So I went up to work (5 hour drive away) on my buddys 1977 2wd f250 400/4-speed truck that he recently purchased. His Grandfather-in-law purchased it new, shortly after buying the new truck in 77' it developed a knock, Ford warrantied it and supposedly bored the engine to 460??Not sure on that number? Sounds odd to me...anyway that's just what the family says about it....Someone in the past put an aluminum 4 barrel intake with a 2-barrel adapter and small Holley carb. I thought that was kinda weird, but anyway.... First thing I noticed when he fired her up, was a real noticeable miss fire, sounded and felt like it was running on 7 cylinders. It would almost smooth out when you revved it up, but the engine was pretty bouncy at idle. So I started checking spark plug wires and stuff and found that #3 cylinder wasn't firing. The plug was a bit oil fouled, ALL the others were really white/ashy lean looking?...We replaced the plugs, the old wires and cap/rotor. The miss was still there. I then checked compression, all cylinders had 140* with one cylinder at 135*. Now what? So I hooked my vacuum gauge to the intake manifold, and at idle it was bouncing between 14-10, if I rev it up, the engine smooth's out some, but the vacuum needle vibrates erradic on 16 I think? I checked for exterior vacuum leaks with B12 Chemtool, couldn't find any, the carb idle air screws are set correctly and have a dramatic effect on idle (kill the motor) if screwed in like they should. I played with the timing to no effect on the missfire. Timing was set to 12*, I backed it of to about 10.5* because the engine was wanting to run on after warm shut down, and it felt a little advanced. I'm unsure where to go with this? Could it have weak valve springs? maybe leaky intake manifold issue? If I had the truck in my possession I would probably pull the valve covers and look at the rockers and etc, I didn't have time on this visit to dig deeper...He hasn't had the truck long enough to know if it burns any oil. I told him to just drive it for now (I'm a little worried about the lean condition though) it runs like a raped ape, it will burn the tires off in 3rd gear on dry pavement believe it or not. I was amazed. Does this sound like an issue one of you gooroo's have seen?? Thanks

 

I would run a compression check along with replacing the dist cap, wires, etc.

 

The vacuum gauge bouncing like that is classic worn valve guides. It should be stable in the 19-22 inches of mercury.

 

I agree with you,pull the valve cover and look for a broken valve spring. I had that happen to a 351M that was only a couple years old. As far as driving the truck, not a good idea. If a spring is broken and that valve drops into the cylinder, good bye engine.

 

ok, thanks for some input

 

Already did this, Thanks

 

So.....I got a little history on this motor last night. After telling my buddy not to drive it until I can get back up there, or I would also walk him through pulling off a valve cover to see if there is anything obvious going on before I could get back up there, he talked to his father-in-law, and he said in 2002 they were towing a trailer with the truck and the engine started to miss terrible, they took it to a mechanic and it "broke a valve". I'm not sure what he meant by "broke a valve", but now I know it's had head issues in the past, and I have no idea what kind of "fix" the mechanics did on the "broken valve".....So the heads are more than likely coming off and going to the machine shop. Hopefully the rockers, pushrods, lifters and cam are good. I'll post what I find later.

 

Broke a valve? How about "burned a valve"? Sounds more reasonable, but either way, methinks the heads need to come off

 

yes exactly..."broke a valve" was all the info I got? Who knows?? Wish I had more info on that. I'm traveling back up to his house and digging in to the motor in a few weeks. I do know there is no metallic sounds coming from the motor now, I would think there would be a "click" or something if a spring was broke? Maybe not...idk We'll see.

 

I had a valve spring break on me once. I couldn't see it but I knew it was broke because it ran rough and of course the exhaust sounded funny. I guess I got lucky that it didn't break the stem or the keeper because I was 3 hours from home at that time. Since I knew the engine was tired I took it to a shop and they replace just the spring that was broke. Drove it for another year before I rebuilt a 400 to replace the 351M.

 

I'm pretty sure that is what broke and what was fixed in 2002, probably just replaced a valve spring. I doubt the heads ever came off.

And yes the exhaust sounds funny too....I can't wait to tear into it.

 

I fixed the mystery miss......

This last weekend I made the trip to my buddy's house, prepared to possibly pull the heads and get them rebuilt. Of course, I wasn't going to pull the heads unless I found concrete evidence. I started by removing the passenger side valve cover and inspecting the valve train, found nothing abnormal... I then ran the truck without the valve cover to watch the rocker arms working, looked great. I then pulled and inspected #1 & #3 intake/exhaust rocker arms and pushrods, all good. I was able to get some movement side to side on the those valves, but again nothing concrete. #3's intake valve had the same side to side wiggle as 1&2, but #3 fired normal...So....While running it some more, I found that #2 cylinder had the same miss as #1, OK....I determined that they must not be getting fuel at idle, and then possibly "some" fuel as the engine rpms increased, but they still misfired. I put the valve cover back on and called it a night. The next morning I got up early and changed the oil, it was 1.5 quarts low, some of this loss was from leaking off of the head when I was running it, but the other loss of oil is a mystery? Maybe valve guides? Going back to my first visit looking at this truck, I used B12 Chemtool to look for vacuum leaks, and I didn't find any. Now Im back for my second visit to try and fix/trouble shoot this motor, and when I asked for that can of B12, my buddy said it got tossed or something?? So we went to the local parts place and bought a can of starting fluid. I ran the motor and had my vacuum gauge hooked up to the manifold, the vacuum at idle was still erratically bouncing from 10-20 at idle, I sprayed starting fluid around the intake and VROOM!! The vacuum gauge smoothed out, and the engine purred for that split second! I found my HUGE vacuum leak on the intake manifold gasket on/near the #1 hole!! YAY!! NOW I can fix this sumbich. I removed the intake and found that whoever installed this aluminum manifold/Holley 2 barrel carb, completely axed the gasket job, the gasket was sticking out just slightly on #1. They were fiber gaskets, no turkey pan. I purchased the turkey pan style gasket, cleaned up and installed. Tuned the carb and adjusted the timing slightly. This engine had been tuned? to run with this vacuum leak for quite some time, it would smoke on cold start up when using the choke, OH and you would have to choke it, or it flat wouldn't start. He doesn't need to choke it now that I got the vacuum leak fixed, he actually flooded it due to old practices!! It was habit to always manually pulling the choke to start it, but now on cold start it fires right up without the choke I guess. I was glad to hear that. I forgot to take pictures of the bad gasket job, but my buddy took a couple random pics. I need to get rid of the plastic oil pressure line on the rear of the block, I'm hoping to find the factory oil pressure wire and just install the original sending unit for the dash gauge.

 

 

Can anyone recommend an aftermarket crank case push in breather that will fit under the AC housing on a factory valve cover? I'm not sure if this would need to be a low profile one, or what...We put a chrome air cleaner on it because the factory aluminum one was beat and cracked to hell....Thanks

 

That "460" could possibly be a "406" That is a "400" bored out .020