IO360-A1B6D Square tip prop vs IO360-A3B6D Round tip prop

[John Mininger]

I have a 1977 M20J, the first model year for the J. The engine was originally an IO360-A1B6D with the squared tipped McCauley prop. At some point, the engine was changed to a A3B6D. And last year I replaced the engine with a rebuilt A3B6 (non-D). I still have the square tip prop.

Does anyone know the reasons and history of why Mooney started the J line with a A1B6D, square tipped McCally, and immediately in the next model year went with the A3B6D and a round tip McCauley?

[John Mininger]

Thanks Jim.

But I have to admit that I'm a bit disappointed to hear that my square tipped Mac can only by used on a 77 model. It kind of cuts the potential pool of buyers way down if I try to sell it and replace it with an MT. 

[carusoam]

Might be a good idea to invite an MSer with some prop experience to the conversation.... @Cody Stallings
 

Best regards,

-a-

 

[Hank]

15 minutes ago, carusoam said:

Might be a good idea to invite an MSer with some prop experience to the conversation.... @Cody Stallings
 

Best regards,

-a-

 

Don't forget Norm! @testwest

[PT20J]

Per the Lycoming TCDS 1E10, the difference between an A1B6D and an A3B6D (or A3B6 neglecting the magneto) is a 120 degree clockwise change in the prop index.

Skip

[Cody Stallings]

I can’t say with any degree of certainty as to why they made the change, but I can tell you a square tip prop performs better than a rounded tip but with the added expense of increased noise.

Also, using the -16E Blade May have been a move to Standardize the propellers even though the J has a Lycoming flange an the K’s have Continental flanges.

That was something I never understood about McCauley. 
using the same blade for both 4 an 6 cylinder.

You will never see that with a Hartzell.

[Guest]

SB M20-206 allowed for replacement and repositioning of the propeller drive bushings in the crankshaft.  This changed the A1 engine into an A3 engine. According to the SB it allowed for smoother operation.

https://cdn2.hubspot.net/hubfs/4147179/technical_documents/service_bulletins/sbm20-206-1.pdf

Clarence

[John Mininger]

Thank you Clarence.

That explains why I remember that conversion being a rather simple entry in my engine log.

Since the conversion to the rebuilt (remaned) A3B6 last year, I no longer have that log book.

[bradp]

I also recall Dorn telling me that the round tip 214 had less harmonics in the caution range compared to the square tip 

[201Steve]

I am researching this now from a tip by Clarence. I have a 77 with A1 variant. Going up for engine Teardown tomorrow. I have mostly ruled out dropping the D but am wondering if I should have them go through the formalities of an A1 to A3 conversion. If it’s worth anything, and to the OP’s point, why they did it. 

[PT20J]

The only way I know to get rid of the D is to exchange the core for a different engine as it’s not a simple modification.

The Mooney SB states that the change in prop indexing made the engine run smoother, so I would do it if it were mine. 

Skip

 

[201Steve]

34 minutes ago, PT20J said:

The only way I know to get rid of the D is to exchange the core for a different engine as it’s not a simple modification.

 

 

Note the clarification here before it goes into another D thread (too much D is never good), this is NOT a discussion of D vs Non- D.    It compares:    A1B6(D) vs A3B6(D)     . As further explained in my other thread, this is part of the problem. People see A1B6 and A3B6 and see it as the same thing. Resist fixation on the D (remember, the too much D rule).

Confusion only applies to 1977 J models through SN: 24-0377

[PT20J]

27 minutes ago, 201Steve said:

Note the clarification here before it goes into another D thread (too much D is never good), this is NOT a discussion of D vs Non- D.    It compares:    A1B6(D) vs A3B6(D)     . As further explained in my other thread, this is part of the problem. People see A1B6 and A3B6 and see it as the same thing. Resist fixation on the D (remember, the too much D rule).

Confusion only applies to 1977 J models through SN: 24-0377

I understand and only meant my comment as clarification because of your statement: I have mostly ruled out dropping the D, that some might take that to mean that converting to two mags is an option at overhaul. 

 

[rotorman]

On 1/17/2021 at 9:02 AM, PT20J said:

The only way I know to get rid of the D is to exchange the core for a different engine as it’s not a simple modification.

The Mooney SB states that the change in prop indexing made the engine run smoother, so I would do it if it were mine. 

Skip

 

Skip, do you know the SB number?

[EricJ]

14 minutes ago, rotorman said:

Skip, do you know the SB number?

It's M20-206:

https://cdn2.hubspot.net/hubfs/4147179/technical_documents/service_bulletins/sbm20-206-1.pdf