62 340 Ignition Timing

[Greg S.]

I replaced an 8" service replacement harmonic balancer with an original rebuilt finned 8 " balancer. The ring of the service replacement had slipped so initial timing was somewhat guesswork. I re-timed the engine to 13 degrees BTDC on the new balancer using a dial back timing light. The engine seems to want more initial advance. At 13 degrees it gets hotter at idle than before and it wants to run on at shut off. This engine has flat top pistons with a compression ratio of about 9-1. All other components are as original. Considering the lower C.R. how much initial advance can I safely run with this engine. If the engine doesn't knock at 18 degrees why not run more advance?

Also out of curiosity I checked advance at various RPM using the dial back timing light. Readings were:

Degrees / RPM
13 / 800
14 / 900
20 / 1100
23 / 1400
28 / 2100
32 / 2400
34 / 2800
38 / 3200

Is this a typical advance curve for a dual point distributor?

[Terry D.]

Re: 62 340 Ignition Timing

Greg
A couple of questions, are you running the original dual point distributor? Are you sure the dwell is set right, can really alter timing if not. Is the 38 degrees at 3200 the total advance? Not sure when that should peak out but someone with way more knowledge than me, John Hickley hopefully, we jump in and solve that problem
Terry

[Greg S.]

Re: 62 340 Ignition Timing

It is a dual point dist. Dwell is set at 29 each point 34 total. I stopped checking advance at 3200 RPM. I think 25 degrees is the total advance expected from the centrifical advance. 13 initial and 25 centrifical adds up to 38 total expected advance. Thats why I stopped at 3200 RPM. I could be wrong.

[Mike McKown]

Re: 62 340 Ignition Timing

I don't see anything wrong with your timing curve. I do suspect your initial timing is off because of uncoordinated timing marks on your new balancer and the timing cover. Use a piston stop to find true TDC and then go from there. Once you find that you'll have your starting point. Then, I'd rev the thing until it stops advancing to find the true total you have in your centrifugal advance.

If you're lazy like me, you can crank about ten more degrees intial in it and see how it runs. If it's better and it doesn't rattle, you can just about bet your timing marks are off.

[John H.]

Re: 62 340 Ignition Timing

The timing index line on the inertia ring must be exactly intersected by a radial line from the hub keyway that passes through the center of the pulley bolt hole. If so, your timing index line is on the money, and you can go from there. As Mike said, don't stop checking at 3200 - keep revving it until it stops advancing so you know exactly what your total timing is and when it's "all in". Let us know what you find.

[Greg S.]

Re: 62 340 Ignition Timing

Mike, the new balancer has the timing mark in line with the keyway for the crankshaft which I assume is correct. I am not sure about the timing tab on the timing cover. I believe it to be correct for the 340 horse engine but am not certain. The engine really idles better and about 20 degrees cooler when advance is set at 18+ degrees vs 13. I don't have a piston stop but will see if I can get one at local auto store. Is it possible for the distributor to be off a tooth causing this type of problem and still run OK?

[Mike McKown]

Re: 62 340 Ignition Timing

Being off one tooth will not cause this problem. I'm sure you know which wire is #1 but if you're timing light is on the wrong wire, that will cause the problem.

Sounds like your balancer is okay for an original '62 timing pointer. The piston stop will tell you the rest of the story.

Just thinking about what you're saying, you may not have a problem at all. Any SHP 283/327 I ever fooled with does like more than 12 degrees at idle. They like 20-25 better but they'll tend to kick back on the starter plus unless you limit the total advance, they will have too much advance. This is why they will idle better with the vac advance pulled in which you do not have.

[Chris H.]

Re: 62 340 Ignition Timing

Here is an original timing cover for a '62 340

http://www.photodex.com/sharing/viewfile.html?fl=1686143&alb=79760

user name /passord is Chenige

[Greg S.]

Re: 62 340 Ignition Timing

I have the same timing cover tab as you. I am going to run more initial advance as Mike indicates. I will try it this weekend and drive to see if it pings or kicks back on the starter.