Surefly base timing 20 or 25?

[Shadrach]

 

 

40 minutes ago, carusoam said:

Ross,

Hard to tell during the start up process...

Since the timing is set to TDC on the mag used for starting... for both 20 and 25°BTDC mags...

Yes/no?

Best regards,

-a-

For impulse couplings it depends on the application and the lag angle (I believe some applications fire slightly ATDC). SOS systems are typically set to retard the timing to TDC.

Edited February 20, 2021 by Shadrach

[Shadrach]

18 minutes ago, PT20J said:

The impulse coupling lag angle is 5 deg less than the advance, so I believe it fires at 5 deg BTDC in either case. 

Skip

Which got me thinking. I reread the timing service instruction. The reason for the timing change per the SI is cooler CHTs and lower risk of detonation in extreme cold.  Easier starting is not mentioned, in fact the only mention of starting is with regard to lag angle which is changed from 20 to 15 to ensure ignition timing during start stays at 5BTDC.  I have no issue with decision to make 20° optional. I just wish 25° was also an option for engines produced after 1975.

[PT20J]

3 minutes ago, Shadrach said:

Which got me thinking. I reread the timing service instruction. The reason for the timing change per the SI is cooler CHTs and lower risk of detonation in extreme cold.  Easier starting is not mentioned, in fact the only mention of starting is with regard to lag angle which is changed from 20 to 15 to ensure ignition timing during start stays at 5BTDC.  I have no issue with decision to make 20° optional. I just wish 25° was also an option for engines produced after 1975.

I discussed this at length with my Lycoming field rep when I ordered my rebuilt. Lycoming evidently has to get FAA approval for every variation so it minimizes the options. It comes the way it comes and if you want to change it after delivery that’s fine with Lycoming. Another instance is the prop governor line that interferes with the M20J motor mount. Lycoming lists in the IO-360 IPC a Mooney-specific line. But, they refuse to build you an engine with that line. You have to order it separately (it’s several hundred bucks and long lead because the make them to order) and install it yourself. Most mechanics just bend the standard line a bit so it clears the mount.

Skip

 

[Shadrach]

49 minutes ago, PT20J said:

I discussed this at length with my Lycoming field rep when I ordered my rebuilt. Lycoming evidently has to get FAA approval for every variation so it minimizes the options. It comes the way it comes and if you want to change it after delivery that’s fine with Lycoming. Another instance is the prop governor line that interferes with the M20J motor mount. Lycoming lists in the IO-360 IPC a Mooney-specific line. But, they refuse to build you an engine with that line. You have to order it separately (it’s several hundred bucks and long lead because the make them to order) and install it yourself. Most mechanics just bend the standard line a bit so it clears the mount.

Skip

 

Good to know. I’ve been given a lot of conflicting/untrue info. Everything from 25 is no longer allowed to lycoming mandating that a new data plate be purchased.

[jetdriven]

The service instruction says you stamp zero over the five to make it 20°, so why not just stamp a five over the zero, and effectively completely 180° undo the service instruction? 

[Shadrach]

15 minutes ago, jetdriven said:

The service instruction says you stamp zero over the five to make it 20°, so why not just stamp a five over the zero, and effectively completely 180° undo the service instruction? 

The Mag data plate gets stamped not the engine data plate.  Item three in the SI says that the engine data plate is to be replaced with a new plate P/N 61548 reflecting the 20° timing.  If you still have the old data plate, I suppose you could reinstall.  As for post 1975 engines or folks who did not save he original engine data plate, word around the campfire is that Lycoming does not make nor sell a 25° data plate.

Edited February 20, 2021 by Shadrach

[802flyer]

Reviving this old thread to see if anyone can comment on the original question after a few years of experience: Have you installed a Surefly at either 20 or 25 degrees, and what has your experience been?

A crack was found under my #2 cylinder at some recent maintenance, so my engine is getting overhauled and I'm likely to put a Surefly on the left, and trying to decide how to time it. My engine was at 25deg with slick mags, so I'm inclined to stick with 25 unless there's data/experience suggesting that 20 is the better choice given Surefly's timing advance feature.

Thanks!

[Marc_B]

@802flyer look at the Surefly install manual. I believe you install it at 0 deg and the timing is controlled by the dip switches. But should be covered in the application install notes. 

[802flyer]

[mention=20374]802flyer[/mention] look at the Surefly install manual. I believe you install it at 0 deg and the timing is controlled by the dip switches. But should be covered in the application install notes. 

This is correct with regard to the physical mounting of the unit. But it is programmed to then fire at the “proper” number of degrees BTDC for the given engine. And since the programming is done by SureFly, one has to choose either of the “proper” settings for the IO-360 when ordering.


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[PT20J]

15 minutes ago, 802flyer said:

This is correct with regard to the physical mounting of the unit. But it is programmed to then fire at the “proper” number of degrees BTDC for the given engine. And since the programming is done by SureFly, one has to choose either of the “proper” settings for the IO-360 when ordering.


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@Marc_B is correct. The advance (20 or 25 deg) is set by dip switches when you install it. So, you can set it for 25 and if you don't like it you can change it to 20. (You will have to remark the engine data plate if you change the timing and make the appropriate logbook entry). The only choices you get when ordering are whether you are replacing an impulse coupling mag or a non impulse coupling mag.

Edited January 8 by PT20J
Added table from SureFly installation manual

[802flyer]

[mention=20942]Marc_B[/mention] is correct. The advance (20 or 25 deg) is set by dip switches when you install it. So, you can set it for 25 and if you don't like it you can change it to 20. (You will have to remark the engine data plate if you change the timing and make the appropriate logbook entry). The only choices you get when ordering are whether you are replacing an impulse coupling mag or a non impulse coupling mag.

Mea culpa, I had received some bad info and just assumed it was correct. Thanks to you and @Marc_B for setting me straight, and for the good news that it is field changeable (with the dataplate marking as you say)!


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[PT20J]

6 minutes ago, 802flyer said:

Mea culpa, I had received some bad info and just assumed it was correct. Thanks to you and @Marc_B for setting me straight, and for the good news that it is field changeable (with the dataplate marking as you say)!


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No worries -- none of us knows everything and we are here to help each other.