Mallory, Timing Issues

[Jim Marshall]

I finally am getting some of the little issues resolved on the '74 Ford 302/Volvo rebuilding project. I replaced the point ignition with a Mallory Marine ignition and have it running to find I have some Edelbrock/Holley carb match-up problems.

I was talking with my engine rebuilder about the timing. My valve covers specify 8 degrees tdc at 600 idle. He was telling me that the higher RPM timing was more important which is a function of the distributor. He said 2400 RPM should fully advance it for timing purpose. Too advanced timing, he tells me can ruin a piston.

Can someone who is more in the know about these things comment on the Timing x RPM issue?

Also, I notice there seems to be a mistrust of Breakerless ignitions to the extent that some carry a standard distributor. Any merit to this?

Thanks again for all the advice on this forum.

Jim

 

[JustJason]

Re: Mallory, Timing Issues

Fuel burns at a constant rate, regardless of rpm.

In order to take full advantage of the power gasoline has to offer, you have to compensate for rpm by lighting the mixture off earlier (ie- advancing the timing).

Once the gas is lit, it explodes and starts to expand, but as it's expanding, the piston is still comming up and compressing the mixture.

If you advance the timming to far, you'll light the mix off to early.

If it's lit to early it will still start to expand, but because the piston is to low in the cylinder and still on its way up, the pressure of the lit mixture x's the compression pressure of the piston comming up to compress the whole thing becomes to much.

When pressure goes up, temperature goes up. If temp goes up to high obviously things start melting, including pistons. The engine will start to knock. (although you can't hear high RPM knock)

The whole idea of it all is to advance the timing to the point of spark knock, then back it off a few degrees. If you can do that then you'll get the most power out of the fuel and engine. On the opposite side, if you don't advance the timing enough, nothing bad happens, the engine just won't make full power as designed.

Hope that helps explain it!

 

[Aloysius]

Re: Mallory, Timing Issues

Your mechanics advice is correct. I run 36 degrees total advance on my 302's. All in at 2800 rpms.

8 degrees initial ONLY works if you've got 24-28 degrees advance(crankshaft) in your existing distributor, and you know precisely what the advance curve is.

i've gotta distributor machine, and do this as a sideline. Most old marine distributors need work! Take yours to a competent shop with a distributor machine and get it dialed in. Buy a "timing tape" and install it on your damper..set the timing after it is fully advanced, and ignore the initial setting.

I'll bet it runs much better after this is done!

 

[Jim Marshall]

Re: Mallory, Timing Issues

Thanks JustJason and Aloysius.

The Mallory distributor is new. I suppose I should be able to get some information on its advance curve somewhere. I also have a Mallory Procoil that I was thinking of hooking up to it.

Jim