IO360A1A vs IO-360-A3B6D

[Gary0747]

I have never really understood why Mooney considered the change from the IO360A1A to the IO-360-A3B6D when they came out with the 201 as an improvement?  We all know the saga of incidents with the single drive mag. But also the IO-360-A3B6D has counter weights on the crank.  The A1A has no counter weights and have ridden behind both engines I have never been able to tell if the counter weights made the IO-360-A3B6D smoother?  I see the old ADs on the counter weights plus the seem like one more piece to be thrown off in case of an over speed incident. I assume the overhaul costs are more but never really checked that out.  Am I wrong on this or missing something?  Maybe I am biased owing an F.  

[ArtVandelay]

The A3B6 solved the single mag problem.
The counter balance can help but only if the propeller is balanced.

[N201MKTurbo]

The counterbalances reduce the torsional stress on the crankshaft. You can’t really feel these , but your prop and crank can. 

That being said, I wonder if there is a measurable difference in the failure rate of the two models?

[N6018Q]

One advantage of the B6D over the A1A, if you have a Hartzell prop, is that the intermediate RPM No Continuous Operation zone (mine was 2100-2350) is no longer applicable. At least according to the Hartzell factory rep I spoke to.

[mikebroady]

Hi all. I know this is a late post but it's the best thread I can find for this question. I'm a UK pilot and I just had an engine failure but managed to get the aircraft down, wheels up, into a field with very little damage. The engine (IO-360-A1A) is destroyed and I'm looking around for a replacement. One contact has an A3B6BD available, which I could possibly afford to O/H. I know the difference is the mags and counterweights but has anyone replaced one or has any advice on the practicalities of swapping. Currently I can't find a used A1A in the UK and a new unit cost makes it uneconomical.  It had a 3 blade Hartzell fitted before I bought it btw.

[EricJ]

34 minutes ago, mikebroady said:

Hi all. I know this is a late post but it's the best thread I can find for this question. I'm a UK pilot and I just had an engine failure but managed to get the aircraft down, wheels up, into a field with very little damage. The engine (IO-360-A1A) is destroyed and I'm looking around for a replacement. One contact has an A3B6BD available, which I could possibly afford to O/H. I know the difference is the mags and counterweights but has anyone replaced one or has any advice on the practicalities of swapping. Currently I can't find a used A1A in the UK and a new unit cost makes it uneconomical.  It had a 3 blade Hartzell fitted before I bought it btw.

The -A1A is the only engine specified in the TCDS for the M20F.   There may be some STC conversions available, but those would require all of the STC permissions and paperwork as well, if available.

I don't know if you have more latitude for changes with a UK registration, but that's the situation in the US for an N-registered airplane.

Glad you got down ok.   That hole in the case doesn't look good.

 

[KSMooniac]

I can't remember if LASAR or Mod Works/Mod Squad has or had an STC to fit an A3B6D on an F, but I believe there was an STC at one time.  You can search STC's on the FAA website.  If it was LASAR, they may still have the ability to sell you the package.  If it was Mod *, then you're not going to be able to use it.  I don't know the rules under EASA to use a US/FAA STC, though... perhaps it isn't a big deal.  I see you have a G- registration, so that definitely falls under EASA.  I do not remember if that STC required different parts such as engine mount, cowl, oil cooler configuration, intake, etc, which are all different on the J models.

Is it economical to source overhaul parts from the US?  I suspect you could get a replacement A1A case without too much trouble.  Perhaps the rest of the parts to complete a rebuild as well.

Nice work putting her down safely!  I hope you can get her back in the air in a reasonable fashion soon.

[A64Pilot]

From what little I know about the UK it’s not likely at all that he can deviate from the TC, not even a little bit

[Ragsf15e]

I agree that you might be able to source a case and rebuild your current engine.  Good luck and nice job!

[Ragsf15e]

If you’ve got cash burning a hole in your pocket, you can buy an io-390 from lycoming and add 10hp.

[EricJ]

On 5/15/2020 at 1:24 PM, N6018Q said:

One advantage of the B6D over the A1A, if you have a Hartzell prop, is that the intermediate RPM No Continuous Operation zone (mine was 2100-2350) is no longer applicable. At least according to the Hartzell factory rep I spoke to.

That's in the prop manual as well for the Top Prop.