M20J not producing thrust

[aaronk25]

25 degrees of timing in a mooney Io360 is the best way to go. If you can legally do it (dual mag) great. If you got separate mags which are at 20d timing search on this forum for jetdriven post about how to do it. It brings the mooney to life! 20d is terrible. Now you won't cruise below 2400rpm and most likely 2500 rpm with 25d of timing as the engine will growl at lower rpm, but with /20d of timing you won't run more than 2500 rpm or you will be grossly inefficient. We didn't buy a Mooney to go slow right? Chts will be higher but if you can't keep them below 380 then adjust cowl flaps, tweak baffles until you get it to work. It's worth 6kts in my J and 1-2mpg. Go 25d!

 

 

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[laytonl]

Lynn at AGL will figure this out for you.  He's good. Lee

[nels]

I hear in this forum that advancing the timing increases cylinder temp and decreasing will raise cyl temp. I assume it must be correct but I've never tried it myself but I know in an automobile engine overheating problems can sometimes be eliminated by advancing the timing. I know this to be factual as I have done it. Why is there a difference aircraft to ground craft??

[jetdriven]

retarding timing, all else equal, will lower CHT somewhat.

[carusoam]

Just to confirm...

1) retarding the timing means going closer to TDC....

2) advancing the timing means going further away from TDC....

3) 25° is more advanced than 20°....

4) 25° burns more fuel in the cylinders for a longer period of time, allowing more heat to the cylinders.

5) 25° leads to more efficiency with the cost of higher CHTs...

6) Continental uses 23° BTDC, I believe...

Best regards,

-a-

Edited February 17, 2017 by carusoam

[wishboneash]

Mine is 20d timing (A3B6 engine) and consider myself in the "slow J" category. Rigging is probably the culprit since I can climb well, engine FF is close to 19gph at take off and RPM makes 2700+. 

A trip to Texas see DMax might be a good idea.

I don't think a topic like this comes up in the Cessna group!

[Brian Scranton]

Interesting--the info plate on my IO360A1A has the 25 scratched out and a 20 stamped on it right below. Checked the mags today and they are at 20...

[carusoam]

Many got their timing changed a while back...

Knowledable pilots may want the 25° timing depending on their situation.

Somebody posted what it took paperwork wise to undo the unwanted change...

Stuff I read around here, I'm not a mechanic, just a PP...

Best regards,

-a-

[EtradeBaby]

On 2/9/2017 at 11:57 PM, lukejb said:

I'm interested in learning more about the timing.  So what should the timing be set to in on an io-360 with a dual mag?  I am wondering what my mechanic is setting it to.  At 25 will you get more power than at 20?  I'm pretty clueless when it comes to this and feel like it is something I should know and do want to make sure I am getting optimal performance from my engine.

Think of timing as an adjustment for cylinder pressure. Fuel is designed to burn not explode (exploding fuel is called detonation. Very harmful). Since it's not exploding it takes time for the flame front to propagate to the cylinder walls and build sufficient pressure to force the piston down. Because of this you must ignite the mixture at a point prior to the the piston reaching TDC (top dead center) this is referred to as degrees BTC (before top dead center). The maximum amount of power to be achieved from timing would be to set It at a point early enough in the cycle to achieve maximum pressure just after TDC. Many things contribute to your cylinder pressure however and I don't believe any two engines in existence should be treated exactly the same. I.e. Just because this guys is 25 mine also needs to be 25.

Also, You are not burning more fuel. You are using the fuel you burn more efficiently. The price you pay for efficiency in any engine is heat. Since you are converting more heat into motion by advancing the timing your engine will run at a higher temperature. 

[Llcrt]

Sfurr201,

 

     You and I are in a very similar boat with speed.  If  you don't mind, I would like to chat on the phone and see what you have done vs what I have done and see if we can't solve this speed problem.  My number is 619-723-7155 and my name is Shawn.  Thanks

 

    

[carusoam]

Llcrt,

if you are trying to reach somebody related to a post...

It helps to drop their name like this... @Sfurr201

This way he will get a small notification that you have mentioned him... the @sign is the key...

if you really want to be specific, push the 'quote' button on his post and type your message below his re-printed message...

Sort of excerpts from MS101, there is no official training, just stuff I learned from being here...

Best regards,

-a-

Edited June 25, 2017 by carusoam

[jaylw314]

The TCDS for the IO-360 notes the following:

"All models except IO-360-A1B6D and -A3B6D have optional timing of 20°BTC"

That should mean you can get your A&P to switch it and only log it as a minor alteration if you have the A3B6?

[jetdriven]

Its on the TCDS. That's your authority.  Get the proper magneto and make a log entry.  Enjoy your 3-5 knots free, for the same fuel flow. 

Edited June 26, 2017 by jetdriven

[jaylw314]

1 hour ago, jetdriven said:

Its on the TCDS. That's your authority.  Get the proper magneto and make a log entry.  Enjoy your 3-5 knots free, for the same fuel flow. 

The part I wasn't sure of is if the reference to the A3B6D was intended to include the A3B6 (or if the writers were too lazy to specifically say not), since it seems like the TCDS implies this in a few other places.  Color me paranoid.

I might just ask my A&P to retime my magnetos while wearing someone else's glasses, so I end up with 22 BTC...

[ArtVandelay]

Its on the TCDS. That's your authority.  Get the proper magneto and make a log entry.  Enjoy your 3-5 knots free, for the same fuel flow. 

It's also stamped on the engine plate, 20° for my A3B6 new from factory in 1996. You may have a tough time arguing around that.

[jetdriven]

I have an email from the lycoming factory rep and he admitted its legal. But if it wasn't legal it wouldn't be on the TCDS.  It's an option granted via a service letter. Option means you can opt out.  He tried to threaten me with the warranty coverage but I'd like to see that. 

Edited June 26, 2017 by jetdriven

[201er]

4 hours ago, jetdriven said:

 

What does 25 degree timing have to do with avoiding LOP? Engine runs much better LOP with the advanced timing.

[Hank]

1 hour ago, 201er said:

What does 25 degree timing have to do with avoiding LOP?

"Because it burns up valves!" Doncha know?????    Seriously, I've had two different A&Ps tell me this while working on my magneto problems this spring, one each in NC and AL. But no, they are limited to the South . . . .

[N201MKTurbo]

There is an advantage to running LOP with more advanced timing. A lean mixture burns slower than a rich mixture. LOP requires more advance so the maximum pressure happens at the same crank angle as ROP (Approx 15 deg ATDC) . Anybody who says that LOP and 25 degree timing don't mix doesn't know what they are talking about. Besides it is all about temperature, so keep your temps in control and you will be fine.

[Cyril Gibb]

50 minutes ago, N201MKTurbo said:

There is an advantage to running LOP with more advanced timing. A lean mixture burns slower than a rich mixture. LOP requires more advance so the maximum pressure happens at the same crank angle as ROP (Approx 15 deg ATDC) . Anybody who says that LOP and 25 degree timing don't mix doesn't know what they are talking about. Besides it is all about temperature, so keep your temps in control and you will be fine.

Correct.  Too bad a regional manager for Lycoming doesn't understand engine technology.

To expand on N201MKTurbo:  the objective should be to get the max cyl pressure at the sweet spot approx 15 degrees after TDC.  If earlier, the CHTs rise unacceptably.  If later, you waste energy out the exhaust.

RPM: given the same mixture, Increasing RPM pushes the peak later.  Reducing RPM pushes the peak earlier.  Higher RPM also wastes power because of increased internal engine friction.

Mixture: Burn rate slows for either richer or leaner than "ideal mixture".  If you lean more, the burn slows and pushes the peak later.  If you enrichen more you also push the peak later.  That's why we enrichen for takeoff.  The mixture burns more slowly and pushes peak pressure later, keeping temps down.  (excess fuel has nothing to do with it, it's just to slow the burn and delay the pressure peak) ... for those that understand engine dynamics, with more precise and automated control (that we don't currently have), LOP takeoff would also be ok.

20-25 degree advance:  with 25, you have the flexibility to use rpm and mixture to get the peak in the right spot.  With 20, you have less options and have to get a faster burn to get the peak in the correct spot using excess fuel that doesn't burn completely and pressure also doesn't last as long.  Also, the power advantage that people see in fine wires is because of less shielding around the spark that traditional massives have.  Fine wires give a larger initial flame front resulting in a marginal advance. BY plugs (in theory) do the same by initiating a flame front deeper in the mixture.

[aaronk25]

I wonder if the Rep realizes that people fly experimentals running Mogas at 25 btdc 8.6 compression 200hp -so the exact same motor to TBO LOP! Sure lot more factors but really he thinks this motor can actually detonate on 100ll. Sure you can get it hot and melt it down but 100ll is good stuff!


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[bradp]

Just remember for those with impulse coupled mags - if you are going to do the Byron method and change your magneto timing make sure that your mags impulse coupleing correspond to that timing.  For example if you have an impulse coupling of X degrees of "retard" on a mag of Y degrees, during starting the spark occurs at angle Y-X degrees, which should occur at or slightly after TDC.  If you make the new timing of the Mag Y+5 without changing the impulse coupling to X+5 you will get spark at X+5-Y, which can occur before TDC enough to cause hard starts and "backfires", YMMV.