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vacuum gauge to set timing


old-tank
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First a little background. I am working with a 55 264 nailhead that had been "rebuilt" by probably the most inept individual in Texas. Already discovered problems include rocker shafts installed upside down flooding the valve guides with oil, 56 lifters but the longer 55 pushrods were used resulting in bent pushrods and low compression on some cylinders, and a replacement cam that has none of the markings that the stock cam for a 264 would have. These issues have been fixed. Anyhow timing with a timing light and set at the recommended 5* BTDC it will barely run, but smooths out at ~20* BTDC...this is at 400 rpm and the vacuum advance disconnected. The centrifugal advance and vacuum advance work OK connected and rpms increased. I have seen troubleshooting guides for vacuum gauges and one mention that timing can be approximated by rotating the distributor until maximum vacuum is attained. Now after all that, when using the vacuum gauge: at what rpm and is the vacuum advance connected or disconnected?

(This is not an issue with a slipped harmonic damper since the 264 has a simple pulley.)

After finding all the other problems with the "rebuild" I should have disassembled and checked everything, but it was running when pulled a few years ago--not well--but running and seems to run well at 20* BTDC.

Thanks in advance, Willie

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NikeAjax is right, Willie. Pull the vacuum advance hose off your distributor, plug it, and use a good timing light. Amount of vacuum has very little to do with ignition timing. We use low rpm during timing because we don't want the centrifugal weights in the distributor to affect the timing light 'reading'.

I assume your TDC mark on your crank pulley is correct, and your cam is timed with the crank properly.

Your nailhead should run smoothly, and strong enough to pull a trailer.

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My thoughts were the same are you sure when number one is at TDC the rotor is in the correct position and your timing mark on the crank matches. Had a fellow I know who was a "mechanic", pulled a dist and never marked anything, put it back and could not figure out why the car would not start. I checked and he had the dist 180 degrees out. Got number 1 at TDC pulled the dist pointed the rotor to fire on number one and she fired right up.

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I'm not familiar with 264s, but that really doesn't sound that unusual too me. Typically, you'd have 12-15 degrees vacuum advance, so should idle OK with 5 degrees static. Mechanical should kick in somewhere in the 500-750 rpm range. I usually run a few degrees more than the book says; I'd probably set it at 8 and see how it behaves. If you get too much it will crank hard when hot, rattle under load, or run-on when you shut it off.

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Thanks everybody. I don't know if the cam is correctly indexed with the crank and do not know the specs on the cam. I did try installing the distributor one tooth either side of where it is now and it will not start, so that is ok. When it is running the best with the highest vacuum (20 in Hg with the vacuum advance disconnected at 400 rpm) the distributor is in the same position relative to landmarks on the engine as my three 322 nailheads. I will leave it there until I get the vehicle (engine swap into a 51 F-1) on the road. Then I will advance or retard timing depending on pinging under load and check the timing and vacuum again.

Willie

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