'46 CJ-2A

Flywheel, Crankshaft, Cam & Oil Pump Timing

There seems to be much confusion & myth concerning parts assembly as regards overall ignition timing.  I hope to clear some of it up.

Ignition timing, and your ability to set it as Willys intended, is dependent on correct assembly of 3 mechanical combinations:

  1. Flywheel to crankshaft: Due to the 2 special tapered bolts, the flywheel can only be mated to the crankshaft in 2 orientations.  Correctly, and 180º off (assuming  they were manufactured correctly, see note below, and the tapered bolts haven't been replaced w/regular bolts).  This seems to be where most assembly errors occur.
  2. Camshaft to crankshaft: the timing marks on crank gear and cam gear have to align.  If they don't, then the next step is irrelevant.
  3. Oil pump to camshaft: the oil pump gear needs to mate with the cam gear in a position such that the distributor shaft will engage it so that the rotor is pointing to the "normal" #1 position on the distributor cap, as Willys intended.

Of the above, only #2 is critical, since it controls valve timing.  #1 & 3 can be compensated for without any disassembly.  See: "Workarounds", below.


Flywheel to crankshaft

See "Myth Busted!"
If you have original parts, there SHOULD be an arrow stamped into both the flywheel and crankshaft. (photos link to larger images)


These arrows point directly up when #1 cylinder is at TDC (top dead center).  Regardless, mount the flywheel to the crankshaft so these 2 arrows coincide, and you've done it correctly.  If done incorrectly, the arrows will be 180º opposite each other.

Replacement flywheels and/or crankshafts may not have the arrow marks.  If not, then simply turn the crank so #1 & #4 cylinders are at TDC, and mount the flywheel so that the timing marks are on the passenger side of the engine (approx. 9 o'clock as viewed from the front of the engine).

*** NOTE:  It has been rumored that some flywheels were incorrectly stamped with the timing marks in the wrong place.  If you have one of these, then the timing marks will NEVER line up with the hole in the backing plate, and you'll need to add timing marks to the front of the engine (pulley & timing cover) to facilitate use of a timing light, or get another (correctly marked) flywheel (but also see "Balanced" below).

See: "Checking The Flywheel & Crank", below.
Camshaft to crankshaft: There are TWO ways to get this right, and dozens of ways to get it wrong.  If you get it even slightly wrong, your engine will most likely not run, much less be time-able.  If you get it 180º wrong (with respect to flywheel timing marks) the engine will run fine, but all your timing will have to be done using either #2 or #3 cylinder.  The pictures should be self-evident.  If you don't already know how to do it right, get a repair manual that explains the procedure (with pictures), or find someone who does know how.
Oil pump to camshaft: The oil pump gear mates with the camshaft driving gear in just the right way, because the oil pump shaft determines the rotational position of the distributor shaft & rotor.  I'm not going to re-explain this. The repair manuals do a good job.  If you don't already have one, get a manual and read how to do it right.

Workarounds for incorrect assembly of parts:

Flywheel to crankshaft This is a simple fix, but potentially not acceptable.  See "Balanced" below.

If you've mounted your flywheel 180º off, use either #2 (or #3) cylinder to set your timing.
Camshaft to crankshaft You're up the creek, as there is no workaround for this.  You'll have to remove the cam gear and/or chain, rotate the cam, and reassemble the gear/chain in the correct alignment to the crank gear.
Oil pump to camshaft Remove the distributor cap, loosen the distributor body, rotate it into the desired position, and note the position of the rotor.

Place the cap back on the distributor, and see which plug wire post most closely corresponds to the rotor position.  Use THAT post for the #1 plug wire, then wire the other posts in the correct sequence.

Retime the ignition.

Checking the flywheel & crank for correct timing marks:

To check if a flywheel mis-marked or not, position the flywheel so that the timing marks are at the 9 o'clock position.  Of the 6 bolt holes in the flywheel flange, 2 are larger than the others.  Note the location of these holes.  They SHOULD be at 9 & 3 o'clock positions.

Now position the crankshaft so that the #1 & #4 rod journals are up (corresponds to them being at TDC).  The larger holes in the crank flange should also be at 9 & 3 o'clock.

It's possible that Willys did not always machine the exact same holes during manufacture, but as long as the relative position of these larger holes is the SAME on both crank & flywheel, then the timing marks are correct.  (Possible large hole locations are: 1 & 7 o'clock, 3 & 9 o'clock, and 5 & 11 o'clock).

Balanced flywheel & crankshaft:

According to the Willys Service Manual, for "Jeep" Universal, publication SM-1002-R5, 1965 (first edition print date unknown), para. D-64, pg. 44:

"The crankshaft, flywheel and clutch assembly are statically and dynamically balanced separately and as a unit; therefore, these components should be assembled in their original relative positions to maintain this balance"

So, depending on how far out of balance the crank & flywheel were with respect to each other to begin with, reassembling them 180º off may result in unacceptable, and possibly detrimental, imbalance and vibration.  OTOH, it may be insignificant, it just depends on your crank/flywheel combo.

It's best to "get it right" the first time.  If you have to replace either the flywheel or crankshaft, consider having them rebalanced together w/the pressure plate..