I just recently installed a 351m in my 73 f-100. I was told that the engine had been rebuilt. It runs pretty good, sounds solid, doesn't hesitate. The problem is at idle there is very little smoke coming from the exhaust, but when i step up the rpm to about 1500-2500 it starts smoking very bad and doesn't stop. It bellows out blue smoke and I am sure that it will not pass an emissions test. I thought that maybe the valve seals had dried out so I replaced those,still smoking badly. I disconnected the trans. modulator and plugged the vacuum port, still smoking badly. I am not sure if the valve guides are bad or if the oil rings are bad. Any advice would be helpful.

Thank you
Ion Kendall

 

it could be sucking oil from the lifter valley through the bottom edge of the intake ports. what kind of gaskets did you use? or are you going to use? are all of the spark plugs about the same or is there one or a couple that look oily? keep them in order when you take them out and try to figure out which cylinder(s) it is.

 

I recently replaced the 2v manifold with an aluminum holley 4v manifold. I used the felpro gaskets ( 4 pc., 1 for each head, 1 front cork style and 1 rear cork style ). I also pulled all the plugs and the are all wet with some carbon on the tips and part of the base. These plugs are new with about 1 - 2 hours of run time. Thanks for your continued help.

Ion Kendall

 

so it smoked the same before and after you changed the intake? did you notice any imperfections or excessing buffing on the sealing surfaces, particularly at the bottom edges?

how bout the PCV valve? is there one on it? have you tried running it with it removed and the vacuum line blocked? oil in the fresh air tube to the valvecover?

if there is a good amount of oil all through the engine, it could take a little while to clear it out.

 

FYI: Cork gaskets shrink and dry out...it is usually necessary to soak them in water before using them.

The late 70's 351M and 400's had a problem with cracked heads, too.

btw...What some people consider "rebuilt" may only consist of a tune up, or a can of oil additive added.

When someone says rebuilt to me, I ask to see the bills.

 

Run some seafoam top engine cleaner through the carb to clean everything out.It works great,you can get it at any autoparts store for $5.00.It will smoke like crazy for a while after doing this.A clean engine will only smoke for 5 min,but a dirty one will smoke for about 15min.It cleanes out carbon,oil residue and everything.


Tim

 

Thanks for all the suggestions. I had a thought. While I was replacing the valve seals I noticed that the seals did not stay in place on top of the head. The valve seal actually rides up and down with the valve stem as it is being moved by the rocker arm. This doesn't seem normal to me. Is this normal or should the seal stay fixed to the head and the valve stem should move inside the seal.

Thank you
Ion Kendall

 

An umbrella type seal does exactly that, and it is the most common seal used oem.

The guides would have to be machined for a positive seal if so desired.