I connected a timing light, and spotted the marks show while cranking the engine. This isn't a picture from the timing light strobe. I positioned it manually and took the picture with my phone. When cranking, the pointer split the difference between the line and the first dot almost perfectly. If I have this straight, the spark is lighting about 5* before the rotor flattens out against the spark plugs, which is top dead center, is translated as 5* BTDC. My goal was to move the VR pickup to where I would get 25* of timing advance that Lynn recommends without any input from the ECU.
Question: Is it worth the effort of moving the mount to get 25* of advance vs 5*?
This method applies to starting new or rebuilt engines that have accurate timing marks on the front pulley. It is good enough to drop in a distributor or crank angle sensor and start the engine. Then you could time the engine with a timing light.
It does not produce an accurate depiction of TDC. It will give you a point that is from 4 to 9 degrees BTDC, Before Top Dead Center. This is because the plugs are mounted higher or lower from year to year, and the distance between the plugs is also different. Probably done so the cars can be sold in California.
Use the minimum volume procedure. Squirt some thick oil into number one housing through the trailing plug hole. The Housing furthest from the PSRU and the upper plug hole. Turn the engine over a few times to spread the oil out. Bring the crank to a position that you suspect is near TDC.
The mark you have now is close. Screw some food quality vinyl hose into the plug hole. Use silicone if it seals poorly. Stick the other end in your mouth. Put your tounge over the hose end.
Rock the engine back and forth. That null where neither suction nor pressure is felt, is actual TDC.
Notice that the null may include about a 1/4" of flywheel movement, Maybe less. Actual TDC is the center of that null distance. You can also stick the hose in a glass of water. Same idea. Or, drape the hose into a "U" shape (Monometer) and put in some ATF and watch the lack of movement as the null. Same idea. You can get inside of one degree of angle this way. Probably more accurate than the factory pulley mark.
Use marks on the starter ring teeth for TDC and any advance you want to run. Try 20 to 24 for low octane car gas. If you have to run 110 or high octane car gas then 26 to 27 degrees.
That 20 degrees and low octane car gas works fine up to 9,000 RPM. Should be plenty to get started. Once the dyno is flying you could dial in a bit more and watch the Temps, speed and EGTs. (1600 degrees).
Lynn E. Hanover
-----Original Message-----
From: Ernest Christley <echristley@nc.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Apr 11, 2011 8:46 pm
Subject: [FlyRotary] Help with timing
I'm using an EDIS-4 system for ignition. A robust system that provides for a limp-home mode if the ECU decides that it is tired someday. It uses a 36-1 gear, so each tooth represents 10 degrees. Today, I began the process of verifying that the spark happens when I want it to happen.
I used the "spot the apex seals through the spark plug holes, then split the difference" method to mark a rough approximation of TDC. I put a silver line on the timing tooth gear, following the line of the stock pointer. The mark just happened to fall in the space vacated by the missing tooth. As the engine rotates, it moves to the left.
I connected a timing light, and spotted the marks show while cranking the engine. This isn't a picture from the timing light strobe. I positioned it manually and took the picture with my phone. When cranking, the pointer split the difference between the line and the first dot almost perfectly. If I have this straight, the spark is lighting about 5* before the rotor flattens out against the spark plugs, which is top dead center, is translated as 5* BTDC. My goal was to move the VR pickup to where I would get 25* of timing advance that Lynn recommends without any input from the ECU.
Question: Is it worth the effort of moving the mount to get 25* of advance vs 5*?