HEI mod to get rid of the vacuum advance for clearance

or something like that.

Pictures are at the end of this article.

This is for the oddfire 225 v6 HEI conversion using an oddfire distributor. I have noticed that several people have been able to just grind some off the intake manifold, replace the bolt with a torx or button hex, drop a GM HEI distributor in, time it and roar off. I have also noticed that some people ran into some trouble with clearance other than the intake. Usually with the thermostat housing and radiator hose or the fan clashing with the vacuum advance sticking out.

True to form I wound up not only in the latter group but had both problems. The only way I could fit it in would put the timing either way off or at TDC. In both those compromise positions the new dist cap would block against the edge of the ground down intake manifold. The large dist cap would prevent me from advancing or retarding the timing enough to attain 5* TDC. No amount of relocating which tower would be the #1 cyl would work. It would always be just off enough so that the lobes on the dist shaft would not line up cluse enough with the proper points on the sensor. Since the oddfire sequence is not simply evenly spaced as in the even fire simply moving it one over will not work. It must be two towers or or four towers. (see the following diagram http://home.off-road.com/~merls_garage/oddfire/cap_evnodd.jpg

I tried a fan spacer but ½” was too thin to clear the vacuum advance, 1” was too close to the radiator and fan blades and radiator cores just don’t get along well.

My solution was to remove the vacuum advance altogether. That left the sensor ring free to move while the engine was running and unless you like loud noises and some risk to your engine’s internals, I don’t recommend trying to start the engine without the minor mod I came up with. It costs next to nothing. I haven’t noticed a problem without the vacuum advance. According to the Jeepster site, the new advance is too sensitive for the 225 oddfire and a carb vacuum line. The FSM says that the normal vacuum advance should be no more than 8*.

After you have removed the vacuum advance replace the original hold down screws in their original holes in the floor of the distributor.

Next remove the distributor (if it is installed in the engine). Plug the mounting hole in the engine with a clean cloth. (murphy’s law dictates that if you don’t cover it, something within a 12 foot radius of the engine will fall down that hole into the engine).

On the floor of the inside of the distributor there is usually a raised “pad” cast into the floor. Stuff a rag all around/over everything inside the distributor except the pad mentioned. Position the advance lever of the sensor over that and use the hole in the lever as a template to drill a small hole through that spot. Clean all the metal shavings out of the distributor. (I drilled mine with the dist. On its side and rotated so that the pad was at bottom and slightly tilted toward the floor so most of the shavings fell out as I was drilling)

Position the advance lever so you can fit the self tapping screw through it and into the new hole in the pad. Tighten it up so it’s snug but not bent. Place a drop of blue locktite on the shaft of the screw.

Seal the screw holes on the bottom with a little dab of high temp silicone gasket sealer (black, don’t use the kind with copper or metal mixed in).

Replace the distributor as per the normal procedure for HEI conversion. Remember that the points on the shaft should point to the sensor point on the LARGE lobe of the sensor ring. (see the diagram at http://home.off-road.com/~merls_garage/oddfire/heicontacts.jpg
http://home.off-road.com/~merls_garage/oddfire.html ).

Button it all back up, connect the electrical, time it after it’s warmed up, lock it down, and then “carefully” plug the opening where the vacuum advance poked through the distributor housing with black silicone high temp gasket sealer. You don’t need much and you don’t want it gooping up the inside of the distributor. Let the sealer set.

 

You can initially point that advance can anywhere you want. Just make #1 post a different position.

jB

 

tried that. had trouble still with clearance. either the can hit the fan, radiator hose or the conection snout on the cap was blocked or the bulges from the from the hold downs for the cap jammed against the intake mani.

by simply moving the #1 timing to an even lobe, it wouldn't run right. this way i could get the #1 to match to any odd lobe on the sensor i wanted.

 

Great writeup Steve. I actually understood most of it - especially this part:

"That left the sensor ring free to move while the engine was running and unless you like loud noises and some risk to your engine’s internals, I don’t recommend trying to start the engine without the minor mod"

I did drive aroung with the vacuum advance completely removed and bad noised did happen. Some of us learn by our stupid mistakes.

I went to NAPA and looked at a whole book (ok at least a chapter) of different vacuum advances to fit the HEI. There's a bunch of 'em, all different shapes, sizes, and vacuum vs. advance ratings.

Thanks for taking the time to show the rest of us.

 

thanks! i appreciate the feedback
most of us learn from our "stupid" mistakes. some just cost more than othersR)
they also make adjustable vacuum advances if you can get someone to order it.

 

Good Idea, The only real reason there is a vaccum advance is to help with fuel economy which I doubt too many people with Jeeps are worried about.