Specifications for F4-134 Engine

glfarnes

Bigger Hammer
Oct 7, 2015
80
Warm Beach, WA
First Name
Gerald
Willys Model
  1. Pickup
Willys Year:
  1. 1951
Does anyone know where I can find all of the rebuilding specs for a 1951 F4-134 engine? I've come across later specs from the sixties but nothing for the old fifty one.

My engine is off to Tatom Custom Engines but he can't start until he gets the proper info.
 

diggerG

Well Oiled
Oct 2, 2011
5,313
Wrentham Ma.
First Name
Greg
Willys Model
  1. Wagon
Willys Year:
  1. 1963
I have no clue why the specs would be different. Same rods, pistons, etc.
diggerG
 

glfarnes

Bigger Hammer
Oct 7, 2015
80
Warm Beach, WA
First Name
Gerald
Willys Model
  1. Pickup
Willys Year:
  1. 1951
I have no clue why the specs would be different. Same rods, pistons, etc.
diggerG

There was at least one change that I know of and that was a compression change from 6.9/1 to 7.5/1. I don't know when that change took place but the specs would have had to change somehow.
 

diggerG

Well Oiled
Oct 2, 2011
5,313
Wrentham Ma.
First Name
Greg
Willys Model
  1. Wagon
Willys Year:
  1. 1963
Gerald
The pistons are all flat, the difference (if any) would have been the cyl. head. You might be reading the compression for the 4L as 6.9, not the 4F. Jeep used the 4L and 4F engines during the same early 50's time period. DJ3A's went into the 60's still using the 4L.
diggerG
 

dlj

Sharpest Tool
Nov 16, 2009
309
Wis
Willys Model
Willys Year:
Google cj2a torque specs. Do you have a manual for your jeep,that is almost a must have.
 

mathman

Well Oiled
Mar 14, 2012
2,960
AR
First Name
David
Willys Model
  1. Pickup
  2. Forward Control
Willys Year:
  1. 1950
  2. 1964
There was at least one change that I know of and that was a compression change from 6.9/1 to 7.5/1. I don't know when that change took place but the specs would have had to change somehow.

That's not a change, there were three different compression ratios used. From the 1946-1953 Mechanics Manual:

F-Head
4-Cylinder
3-1/8" bore
4-3/8" stroke
134.2ci Piston Displacement
Standard Compression ratio: 7.4
Optional Compression Ratio: 6.9 and 7.8
Horsepower- Max. Brake: 72 @ 4000rpm
Compression: 135 lbs.
Horsepower: 15.63
Maximum Torque: 114 ft. lbs. @ 2000rpm
Firing Order: 1-3-4-2

There are still 2 more pages of specifications...
 

diggerG

Well Oiled
Oct 2, 2011
5,313
Wrentham Ma.
First Name
Greg
Willys Model
  1. Wagon
Willys Year:
  1. 1963
Google cj2a torque specs. Do you have a manual for your jeep,that is almost a must have.

I have a stack of Jeep manuals higher than your Jeep. been working with Jeeps since 1971. Parted out over 1000. Built a dozen or more 4F's in that time. Always used the same torque specs. Machine shops in New England called me for Jeep blocks, cranks, etc. for rebuilding. Nobody ever asked me about compression ratios for 4F's. 4L's they have.
I certainly believe Mathman though. He's very thorough. I bet nobody ever ordered a 6.9 comp.head. Why would they? Kerosene? And a 7.8 would certainly be high altitude. Not around me. ((New England)
I have about a dozen 4F heads off, I will look them over for differences though.
Let's have some fun! Anybody out there who KNOWS they have a 6.9 or 7.8 4F head chime in with your casting numbers so we can learn something. And same for those California pollution pump heads from 1970.
diggerG
 

gasoil

Precision Fit
Aug 9, 2013
840
Vermont
First Name
Phil
Willys Model
  1. Wagon
Willys Year:
  1. 1963
How would you tell if it is high compression or not.? I do not recall my manuals saying anything about it.
 

diggerG

Well Oiled
Oct 2, 2011
5,313
Wrentham Ma.
First Name
Greg
Willys Model
  1. Wagon
Willys Year:
  1. 1963
How would you tell if it is high compression or not.? I do not recall my manuals saying anything about it.

Phil
So I actually did look in a Jeep manual. It states 6.9 was optional for 4wd, and 7.8 was optional for 2wd. That tells me right off that both will be very rare. There must be a different casting number or stamped code. Can't do it any other way. You COULD measure the capacity of the combustion chamber. Or someone COULD shave off the cyl. head for more compression. Lets see what this posting scares out of the woodwork. I'm guessing not much. I've got 1 2wd 4F Jeep (panel) left with the motor, but I'm sure not going to tear it apart just to look at the head. And WHY offer the 7.8 in 2wd only? All that extra power for vacation travel?
diggerG
diggerG
 

mathman

Well Oiled
Mar 14, 2012
2,960
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First Name
David
Willys Model
  1. Pickup
  2. Forward Control
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  2. 1964
How would you tell if it is high compression or not.? I do not recall my manuals saying anything about it.

It's supposed to be stamped on the top back of the head, around where the heater valve connection. In this picture, looking down at the top of the head, it should be between the red circle at the top right and the heater valve just to it's left.



I have an NOS head in the shop - I'll try to get a better picture of it later this afternoon.
 

glfarnes

Bigger Hammer
Oct 7, 2015
80
Warm Beach, WA
First Name
Gerald
Willys Model
  1. Pickup
Willys Year:
  1. 1951
It's supposed to be stamped on the top back of the head, around where the heater valve connection. In this picture, looking down at the top of the head, it should be between the red circle at the top right and the heater valve just to it's left.
I now have all the specs, so this just becomes a question of why? My engine guy says he really doesn't care and it wouldn't according to him make a lot of difference. I guess my question back to you David is what is the stamp and what does it mean?
 

mathman

Well Oiled
Mar 14, 2012
2,960
AR
First Name
David
Willys Model
  1. Pickup
  2. Forward Control
Willys Year:
  1. 1950
  2. 1964
I now have all the specs, so this just becomes a question of why? My engine guy says he really doesn't care and it wouldn't according to him make a lot of difference. I guess my question back to you David is what is the stamp and what does it mean?

The stamp is the compression ratio. Here's a shot of the head I have in a box:



Note the 7.4 - that head has a 7.4 compression ratio.

Here's a shot of the head in the box:

 

Auggie

Well Oiled
All-Star
Jul 3, 2012
2,363
Gardner Kansas
First Name
Bryce
Willys Model
  1. Pickup
Willys Year:
  1. 1958
in the barn back home i have a f134 out of a 56 cj5 that came from colorado. i believe is it to be there originally. if i can get to the engine when i get back there next week i will take a look to see what compression ratio we have.
 

Ken_Parkman

Sharpest Tool
Oct 28, 2013
431
Ontario
First Name
Ken
Willys Model
  1. Pickup
Willys Year:
  1. 1962
A couple of general statements to add is back then the fuel was terrible for octane, they had not hit the HP race and there was not much need for high octane. Most stuff back then was very low compression. Another observation is HD stuff (gasoline trucks) often had very low compression because of the probability of sustained high engine load causing detonation and melting the pistons. Maybe that's why lower compression on the 4wd - they were worried about a big load and it being to the pin for an extended time on a hill.

For today around here (Canada) the guaranteed no ethanol fuel is Shell high test, 91 octane. That's what I run in old weird low use applications to stay away from the ethanol. Absolutely no worries about detonation, whack all the compression to it you can if your use is like mine.
 
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