i have a 79 f250 4x4 with 351m. I think the rod and or mains are bad. my oil pressure is at 70lbs cold but drops to 5 lbs at idle hot. it knocks a little bid at high idle. i held it in low gear at at 3500 rpm it knocks noticeably. i also noticed on the highway when i floor it smokes. i cant tell if its blue or white. it does not consume coolant but it does use a quart of oil every 100 miles. i just got the truck and before i bought it it sat for 1 year.

 

rustynuts, After seeing this post. It sounds like the motor needs to come out. You have a bearing issue more than likely, but sounds like a ring issue also.

You may get some replies saying try this and that.

I was exactly where your at a year ago. My 400 got to where it used a qt to a 100 miles. I tried this and that. I had new stem seals put in, then moved on to new valve guides as they were shot. I had good compression surprisingly, good vacuum, turned out I had broken oil rings. It just boiled down to, it was wore out. Its all healed up now with a fresh 460.

But I don't know if a rebuild is in your budget.

You may find a good used 400 to set back in there. It would be a straight drop in. Transfer everything from your 351M right to it. That would be my first choice over messing with the 351M. The 400 does make very good torque at low rpm in stock form. You would see a nice difference in power from the 351M to the 400 even in stock form.

 

Ditto on Superdave's advice.


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if the oil ring was broken wouldnt it smoke all the time? it only smokes when i accelerate hard. i had a pontiac that did this and found out the carb was dumping too much fuel.

 

Well the oil has to be going somewhere.....Unless it's got a terrible leak it's got to be burning it. Your best bet it to pull the engine and rebuild or replace.

 

[updated:LAST EDITED ON 22-Nov-02 AT 03:41 PM (EST)]rustynuts, My 400 "only really smoked at start up". I know its hard to imagine. I had no leaks either. As I said , I did the checking this and that for months, and thinking to myself this should be belching out the smoke. For some reason it just didn't. I wound up facing the fact, I had a wore out motor.

You could run the snot out of this motor and it would just puff a little here and there. Yet 1 qt of oil to a 100 miles. Matter of fact the motor still ran decent when it was pulled out. Set the choke hit the key and it was running.

As for your Pontiac dumping to much fuel, I know that this situation will wash the oil from the cylinder walls, which will wind up damaging the cylinder bore's. It washs away the film of oil between the piston rings and the cylinder bore, causing scuffing. The after effects of this could cause smoking. As a scuffed cylinder will eventually damage the rings.

As far as the oil rings, I just said that was my situation.

By the way, I'm not meaning to be nasty. After re-reading my post it does sound that way. This was a very frustrating situation for me as well.

 

can my oil rings be stuck? when i pulled the plugs out none of them indicated any oil residue. they looked new. it does not have really any blowby coming out of the valve covers. i just found an ad in the paper for a 78 351m that supposedly runs good for 300.00 obo. i am thinking of buying it and taking my chances with it. the current motor in my truck only has 56000 oringinal. if i decide to buy the used motor i will put a new oil pump and rod, main bearings just for the hell of it. do you think its a good idea? i just cannot afford a rebuild right now.

 

[updated:LAST EDITED ON 22-Nov-02 AT 11:30 PM (EST)]The used motor might be good or might not. Pull the pan before you buy.

If you haven't driven it very many miles since it sat, the rings could have gummed up and caused this. If they did they might also cause some piston slap. As for the low oil pressure you probably need to slap some bearings in it. I would not drive it very far or hard until you get the knock remedied. You might egg shape the big end of a rod and ruin the crank.

For some unknown reason a lot of 351/400's ate the bearings early in their life. Fortunately they usually keep going strong.

As far as the oil consumption. Rings/valves-guides/pcv system are usual suspects. If you burn a quart every hundred miles you should see a pretty good cloud of blue smoke intermittently or constant. Try letting someone else drive while you follow your truck. You might be shocked how much smoke you don't see when you are driving.

Good luck and keep posting if you continue to have problems.:-X12

P.S. What weight of oil are you using and what climate are you living in. Anythingless than 10-40 will not hold any hot pressure. If you must you can try using straight 50 or 60 weight valvoline racing oil. Or similar if you hate valvoline. In drastic circumstances I've seen 85-90 weight gear oil run. I thought they would break, but as long as temps were above 80 degrees you just had to stay off the gas until the temp got up.

"If it works it's not stupid, maybe unconventional, but not stupid"

 

i have put about 200 miles on it since it sat. i live in chicago. one thing i did notice is that when i changed the oil and checked it after 100 miles it was black already. so i am thinking the motor might be gummed up inside. i am going to pull the pan, replace bearings, oil pump, and also pull the valve covers and clean the oil return holes. i hope this works! do you recommend an oil additive that frees stuck lifters and rings? or maybe engine flush?

 

i got the pan off and removed main and rod bearings. all are worn into the copper. crank looks good. i am going to replace the bearings and oil pump. i am worried that the cam bearings are worn but do not have the time or energy to replace them. do you think it will be ok? also i thought i had a 351 but i know now that i have a 400. the spark plugs i put in are for a 351m. are there any differces?

 

>i got the pan off and removed main and rod bearings. all
>are worn into the copper. crank looks good. i am going to
>replace the bearings and oil pump. i am worried that the cam
>bearings are worn but do not have the time or energy to
>replace them. do you think it will be ok? also i thought i
>had a 351 but i know now that i have a 400. the spark plugs
>i put in are for a 351m. are there any differces?

Cam bearings take quite a bit less of a beating than the rod & main bearings. They do wear of course but the cam shaft rotates in a single plane and doesn't have to absorb the stress of thousands of explosions per minute that the rods & mains do. You should be fine. I wouldn't sweat the spark plug choice either.

 

rustynuts,

>>one thing i did notice is that when i changed the oil and checked it after 100 miles it was black already.<<

This was my engine made over. I could change the oil and filter in my 400 and in 20 miles it would be coal black, nasty and gritty.

And once again, I can't explain why, but my motor hardly smoked at all for the oil it was using. And "I did follow it down the road", while my son was driving it and thrashing it trying to get it to do something.

And like the above post said, cam bearings are not as bad about wearing as the bottom end bearings are.

Once again I don't mean to be rude, but I will be honest with you, I don't have high hopes for your engine.

Yes the bearings will help the oil pressure problem but will do nothing for the oil consumption problem.

 

>>i got the pan off and removed main and rod bearings. all
>>are worn into the copper. crank looks good. i am going to
>>replace the bearings and oil pump. i am worried that the cam
>>bearings are worn but do not have the time or energy to
>>replace them. do you think it will be ok? also i thought i
>>had a 351 but i know now that i have a 400. the spark plugs
>>i put in are for a 351m. are there any differces?
>
>Cam bearings take quite a bit less of a beating than the rod
>& main bearings. They do wear of course but the cam shaft
>rotates in a single plane and doesn't have to absorb the
>stress of thousands of explosions per minute that the rods &
>mains do. You should be fine. I wouldn't sweat the spark
>plug choice either.

Ditto here. You can get bearings .001 undersize if you check the crank and it will have too much clearance. Otherwise just use original or whatever it has in it. Be careful with the rods and put assembly lube on everything. Watch out for the rod bolts coming loose or moving when you push the pistons up. I would go with hi-volume oil pump to make up for the extra clearance. Check the oil pump pickup for debris. The valvestem seals are good about plugging the screen up. When you clean up the valve drains do it with the pan off. That way all the crud will wash straight through and you can clean it out of the block. Look at the umbrella seals while you are there. While you have the pan off look at the timing chain and check the play. If you see any pieces of white colored plastic in the pan you need to put in a timing chain set ASAP.

As for the oil consumption. As long as you can afford it and it doesn't foul the plugs every week. Who cares. If you don't see a cloud of smoke following you then you have nothing to worry about. I've driven plenty of vehicles that used more oil than that. If it does foul the plugs, buy hotter plugs or put in some non-foulers. (The old timers on this site will know what I'm talking about.) As for the longevity. If you have good bearings and the timing chain is tight, then you could stretch a good 20-50 thousand more miles out of this thing.
You mentioned something to clean the lifters and such. I've always had good luck with adding one quart of Type F automatic transmission fluid and running it for the duration of the oil change. Many may tell you that this is a bad idea, but I've seen a lot worse things done to engines and it helped rather than hurt.

Good luck and keep us posted how it turns out. Remember, if you have more time than money many of the mail order outfits can save you 25-50 % in parts cost. It just takes longer to get the pieces.

 

>i got the pan off and removed main and rod bearings. all
>are worn into the copper. crank looks good. i am going to
>replace the bearings and oil pump. i am worried that the cam
>bearings are worn but do not have the time or energy to
>replace them. do you think it will be ok? also i thought i
>had a 351 but i know now that i have a 400. the spark plugs
>i put in are for a 351m. are there any differces?

The 351M uses a autolite 25 and the 400 uses a autolite 26. I belive the 26 is a slightly hotter plug but I've never noticed any difference between the two..


79 250 Ranger Lariat 4wd 400 C6 3.55's 33x12.50 16.5's
78 Bronco Custom 4wd 400 C-6 3.50's 31 10.5 15's
66 Mustang Coupe Sports sprint 200 c-4 cruise o matic 3.00's
99 Grand Prix GT 230 ft/lbs torque out of a non turbo'd 6 cyl hehe

 

If it matters...I have been thru two 351M's this summer...both bought used for $200 ea and supposed to be good and both blown within 3000 miles of purchase. One blew a connecting rod and one broke a camshaft (I think) ...I have had both of them apart and the CAM and Main bearings seem ok even though the camshafts themselves were toast. Check the camshafts too ! I have high regard for the 351M/400 family but will never trust a used one again.


I am currently REALLY rebuilding a 400 as per all the advice and instruction you may read on here..putting about $2000 in it and hoping never to be left on the side of the interstate again :-(

Im with that guy that keeps saying fix it right the first time from now on!!