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MGTF1250Dave
04-20-2005, 10:55 PM
Aloha All,

I'm having difficulty setting the ignition timing on my TR3A to eliminate heavy pinking on acceleration. I've followed the Haynes manual procedure for the initial static setting and I'm using a test light to determine the distributor position "as the points begin to open". I can't get the vacuum advance adjustment retarded to the point that it goes away. If I slowly accelerate, there is little or no pinking, but rapid accelerating causes heavy pinking. Any suggestions or advice will be greatly appreciated.

I've tested the vacuum advance with a mityvac and it appears to be working, the mechanical advance weights are free and will open.

Safety Fast,
Dave

Geo Hahn
04-20-2005, 11:56 PM
What grade fuel are you using? My TR4 will pink on anything less than premium no matter what I do with the timing.

OTOH - my tired TR3A engine runs great on regular -- would probably run on coal oil if I knew where to get it.

MGTF1250Dave
04-21-2005, 12:08 AM
Aloha George,

I'm using regular unleaded, 87 octane.

Safety Fast,
Dave

dklawson
04-21-2005, 12:37 AM
The first thing to try is Geo Hahn's suggestion and buy a higher octane gas since you've tried retarding the ignition. You can also try a colder spark plug. These two could also be combined by running a slightly richer mixture to keep things a little cooler.

Then there is an expensive solution, you could seek out and instal a Spearco water injection kit. I ran one on a Toyota many years ago. It allowed me to run 10.5:1 compression and regular gas without pinging. However, I did a lot of city driving at the time and I started going through a lot more exhaust pipes.

Geo Hahn
04-21-2005, 12:50 AM
My advance is 4 degrees (static) or maybe a bit more... about 1/4" on the rim of the crank pulley. That and 91 octane is what seems best for mine. Again, this is a TR4 (87mm) with good compression.

trboost
04-21-2005, 07:55 AM
Your static timing is usually set to get the car started, then you do a dynaminc (car running) to actually tune it. I would also use a dwell meter to acuratly set point gap, this also affects timing. Inside you distributor the advance plate should be stamped with number signifying timing adv, this number & your dynamic BTDC initial advance will give you your total "in" advance. With a timing light you should see your total advance by 3,000 rpm.
I don't know the history of your car but if the head has been milled to increase compression this would also be a factor. Heavy carbon build up can cause this also but it's gotta be pretty severe.

piman
04-21-2005, 03:37 PM
Hello Dave,
what do you mean that you can't get the vacuum retarded? It could be interesting to disconnect the vacuum advance and try the car. If the mechanical advance is free as you say start from your original static timing and then retard your timing until it doesn't pink. 87 Octane doesn't sound very high to me, by the way. I think of 93 or so as being low.
Also the number stamped on the distributor cam plate is half of real engine advance, e.g. 8 degrees distributor is equal to 16 degrees engine.

Alec

dklawson
04-21-2005, 04:17 PM
I assumed when he said he couldn't get the vacuum advance adjusted, that he meant the advance/retard knob on the vacuum advance actuator wasn't changing the pinging he was experiencing. I hadn't thought about it before now, but that could also indicate that the advance plate is bound up in the dizzy. That would mean the car isn't effectively using any vacuum advance. You could still adjust your timing advance by rotating the entire dizzy in the block.

MGTF1250Dave
04-21-2005, 05:50 PM
Aloha All,

Thanks for the input. The head has not been modified, so compression is "standard". There are three choices of gasoline grades in Hawaii, unleaded regular, mid grade unleaded and premium unleaded, with (R + M)/2 octane ratings of 87, 89 and 92 respectively. In the past, pinking was not a problem using unleaded regular. I've tested the vacuum advance with a mityvac and have observed it move the advance plate move in the distributor. I'll take apart the distributor this weekend to see what the cam plate max advance number is. I have a DM2 distributor, so I think it should be 15 degrees.

Last night I found a different technique on the Internet. It suggested setting the crank pulley TDC mark 3/8 inch left of the TDC pointer on the engine. Next move the distributor to the position where the points just begin to open. This should be 8 degrees BTDC. If this was done with the vacuum unit set in the 8 degrees position (two complete divisions on the scribed scale), it seems I should be able to retard the spark between 8 degrees BTDC to TDC using the vernier adjusting nut. Is this a correct assumption?

Perhaps I'm confused by the meaning of division marks on the vacuum unit. Haynes states "each complete division corresponds to 4 crankshaft degrees." I notice that the scale has long marks and short marks, a repetition of a long mark, two short marks and a long mark. I have been been using the first short mark to mean 4 degrees. Is a complete division between the two long marks or between two marks regardless of length?

Mahalo (thanks) for all the help.

Safety Fast,
Dave

dklawson
04-21-2005, 06:07 PM
Something you may wish to invest in is a timing light with an advance setting. The advance setting on the lamp allows you to "dial in" advance. Here's how it works. Hook up the timing light, set it's advance knob to "zero" and start the engine. When you shine the light on the timing marks you'll see one of the marks you're talking about relative to the "zero" mark on the pulley. Now start dialing in the advance on the light until you get the zero mark on the pulley to line up with the zero pointer. Look at the reading on the light's advance dial. That's your degrees of advance.

Using the light "backwards" you can dial in the advance on the light to be "whatever you want". Then with the engine running, you turn the dizzy housing in the block until the zero pointers/marks line up. This is also the method used if you want to set your timing to the "maximum dynamic" value. In this technique you hold the engine between 3- and 4-k RPM and set your maximum advance close to 30 BTDC. The advance at idle isn't that important anyway... except how it affects starting.

JFS
04-21-2005, 07:58 PM
I use Doug's method ("maximum dynamic value) on my TR3 which has 10:1 compression. I also use high test gasoline. It's run great this way for well over a decade.

piman
04-22-2005, 04:23 AM
Hello Dave,
the knob on the vacuum advance shaft is best put midway after setting the static timing, this gives maximum scope for adjustment. The reason I said to disconnect the vacuum advance was in case it was a bit sticky in returning to zero because as you accelerate heavily the vacuum advance should not be operating. Also check that your mixture is not too weak and that your dashpots are topped up.

Alec

dklawson
04-22-2005, 09:10 AM
Not to contradict Piman, but set the nut for the vacuum advance mid-travel "before" setting the static timing. If you set it mid-scale after static timing... you undo the static timing you just set.