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MG MGA - MGA Ignition Timing
|Hello people. I've got a 60 MGA, original engine, rebuilt, with a mild cam (Delta KB).|
I've no problem doing a static timing on the car; it's the dynamic timing that I need help with.
From the web, I get figures of 20 degrees at 800-850 rpms w/out the need to disconnect the vac advance, 20 degress at 1,000 rpms w/vac plugged, 28-30 degrees @ 3500 rpms vac plugged, 32 degrees @ 3500 vac plugged. The fellow who rebuilt the engine indicated 14 degrees@800rpms w/vac plugged and 35 degrees@3,000rpms vac plugged.
There may be other specs floating around...
The 20 degree approach seems easy enough to estimate from underneath with a timing light; just double the distance from TDC indicated by the 10 degree advance pointer.
Eyeballing 28, 30, 32 or 35 degrees seems a bit ballpark-ish. How do you do it?
And how do you keep the engine at 3500 rpms while looking at the damper markings with your timing light, while turning the distributor to the right spot without 1 or 2 helpers?
Lastly, I've run across references to a type of timing light with a dial or digital readout on the back where you don't have to use any of the timing marks on the timing chain cover except TDC; does that ring a bell with any of you?
Let me know how you approach it, and thanks... :)
|I bought a timing light with an adjustable advance from Sears. There are lots of others available from other sources. I then turned my crankshaft by hand until it was at TDC, and painted a line of white paint on the front of the timing chain cover just above the crankshaft pulley that is visable from the top. Then I put a dot of white paint on the pulley ajacent to the painted line. I can now shoot the timing light down from the top and see the new timing marks that I have painted on. It works for me, maybe you can do something similar.|
|To get your engine to run at 3500 RPM, screw your choke fast run screw in, then pull your choke control out until you get the desired revs. If you turn the screw in far enough, you will reach the desired RPM before the choke control starts to lower the carb jets, so you won't richen the mixture. I find on my car, I have to turn the fast run screw nearly as far as it will go. Don't forget to reset the fast run screw when you have finished. Your neighbours will love you if you do this nice and early on Sunday morning!|
|God, I love it. Two brilliant solutions... Keep 'em coming. Anyone else?|
Yes, Sunday morning; a great time to get even for boom-boxes and barking dogs!
Ed; I've never used, much less seen one of those adjustable advance lights. Is the following correct?.. Do what you did with the paint marks. Set the light to the desired advance setting, and, at the desired rpms, point the gun and turn the distributor until the marks line up. Clamp distributor. Even though the marks lined up at TDC under the strobe, it was actually advanced at that point to whatever setting you input into the light's advance setting earlier. Is that how it works?
|That's the way it works. Seems too simple, but it's a neat feature. I was bummed about my old timing light finally giving up and quitting on me but when I bought the new one with the advance feature I was wishing the old one had given up sooner. Everyone should have one to play with.|
|I've got a Snap-on one, it's brilliant! You can check your timing at different revs and plot an advance curve with it to see if your advance/retard is working properly. Also use it to check the function of you vacuum unit by disconnecting, then reconnecting the vacuum pipe and checking the before and after advance readings; they should be different.|
|LR, I made a 'protractor' with the degrees marked on it radiating from the centre of the crankshaft pulley when positioned just below the pulley on the chassis cross member. It sits quite close to the pulley when the engine is running - say 3 or 4 mm away and with a strobe light you can get the dynamic timing reasonably accurately. You might need to steady it with some clear silicone if your engine is vibrating too much.|
|J H Cole|
|Meant to attach this pic.
|J H Cole|
|Lindsay-thanks for rounding out the practicality of those timing lights, and JH thanks for the protractor idea; the pic helps put it together.|
For months, literally, the thought of getting around to doing the timing intimidated and bummed me out to no end. I'd walk into the garage, flip open a few manuals, look at what was expected of me, sit and stew for a few minutes, utter a few Klingon profanities , close the manuals and walk away.
How we managed before the internet is beyond me; I'm off to grab one of those newfangled timing lights.
Thanks to all of you for the help.
|L.R. Don't forget to check ebay on used timing lights with adjustable advance, Mac, Snap-on, Sears Penske. Right now looking at a never used Sears with the advance feature for $25. If your attention is really focused and you set it to spec varying the setting a few degrees more advanced and then more retarded from spec 'you can hear the right harmonious sound coming from the motor when you've found the spot.' Call this the Kinsey Institute method.|
|Martin, talk some more about this "harmonios sound" and how you go about achieving it. Do you do it at tickover or with some revs on?|
|Lindsay, Its subjective. You can fine tune the timing once your in the ballpark (set by spec.) by closely listening to the exhaust note at idle (obviously not in a closed garage.) There is a precise point of adjustment where the motor sounds as if its running easier and there is an extra mellow sound to the exhaust. Its like if your running (jogging) and at a certain pace you fall into your grove and in this grove you experience a smoothness and harmonic breathing with the physical exertion of your body that makes you feel less tired for the amount of physical work. I do the same approach with tuning the carbs. After getting in the ballpark with micrometer readings of the jet depth and plug readings at different RPMs (driving and then coasting to a stop) my fine tuning is the exhaust sound during deceleration and acceleration, sharp-not dull edge and with a good musical change to the sound at the different RPMs. -M.S.|
This thread was discussed between 07/07/2010 and 09/07/2010
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