Jump to content

A1B6 vs A3B6


201Steve

Recommended Posts

I have a 77 J, it's the only one that I'm aware of that has the IO-360-A1B6D.

I'm looking at overhaul options, and as other threads have discussed, many have considered Lycoming exchange from A3B6D to A3B6.

I'm considering going from A1B6D to A1B6 but curious, would there be any good reason (or good reason not to) to exchange from an A1B6D to a A3B6?

Again, I believe the 77J is the only model that has the A1 rather than the A3. Wondering if anyone with a 77 has ever had this discussion?

Link to comment
Share on other sites

Another consideration is going for the IO390...I would only do this if my prop was at end of life as you need to go to a 3 blade assembly.

many say you can only use the extra power for only 5 minutes...which is great for take off...especially with a 3 blade.

How many run their engine at full power for cruise...no one does...and virtually any power setting you will pick up HP and speed

  • Like 1
Link to comment
Share on other sites

On 1/11/2021 at 10:22 PM, M20Doc said:

You can convert your A1 to an A3 by a Mooney SB.

It looks like I’m going to be OH’ing my engine, would you suggest having this done while down? It suggests it makes engine smoother, but this is the first I’m hearing of such conversion. 
 

worth it?

approximate cost in parts? (Doesn’t look like much)

Link to comment
Share on other sites

1 hour ago, 201Steve said:

It looks like I’m going to be OH’ing my engine, would you suggest having this done while down? It suggests it makes engine smoother, but this is the first I’m hearing of such conversion. 
 

worth it?

approximate cost in parts? (Doesn’t look like much)

It would be easily done while your crankshaft is out being overhauled.  Ask your overhauler for pricing, it requires new drive bushings.

Clarence

Edited by M20Doc
Link to comment
Share on other sites

On 1/13/2021 at 5:23 AM, larrynimmo said:

Another consideration is going for the IO390...I would only do this if my prop was at end of life as you need to go to a 3 blade assembly.

many say you can only use the extra power for only 5 minutes...which is great for take off...especially with a 3 blade.

How many run their engine at full power for cruise...no one does...and virtually any power setting you will pick up HP and speed

It’s 5% extra horsepower, so an extra 7.5 HP at 75% cruise.  

Link to comment
Share on other sites

On 1/13/2021 at 5:23 AM, larrynimmo said:

Another consideration is going for the IO390...I would only do this if my prop was at end of life as you need to go to a 3 blade assembly.

many say you can only use the extra power for only 5 minutes...which is great for take off...especially with a 3 blade.

How many run their engine at full power for cruise...no one does...and virtually any power setting you will pick up HP and speed

Let’s look at this as three individual issues...

1) Tossing out a good prop isn’t normal, but, they can get traded in... and... ground strikes happen, even when you are three towns away... at least four have occurred around here that I remember... where the pilot was not at fault...   Missile, Bravo, Ovation, M20E...  two fell in unmarked holes, one had a Jack collapse, the other got hit while it was tied down...

2) normally aspirated engines don’t stay at full power very long... As the output drops with altitude...   Climbing out with excess power... you can be pretty high before needing to reduce the MP...  MP drops off 1” per 1k’ in altitude...

3) Owners of NA engines often operate at WOT... not the same as 100% power, but... the added cubes will still be working and making a difference at higher cruise altitudes...  until efficiency becomes the PIC’s main driver... then he can throttle back on that flight...

Having options is an added bonus...  

Small increases in power, show up big in two places... Take-off roll, and climb rate... rule of thumb (?) a 10% increase in hp, can decrease T/O distance by 30%... climb rate increases in large chunks in a similar way...   oddly, T/O and climb don’t last very long... so the overall increase in total fuel used isn’t very big...

What the bump in power doesn’t do very well... conserve fuel while going faster...

To go Ovation fast... expect your fuel flow to increase to Ovation FFs...  :)

When testing out new levels of excess HP... bring Byron along.  Byron helped document some performance numbers for my O while still breaking in my 310hp IO550...  Climb rates can be unbelievable... fortunately Byron had his camera handy... :)

PP thoughts only, not a mechanic...

Best regards,

-a-

Link to comment
Share on other sites

I'm documenting this for future lookers, and a potential experience response that may or may not be out there, but it seems there is some confusion still lingering out there on this issue (including me). It is a question that, suprisingly, has not been discussed and/or resolved anywhere in the archives.

It only affects 1977 J owners, as this was the only year Mooney installed an A1B6D rather than the more common A3B6D (1978 - on). A couple of points discovered in the fragmented talks is the correct indexing of the propeller. This captured my attention because, the first annual I went in for, I got the call that my prop needed to be taken off to be Re-indexed and that it was hung wrong. What I think happened with me, and I've read has come up before, somebody identified the prop as being "mis indexed" because they were used to assuming the mx manual for the much more common A3B6 variant. It is unclear as of now, whether my propeller was originally installed with A1B6 indexing and then mistakenly re-hung with A3B6 indexing OR if it was originally mistakenly hung as A3B6 indexing and then converted back to A1B6 indexing. My gut tells me this is more common than is realized, but whether or not it really matters, I don't know. Thanks to Clarence for pointing me in the direction of Mooney SB M20-206 as a clarification of the difference between the two motors. I was not anticipating a "more to the story" scenario when reading it. My airplane life flashed before my eyes, as I traveled through time, back to that phone call in 2018 that "we need to pull the propeller, some idiot put it on wrong, we might as well send it off for a re-seal, it's only going to cost you a couple thousand, it's only going to take an extra 3 weeks..." OK, yes I am being dramatic, but I did think, wow how could you screw that up? Mis Index the prop? You just have to not be paying any attention to detail. Well, turns out, I believe I was the victim (or either the previous owner) of mechanic just not realizing that indeed, the 77 is unique, is not like all other J's, and yes, the prop stops/rests at a different index point than all other J models.

 

Discussions not yet solved within the archives:

-Why did Mooney change from A1B6D to A3B6D. Was it just a simple discovery that the engine runs a little smoother with a slight change in prop index? Extra credit reading, Why would something so minor necessitate a change in engine model number and not just a change in the service manual?

 

-If you are a 77j owner, is there any good reason to convert or not to "convert" your A1B6D to an A3B6D via Mooney SB M20-206? One would think, if THAT important, Lycoming and/or Mooney would just discontinue further talks of an A1B6 engine. "Oh, that's the old variant of the A3B6, we don't recognize it anymore, we just consider them reindexed A3B6's now." With as simple as a change that it is (from my understanding of the reading), it would just be a no brainer when doing any engine work. Yet, as discovered here, it's rarely discussed and even unknown in some cases.

 

-How many A1B6 J models are indexed incorrectly due to the natural assumption, "it's a J and they are all the same." And does it matter? It's ALMOST an A1B6 to A3B6 conversion simply with a re-index of the prop, but apparently there is also the need for a bushing and a new Lycoming serial plate. How big of a deal is this. If the difference in model variances in appreciable, you would think it would be noticeable or more commonly identified.

 

-How much time/money does the conversion cost between the new parts, the labor of re-indexing, and having a new Lycoming model plate installed. If going into Overhaul at any point, should it be a no brainer to have converted. Can it be done easily enought/Should it be done during an annual inspection?

 

My sense is that, none of the above matters much, since it's not discussed often, and only affects SN's 24-002 through 24-0377 of the 1977 J model. That said, I'm interested in being armed with the facts for upcoming overhaul and will attempt to reach out to Dmax and such to confirm if there isn't any consensus here. Also, let this serve as warning to those within the serial sequence to confirm whether they've had the conversion, and whether or not a would-be shop suggests moving it around if it doesn't need to be moved around.

  • Like 1
Link to comment
Share on other sites

Excellent discussion of model A type issues... things that got changed for the bravo model...

Looking back to what came before... What engine did the M20F last have?

There are a couple of Mooneys that have a different index... they are most noticeable at Mooney fly-ins...

The other Mooney that had the NA Continental IO360 engine stood out... mostly for its flaming cowl paint job, and for its odd indexing... in a row of ordinary M20Js...

PP thoughts only...  all Mooneys are special...

Best regards,

-a-

Link to comment
Share on other sites

11 minutes ago, 201Steve said:

My sense is that, none of the above matters much, since it's not discussed often, and only affects SN's 24-002 through 24-0377 of the 1977 J model. 

I had the same issue, with the prop being "reclocked" before I bought the airplane.   I *think* it got reclocked to the A3 position, but I'm still not certain.

We had the prop off last year to get it checked as part of the debugging when my governor failed.   I mentioned to my IA at the time that maybe it was an opportunity to check to see whether the clocking should be changed, and his opinion was that if I'm fine with how smooth it's been running we probably shouldn't mess with it.   I realized I agreed with that and whatever it is, we left it the way it is.  ;)

  • Like 1
Link to comment
Share on other sites

37 minutes ago, carusoam said:

Looking back to what came before... What engine did the M20F last have?

IO-360-A1A was on the 77 F model accorind to Mark Napier's chronolgy spreadsheet. Again, unique to the only the 77J and I believe a Cessna Cardinal. Maybe Cessna has a similiar SB? Perhaps more feedback?

Edit: According to Cardinal Flyers, the IO360 A1B6D was installed in the Cessna Cardinal from 1972 - 1978. All other things equal, and the relative ease of changing from A1 variant to A3 variant, the fact that Cessna saw no benefit in adopting the A3 throughout the end of life of its' Cardinal life says something about the worth/value. Don't know about the prop or how it would or wouldn't affect this in a Mooney/Cessna comparison.

  • Like 1
Link to comment
Share on other sites

On 1/13/2021 at 3:17 PM, 201Steve said:

Sounds expensive for a little climb performance :huh:

Expensive? A Rebuilt the 390 is $2,500 LESS than a Rebuilt 360. If new is your plan than it is $16,800 less

Forgive me for the pictures. Airpower doesn't play well on my phone. 

If you search on airpower for a 390 it doesn't come up and that is why I reached out to them for a quote.

A quick search on a Van's forum shows many peoples positive opinion of a 390 vs a 360. Its no 550 but it is noticeable.

Another example is a Bonanza 520 to a 550 conversion is 15HP (5%) increase in power but it is a big deal in reality. 

I dont have any hard evidence but I have heard that a 550 was certified at 300 under real rather than ideal conditions so it likely makes more than 15 hp more than a 520 in the same conditions. Maybe a 390 was certified the same way and makes more then 15hp (7.5%) in the real world. 

 

Screenshot_20210117-124117_Outlook.jpg

Screenshot_20210117-124640_Chrome.jpg

Screenshot_20210117-124655_Chrome.jpg

Link to comment
Share on other sites

On 1/13/2021 at 3:21 PM, Andy95W said:

Agreed.  And a great argument to just go with a roller cam IO-360-A3B6 with Powerflow exhaust.

The savings of a 390 would buy more than half of the cost of a powerflow exhaust. 

IO-390+powerflow+ an electronic ignition:D

Link to comment
Share on other sites

I wonder if Airpower would charge an "unlike core" fee on an overhaul or rebuild if you sent them an IO360 for an OH'd or rebuilt 390. If not and you're considering factory unit, besides hose and accessory work, i don't see why you wouldn't, but there is a strong argument not to get it if you're going with a field overhaul. Price Delta is significant. Quoted price for overhaul from Jewell, which includes remove/reinstall, is a significant Delta. So, I agree if your comparing Zephyr/Western Skyways/Etc to Factory, it's a manageable and sensible reach. If you're just trying to fix your airplane and get new internal guts without pretty paint, it's way over the budget.

Link to comment
Share on other sites

1 hour ago, 201Steve said:

IO-360-A1A was on the 77 F model accorind to Mark Napier's chronolgy spreadsheet. Again, unique to the only the 77J and I believe a Cessna Cardinal. Maybe Cessna has a similiar SB? Perhaps more feedback?

Edit: According to Cardinal Flyers, the IO360 A1B6D was installed in the Cessna Cardinal from 1972 - 1978. All other things equal, and the relative ease of changing from A1 variant to A3 variant, the fact that Cessna saw no benefit in adopting the A3 throughout the end of life of its' Cardinal life says something about the worth/value. Don't know about the prop or how it would or wouldn't affect this in a Mooney/Cessna comparison.

The Cessna 177RG TCDS (A20CE) only shows the IO-360-A1B6 or -A1B6D as certified for the airplane.    

The Mooney M20 TCDS (2A3) shows IO-360-A1B6D, -A3B6D, or -A3B6 as certified for the M20J. 

So if people want to swap to separate mags from a dual mag, on the Mooney it has to be an -A3B6 and on a Cardinal it has to be an -A1B6.  That's kind of interesting.   Whatever the operational difference is, it must not be that much.

 

Edited by EricJ
  • Like 1
Link to comment
Share on other sites

25 minutes ago, 201Steve said:

I wonder if Airpower would charge an "unlike core" fee on an overhaul or rebuild if you sent them an IO360 for an OH'd or rebuilt 390. If not and you're considering factory unit, besides hose and accessory work, i don't see why you wouldn't, but there is a strong argument not to get it if you're going with a field overhaul. Price Delta is significant. Quoted price for overhaul from Jewell, which includes remove/reinstall, is a significant Delta. So, I agree if your comparing Zephyr/Western Skyways/Etc to Factory, it's a manageable and sensible reach. If you're just trying to fix your airplane and get new internal guts without pretty paint, it's way over the budget.

They don't charge an unlike core on any engine. Its a great way to get rid of any engine from an ancient narrow deck to a dual mag "D" engine.

  • Like 1
Link to comment
Share on other sites

On 1/17/2021 at 11:06 AM, Tim Jodice said:

They don't charge an unlike core on any engine. Its a great way to get rid of any engine from an ancient narrow deck to a dual mag "D" engine.

It's not Airpower that decides the core exchange policy -- it's Lycoming. Lycoming sets the policy depending on what they are trying to incentivize. Lycoming retains the right to surcharge dissimilar cores but now they seem to want to get more IO-390s in the field. When I traded in my IO-360-A3B6D for an A3B6, I got a discount for retiring a D which Lycoming would like to get out of the field.

Skip

Link to comment
Share on other sites

The Mooney service bulletin M20-206 is pretty clear:

1. Changing the prop indexing from 1 to 3 makes the engine/prop combination slightly smoother particularly at high power settings

2. Doesn't change the caution range on the tachometer

3. Is optional at the owner's discretion.

The effect is likely small. If I got a good dynamic balance on 1 index, I would not spend money messing with it. If I were rebuilding an engine, I'd change it to a 3 because that is presumably better and more common and the incremental cost and effort would be insignificant.

You can't accidentally install the prop incorrectly because of the bushing arrangement. In order to change the indexing, you have to change bushings.

A prop indexed to 3 will hit TDC when the blades (viewed from the front looking aft) are positioned approximately 2 and 8 o'clock.

Skip

Link to comment
Share on other sites

@PT20J

Yes, good point about dynamic balance. This SB and the change in general from 1978 on was before DB was a thing, and likely makes the whole endeavor futile. I've decided it's likely imperceptible and thus am unlikely to even bother. To spend money on anything that is "presumably better" is spending money on hunch nonetheless.

10 minutes ago, PT20J said:

You can't accidentally install the prop incorrectly because of the bushing arrangement. In order to change the indexing, you have to change bushings

Can we get @Cody Stallings to chime in on this? What you say makes sense, I guess, but my prop was absolutely indexed one way, and re-indexed another way. It used to rest at 9 o'clock and 3 o'clock, which is really a nice place for it to stop. But, it was noticed as odd and changed where it now rests at like 10 and 4 (facing the prop from front). I do not recall any discussion nor spending of additional bushings, etc. It's like it was just unbolted and rebolted. Perhaps the bushings can be moved? I've never seen a prop installation so I don't have any reference on this, but interested to know.

Link to comment
Share on other sites

14 minutes ago, 201Steve said:

Can we get @Cody Stallings to chime in on this? What you say makes sense, I guess, but my prop was absolutely indexed one way, and re-indexed another way. It used to rest at 9 o'clock and 3 o'clock, which is really a nice place for it to stop. But, it was noticed as odd and changed where it now rests at like 10 and 4 (facing the prop from front). I do not recall any discussion nor spending of additional bushings, etc. It's like it was just unbolted and rebolted. Perhaps the bushings can be moved? I've never seen a prop installation so I don't have any reference on this, but interested to know.

The different part numbers on the bushings are because they're different diameters.   The prop will only fit over them when properly oriented, or at least that's the idea.

  • Thanks 1
Link to comment
Share on other sites

1 hour ago, EricJ said:

The different part numbers on the bushings are because they're different diameters.   The prop will only fit over them when properly oriented, or at least that's the idea.

So again I would say.... how did my prop get oriented in two configs with the same bushings...?

Link to comment
Share on other sites

45 minutes ago, 201Steve said:

So again I would say.... how did my prop get oriented in two configs with the same bushings...?

Either they re-used the old bushings, which is not supposed to be done, or somebody had some laying around or were able to get them quickly.    I think they're pretty commonly-used parts.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.