My buddy that rebuilt my 79 351 m came up this weekend to start it for the first time and get it dialed in. Wow, not a good trip. Engine has ALL new primary and secondary ignition parts on it, plugs, plugwires, rebuilt original 2150-2v carb. He set the timing to factory 8 btdc . Started well. But to keep it running he had to advance timing way up. Pulled distributor and moved it the shaft gear one cog. No help. Had oil pressure gauge hooked up, engine running 75 psi at 2000 rpm. Kept vac guage on it all the time , but had a hard time keeping 15 in. of vac at idle. At idle and above, the vac guage "flickers" at about 15 in. at 2000 rpm.

Removed and plugged all vac lines except dist line, put in back on after getting initial timing set. . Radical adjustments on rebuilt original 2150-2v carb, were no help. Went and bought a new reman 2150-2v and installed it, no change regardless of adjustments.. Checked all plug s/wires for fire, o.k. Engine just idles rough, regardless of carb settings, the vac guage "flickers at 15 in. of vacuum all the time. Only way engine will run ( and ruff at that) is to advance the timing greatly.

When he rebuilt it , he said he was CERTAIN the new Rv cam and crank alignment marks were dead on when he installed them, new roller timing chain installed too, at that time. He is coming back later in the month and we are going to pull a valve cover, use a dial indictor and big timing degree chart that goes on the crank shaft pulley to see if the valves are opening at the right "time" for compression. This ones got us stumped. Any other ideas we could do to help out ?? thanks

 

Were the heads or block shaved? It sounds like the lifters may be set too tight and the valves are not closing properly? If you put a new cam in it, you may have to shim the rockers to get the preload set.
You either need an adjustable rocker or shim the fixed rockers.

 

yes, the block was squared and decked, heads milled flat, block crank journals line bored , heads ported/polished with 3 angle valve cuts, cylinders bored .030 over, new RV cam with HV oil pump. He didnt write in the logbook how much was taken off to get the heads/block flat, but I remember him telling me how bad everything was out of range. I'll ask him about this. It may be something we will find out when he gauges and dial indicators the valves ?

He just called ten minutes ago ,and after asking his boss at the machine shop he works at about my engine problem, his boss said it sounded like a egr/spacer problem. We had the egr blanked off with a solid gasket to isolate it. But, the vac would go to "o" when the engine was allowed to drop to 1000 rpm, then it would die. Could there be a crack in the egr spacer letting it have a castastropic vac leak also? thanks

 

I would check valve train geometry. Shims are for fine tuning. At some point you have to buy shorter push rods. Always recheck geometry after shiming.

 

Maybe the egr gasket blew out as soon as it started, When I block off egr's I make a solid plate to put between the valve and the valve mounting plate with a gasket on either side just to make shure that exhaust doesnt get through

 

Greg,

I am with Danlee and Mark on this one. I would bet my next paycheck that that there is way too much lifter preload which means the valves aern't closing properly.

Here is a simple check that may help: Take a valve cover off and pick a cylinder that obviously has a valve open. It doensn't matter which cylinder. Let's say it is the intake valve that is open. If the intake valve is open, then the exhaust valve should be closed. Loosen the bolt holding down the exhaust rocker arm, wait a few minutes for the lifter to get back to normal, then slowly tighten down the rocker arm bolt while spinning the pushrod back and forth between your fingers. As soon as you feel some resistance in spinning the pushrod, stop tightening the bolt. This will be the point where all of the slack is taken up between the lifter and the rocker arm. Any further tightening of the bolt will now be pushing the plunger down that is inside the lifter, which is known as lifter preload. I think that the preload should be between .020" minimum and about .060" maximum. Put your socket back on the rocker arm bolt and tighten it all the way back down and count the number of turns it takes. Since the bolt is a 5/16-18 bolt (18 turns = 1 inch), one turn should be about .055". If it takes 1.5 turns, 2 turns, or more to tighten it down after taking up the slack, that means your pushrods are too long.

Ford designed all of this to work out right with a certain deck height on the block, a certain thickness of the cylinder head, and a certain thickness of head gasket. When you have all of the original stuff in the factory and bolt it all together, the preload works out right for the lifters. If you start taking material off of the deck of the block, material off of the bottom of the cylinder heads, etc., you start bringing the lifters and rocker arms closer together, which in turn makes your pushrods too long.

Sorry for being so long-winded. I wanted to be clear for those who are learning.

 

If it is new rings , I would say they are not seated yet, This is why I use 2 stroke oil on the ring they will seat faster. If you used STP on the rings it will take 2-3 weeks to seat.

 

Sure sounds like vacuum leak, I agree could be caused by tight valves. When I was running a hydraulic in my Cleveland I was able to shim rockers up to correct preload. Sounds hokey, but I was able to use plumbers tape, was perfect thickness to give minimum preload for my situation. Cam/lifter combo had recommended minimum preload.

 

First off what is the firing order that your using? I rememeber when i rebuilt my motor this summer i was in a hurry and wasnt thinking and set my firing order for a 460 instead of a 351. Surprising it ran it just sounded like it was missing on a couple cylinders until 1500 rpm or so and then it smoothed out. Freaked me out at first as to what it was until i finally double checked my firing order and figured out that i was a idiot. Not real hard to do so check that before u get too deep into the motor.
Dick

 

thanks 278, a very good post ! I am not a mechanic , that is why I trusted my buddy, who is a machinist that has been rebuilding engines for 25 years , to build my engine. From what I have read on here , and in engine repair manuals I have seen, the flickering vac reading is indicative of a valve not seating properly so I believe everyones tips here on the valve train/seating/ geometry, has hit the nail on the head. It also smells like it is not burning all the fuel at the exhaust pipes too , it has a very raw , eyeburning exhaust fume . I will post back when we find the answer. I am wore out with it for now and am going to get away from it for a while. I'll be back later to post findings of what we found out , when we get it running like it should be. Many thanks to all who replied !

 

Total nonsense...

 

The Last che^y was a 385 with 462hp at the flywheel, ran it on the dyno 4 hours to tweek it.

 

Hi, guys I am back in to this one again, after time out for knee surgery
.

My buddy that built the engine is on third shift now, lives a hundred miles away, so I am trying to solve this one myself, ANY tips is GREATLY appreciated.

Yesterday I performed a compression check on all the cylinders. They all came in a 150 psi each. After removing all the plugs for the comp test, I noticed #4 sparkplug was like new, never fired. So, after the comp test, I reinstalled the 8 plugs, made sure all vac openings were plugged, started it, still runs awful, with vac guage flickering at 15 hg. So, I run the stumbling engine with the #4 plug wire on the plug, held the SP against a good ground, and a strong spark fired at the electrode. So, # 4 is dead, and has been from the initial start up, because the other 7 plugs have light grayish brown burns on them. And I did have ALL vacuum openings plugged at that time, even the brake booster, no egr kookups, no openings nothing left plugged. ..

So, it looks to me like a major vac leak is killing number 4 cyl ?? . Can a newly rebuilt engine have 150 psi compression , with a no plugs in it, using a cranking over type test, and have a bad valve seat, or pushrods not the correct length ? Would valve train geometry being off just kill #4 ? ..

I called my buddy telling him what I just typed, he said the intake manifold was suspect. But at that he did not understand it, because when he was re-building the engine, he cleaned and magnafluxed it, it showed no cracks. So, with it running , I have sprayed starting fluid ALL over every piece of the intake, gaskets, carb body, with no increase in engine rpm's noted. So, should I pull the intake anyway ???

P.s. The sad part is , the engine was running fine when I started the restore on my 79 F150, 5 years ago. But wanting a totally fresh restore , I had him re-build the engine anyway. Today, after having over 2 grand invested in the engine by me, it now runs like a paint shaker. And THAT just sux major, I want this project DONE and over SO bad, so I can DRIVE it again ! thanks all for any guidance here,

 

First you should do a leak down test on all cylinders. Compression tests do not always show valve problems.
Second, pull off one wire at a time on each cylinder. see which cylinder do not make it run worse.
Third, replace the plug wire and plug on cylinder #4, a spark in air doesn't mean that there is a spark in the cylinder.
Fourth, check your timing and idle mixture.

Do these in any order that is convenient.

 

O.k. I will do that. How is a "leak down" test performed ?