View Full Version : L-head and F-head Tid-bits

09-05-2015, 04:39 PM
Remember the Sesame Street jingle that says " ... one of these things is not like the other..."? That often applies to L-head and F-head engine swaps. Willys, Kaiser, American Motors – all makers of Jeep vehicles, used a lot of bits and pieces for a long time and, as a result, many things look a lot alike and – are largely interchangeable. But, when you start rebuild projects you find out that there are some differences that can, at the least, make you scratch your head and go Hmmmm. Others end up being an Aw-pooh! Some other differences make you go – well – I won’t say on a family page.


Carburetors: The Carter YF is a common carburetor for a lot of years on the L-134 and F-134 engines. But, depending on application (truck, station wagon, CJ-series), different throttle linkages were used to match how the engine and chassis fit together. When you get a YF with a bottom throttle linkage and try to install it in a top-linkage application – that’s a bit more than a Hmmm …. Or Aw-pooh.

Rear Engine Mounting Plate: F-head and L-head engines pretty well drop into the same places. Important dimensions match up (early F-head engine block castings are obviously L-head castings with just minor changes), but as the F-head engine evolved, product changes made a few things not match up. Here is an example; the rear engine mounting plate was the original L-head plate that came with the truck. The engine is an F-head, probably an earlier version than a later one. Notice in the pictures that the casting covers the hole to check timing marks. If I remember correctly, the “new” engine didn’t come with a flywheel, so I used the old one (L-head version) after some minor drilling and machining – exactly what I don’t recall. It took some looking to find timing marks as we put this back together. (The plate that covers the hole doesn’t fit either; it will take some work with a Dremel tool to fit it.) This one qualifies as Hmmm… finding

Oil filler/dipstick: The early F-head engines kept the oil filler tube/dipstick arrangement of the L-head engine. The oil fill tube cap is at the top of the engine about at the head/block split line. It also retained the vent tube to connect to the hose between the air filter and the carburetor air horn. (See attached photo). This configuration needs an air cleaner to carburetor crossover tube. Later version engines (see the attached picture from a recent posting) had a change to the block casting and used a conventional dipstick, with oil fill through the crankcase breather on top of the valve cover. Since the truck version of a crossover tube is rare, this qualifies as an “Aw-pooh” sort of task.

28 September 2015 - Update

I was looking through the Willys Mechanics Manual - an absolute must item if you have an early Willys Vehicle (pre-'53). There , on page 30, the issue with the covered up timing hole is discussed. Willys tells us:

"A 4 1/2" inch starting motor was placed in production of Model CJ-2A effective with engine No. 130859. To use the larger starting motor it was necessary to increase the width of the cylinder block flange.. . This increased flange width partially covers the location of the flywheel timing mark inspection hole making it impossible to provide an opening for timing purposes. This is not important however as timing marks are provided on the timing gear cover and crankshaft pulley." Evidently this change worked its way into other models at some time.

If you needed to use the flywheel marks, Willys had a solution.

"Cut away the mounting flange to uncover the inspection hole in the engine plate". No problem, just grind away the 1" thick cast iron engine block to open up access to the hole.