I'm currently working on a 68 F100 in shop. It's got a 300, which is not a new motor to me (76 has one). When we got the truck, the owner said it had dropped a valve.

After some diagnostics, I found everything in the valvetrain was intact. The truck hadn't had a tune up in years, and wasn't getting spark. So, I did a full tune up of cap/rotor/plugs/wires/points/contacts and coil, cleaned all the electrical connections, etc. After a new battery, I got the truck cranking. Yet, it won't start. There is spark at all the plugs, cylinders seem to have good compression (I'll be doing a test tomorrow), and starting fluid is getting into the cylinder. It'll catch one or two times, but won't start/stay running.

I was thinking that the timing might be off, and so I've both advanced and retarded the timing at the distributor, and no improvement. I'm wondering if the distributor might be flipped 180. One of the things I noticed that was on the 2 other 300's that I've worked on from mid 70's era trucks, is that the vacuum advance on the distributor is pointing forward, and on this truck is pointing right at the firewall. Is it supposed to be there?


Other than that I'm stumped. If anyone has any ideas on why she won't start, I'd appreciate it.
-Jameson

 

Check the timing. Put the engine on TDC and see if the rotor is pointing to #1 spark plug. Both valves have to be closed with the timing pointer on TDC.

 

The vacuum advance on my '70 300 i6 is pointing at the firewall.

 

With the dizzy cap off rock the engine over back and forth to see how much play
is in the timing chain. The rotor cab should move almost at the same time the engine does. It may well have jumped time and now who knows what as to plug wires being
moved around the cap or the dizzy out and back in wrong and like that. And it may well have punch a hole in a piston or bent a valve.

 

no chain on the 300. it's gear to gear if I remember correctly.

 

Normally this would be great advice. But in this particular instance 300's don't have a chain. They are gear to gear.

 

Thanks, I had forgot that.
Note to self: Take better Meds. Or at least more, Meds are gooood.

 

With "Crown R" up there in the Arctic to help keep warm too!

 

BV and Coke. Wet Coke that is.

 

Static timing turned out good. #1 piston at tdc and the rotor was pointing at the #1 plug wire.

Started on a compression test, only got 1 and 2 done. Assuming that the tester is correct, 1 has 90 psi and 2 has none.

More tomorrow

-Jameson

 

Ya might pull the rocker/valve cover and see if all the valves are working.

 

Two options at this point, leak down test(put air in spark plug hole while at tdc compression, see where air comes out) Or remove the rocker arms and retest compression.

Are you sure, how do you know? I assume you pulled the valve cover and inspected?

A bent or sunken valve can hide, if you pull the valve cover and rockers lay a strait edge on the top of the valves, look for gaps between it and the valves. A gap at one means that valve is lower and thus most likely bent. If one is high, it's likely sunken, this happens to exhaust valves when they get too hot/worn out in older engines with "new" unleaded fuel. They beat themselves deeper into the head, sinking them in the head making them stick up.

 

Be suspicious of the ignition switch. The coil gets its voltage off the solenoid from the "I" terminal when you are cranking. Once the ignition switch goes from start to run, voltage comes from the switch directly.
Take a voltmeter and check voltage at the + coil terminal with the ignition switch on and the truck not running. You should have something between 7 and 12 volts depending on what is in the distributor and whether or not the points are closed.
Semper Fi

 

You mentioned that it will catch a few times on starter fluid but won't stay running- are you sure it's getting fuel?

 

It sounded like it would fire, but after cranking there was still starting fluid in the cylinders. Leading me to believe it wasn't actually igniting

The valve cover was off when I started in on it. At the time, nothing looked unusual. I popped it off again today and cranked the engine over. All the valves are moving normal. I didn't see in any valves that had those indications for bent valves.