will need its data plate changed which is usually only at the STC level in the field.

 

[Kiddo's Driver]

And have the approved data to complete the 337. Without that, nothing happens.


As I noted above, you'll have a D2A with a 4371 mag installed and not a D3G. For it to be legally a D3G, it will need its data plate changed which is usually only at the STC level in the field.

Still processing. This feels like something covered by an old SI that only 5 people know about, and those 5 are getting close to triple-digit age.
Going from CS to fixed pitch or from fixed pitch to CS is covered by an SI and is handled by a field approval. I would bet that somewhere there is a document that talks about switching between the various suffixes.

 

[Bell206]

Going from CS to fixed pitch or from fixed pitch to CS is covered by an SI and is handled by a field approval.

Except if there is an OEM bulletin, ie., the Service Instruction, there is no field approval or 337 required because that change is part of the aircraft specification, ie., type design, and is not defined as a major alteration as shown below. So, for example, if Lycoming intended the installation of the Slick mags to convert a D2A to a D3G, then SI 1443 would also provide the instruction to modify the engine data plate, which Lycoming has done in other model change bulletins. Better?