Thanks Bill,

What I was referring to was the spark events per combustion event, I believe there are 3 spark events per combustion event - firstly the leading at 25 degrees BTDC and then the trailing at 10 degrees BTDC ( 15 degrees later) and I believe the leading fires again ( from memory) but I don't know when?

George (down under)

George,
My standard housings only have 2 plug holes! Do you have some Lemans engine housings? Or perhaps you are refering to a MSD multi-spark system. If that is the case you should know that the MSD box will make a second spark at the same location in a few miliseconds. Even before the trailing fires if you have a standard split. Lots of people aren't even using a split. Power wouldn't change much. The efficiency might change a fraction which is worth something.
Cheers,
Bill Jepson

-----Original Message-----
From: George Lendich <lendich@optusnet.com.au>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Wed, 19 Sep 2007 3:30 pm
Subject: [FlyRotary] Re: TDC

Can someone answer this questions, if the timing is set at 25 degrees BTDC and the leading fires at 25 degrees BTDC and the Trailing fires 15 degrees later (10 degrees BTDC) - when does the third spark event fire, is that another 15 degrees with the leading firing again?

The pulley end keyway points to 9.00 at TDC ( plug sides) on the housing closest to the pulleys ( Front/ our rear) - is this what is referred to as No1 housing?

George (down under)

<snip>

In a message dated 04/26/2005 12:00 Central Daylight Time, Lehanover writes:

<< In a message dated 04/25/2005 07:00 Central Daylight Time, jwvoto@itlnet.net writes:

I can look into the spark plug hole and see the apex seal go by, so are you calling apex seal crossing leading plug TDC?

There are a number of gags to locate TDC close enough to get the engine to run.

(1)

Remove one spark plug from number one housing. Screw a length of hose into the plug hole. Put your tongue on the end of the hose. Gently turn over the engine. When you get a null, where there is no pressure and no suction on your tongue, that's TDC. Good to within a few degrees.

(2)

Or,

Bend up a piece of welding filler rod so as to make a pointer that can touch a flywheel (flexplate) tooth. Bolt or clamp the wire to the rear iron.

Take both plugs out of number two rotor housing.

Turn the engine until you see an apex seal in the center of the trailing plug hole.

Bend the filler rod so that it points to the center of a flywheel tooth. Put a white paint drop on that tooth.

Turn the engine in the running direction, until that same apex seal appears in the center of the leading plug hole.

Put a paint drop on the tooth the rod is now pointing at.

Count the teeth between the paint dots. Divide by 2.

The point half way between the two paint dots is TDC in the number one housing.

Good to within a few degrees.

Also, you can count the total number of teeth and divide that number into 360 to get the number of degrees per tooth. Paint the correct tooth yellow and make the rod a permanent piece, for setting accurate timing in an easy to see location.

(3)

Or,

(Similar to above)

Take both plugs out of number one.

Turn engine in running direction until an apex seal appears in the trailing plug hole.

Gently turn the engine backwards until an apex seal appears in the leading plug hole.

Half way between those two events is TDC. With practice, accurate enough to do by just feel and rocking back and forth by hand and to find TDC within a few degrees, or close enough to drop in the distributor and have the engine fire instantly and run fine.

(4)

If you used grease or Vaseline on the side seals, you can have a plug prepared with the center knocked out of it and a plug in place with a piece of brake line soldered through the center. Screw this special plug into the bottom plug hole. Push a length of plastic tubing over the piece of brake tubing. Pour auto trans fluid through the top plug hole. Reinstall the top plug. Hold the hose in the vertical. Turn the engine until the fluid level nulls.

That's TDC number one with a degree.

(5)

The flywheel end counter weight is centered between the plugs on number two rotor housing. That's TDC number one within about 10 degrees. But you can get good at it, and get more accurate.

(6)

If you have the front pulley bolt and washer off, looking from the front

pulley end,

the keyway in the 9:00 O'clock position is TDC number one within a few

degrees.

My TDC rig is for setting up port timings and requires a disassembled

engine, so that won't help you. Good for inside of one degree.

(6)

Quick and dirty.

Take out either plug from number one housing.

Wet a finger. Hold it gently over the empty plug hole. Turn the engine in

the running direction. When the air quits pushing past your finger, that's TDC

within 10 degrees or less.

Lynn E. Hanover

<snip>

On 9/19/07, bmears9413@aol.com <bmears9413@aol.com> wrote:
Changing the subject a bit, I want to make sure i have my motor on TDC to set my timing marks on the flywheel. This is my plan, tell me what you think. I'm building a fitting to screw in the spark plug hole, and running a vacuum line to a small suringe (like a insulin suringe). I can eyeball the rotor location close to TDC, the install this contraption and rotate the motor so the suringe moves out to the end and starts back in. then back the motor up again till the suringe tops out. I figure that outa be and accurate TDC. Whadda ya think???

Bob Mears
Supermarine Spitfire

-----Original Message-----
From: Ed Anderson <eanderson@carolina.rr.com >
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Wed, 19 Sep 2007 1:16 pm Subject: [FlyRotary] Re: Strange Ignition?

I do not believe that is a significant factor, either, Al. After all, we're suppose to do our ignition checks on the ground before take off {:>). My understanding is that best power on the 13B has ignition timing between 25-28 deg BTDC, so not surprising that the 20B would fall in that range also. Sounds reasonable to me.

Ed

----- Original Message -----

From: Al Gietzen

To: Rotary motors in aircraft

Sent: Wednesday, September 19, 2007 3:08 PM

Subject: [FlyRotary] Re: Strange Ignition?

I wondered if perhaps one issue was that I was doing the ignition check static, on the ground; where the combination of RPM and MAP would be different than in the air. But on checking with Tracy 's spreadsheet on the timing settings, over a fairly broad range above about 4900 the timing is (should be) in the range of 26 to 28 degrees BTDC.

Al

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