Ford 390 FE Engine mystery

[Bob Shafto]

Here's a mystery several very good mechanics who've looked at the car are unable to explain. I installed a new 390 long block in my '66 Galaxie over a year ago. Since then, it has never run quite right. What can't be explained is why it only has 80 lbs of pressure in all cylinders and only 5" of vacuum at the manifold. Those numbers are way below normal. A dry and wet compression test confirms that the rings are sealed properly and the valves are opening and closing in accordance with the timing (and the timing gears are aligned properly). With a lot of careful carburetor tuning and close attention to setting the timing, it manages to run reasonably well but it is clearly not right. There are none of the usual suspect vacuum leaks (intake manifold, carburetor mount, etc.) so it would appear to be an internal engine problem. But what?  Any ideas much appreciated.

[joe_padavano]

What are the cam specs? Have you actually dialed it in? Verified TDC on the balancer? What pistons? Who assembled the "new" long block?

[Oldtech]

I would suspect incorrect pistons.

[John Byrd]

I may be way off base, but I once had a little 289 Falcon Sprint that someone else had just assembled, and it sounds like the same symptoms. My cars problem was the rocker arm push rods were the wrong length !

[Jubilee]

1 hour ago, Oldtech said:

I would suspect incorrect pistons.

I agree. Incorrect overall rod/piston assembly length. Rods, pistons, or both.

[Bob Shafto]

Great suggestions guys, thanks. Too much volume in the cylinders would produce lower compression and less vacuum. My difficulty now is determining the correct size of those parts, starting with the push rods. 

[Bloo]

390s do have selective length pushrods. I wouldn't expect that to be the problem if the compression is even, The potential trouble would be with holding valves open (and no compression) if the pushrods are too long, and rattling if they are too short.

 

One thing that has not been brought up yet is the timing chain. Is it the correct year? I saw you checked the valve timing, but if you only checked the marks and did not verify it with a degree wheel, the timing could still be wrong. In the early years of emission controls, cars in general had retarded cam timing. Unlike most others, Ford in some cases used the same cams they had been using, and made a different timing chain set with the key in a different spot to retard the cam timing. I don't know for sure this exists for the FE engine. If I remember correctly the FE stayed in production in trucks until 1976, so it probably does. I checked mine with a degree wheel just to be sure.

 

[Bloo]

Regarding the pushrod length, I just had to deal with this a couple years ago when some two year old gas glued my valves in place and bent a bunch of pushrods. The pushrods are selective on FE engines. Ford's procedure for setting the preload in the manual may be defective. My engine was all original and had obviously not been set up "by the book" at Ford so apparently they were not following their own procedure. Lots of things can affect the needed length, such as head milling, deck milling, head gasket thickness, rocker arm wear, reground cams, reground lifters, different lifters, etc.

 

The rocker arms and shafts are usually worn out on FE engines, and are available new, but rarely actually get replaced. The rockers themselves do not have enough metal there to rebush without weakening them significantly, so often they get run as is. My engine got repaired, not rebuilt. The guy who reground the original cam and lifters recommended setting the lifters to about .060" preload. This is a lot less preload than Ford says. His reasoning is that if the lifter piston is halfway down like the shop manual wants, the lifter piston can block or partially block the holes in the side of the lifter. Any engine will have a valve or two open when the engine is shut down, and those lifters will bleed down overnight because the valve spring pressure is against them. If the hole in the side of the lifter is wide open, it will fill instantly when the oil pressure comes up. If the hole is blocked or partially blocked it might take a while.

 

Food for thought, but your symptoms don't really sound like pushrod length to me.

 

Edited July 16, 2022 by Bloo (see edit history)

[Rusty_OToole]

Now you have me curious. What do you do about the pushrods when you rebuild one of those, or do a valve job? Do you measure the pushrods one by one and get all different lengths or get a set with the right average length all the same? Where do you get pushrods of various lengths? Or do you make them up ?

[Bloo]

Good question. I don't know. They sell selective lengths of pushrod. I think Fords come from the factory with an assortment but offhand I am not sure. Ford would have you collapse the lifter with a lever and check in the shop manual if I remember correctly. It would behoove you not to soak the lifters in oil before installing them. My 202,000 mile engine wound up with about 3 unbent originals in different spots than they came from, a bunch more bought from the cam grinder, and the last 5(?) from Smith Brothers Pushrods in a custom length that Ford never offered. That was to achieve the .060" the cam grinder recommended plus or minus .020". I don't remember how many different lengths altogether. Several. That much precision is not strictly necessary, although in my case I couldn't get some of them even close to reasonable with off the shelf pushrods.

 

I think most guys don't have a bunch of bent pushrods like I did, and so they just put in whatever they took out and hope for the best, probably not even realizing it is an adjustment. Since the rockers wear out and never get replaced, it probably winds up looser than it was when it left Ford and still runs. Maybe it's noisy. Once in a while one won't start because the valves won't close.

 

I always poke holes in cardboard and keep track of what order the pushrods come out of any engine so they wind up on the same valve going back in. Ford wasn't the only manufacturer who used selective pushrods. I draw a fan at the front of the cardboard so there is no doubt. On an engine overhaul I always check the preload, because the pushrod length might be all wrong.

 

Edited July 16, 2022 by Bloo (see edit history)

[Oldtech]

When I did valves on these - {some time ago}, I would grind any valve stems that stuck up too high and at least get them all even, then check pushrods. always used a set. Usually the originals were ok, and usually someone wanted to spend the least money possible.  Never had a failure. 

[Bob Shafto]

This engine doesn't have a timing chain, so no issue there. The marks on the timing gears are in the correct position and the valves also in the proper position at TDC. I'm learning a lot from this conversation!

[TexRiv_63]

2 hours ago, Bob Shafto said:

This engine doesn't have a timing chain, so no issue there. The marks on the timing gears are in the correct position and the valves also in the proper position at TDC. I'm learning a lot from this conversation!

A stock 390 FE ford definitely has a timing chain, show us what you have in there.

[m-mman]

2 hours ago, Bob Shafto said:

This engine doesn't have a timing chain, so no issue there.

Huh? FEs typically have timing chains. . . So this is a (highly) modified engine? 

For me the 80 pounds of compression is not the biggest concern.

What lights up in my mind is that you are reporting only 5" of vacuum(!) 

Any engine is really just an air pump. It sucks in atmospheric pressure because of the suction of the piston moving down. (actually it doesnt even "suck" in the air the air is PUSHED in by atmospheric pressure) 8 pistons moving down has to be drawing in more than 5" of Hg. Espically when you say the the engine is running in that condition. 

You say that you have no vacuum leaks (OK), to me this screams valve timing. . . . . and you are not running a factory chain set up? 

Edited July 16, 2022 by m-mman (see edit history)

[Bloo]

3 hours ago, m-mman said:

Huh? FEs typically have timing chains. . . So this is a (highly) modified engine? 

For me the 80 pounds of compression is not the biggest concern.

What lights up in my mind is that you are reporting only 5" of vacuum(!) 

Any engine is really just an air pump. It sucks in atmospheric pressure because of the suction of the piston moving down. (actually it doesnt even "suck" in the air the air is PUSHED in by atmospheric pressure) 8 pistons moving down has to be drawing in more than 5" of Hg. Espically when you say the the engine is running in that condition. 

You say that you have no vacuum leaks (OK), to me this screams valve timing. . . . . and you are not running a factory chain set up? 

This exactly.

 

5" of vacuum stands out to me, too. If the rings and valves are sealing, that has to be valve timing, or extremely retarded ignition timing, or both. Well, I guess it could be an enormous vacuum leak. Does the car have power brakes? If so, I would disconnect the hose and plug the port at the engine for a test. The PCV valve should be connected to the plate under the carburetor. Is it?

 

[Bob Shafto]

You're right of course, it does have a timing chain. My faulty memory! It's been 13 months since the engine was installed.

 

 

Edited July 16, 2022 by Bob Shafto (see edit history)

[Bob Shafto]

Here's a summary of what the latest mechanic did with the car (a very experienced guy who knows old motors). To add insult to injury, the new set of points installed with the engine failed while driving the far to the shop, creating a backfire which blew out the muffler!

Edited July 16, 2022 by Bob Shafto (see edit history)

[Bob Shafto]

Yes Bloo the 5" of vacuum is very significant. There are no vacuum leaks; the dry and wet compression tests show the rings are seated properly, and the valves are in the correct position. The mechanic did say he had to advance the timing significantly to get it to run the way it's running now. The camshaft is suspect however.

 

Clearly something was done incorrectly by the rebuilders. I hope they will honor their warranty, but can't say I'm very confident about that.

Edited July 16, 2022 by Bob Shafto (see edit history)

[misterc9]

 This strikes me as a wrong parts combination. Wrong pistons or heads or just an incompatible combination. A wrong timing gear or camshaft.  Maybe one of the offset keyed racing timing gearsets that has been installed wrong . 

[Ben Bruce aka First Born]

Well, methinks time to s++t or get off the pot!!   Open the bugger up and see.  SOMETHING wrong.

 

  Ben

[32plywood]

one thing you may try --- pull the oil fill cap off the valve cover --- plug the PCV hole in other valve cover ---- put the plam of you hand over the oil filler hole -- have someone start the engine and see if you have alot of vacuum on your palm --I now what you are thinking but this will check to see if the intake gaskets have sucked out inside the motor --- the FE motors where terrible about this. --Allan

 

 

 

[32plywood]

when I work at ford we could get push rods -- stock   .030 .060 and .090 shorter but this was not a problem unless you rebuilt the motor or cut valves to deep.  I normaly just cut the valve stem tips a bit.

 

[m-mman]

10 hours ago, Bob Shafto said:

To add insult to injury, the new set of points installed with the engine failed while driving the far to the shop, creating a backfire which blew out the muffler

No, it wasn’t the “points” it was the condenser.  Very common problem today.  Poorly made new parts and deteriorated old parts make this a common occurrence.  
Seen it on several “just repaired” cars and had an identical reaction on my 1966 Mercury with a brand new 410, blown muffler and everything. 
 

10 hours ago, Bob Shafto said:

and the valves are in the correct position

And exactly how is this being determined? If the timing components (gears & chain) are off by one tooth or so, it can be the source of your symptoms and impossible to verify without removing the timing cover and seeing for yourself.  

[Bob Shafto]

The "palm test" was done but did not indicate a problem with the intake gasket. 

 

I believe the dry compression test was done by blowing 150 lbs of pressure into each cylinder with the valves in the closed position. There was no blow by through the rings or valve train. 

 

I'm going to try and get my mechanic to join this thread. He can be much more specific about all the diagnostic tests he did. Meanwhile, keep the ideas coming and thanks for your contributions.

 

[TexRiv_63]

My guess is wrong pistons too far down in the cylinders.

[sowesellit]

leak down test would eliminate ring /vale problum . ford like to use the same piston [like 289 / 302 , 360 / 390 ] and change  rods. but could it be that it was put together with a 360 crank ? guy i worked for years ago told me he got side tracked and  put a 144 crank in a 170 .   

[Bloo]

In addition to the condenser @m-mman suggested, when blowing up mufflers, always check the ground wire inside the distributor from the breaker plate to the housing.

 

[Bloo]

20 hours ago, Ben Bruce aka First Born said:

Well, methinks time to s++t or get off the pot!!   Open the bugger up and see.  SOMETHING wrong.

 

  Ben

I understand the reluctance to take it apart without knowing exactly what is going on. The intake manifold on one of these weighs about like an engine block in a small car. I have done this semi-recently and my back hurts just thinking about it. An engine hoist would have been nice. I guess it wouldn't be too bad to get at the timing chain, but that involves disturbing the pan gasket. I don't think the pan needs to drop like it would on a small block Chevy. I think you can leave the pan in place if you want, but you would still have to splice the gasket.

 

[roysboystoys]

Here is a speculative reason to remove the timing cover. This is supposed to be a 390 timing gear.

It's pin driven. I had an engine at a dealership I worked at , new that had that pin sheared.

Timing would keep changing. Took a while , but I gave in and pulled the cover. Was off a half tooth?

WTH! , pulled the gear and found the pin sheared. New car.

The timing can be off one tooth , and still get the car down the road.

Seems your mechanic did everything else, time to open it up.

[m-mman]

2 hours ago, Bloo said:

I don't think the pan needs to drop like it would on a small block Chevy. I think you can leave the pan in place if you want, but you would still have to splice the gasket.

Correct, the FE oil pan (and mounting surface) is completely flat. Remove, Water pump, fuel pump, crank pulleys and timing cover. The timing gasket set comes with the little bit of pan gasket that is disturbed and would need replacing.  Not difficult. 

Edited July 17, 2022 by m-mman (see edit history)

[Bob Shafto]

Good advice on the timing. I'm thinking that the best way to check for the correct pistons might be to find another 390 motor, measure the distance down the spark plug hole with #1 at TDC, then compare the same measurement on my engine.  Anyone think that will work?

[m-mman]

57 minutes ago, Bob Shafto said:

Anyone think that will work?

Not me.  Too many variables. Heck you might just as well use a bore scope to look in a plug hole, for whatever that will tell you. 

The problems you are trying to solve are going to require a tear down and careful examination. 

Again I vote for removing the timing cover first. 

I dont see any shortcuts here. 

[Bob Shafto]

I assume the timing wouldn't explain the low compression though, so it looks like I either get a new replacement engine or completely tear down the existing one. It is supposedly warranted for a year, but I guess we'll see whether they'll honor that or not. ☹️

[Bloo]

Bad valve timing will make low compression across the board. It is about the only thing that will other than completely wrong pistons or something like that. I also think the wrong piston thing would be hard to do on an FE engine. So many of the FE pistons have the same pin height. I don't think wrong pistons alone will do it. Going purely on memory, which might be all wrong, I think it would take something like a 360 crank with 390 rods and 410 pistons to get the pistons ridiculously low in the bores. I'm not even sure if that will all fit together.

 

Absolute numbers in compression tests don't usually mean much, but when they are all down as much as yours it usually means the timing chain has jumped. Even if they put the wrong timing set in, using one from the smog era, it is going to be only wrong by about 4 or 6 degrees. It will have an effect for sure and lack performance, but I have a hard time believing it could get you down to 70 pounds. That sounds like it might be a whole tooth off. Or maybe it sheared the pin like @roysboystoys suggested.

 

You might be able to tell something by watching the overlap on the opposite cylinder as you crank forward by hand through #1 TDC on the firing stroke, with the spark plugs out and the valve cover(s) off. The intake opening and exhaust closing events (overlap) will be more or less centered around TDC. Any car with a conventional timing chain set will have more slop than it should. Hydraulic lifters muddy the waters a bit as well. Still, the shop manual will give you the design opening and closing points, and that's better than just knowing it should be sort of centered around TDC. If you can figure out from the pictures in the shop manual how many teeth are on the crank gear, divide 360 by the number of teeth, then you know how many crank degrees a tooth is. Slop will muddy the waters a bit, but only crank in the forward direction so the slop is predictable. If the valve timing including the slop is off more than enough degrees to account for a whole tooth, you have found your problem.

 

390 Cylinder numbering, starting on the passenger side, (front to rear), is 1-2-3-4, continuing on the driver's side (front to rear) 5-6-7-8. Firing order is 1-5-4-2-6-3-7-8. so the opposite cylinder is #6. As #1 (passenger front) passes top dead center on the compression stroke, #6 (second back on driver's side) should be going through overlap.

 

 

 

Edited July 18, 2022 by Bloo (see edit history)

[m-mman]

50 minutes ago, Bob Shafto said:

I assume the timing wouldn't explain the low compression though,

Remember an engine is just an air pump/compressor. 

The piston has a stroke, BUT what IF the intake didnt open until the piston was half way down on its stroke? (valve timing incorrect) Then the cylinder is filled, but with only half as much air as it is supposed to be. Intake valve closes and piston moves up and has low compression because There is only a small amount of air in the cylinder to compress. 

If the valve/cam timing is off . . . . then you would get the same conditions for every cylinder. 

 

Low manifold vacuum? Full race engines with radical cams have low manifold vacuum because their valve timing is set to be functioning optimally at wide open throttle. Hence the reason a full race engine wont idle smoothly. Their timing is "way off" from a stock engine. 

[Steven Meixner]

I wonder if the exhaust is plugged somewhere? Unbolt the pipes right at the manifold, let them slide down maybe an inch, and re test vacuum.

[Bob Shafto]

m-mman or Bloo === any idea where I would find the valve specs. They aren't in the shop manual and I haven't seen them on-line. The plan is to do a dial spec test next.

[Bloo]

Bob, I don't know where I put that info, it may be buried pretty deep and might not apply to your car anyway. Is it a 1966 390 then? Two barrel or four? Is your new engine the same year as the original one?

 

My engine is a 1970 390 two barrel, and if I remember correctly the original cam I found in it was marked AU with the A upside down, so it was probably C6AZ-6250-A. Using this confusing chart (use the first line where there are 2 lines for the valve events):

http://www.mercurystuff.com/fe-camshaft-specs.html

We expect the overlap period to be more or less centered around TDC OVERLAP, in other words when #1 is coming up on the compression stroke (only happens every other revolution), then #6 is coming up on overlap.

From the chart, using my cam as an example, the intake valve opens at 13 degrees before top dead center and the exhaust valve closes at 21 degrees after top dead center. It also says this particular cam has 37 degrees of overlap. That adds up. So far so good.

So, as we rotate the crankshaft clockwise through top dead center on the compression stroke on #1 (you'll want to have the plugs out and do this slowly with a wrench), the intake valve on #6 should open at 13 degrees before top dead center, and the #6 exhaust valve should close 21 degrees after.

At least that is what SHOULD happen. You may even have marks on the balancer out to 10 or 15 degrees from the factory on an FE so you can see about where 13 degrees is.

That won't happen though. Every old American V8 has a shot timing chain if anyone has been driving it around. It doesn't really matter if it was new a short time ago. It is shocking how fast they wear out, and if it is a stock timing chain, or a "double roller" chain, one that is not also a "true roller" chain, it will have enough slop in it that the Ford shop manual will say it is worn out. This is normal and does not matter. People have no idea because they never take new rebuilt engines back apart unless there is a big problem. By the time the engine comes back apart for another overhaul it has 100,000 miles on it or more and nobody is surprised the timing chain is shot. They have no idea it has been that way since 10,000 miles. You need to know it because when you test like this you will probably SEE it. It will be significant, but will not be close to a whole tooth.

Lifters that bled down from sitting affect these valve opening and closing events too. Also manufacturing tolerances of the cam and so on. You can still tell if there is a problem though.

I looked up a stock-type timing chain on Summit Racing and it has 18 teeth on the crank sprocket. If you have double roller or true roller or something else you might need to find a picture of it and see how many crank teeth you have.

Anyhow for this stocker we have 18 teeth. 360/18=20 degrees per tooth. So, if the timing was a tooth late and there was no slop, the #6 intake valve would be opening -13+20=7 degrees after(!) top dead center, and the #6 exhaust valve would be closing 21+20=41 degrees after! In the real world it is going to be even worse than that due to timing chain slop, lifters bled down, and so on.

If the timing was a tooth early, the intake would open at 13+20=33 degrees before top dead center, and the exhaust valve would close 21-20=1 degree after top dead center. In reality these would be a bit later due to the chain slop and lifter bleed, but intake opening wont be close to the 13 degrees (minus the chain slop) from the chart.

In either case, the overlap period is no longer even close to centered around TDC. That should stick out like a sore thumb if it is the problem.

 

Edited July 20, 2022 by Bloo (see edit history)

[Bob Shafto]

Thanks so much for your thoughtful and detailed post Bloo. The new engine has a C6ME - A block, the same as the original 390 FE 2 barrel engine that replaced it. 

[EmTee]

10 hours ago, Bloo said:

That won't happen though. Every old American V8 has a shot timing chain if anyone has been driving it around. It doesn't really matter if it was new a short time ago. It is shocking how fast they wear out, and if it is a stock timing chain, or a "double roller" chain, one that is not also a "true roller" chain, it will have enough slop in it that the Ford shop manual will say it is worn out.

Thank-you for that nice summary explanation!  So, given the observation above, is this why some aftermarket timing sets provide optional/offset key slots (e.g., 4*)?  Given the inherent 'slop', does it make sense to install a new timing set 4* advanced in anticipation of chain stretch during service?