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post #1 of 5 (permalink) Old 07-15-11, 06:00 PM Thread Starter
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1978 F250 Timing issue

I have a 1978 f250 with a 400 in it, lots of miles not pretty but has been a dependable truck. My wife was driving it hit a bump and it died and wouldnt start, no spark to plugs so I tested the coil and ICM and there both good. Went looking at the distributor and walla when cranking the rotor wasn't turning . So obviously I pulled the distributor as its the easiest,check the gear and its on tight roll pin firmly anchored altho it feels like theres some play between the top and bottom of the shaft (not sure if this is normal) almost springy feeling but only an 1/8th of an inch play. Flashlight down the distributor hole the camshaft is turning, valve covers off all valves opening and closing. Put distributor back in, crank vehicle rotor doesn't turn , distributor shaft doesn't turn rockers move opening valves. Take distributor back out turn motor over several times while watching cam gear no broken teeth no unusual wear on the gears not metal shavings nothing. Any ideas or help would me greatly appreciated.
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post #2 of 5 (permalink) Old 07-16-11, 10:54 AM
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Re: 1978 F250 Timing issue

Are you sure the distributor drive is not sheared and the gear is slipping on the shaft when under load ?
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post #3 of 5 (permalink) Old 07-16-11, 11:45 AM Thread Starter
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Re: 1978 F250 Timing issue

I tapped on the gear with a hammer (gently) and it didn't move, put the distributor back in put a pair pf channel locks on the top and attempted to twist the shaft no movement other than the initial play (which I assume is the advance mechanism) the gear for all intensive purposes appears to be locked in place as it should be. I will admit I have not put alot of strain on it (kinda afraid to) so no where near what would match what the motor is doing, but with the ease of the distributors shafts ability to be moved would it staty stationary? I would expect to see some movement in it other than the initial twist it does and then nothing. As tight as the gear is to the base I figure it should move a little if not sporadic but still more movement than it has.
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post #4 of 5 (permalink) Old 09-12-11, 12:14 AM
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Re: 1978 F250 Timing issue

the only thought i have is that the gear has slipped up the shaft and when installed the dist geas is no longer in contact with the cam gear . sorry if no help.
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post #5 of 5 (permalink) Old 09-12-11, 08:04 AM
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Re: 1978 F250 Timing issue

When you reinstall the distributor, you know you have to bring cylinder #1 up to top dead center on it's compression stroke to the crank pointer's alignment with Zero line on the crank damper.
Then place the dist in place so the rotor points to the #1 cylinder in the cap.
In doing this, the dist has to turn the distance of about 1 cap cylinder spacing to seat in the block before settling at the cap positon 1. The cam gear to dist gear engagement forces this to happen. Also the dist shaft has to engage the oil pump drive shaft at the same time to be able to set on the block and clamp down properly in place.
Does it do this?
If so it has to turn when cranking the motor because it geared to front of the cam when in place.
As to the rotor moving about a 1/4" or so, this is the centrifigal advance and is held in place by small springs. The rotor has to move a small amount in relation to the main shaft or the motor gets no timing change vs RPM change.
Next question is has the timing chain jumped teeth on the crank gear.
If yes, the motor either will start and have no power or be hard to start or not start at all.
How to tell: Valve cover off bank 1 and use plug hole in cylinder #1 to determine when the cylinder is up top dead center on compression.
Look at the valves. Are they fully closed for compression AND does the crank pulley mark alighn with the pointer?
If yes, the chain is in proper position, if no the chain has jumped teeth out of position and needs to be replaced with new chain, crank and cam gears.
There is no mistery. Either it is or is not.
Look at the dist gear. It has a spring pin holding it in place. If the gear has moved up the shaft you should see this as a difference in shaft color where it was at before the pin sheared.
Good luck.
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