I'm new to having a 351M. Of coarse the day I bought the truck it was a 400. I have a 79 F150 4x4 w/ NP435/NP205. I haven't actually measured the stroke, but the numbers in the VIN and the valve covers indicate 351M. I've had prior experience with a couple of 302's and a couple of 390's.

I'm aware that the 351M/400 has a reputation for poor oil pressure on worn engines. Mine seems to be no exception. When I first start the motor, it is quietest and the oil pressure gauge reads slightly to the higher side of the normal range of the gauge. It doesn't take long to see the gauge start to read less and less. It hasn't gotten out of the "normal" range as defined on the stock gauge yet but it gets to the low end of it especially when its warmer out. I had the lube place run an engine oil flush, and refill with 10/40. I've had the valve covers off and noted filthy carbon crud coating the pushrods and rockers which I wiped away. I figure the engine is pretty filthy inside.

I had a shop that was working on my front hubs/brakes look at the engine. They looked under the passenger side valve cover and reported some slop on a couple of the rockers, and milled down the rocker arm pedestals to tighten up the valve lash. I think that things are a bit quieter, but I feel the same procedure needs doing on the drivers side. I figure that this is a temporary band-aid, and wonder about whether I'd regret this milling to my heads if and when I decide to rebuild the engine (if I rebuild this engine).

The symptom now seems to be mostly at an idle and during deceleration. It sounds a bit like an exhaust leak, but I can't find any exhaust leak evidence on the stock manifolds. Accelerating minimizes the noise, idling maximizes it. I don't hear it when I first start up. I listened to the ticking Utube post on this forum, not nearly as loud. The ticking I have does seem to correspond with some engine vibration, like I'm not running on all 8. I have verified that I don't have any pushrods bent in half like I've found on one of my FE engines. My personal theory is that at an idle I have poor oil pressure and the lifters aren't pumping up as much as they should, so the valves aren't opening uniformly.

Questions would be:
-is milling down rocker arm pedestals, a bad thing to do?
-should I consider a different oil weight such as 30w or 20/50?
-are there any advantages to getting rid of some of the smog stuff? ie: I've heard that EGR is actually a good thing when it's working correctly. Any advantage to ditching the air injection into the intake?

For the future:
Pro's and Con's of converting to 400 how much MPG hit would I take going to 400? If I made CR improvement, intake/exhaust manifold upgrades, cam timing, would I notice improved torque in the 351? I'm not requiring gobs of power for any particular needs. I don't tow, and rarely carry appreciable weight. The main impetus for 4x4 is to get around better when it snows. I use my trucks for general yard and home owner utility and carrying around band gear once in awhile. I also simply like driving them.

I really like the 390 I have in my 2wd, and I have another on an engine stand ready for a rebuild. Or I could give in to the 460 conversion. I also have been tempted to think about another 302. I know that in 2wd trucks, the 351M/400 share the same engine perch as a 302. I already have a smallblock bellhousing sitting around. Could I drop a 302 or 351W onto my existing engine stands and be properly located to my transmission (utilizing a 79 2wd 302 bellhousing)?

I have dual tanks, how much of a hassle is involved in headers? Currently I have a bone stock catalytic converter single exhaust. I'm wondering how the exhaust routes around the tranny/Tcase/side tank?

The good about my 351 compared to my 390. The 390 (with Motorcraft 2V) is really cold blooded to start when cold or not been run in awhile, the 351 still has virtually all it's smog stuff and fires up much more easily. The 390 has noticably better (felt in the seat) torque and sounds way cooler (it has dual exhaust). The 390 in my 2wd is running pretty smoothly with decent oil pressure.

I'd appreciate hearing opinions born from experience

 

i can at least answer your cam question. if you correct the timing on the cam, even in the 351M, you will notice substantial increase in HP and torque. you wont be making the numbers the 400 does when you do it, but that truck WILL feel quite a bit more peppy afterwords.