Engine identification/ trans fitment

[Hiredguns]

Ok, I'm not even sure if this belongs in tech or general discussion but we'll try here.

On the J truck in my signature, I need to know if there is a # stamped in the engine block to identify the production year of the engine and where it would be.
Reason I want to know is that a little voice in my head keeps telling me that the engine/trans/xfer may possibly be out of a later model CJ.
I'm actually hoping that it is, as I read somewhere that from about '72/'73 on up the bellhousing Bolt patterns were the same as later model stuff and I've got a chance to pick up a 5 speed trans that came from a 4.0 TJ. Having a 5 speed would go a long ways towards making my truck a more pocketbook friendly DD. This 8.5-9.5mpg thing is rough when you commute 60 miles a day.

[joe]

Theres a tag on front of the right side valve cover
The first digit is year 4=71, 2nd and 3rd digits is month, 5th and 6th digits is day. Of course that's asuming those are the orig valve covers that came with the motor.
Any year 304 block will have the typical 304/360/401 bolt pattern.

[Hiredguns]

I'm going to go out on a limb here when I bet that the chrome valve covers that were on my truck when I bought it are not stock.

But, are you saying that what I read about the bolt patterns being different in '71 was incorrect?

[joe]

71 304 bolt pattern will be the same as any other 304/360/401.
No chrome valve covers were not stock.

[mdill]

The bolt pattern was the same, but I think the 71 had the old style crank flange (Changed for 72 and up ??)

[Billygoat]

looking at a 3550 tranny?
I put 1 behind a 71 360 - get the 4.0 bell housing and it bolts right up - there is some throwout bearing issues, a couple companies have kits...

hmm, now that I think about it I did a crank swap on my (cheaper than getting mine turned) so that may have negated any crank flange issue....

[Billygoat]

Now I see you said latter CJ - so are you looking at a T5?
I started with them - 3 in fact before I got tired of them dying.
again it was behind a 360, and I towed a lot....

but sitll, direct bolt up.

[tgreese]

I would not hope for too much from the 5-speed.

In my opinion, something is wrong with your truck if you are not getting low teens mileage from a 304-T15 combination. What is your axle ratio? I would expect 4.09s. How tall are your tires?

'71 trucks were available with the 304 and 3-speed T-15 transmission. The T-15 from a CJ will not fit - the shifter stalk will come up under the dash. The factory T-15 in a J-truck with a V8 has a 4-5" long spacer between the bell and the transmission, and a very long input shaft. This moves the shifter back into the passenger cabin, and lets the V8 clear the firewall.

It will also help to keep your top speed down. Regardless of the axle ratio or final drive ratio, the aerodynamics of these Jeeps are terrible by modern standards. This is the wrong vehicle for driving in the high speed lane, if only from an economic POV.

Owners with the 304 trucks were very happy with them. They got better gas mileage than the 360 trucks and moved along just fine. 8 or 9 MPG is not normal.

[Hiredguns]

To clarify, I've been wondering if my current drivetrain wasn't at least partially swapped in from a 304/t15 CJ.

Yes, I have a 304/T15/D20setup with 4.09 gears.

The trans I was looking to install is an AX15 from a '98 TJ. But I think that plan has been nixed do to difficulty of mounting my D20 to it.

If there is something wrong with my truck causing the low fuel mileage I wouldn't have a clue what that could be.
The engine runs beautifully, fires right up, idles smooth. Timing set at 9*.
New points, plugs, wires, cap, & rotor. Rebuilt carb. All new brake pads & hardware. All new ujoints, (all of them, even on front axles) every wheel bearing replaced, new king pin bearings on both sides, seals & wipers on closed knuckles replaced. All fluids in the truck were drained and replaced with Schaeffer synthetics.
All this was done myself through October and November of last year just after I bought the truck and before I ever drove the truck out of the garage.
I am 100% satisfied that everything is as it should be.

I've been attributing my high single digit fuel mileage to tire choice as well as driving conditions. 55 mph nets 2600RPM in 3rd gear. My daily commute is steep twisty hilly 2 lane highways through the Ozarks. Tires are an aggressive 31x10.5x15 M/T tire (new) with 23/32 tread remaining on all 4 tires. Not tires that were designed to optimize mileage but tires that were intended to not allow the possibility of getting stuck in snow and/or mud.

My purpose for buying this truck was never because I was expecting fuel mileage. It was because I needed to replace my MJ/Comanche in the role as my "get me anywhere in any conditions" rig. Well, that and the fact that I love these old trucks. ( I've had a '76 J10, '81 Honcho, and a '79 Chief ). If I was only looking for fuel mileage I would drive my ZJ.

I was looking at the possibility of the AX15 of simply a way to make a good thing better and a little cheaper to drive.

[tgreese]

Not trying to start an argument, just saying that I worked in a Jeep dealer back in the early 70s, and customers with this combo liked it, and it did offer somewhat better MPG than the 360, and was a step up in power from the 258. Jeep would have never sold any 304s if they only got 8-9 MPG. The 304 in 1971 was a fine performer, comparable to engines of near-equal displacement from the big three.

I certainly would not be happy with that mileage. 31s are not outrageously large, and the 304 is quite happy spinning 3K all day. Do you have the factory carburetor? Any hop-up parts? An engine can run great and get lousy mileage ... the two aren't necessarily linked.

JMO - I would be disappointed if I did not get 12-13 MPG from this truck as a daily driver. And I would expect to get a little better on a highway trip, if I could keep the speed down. Your commute may be the issue ... being able to drive it at boulvard speeds would be a plus, but if it's really steep and you're trying to maintian highway speeds, that could explain it. In this case I'm especially convinced that the overdrive transmission will not help you much.

Sounds like a nice truck ... I'm glad you like it - mostly.

[Hiredguns]

Not trying to start an argument, just saying that I worked in a Jeep dealer back in the early 70s, and customers with this combo liked it, and it did offer somewhat better MPG than the 360, and was a step up in power from the 258. Jeep would have never sold any 304s if they only got 8-9 MPG. The 304 in 1971 was a fine performer, comparable to engines of near-equal displacement from the big three.

I certainly would not be happy with that mileage. 31s are not outrageously large, and the 304 is quite happy spinning 3K all day. Do you have the factory carburetor? Any hop-up parts? An engine can run great and get lousy mileage ... the two aren't necessarily linked.

JMO - I would be disappointed if I did not get 12-13 MPG from this truck as a daily driver. And I would expect to get a little better on a highway trip, if I could keep the speed down. Your commute may be the issue ... being able to drive it at boulvard speeds would be a plus, but if it's really steep and you're trying to maintian highway speeds, that could explain it. In this case I'm especially convinced that the overdrive transmission will not help you much.

Sounds like a nice truck ... I'm glad you like it - mostly.

Didn't think for one minute you were trying to start an argument. I never took it that way. Sorry if you thought I was coming across as if I did.

I only mentioned everything that I had done in an effort to convey the fact that I went to great lengths to make sure everything on the truck was up to snuff and that I couldn't see any reason for it to have poor mileage.

Yes, the carb is the original 2bbl carb, rebuilt. I don't know what or if anything has been done internally to the engine. Previous owner didn't know either. Only thing I can tell you is that someone spent money on chrome and 3" collector long tube headers with a nice exhaust. That's part of the reason I did everything I did. No known mechanical history. Easier to just do it all and KNOW that it was done and done right.

12-13mpg would be great, but even at 8-9 I still love my truck and drive it often. I don't have to rely on it as a DD, I just like driving it that much.

[Carnuck]

When my J4000 with 304/TH400/QT with OD/PT kit dropped to 10 mpg, I discovered the choke was coming on as I was driving due to the cold. Quick adjustment looser and that was cured (I drove 2 years with it pretty much off) That was 3.73 gears, 33"-36" tires (depending what I was doing and weather) 14 was generally the worst I got with 17 hwy being average.
It has chrome valvecovers too (originally a '77 AMX motor) Check the crank pulley to see if they are held on with 3 or 4 bolts. 4 bolts is definitely newer crank. 3 bolt could be flat flange.

T5 is weak mustard. Sure it can get the job done but when it's finished, it leaves a bad taste in your mouth. AX-15 or stronger is the way to go.

T15 is longer in V8 FSJs than CJs, so unless they changed the input shaft, it won't work.

Early flywheel is hard to come by. There is a made in China but decent quality aftermarket flywheel for the early cranks. It comes with 401 balance weight so it needs rebalancing for 304.

[Hiredguns]

When my J4000 with 304/TH400/QT with OD/PT kit dropped to 10 mpg, I discovered the choke was coming on as I was driving due to the cold. Quick adjustment looser and that was cured (I drove 2 years with it pretty much off) That was 3.73 gears, 33"-36" tires (depending what I was doing and weather) 14 was generally the worst I got with 17 hwy being average.
It has chrome valvecovers too (originally a '77 AMX motor) Check the crank pulley to see if they are held on with 3 or 4 bolts. 4 bolts is definitely newer crank. 3 bolt could be flat flange.

T5 is weak mustard. Sure it can get the job done but when it's finished, it leaves a bad taste in your mouth. AX-15 or stronger is the way to go.

T15 is longer in V8 FSJs than CJs, so unless they changed the input shaft, it won't work.

Early flywheel is hard to come by. There is a made in China but decent quality aftermarket flywheel for the early cranks. It comes with 401 balance weight so it needs rebalancing for 304.

I've actually wondered about the choke either closing, or partially closing while driving. It's been cold for sure.

I've also decided against the AX15 for the time being. I'm just going to stick with the 3 speed for the time being.
Just went out and looked, there are 3 bolts on the front crank pulley.

[Carnuck]

Did you ever get your icon pic?

Don't forget that if it is flat flange and you use the later flywheel, it will bolt on, BUT it will come loose and turn into a flying buzzsaw because there is no way to keep it centered..

[Hiredguns]

Did you ever get your icon pic?

Don't forget that if it is flat flange and you use the later flywheel, it will bolt on, BUT it will come loose and turn into a flying buzzsaw because there is no way to keep it centered..

As a matter of fact, I did get it! Thank you very much for resizing that for me.

After having to tow a disabled bowtie up a snow covered "mountain" today - hey, its the Ozarks. Lol - I think I've come to the conclusion that perhaps a 4 speed with a lower first gear would be of more use to me than a higher top gear.