IO-360-A1A vs IO-360-A1B6

[HRM]

Fellow Mooniacs,

Can anyone here explain the difference between these two engines? On the Lyc site the only thing I could see was that the B6 is for a J and the A1A is for the E.

Also the A1A mags are 4370 and 4345 while the B6 is 4370 and 4372.

[DMM]

According to Wikipedia the B6 has  impulse coupled magnetos and crankshaft counterweights.  I have no idea if these can be installed in an "E" 

https://en.wikipedia.org/wiki/List_of_Lycoming_O-360_variants

[HRM]

2 hours ago, DMM said:

According to Wikipedia the B6 has  impulse coupled magnetos and crankshaft counterweights.  I have no idea if these can be installed in an "E" 

https://en.wikipedia.org/wiki/List_of_Lycoming_O-360_variants

Actually, I have no intention of swapping out the A1A in my E for a B6--I just wondered what the difference in the engines was.

That said, if all it is is magnetos, then why couldn't an E have a B6 and a J have an A1A? The bigger question is why; i.e., why didn't Mooney just put an A1A in the J?

This will take an A&P with deep knowledge to answer.

[Ragsf15e]

It’s not something simple like oil cooler and intake manifold design/location is it?

[HRM]

1 hour ago, Ragsf15e said:

It’s not something simple like oil cooler and intake manifold design/location is it?

I don't think so, at least not from the data on the Lyc site.

[M20F-1968]

The A1A does not have counterweights.  I believe the B6 does.

John Breda

[jaylw314]

Clipped from the IO-360 TCDS:

 

IO-360 A1A Basic Model. Four cylinder air-cooled, horizontally opposed, direct drive, fuel injected, tuned induction engine having oil jets for internal piston cooling. Provisions for single action controllable pitch propeller.
IO-360-A1B Same as IO-360-A1A but has impulse coupling magnetos.
IO-360-A1B6 Same as IO-360-A1B except has crankshaft equipped with one 6.3 order and one 8th order counterweights.
IO-360-A1B6D Same as IO-360-A1B6 except has Bendix Series impulse coupling dual magnetos instead of two S-1200 Series magnetos.
IO-360-A1D Same as IO-360-A1B except has one S-20 series impulse coupling and one S-200 series magnetos instead of two S-1200 series magnetos.
IO-360-A1D6 Similar to IO-360-AIB except has propeller governor drive located on left front of crankcase instead of on accessory housing. Incorporates crankshaft equipped with one 6.3 order and one 8th order counterweights.
IO-360-A1D6D Same as IO-360-A1D6 except has Bendix D4LN-3021 dual magneto.
IO-360-A3B6D Same as IO-360-A1B6D except has propeller locating bushings rotated 120° clockwise.
IO-360-A3B6 Same as IO-360-A1B6 except has propeller locating bushings rotated 120° clockwise.
IO-360-A3D6D Same as IO-360-A1D6D except propeller locating bushings rotated 120° clockwise.

1E10_Rev_28.pdf

[HRM]

1 hour ago, jaylw314 said:

Clipped from the IO-360 TCDS:

 

IO-360 A1A Basic Model. Four cylinder air-cooled, horizontally opposed, direct drive, fuel injected, tuned induction engine having oil jets for internal piston cooling. Provisions for single action controllable pitch propeller.
IO-360-A1B Same as IO-360-A1A but has impulse coupling magnetos.
IO-360-A1B6 Same as IO-360-A1B except has crankshaft equipped with one 6.3 order and one 8th order counterweights.

So does the J, because of the counterweights, not have the RPM continuous operation restriction band? That would make sense.

[EricJ]

15 minutes ago, HRM said:

So does the J, because of the counterweights, not have the RPM continuous operation restriction band? That would make sense.

No, there's still a yellow arc.

[jaylw314]

On 12/24/2018 at 6:07 PM, HRM said:

So does the J, because of the counterweights, not have the RPM continuous operation restriction band? That would make sense.

No, there's still a caution arc with the factory Macauley prop.  The POH says to avoid continuous operation between 1500-1950 RPM below 15" MP.

With the Hartzell 2-blade prop, though there is no such caution or restriction, so presumably it's something specific to the factory combo, and not the motor itself.

[Guest]

Propeller operational limitations are generally found in the propeller type certificate, where propeller/ engine combinations are listed.

Clarence

[HRM]

So was there an improvement from the A1A to the B6? I am just trying to understand the what and why because these motors are pretty much identical except for the counterweights.

Also, where are they? The counterweights that is.

Lastly, could a B6 be put on an E, or an A1A on a J?

[jaylw314]

1 hour ago, HRM said:

So was there an improvement from the A1A to the B6? I am just trying to understand the what and why because these motors are pretty much identical except for the counterweights.

Also, where are they? The counterweights that is.

Lastly, could a B6 be put on an E, or an A1A on a J?

Counterweights are attached to the crankshaft with a sliding mount to allow them to move.  You can find pictures if you google "Lycoming crankshaft counterweights"

In theory, counterweights should result in a smoother running engine.  It might possibly also change restrictions related to max RPM or resonance with various prop combinations, but I know of no specifics.

If it's not in the TCDS, installing a motor would be a major modification requiring an STC (like the Missile and Rocket), or letting the FSDO crawl up your butt...

[EricJ]

As has been mentioned, the TCDS dictates the configurations approved for the Type Certificate, and deviating from that requires an STC or the filing of a 337 form with "approved data" for a major modification.

For most early M20 models with fuel injection the TCDS specifies the IO-360-A1A engine.  For the J model it says:

"Textron-Lycoming IO-360-A1B6D or IO-360-A3B6D or IO-360-A3B6. (Bendix fuel injector, Model RSA 5AD1, P/N 2524054) See Note 12 and Note 20."

So if you want to put anything else in a J model other than what is listed in the TCDS, it will require either an STC from somebody who does the approval work, or solicitation of a field approval for a 337 form for a major modification from your local FSDO, as @jaylw314 mentioned.

The A1 to A3 conversion just reclocks the prop on the hub and can be done via a Mooney Service Bulletin (M20-206).    The suffix D to non-D conversion is the elimination of the dual Bendix magneto for separate single magnetos.   Apparently Lycoming no longer supplies D suffix engines, and even if you send them one as a core you'll get a non-D back.

You can really go down rabbit holes on this stuff, e.g., I have a Hartzell top prop on my M20J, installed via an STC, and there is confusion in the logs as to whether it's installed clocked as an -A1 or as an -A3.  Sorting out whether it really needs to be placarded for a tach yellow arc or not, or whether the propeller is okay to install in the -A3 position is confusing.   The propeller TCDS says no.  The STC suggests yes, but isn't specific.   If it is not okay to install the propeller in the -A3 position, then the engine must have the Bendix dual mag as the -A1B6 (non-D suffix) is not on the M20J TCDS.  Seems to fly fine, so I'm not too worried, but it's one of those things.

[PT20J]

2 hours ago, EricJ said:

Apparently Lycoming no longer supplies D suffix engines, and even if you send them one as a core you'll get a non-D back.

Actually, Lycoming will still overhaul or rebuild the dual mag engines. I discussed this with Lycoming when I recently replaced an IO-360-A3B6D with a -A3B6. You will get an overhauled mag since the dual mags are no longer in production. Since Continental bought the Bendix magneto line, Lycoming has switched to Slicks wherever possible. There are a lot of internal dufferences between the A3B6D and the A3B6 - its not just the mags - and Lycoming will make it worth your while to switch. 

Skip

[HRM]

8 hours ago, HRM said:

Lastly, could a B6 be put on an E, or an A1A on a J?

My question was ill-posed, I frankly have no interest in doing it (B6 ⇔ A1A) as I am more interested in the differences from an academic standpoint. What I am understanding from the discussion is that Lyc put the counterweights in for reduced vibration and better performance near resonance points; as such, a B6 in an E would be an improvement, but most likely not worth the administrative hassle.

There could also be W&B issues in either direction given the J is a long-body. 

What was most important to my questions, and not revealed in them, is the exterior configuration of the engines. Other than the data plate, the two should be identical in exterior appearance and size given the only difference is deep inside on the crankshaft. This would explain the fact that on the Lyc website the same photo is used for each engine on the data pages.

[EricJ]

1 hour ago, HRM said:

My question was ill-posed, I frankly have no interest in doing it (B6 ⇔ A1A) as I am more interested in the differences from an academic standpoint. What I am understanding from the discussion is that Lyc put the counterweights in for reduced vibration and better performance near resonance points; as such, a B6 in an E would be an improvement, but most likely not worth the administrative hassle.

There could also be W&B issues in either direction given the J is a long-body. 

What was most important to my questions, and not revealed in them, is the exterior configuration of the engines. Other than the data plate, the two should be identical in exterior appearance and size given the only difference is deep inside on the crankshaft. This would explain the fact that on the Lyc website the same photo is used for each engine on the data pages.

J's are "mid-body" given that they now make longer Mooneys that are "long-body". 

The A1A and A1/3B6(D) also differ in the accessory case when the dual mag is used.   It makes the packaging a bit different and is why there are some line/hose routing and baffle issues when changing from one to the other.   For the most part, though, they're largely the same.

The counterweight issues and the yellow arc in the tach, to the best of my understanding, deal with torsional vibration modes.   I've been curious myself how much difference there really is, given plenty of each type have been flying around for many decades.

[HRM]

9 hours ago, EricJ said:

The A1A and A1/3B6(D) also differ in the accessory case when the dual mag is used. 

I am not looking at the dual mag at all--in fact, from all the discussion on it over on MAPAlist, it appears to have been a bad idea.

So, my conclusion from all the discussion is that an A1A and B6 are indistinguishable externally, which is what I wanted to confirm. Thanks all.