I have a 79 351m in my f-250 4x4.

When we set the timing, it runs great for a few days and then goes back to pining up a hill and running like crap. I think it is the timing chain, could it be?? My friend says the 351m had a bad factory chain. I have 150k mi on her.

Second question, if I replace the timing chain, can I just replace the chain it self with one from auto zone? Do I meed to but the whole timing set? Here's the chain I am looking at:
<TABLE cellSpacing=0 cellPadding=0 width=334 border=0><TBODY><TR><TD class=bodybold colSpan=2>About this product:</TD></TR><TR><TD class=body width=94>Part Number:</TD><TD class=body width=240>9-149</TD></TR><TR><TD class=body width=94>Weight:</TD><TD class=body width=240>1.1 lbs.</TD></TR><TR><TD class=body width=94>Warranty:</TD><TD class=body width=240>3 MO </TD></TR><!-- BEGIN "APPLICATION" CODE --><TR><TD class=body vAlign=top width=94>Application:</TD><TD class=body vAlign=top width=240>Optional Performance Upgrade
</TD></TR><!-- END "APPLICATION" CODE --><!-- BEGIN "NOTE" CODE --><TR><TD class=body vAlign=top width=94>Note:</TD><TD class=body vAlign=top width=240>Street true roller timing chain; Double roller </TD></TR><!-- END "NOTE" CODE --><TR><TD colSpan=2></TD></TR><TR><TD colSpan=2></TD></TR><TR><TD colSpan=2></TD></TR><!-- BEGIN PRICING --><TR><TD class=bodybold colSpan=2>Pricing:</TD></TR><TR><TD colSpan=2><TABLE cellSpacing=0 cellPadding=0 width=334 border=0><TBODY><TR><TD width=244></TD><TD width=10> </TD><TD vAlign=top align=right width=80>$18.99</TD></TR></TBODY></TABLE></TD></TR><TR><TD colSpan=2 height=10></TD></TR></TBODY></TABLE>
I am on a low, low budget right now, but just want to get the truck running decent. I figure I can afford a chain, water pump, and tining cover gasket.

So, do you think replacing the chain is nescesery? Will my set-up work?

 

Your timing drift as you describe it would not be the chain unless you have been going inside and resetting the chain. Either you're not tightening the distributor clamp properly or there's something really weird going on.

If the timing chain jumps, the engine will not start and will have very low compression.

If you WERE to replace the timing chain, you really don't want to do all that work without replacing the entire timing set with a quality unit. AutoZone is for buying oil and antifreeze. They don't have any quality replacement parts that I have ever been able to discover.

My $0.02,

 

Thanks for the info.

I have been told when a timing chain gets old and streaches it can make the timing go in and out. What you are saying makes sense. The distributor is clamped down; how about the distributor it self?

 

Usually a sloppy timing chain will cause the timing to spike and jump. If you put a timing light on it and watch the pointer on the balancer and you see it jumping around then the chain is loose.

One thing that I would do is have the ignition control module tested/checked. That is the silver box on the drivers side side inner fender well by the master cylinder with 2 plugs. Any autozone, checkers, or any parts store should be able to test that free of charge. Just have them test it about 10 times to see if it will fail any of those. Those modules will adjust the timing also and can do some wierd things when they are on there way out. They are also usually under $30 to replace. My .02 cents

 

Yes a sloppy chain and sprockets will make the timing jump around while the light is on it, but it shouldn't be 10 degrees off one way, then two days later be 10 degrees the other way.

I don't see how the electronics could be causing the problem, but this is not an ordinary problem so when faced with such a situation you have to be willing to believe in almost anything.

 

hmmm, I never thought about the box! Good call. Will look in to on Sunday and post the results.

 

If you have 150k i will change everything the 2 sprokets and the chain. I'll go double roller with straight up (0 degree). Factory are 4 degree off and the cam sproket is made with tefflon to eliminate noisy problem. With straight up you will add a few horsepower.

 

will setting it "straight up" effect my emissions test?

 

My experience with those original cams is that you are just shootin' in the dark by changing the cam timing on them. I've not seen a pattern to those cams that will tell you if it is one that was factory retarded or not.

Maybe someone here has such data. If not, as far as I'm concerned, you won't know that it is right until you change the cam for a good, mild aftermarket grind. By mild, I would not want to go past about 212 degrees @ .050 in the intake. A dual pattern cam would probably be okay as long as you don't go past the 212 intake for towing or other uses requiring low end grunt. BTDT.