hi, guy's

Not sure what engine I got, 351M or 400. How do I tell?
Took the engine out of a 78 f-150 4x4 and put it into my 79 f-150 about nine years ago. Put a 4 bbr holley carb on it and it just came to life. Do realy like the holley. About 4 years ago found out the diff was hitting the oil pan. At some time the engine might have came out of a 2wd. Change the pan and the pickup tube only. When I drop the pan found good size of a rolled out bearing. Check out the engine the best I could. Didn't see anything wrong, put it back together and ran it. Pretty sure there was no problems. In the last two years I starter to use the truck more to haul my car trailer around and work around my first house. started to see the oil gauge drop. Thought that it might be my gauge. Lots of electric problems with the truck over the years. Then the gauge started to read no oil psi at warm idle. Put a good mechinal oil gauge on my door post. Hears what it reads

start up= about 55 psi
temp gauge starts to rise= about 40 psi
start into normal range temp= 20 psi
normal temp= about 5 psi
this is all if you leave it idle, it realy drops fast if start to driver down the road.
when doing 55 mph got 20 psi oil "foot on the throttle"
let foot off throttle oil psi jumps to about 24 to 26 psi for a split second and then drops to about 16 to 18 psi. push in the clutch, same thing but then will drop to about 5 psi after the jump.
there is no kocking coming from the engine.
So what do you think. Ideas that I have
1 sucking air at the pick up tube.
2 oil pump bad
3 this is all a bad dream
4 spun one or more main bearings" hope knot"
5 spun a cam brearing

plain on dropping the oil pan again to check it out again and replace the oil pump.
Any Ideas are welcome. not sure what to do.

 

6 - rod and main bearings are worn beyond acceptable limits and cannot hold pressure, time for a rebuild

 

351M/400 engines are notorious for low oil pressure at high mileage. What you're seeing isn't uncommon. I've got a Galaxie with a 400 in it that literally has almost no oil pressure at all at idle.

If you found part of a bearing in your oil pan though, then all of this is pointless - of course you're going to have an oil pressure problem, at the very least.

To find out if your engine is a 351M or a 400, you'd need to measure the stroke - if you've got the pan off then maybe you'd be able to find the part number on the crank (which would be different between a 351M and 400).

 

As said these engines are well known for this problem and usually the mains and rod bearing are the trouble. If you have a 4X4 it can be done easily from under the truck in about 3to 4 hours, the pan will come out without lifting the engine. In a 2WD it gets to be a bigger job, the engine needs to be lifted about 6 inches for the pan to clear, which means unhooking the exhaust, rad trans lines and a few more goodies. Now you can get at it but the cross mamber is a pain to work around, the long shortcut is to pull the engine out flip it over and change the bearings, super easy to do then and you can work standing up. I just did mine and the total cost was around 200 bucks including gaskets. Have fun

 

I finished my rebuilt and got it running again last night at 4am. same issue as you but I let it go to a rod knock.

 

If you didn't live so far away . I have a 78 f150 351m w/12,000 miles on it's re-build .

 

Putting a oil pump in now would more than likely be a waste of money & time, cause your engine is going bad.

 

Agreed....

 

Time for a bearing job on the engine stand. Go ahead and put a timing set on while you are in there and a good Melling high volume oil pump. The motor should outlast the transmission for sure!

Also check out TMI website and read up on their build projects. Those guys do some amazing things with 335 series engines!

 

Thanks guy's
Not sure what I'm going to do. In some way's I'm out growing the truck. Might need to up grade to a f-250 super/ crew cab. My dad is plainning on down grading his 1990 f-250 super cab to a ranger. The truck has alittle more the 250,000 miles on it. But still strough. Might sell it cheep to me. Not shore about it.

 

Thanks for all the info on the bearing problem. I just bought a 92 F-350 xlt 4x4 7.3L. So I think that I might just run the truck until I get the 92 on the road. Then sell it. Again thanks for the Info.
Matt