Hi all, I think I'm onto the trouble but will run it by this knowledge base. '66 F100, 352, 3sp. I've been driving it daily and aside from a weak cylinder, it has been a good driver...until this weekend when it started to backfire at cruising speed and then died. I messed with the points by moving the distributor lobes with the fan belt to get the points on the high spot, checked the gap and then tried to start it up. It fired both times and got me home without too much drama. I put the light on the timing marks and it seemed to run steady for a while and then the marks would waver back and forth for a few seconds and then smooth out again. My theory is that the timing chain is sloppy and when I moved the distributor cam with the fan belt, I inadvertantly took the slack out of the chain enough for it to run for a while. Does this sound right and is this enough evidence to start in on the timing chain replacement? Steve

 

my truck started doing that same thing the other day except my engine is a 460. i changed the timing chain and it didnt help, so i bought a ford duraspark distributor so that i could eliminate the points and that seemed to fix it, but it started back again so i bought an electric feul pump and i havent had any trouble since. hope it helps.

 

I would check your camshaft timing. The gears and the chain wear and stretch over use. The gears installed by the factory, if aluminum with plastic teeth, were soft, designed to eliminate noises. The teeth often fell off, and the aluminum wore down, retarding the camshaft timing.

The chain accumulates all this wear. The following is an easy check to determine the amount of slack, slop or wear, in your timing chain.

It is not necessary to remove any components as long as you can see the timing marks clearly. It can be done with one person, but a second person can be helpful if the distributor cannot be easily seen while turning the crankshaft from the front of the engine. This test cannot tell if a chain has jumped; it can, however, tell you if there is enough slop in the chain to have let it jumped.

Tools: Breaker Bar with socket to fit the front crankshaft bolt

1. Mark the TDC or 0 mark on the damper clearly. Ensure the rest of the timing marks can be clearly seen; clean them if necessary. You may find it useful to scrape a little chalk over them to highlight them.
2. Remove the distributor cap and place it out of the way. You must be able to see the rotor while turning the engine with the breaker bar. It usually is not necessary to remove the spark plugs, but some high compression engines may require it to get an accurate reading.
3. Turn the engine in its normal rotational direction until the TDC or 0 mark is lined up with the pointer.
4. IMPORTANT: Do NOT turn the crank backwards just to line it up. Doing so will give erroneous results. You MUST rotate the crank in ONE direction only. If you overshoot, just go around again. This is where it may be helpful to remove the plugs.
5. Once the TDC and 0 marks are lined up and while watching the rotor, rotate the crank in the opposite direction. When the rotor begins to turn, STOP. It may help to have a helper push against the rotor's direction of rotation. (Remember, it will be going backwards at this point.) They can feel it begin to move more accurately than you can see it begin to move.
6. Note the value of the timing mark the pointer is indicating. It will be BTC, because you went in reverse of normal rotation.
7. This value is the amount of slop your timing chain has in degrees of rotation. Anything less than 10 is safe, but performance begins to fall off after 5.
8. If you have anything over 25, STOP driving that motor and get the chain and gears replaced! I have seen a motor run with up to 45 degrees - but I wouldn't risk it myself. (Also, that motor jumped while or just after starting it, but it ran very badly. It couldn't be re-started. I only found out how much it had jumped afterwards. I think some of the valves got kissed, enough to bend them, but not enough to punch through the pistons. It never ran again, either.)

 

Do you have a smog pump on your truck?

If so...in addition to the similar looking air bypass valve, there's an ANTI-BACKFIRE valve in the system.

When that valve fails...POW!

C6AZ9B289C .. Anti-Backfire Valve / Use with Thermactor Emission (smog pump) / Obsolete

Fits: 1966/67 F100 352.

 

Banjopicker66, thanks for the proceedure to check timing chain slack. I will perform that exercise after work today. The chain has not jumped as the marks are very close and stay close except for a periodic wavering as stated in my original post.

Dummy, the beast has been de-smogged for years. Thanks, Steve

 

Testing for slack in the timing chain resulted in a measurement of 14 degrees . So I'd say that it's time for a new chain and gears. While I was checking for the rotor movement delay, I noticed that the rotor is not tight on the distributor shaft. I measured the twisting movement at 8 degrees. I never paid any attention to how tight or loose a rotor fit on the shaft. Given that it spins with the shaft, one would think that there is neglegible independent movement of the rotor. Any thoughts on this? Steve

 

It is also entirely possible the roll pin holding the gear onto the distributor shaft has sheared. Be sure to check it when you pull it to change the timing gears and chain.
The bushings in the distributor that keep the shaft straight may have also worn to the point that they allow for slop.
Another thought: Changing the crankshaft timing gear will require removing the oil pan - or at least dropping it far enough to break the seal. You will need to remove it to reseal it properly.
To remove the oil pan, you must raise the engine (with short 2x4s under the motor mounts), drop the pan onto the cross member, and then drop the oil pump into the pan before being able to remove the oil pan out of the truck (with the pump and pickup tube inside the pan).
Ask me how I know this, when a simple timing change job turned into an unexpected project.
I say all of that to make this point:
Save yourself all the extra trouble with the crankshaft gear and don't replace it, unless it has broken teeth - which I doubt.
Since the engine has some wear on it, a used crank gear will make little difference.
Now on the other hand, it may be worth removing the pan to change the gear, so as to clean the pan and the pickup tube, as well as replacing the oil pump.
Either way, there are advantages - but I wanted you to be aware of them to make an informed decision before you started!
If you decide to drop the pan, keep the following in mind when you reaise the engine:
1. You can do it without draining the radiator IF the lower radiator hose is flexible enough to stretch a bit.
2. Watch out for the fan hitting a shroud, if any.
3. Watch out to not tear the fuel line.
4. Remove the accelerator cable from the stand on the intake manifold. If it brushes up against the firewall, you will break it - and there are no factory replacements to be found anywhere!

 

That twisting movement - that is probably you working the mechanical advance, rather than the rotor spinning on the shaft.
Take a second look at it to make sure.

 

That's good advice to look out for the throttle cable. It's easy to get focused on the bottom end of things and start jacking up the engine when all of a sudden you are picking up the whole truck because you are hitting on something on the top side!



Take my advice, I'm not using it!

 

Great advice which I will follow to the letter. The slot in the distributor shaft is noticably wider than the counterpart (nub) in the rotor. I can move the rotor on the shaft 8 degrees without the shaft moving. Untill last weekend, it ran fine with this rotor but somehow that much play in the rotor does not seem right. Steve

 

On the 352, it is not necessary to drop the pan in order to change the timing set. The front four bolts on the pan need to be removed, as they thread into the timing cover.

You'll need to (at lease mostly) drain the cooling system since the water pump needs to be removed. It's a lot easier to do if you remove the radiator entirely.

While you've got the timing cover off, don't forget to replace the front main seal, and if necessary sleeve the spacer that slides through it. Otherwise you may end up with an annoying oil leak. Make sure your gasket kit comes with water pump and fuel pump gaskets also, you'll be needing those.

Careful when you pull the distributor, the oil pump drive shaft is stuffed in the bottom of it. You don't want that coming out of place. If the distributor is worn out, you may consider using this opportunity to upgrade to a Duraspark system.