68 340 timing

[dgoplen]

i have a 68 340 that has some type of mopar cam in it. i also have a mallory distributor with mechanical advance. i tried to put the timing to about 6 btdc and it runs crappy.so i put it back to somewhere before 12 btdc as i cant see the mark behind the water pump. it seems the farther i advance it the better it runs at idle.it revs strong but i dont know what its timed at, any ideas on if my cam may have been advanced? and why does the engine act this way when trying to time it?
tks

 

[67Dart273]

Generally, the "larger the cam" the more initial timing you want. Even a stock 340 "back in the day" specified ridiculous settings FOR SMOG, but most of 'em ran a lot better (I've forgotten) up around 8-12* initial.

I recommend a few things, first so you KNOW where you are, get/ make/ buy a "piston stop" like this:

Remove the battery ground for safety, get a socket to turn the engine, and remove the no1 plug. Be sure the piston is "down a ways" and install the stop. You may have to play with it the first time you use it.

Gently wrench the engine over until it "stops against the stop." This should be SOME distance from TDC, matters not too much how much. At this point, make a temporary mark on the balancer under TDC on the tab.

Do the same thing rotating the engine CCW. Now you'll have two marks some distance apart. True TDC will be halfway between the marks, and if the original is correct, that is where it will be.

NOW, either calculate "how many degrees per inch" around the outside of your balancer, by carefully measuring it AROUND the outside with a small flexible tape

Now either mark the wheel in degrees or buy a timing tape for the proper size wheel.

It's not that hard to mark, just calculate mathmatically using the circumference you measured. One easy way is to calculate for 40*. Make your FIRST mark ACCURATELY by measuring with your flexible tape. Take your time. DO NOT use dividers for this first mark, because you MUST measure "around" not lying flat.

So at this point you should have TDC confirmed or corrected, and a 40* mark.

NOW you can take your dividers and divide in half between the 40 and TDC mark. This halfway mark, which you can confirm from "both directions", that is from the TDC to the middle, and from 40* to the middle, will now give you a 20* mark.

Now divide a 20* segment in half, and mark that as every 10*. Once again, you can check from each 20 mark each way to confirm that the 10* marks are "in the middle."

Last, you can divide again, and get every 5*

If you run a vacuum advance you probably want to divide out to about 50-55* so you can check the vacuum can.

 

[69swinger340391]

Keep advancing it!

Mine likes 18 degrees BTDC at idle, and another 17 degrees of mechanical with the lighter springs so its "All In" by 2200 rpm.

 

[fourspeed]

IIRC, a stock 340 is supposed to have 10 degrees initial...? Anyway, if you have access to an advance timing light, rev the engine to about 3000 and check the advance. Around 36 degrees total advance is common.

 

[67Dart273]

a stock 340 is supposed to have 10 degrees initial...? .

According to my '73 Motors Manual,

68,69 stick is TDC, auto 5*

70, 71 stick or auto, 5*

72 2 1/2 BTC

73 stick 5*, auto 2 1/2 except CA, TDC

74 360, 5 except CA std trans, 2 1/2

 

[crackedback]

Once you put a cam in it,the factory settings are useless, IMO, the factory settings are useless with a stock canmshaft! 15-20 BDTC and do a hillbilly timing tape to the balancer.

Put the balancer mark on the lowest point on your timing tab, go up 15* make a mark, roll that down to the lowest point, make another mark 15* above it. Now you have 0, 15 BTDC and 30 BTDC on the balancer. I usually take a file and scribe a line in it.

Make sure you don't exceed 35-38 degrees total. You will likely have to re-curve the distributor to get the required initial and total in line.

 

[67Dart273]

Once you put a cam in it,the factory settings are useless, IMO, the factory settings are useless with a stock canmshaft! .

Das true, I was trying to illustrate how "useless" they really were. I believe that Mopar knew full well that "we" were all gonna bump the timing up as soon as we cleared the smog check station, anyhow!!!!

 

[crackedback]

67, I wasn't pointing your comment out in particular, it appeared with the number he originally posted, it was from the books or really close.

 

[dgoplen]

thanks so i really have to find out where my tdc is on the balancer and make new marks then.how exactly do you know your timing if you cant see the line behind the water pump housing? also does it hurt to keep advancing the timing at idle it seems the more i advance it the better it runs up to a point.does that make it run hotter engine temps too? tks

 

[67Dart273]

'S exactly what Crack n' I were talking about. DEGREE YOUR BALANCER or buy timing tape, and then you can see the marks on the wheel, by using those and the TDC mark on the tab.