This doesn’t prove that the block has an HO cam. Some trucks evidently use a HO firing order
with a low lift cam. However, it will definitely prove that a cam can’t be HO because the firing order is wrong.
Remove the #1 & #3 spark plugs. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Slowly turn the engine until the TDC mark and the timing pointer line up. Mark TDC on the balancer with chalk or paint. Put your finger in #3 spark plug hole and crank the engine 90 degrees. You should feel pressure trying to blow past your finger. If you do not feel pressure, repeat the process again. If you feel pressure, it is has a HO firing order.
No pressure the second time, remove spark plug #5. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Put your finger in #5 spark plug hole and crank the engine 90 degrees. If you feel pressure now, the engine is not a HO model, no matter what it says on the engine.
Using a small carpenter or machinist square to mark the harmonic balancer off into 90 degree sections may be helpful here.
A 15/16 deep socket & breaker bar or ratchet may be used to turn the engine.
The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8
Putting the distributor back in is fairly simple. Pull #1 sparkplug, put your finger in the sparkplug hole,
crank the engine until you feel compression. Then line up the TDC mark on the balancer with the pointer
on the engine block.
The distributor starts out with the #1 plug wire lined up at about 12:00 with you facing it. Align the rotor
to about 11:00, since it will turn clockwise as it slides into place.
Align the distributor rotor up with the #1 position marked on the cap, slide the distributor down into the block,
(you may have to wiggle the rotor slightly to get the gear to engage) and then note where the rotor is pointing.
If it still lines up with #1 position on the cap, install the clamp and bolt. If not, pull it out and turn 1 tooth forwards
or backwards and try again. Put the #1 spark plug back in and tighten it down, put the clamp on the distributor,
but don't tighten it too much, as you will have to move the distributor to set the timing. Note that if it doesn't
align perfectly with #1 position, you can turn the distributor until it does. The only problem is that if you are too
far one way or the other, you can't turn the distributor enough to get the 10-14 degree optimum timing range.
10 degrees BTC is towards the drivers side marks.
Simplified diagram of what it looks like. Not all the marks are shown for ease of viewing.
ATC ' ' ' ' ' ' ' ' ' '!' ' ' ' ' ' ' ' ' ' BTC
---------------- > Direction of Rotation as viewed standing in front of the engine.
The ' is 2 degrees.
The ! is TDC
The
' is 10 degrees BTC
Set the timing 5 marks BTC. Or if you prefer, 5 marks towards the driver's side.
At this point hook up all the wires, get out the timing light and start the engine. Set the timing where your car
runs best. Don't forget to disconnect the SPOUT jumper connector when you set the timing, and plug it back
in when you finish.
The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8
