Setting your 4.0 to #1 TDC


With #1 spark plug removed, turn the engine over clockwise using the 3/4″ front crankshaft bolt.

You will see the degree marks on your front cover and you will see the timing mark on the balancer. Mark them with chalk or white-out.

While turning the engine over, put your finger/thumb over #1 spark plug hole. As the mark on the balancer approaches the marks on the front cover, if you are coming up on #1 TDC, pressure in the cylinder will push on your finger. If there’s no pressure, you’re at #6 TDC and need to crank the engine over until you see the marks coming together and you get pressure. Set the mark on the balancer to the 0 mark on the front cover.

TDC damper

Revised 1-31-2016

18 thoughts on “Setting your 4.0 to #1 TDC”

  1. /ok
    So, what if your block has a different indicator scale on it?
    Mine is similar, but has a … tube about where your 0 (zero) is.

    Well I hope that tube/ hole is close enough to where the Zero is supposed to be.

  2. Is it really necessary to feel for pressure on cyl #1?

    I mean if you are looking at the rotor and it is pointing to the #1 terminal on the distributor and the timing mark is at 0 deg, isn’t that always TDC for cyl #1?

    Otherwise the rotor would be 180 deg out and pointing to the #6 terminal on the distributor when the timing mark is at 0 deg.

    1. No it is not. You can go by timing mark and rotor position as you described, as long as the dist. was installed correctly. Or you can look at the rocker arms for #1 if the valve cover is removed. Or use a piston stop tool.

  3. I was beginning to set my 89 cherokee 6 cyl. TDC as shown. Short history, I had 4 months prior replaced my rotor and cap. But after running my jeep for another 800 miles one day it would not start. I checked several things fuel pressure, grounds, CPS and spark of which I was showing some small spark, But still wouldn’t start. At the onset of TDC check, I began by pulling the distributor cap. What I found next was the plastic rotor had broke in 3 pieces. Wow, just amazing since I had recently replaced the cap and rotor. If jeep isn’t running, check this first as the rotor part that I had purchased was cheaply made. I went to auto parts and replaced. First turn jeep started. Might be wise to carry and extra rotor.

  4. Hi Cruiser

    I am in the middle of a cam/lifter replacement. I had pulled the head before setting TDC but didnt think much of it as i still had the harmonic balancer and distributor in. So i set it to 0 at the timing marks on the timing cover and the rotor was pointing in the neighborhood of the #1 plug wire and the #1 piston was at the top of the stroke. I thought i was all good until i pulled the timing cover off and the cam and crank gear marks were 180 out in reference to the distributor. Are these supposed to be aligned at TDC? i lined them up to install the new cam but now unsure if i should install the distributor like it was or if i should index it and have it pointing at #1 with the gear marks aligned as well. It didnt run great before but it also had two wiped lobes. I have read these motors will still run with everything 180 out but not sure how accurate that is. Help!! thanks!

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