Hi guys,

Just chiming in to state that the two blocks are rather different in some critical areas. I tried to confirm that they are identical through Ford, machinists, parts cross references, etc., but could not find a solid confirmation.

The back story:
Truck has been knocking for a year. It's slowly getting louder, and if I pull a trailer sometimes the oil pressure dips at idle in cycle with the knock (hotter oil, thinner oil, I suppose). I pulled a 4.2 from the salvage yard, and dropped everything off at the machine shop one Monday. Friday I received a call that the block is cracked. The yard had no other 4.2 engines, so I recalled that 3.8 and 4.2 blocks are the same.

I pulled a 1995 3.8 rwd from a mustang to rebuild instead, because I read somewhere that the 1995 - 1998 blocks should closely resemble the 4.2. First thing I noticed is, it doesn't have a balance shaft. The bore is there but there is no provision for oil. Next, the main caps are wimpier looking, and there is no cradle for the main caps. Oil pan is extremely similar, but has less capacity. Oil pickup is shaped differently to accommodate for shorter pan and lack of cradle over the main caps.

No big deal, I'll do it anyway, it'll just be a suped up 3.8. All of the critical parts fit well. I went to put the heads on earlier, and the head bolts are different too. I assumed that the heads were shorter and that's why my cross referencing showed different head bolts for the two. The heads are pretty close to identical in dimensions as far as I remember, but the 3.8 used shorter long head bolts.




If you've been in one before you might notice the lifter holders are different. The lifters themselves were also slightly different, but they interchange - the older 3.8s (and maybe newer ones) had less surface area for the lifters to slide on.

Anyway, I'm stuck here until I get new head bolts and time to put the heads on. Just wanted to chime in that despite their many similarities, the blocks are actually quite different. Please don't repeat that the 3.8 and 4.2 are the same - they're not. I have my fingers crossed that once I get it together the accessory brackets will hang off of this one like they do the 4.2!

 

Thanks for the info tweak1029
I had a taurus with a 3.8 ,not sure if the fwd and rwd are similar,and other than the bottom
end knocking(antifreeze and bearings don't mix well)I really liked it.
Lots of power and great on fuel

Please keep us posted on your project.

 

How 'bout that! I never had a Ford V6 of any type. I didn't realize that the 4.2L truck V6 was a 90 degree engine!

We had a 3800 Buick which like the original Buick 231 cu.in was 90 degree therefore basically an uneven firing engine. Our Series II 3800 had balance shafts.

Had a Chrysler 3.3L V6, but that was 60 degree, no balance shafts needed!

So on the Ford 3800, they didn't use balance shafts, maybe because of the power loss and fuel economy hit in car application. But the bigger the displacement, the worse the vibration gets, maybe they thought 4.2L was big enough, and wanted better overall balance for truck-use durability.

 

Rebuilding The Ford 3.8L Engine - Engine Builder Magazine

This is an excellent resource on the 3.8s and, to some extent, the 4.2.

For interchangeability and compatibility I apparently should have pulled a 1999 vs the 1995 I used, but it's still pretty similar. I noticed that from around 98 up the head bolts changed length, so my 95 block uses short head bolts. I bolted the truck heads up according to 95 torque specs, and I'll cross my fingers the heads hold tight and don't leak.

I ran into another issue on the timing cover - I threw all the bolts in a box and the way Ford uses so many different bolts, it's hard to say which timing cover bolt goes where. What I'll do is I'll put the oil pan on and when I pull the other engine I'll just yank the timing cover off the one out of the truck, using a cardboard box with an outline to keep track of them and identify which of the old ones go where. I'm planning to either rebuild the 4.2 out of the truck and sell it or, if I don't like the way it runs without the balance shaft, put the newly rebuilt 4.2 back in and sell the one I'm working on now.

I've hit a road block trying to clean up the timing cover and lower intake manifold. I have them soaking in a tub full of comet and water now to loosen the grease, and a couple scrub pads and brass and nylon bristle brushes I'll scrub at. Those parts get filthy! I wish I had a huge ultrasonic cleaner to throw them in.

 

It is complete! It still needs the upper intake manifold and the timing cover (pending bolt location, I'll probably take a pic and some measurements for future reference), but those will go on once the old is removed.

 

Got the rebuilt engine installed over spring break. During the course of the replacement, two sensor plugs were sheared, the knock sensor (which was replaced with one from the first pulled motor), and the ECT sensor, which was replaced with a new BWD unit because I misplaced the used spare.

The truck is now throwing a P0117 code, or ECT Sensor Circuit Low Voltage. Has anybody had issues using BWD sensors before? It bogs down when cold and given throttle. I plan to pull the sensor one of these days when I have some precious time to spare and test it in a pot of water... I expect that because that's the only non ford part used, it's the culprit for my poor running. The plug fit poorly, I wound up using a hammer and punch to drive it until it was fully seated because it wouldn't clip by hand.

For future reference, if anybody purchases the Richporter Technology TK-01 timing kit, the alignment tool for the 97 F150 4.2 is the grey one shaped different than the rest. The other grey fits a jeep (where a toothpick is specified by their manual), and you can pull up an image of the factory tool to compare. I timed it by marking the first time, timed it using the jeep tool the second time, and finally thought to compare pictures the third time, and it's no longer stalling now. The fun thing is it actually starts and runs, albeit horribly, when timed with the jeep tool (~180 degrees off) and what I expect was one tooth off.

The lack of a balance shaft is hardly noticeable. It appears that the flex plate is balanced anyway. Runs as smooth as ever when it's not bogged down by whatever issue it's having. If anybody is worried about that, you don't need to be. It has around 150 - 200 miles on it now and I'm tickled that it doesn't knock anymore. And that it doesn't need 20w-50 oil to maintain pressure lol. I'm still concerned the shorter head bolts won't be up to the task of sealing the engine reliably in the future, but for now they work perfectly. I did use copper coat on the head gaskets.

Update:

Resistance for the ECT sensor came out at 1600 ohms at room temp. Shame on BWD, and also oreillys for refusing to warrant without a receipt. Gonna give BWD a call tomorrow. The new one had 30k ohms at room temp and she runs excellent now. The vibrations are a little bad after all. I assumed the vibrations below idle (idling in gear) were due to it running poorly from the sensor, but they are actually from the balance shaft. Again, not noticeable at or above idle, but when you stop in gear you notice it's missing.

Now I just need to get around to changing the P/S pump and updating a few front end components to eliminate a slight shimmy at 70+, and it'll be a pretty sweet truck.

 

I hate to say it but BWD has a poor record for replacement parts on Ford vehicles.
Good luck.