I just installed a remanufactured 351M in my 78 F-150 4x4. To make a long story short, it fired right up like a champ when I first tried to start it. I set the timing to 14 BTC, and it idled great. I left it idle about 10 minutes while I collected up my tools, and then driving down the road things started to go bad. First it started to get hot, up on the l side of “normal” then it just all of a sudden dropped down to the n-o side of normal, which is where my truck usually ran on the old engine. Then, a couple miles later, it was back on the hot side again. I got to the storage place to put my tools away and turning in the driveway my truck stalled and that is where I’m stuck.
I pulled the air cleaner and checked the carb, its got gas to it. I pulled the 1 and 5 spark plug wires and turned the engine over with them on the valve cover and they both sparked. I would think that with gas and spark it would at least try to start, but I’m not getting any sign of combustion at all. All it does is turn over.
On a separate problem, while turning the engine over, oil came out of the dipstick tube (the one to the oil pan for a 4x4). I figured a crankcase ventilation problem, checked the PCV valve and its fine, checked vacuum lines and found the tranny modulator was disconnected. Reconnected it and didn’t see any more oil coming out the dipstick tube, so that may have been it, but it seems odd to me that that would be enough to cause the crankcase pressure to build to the point that it would blow oil out the dipstick tube.
Also, since that vacuum line was disconnected, I suspect I may have to reset the timing, since you are supposed to set it with no vacuum to the distributor but have the vacuum line plugged. I did notice that when I originally set the timing, when I reconnected the distributor vacuum line I didn’t get an increase in rpm. Normally when you have the engine idling and you pull a vacuum line, the rpm drops, or that’s what the old engine usually did. Maybe that was just when it was running at fast idle, I’m not sure.

As far as the overheating goes, I did re-use the old thermostat and radiator/radiator cap. It does have a new water pump. I knew putting in that damn thermostat that I’d regret it, but I figured I just put it in 6 months ago, it should be ok. But, maybe I’ll go ahead and replace it. I never had a problem with the old engine overheating, so I have no reason to suspect the radiator is bad or the cap is bad. So, in other words, I have no idea why it would be overheating. I don't recall what temp thermostat I have, but whatever it is, its stock, ie, I didn't ask for a higher or lower temp when I bought it.

Ok, so here’s the summary. Biggest problem: I got spark and gas, but it won’t fire. Next problem: it’s overheating. Slight problem that may be fixed: crankcase ventilation may or may not be out of whack.

Any suggestions short of “take it to the shop,” or “that’s what you get for having a Ford” would be greatly appreciated.

 

I should also add in regard to the overheating/blowing oil problems, I suspected that a ring might have broken while "breaking in" and if so it would explain both the overheating and the crankcase pressure being too high. However, when I checked the oil, there was absolutely no froth or bubbles (or water for that matter) to indicate exhaust gases getting into the bottom of the block (or water if a blown head gasket)

 

If it were mine, I'd reset the timing since you set it once and later found a vacuum line off. That alone may do the trick. If you have spark at the plug, your electronic ignition module and coil are good...has to be timing. Hang in there, sounds like you just need a few minor adjustments. If the present thermo isn't rated for that engine, put the right one in...they're cheap insurance against having to walk or call a tow truck.

 

 

I think the first thing I would do is a compression test. You should start there. Obviously if you have fuel, and spark then all you need is good compression. If you have all three then its just a minor problem. Perhaps (as suggested earlier) your timing may be off. As far as your oil blowing out of the dipstick problem goes... it reminds me of my old 72 pontiac. I had bought a sweet set of heads for it, and when I put them on, using new felpro head gaskets I started it up, and it was pumping antifreeze out of the radiator. I double checked everything, taking the top end apart numerous times. Eventually I (if you can believe it) reused the original head gaskets and it solved the problem. Where my original gasket had a 3/8" coolant hole the replacement gasket had a 3/8" X 5/8" slot. It didnt seem like it could cause the problem, but it was certainly the culprit. Every other gasket I ordered had the same slot, so I ended up leaving the original gasket in place. It stayed like that, and ran great for 2 years untill I sold it. I dont know how that could cause your condition with the oil... but it seems oddly similar. Good luck!!

Steve

 

When I first started the engine and set the timing, I noticed that I could really swing the distributor through a wide range and it still idled. Rough, mind you, but it ran. So, even if my timing is way out of whack, I should be getting some firing of some kind on at least one cylinder.

I checked the compression on the 5 and 6 cylinders and they had about 40 lbs each. I know that a brand new engine I should have, hell, 120 to like 150 or 180 lbs (or psi), whatever it is, its gotta be a lot more than 40.

I also pulled a valve cover to check that the entire valve train was working. I know a busted cam was unlikely but just to be sure...

I was thinking that since the long block was set up at the factory, the compression might be low if they torqued the rocker arms too much and the valves are being held open even when the push-rod isn't applying pressure. So, I'll look into that. But, that doesn't explain why it ran just fine, awesome, in fact, for 15 or 20 minutes before it died. If the valves are adjusted and I still don't have compression, could it be anything else besides bad rings?? If so, we're talking I need to take the whole thing out again and exchange it (it's warranted)

 

40lbs is awfully low!! I would expect at least 100lbs. Unfortunately with the remanufatured replacement engines, you never really know what your getting. Most of the companys that rebuild those enignes re-use a lot of the same parts that came out. It's hard to say what could have gone wrong in your engine without taking it apart. I would imagine if you dissmantle it, you will void your warranty. To me, it doesnt seem like it could be a drastic missadjustment in the valve train, because it wouldnt have run in the first place. Unless of course a missadjustment caused it to bend a few valves. It cant be just one bad/broken compression ring, because you said you have low compression in more than just one cylinder. It seems unlikely to have broken several at the same time... I'm just not sure. Possibly bent valves could in fact be the culprit.
I wish you luck with it... and remember at least you have the warranty.

Steve

 

I know this dosen't have much to do with your problem but I just recently ran a compression check on my 82 F-250 4X4 with a 400M in it with 87.000 miles on it and it had 150 to 160 lbs in all cylinders. This is a tricky one, if you have a warranty on the motor you should probably just pull it back out and get another one. I know that really stinks, alot of labor to have to eat, but probably better off in the long run. GOOD LUCK!