4.0 Renix - Timing is off 180° but runs

[Big_Mark]

My timing gearset needs changing so I started working on it and discovered some weirdness, want to fix it but need to make sure I understand what is wrong and how to fix it. I would appreciate the input of the forum to back check me before I try to "fix" anything.

 

Before starting this project, aside from the clacking from the stretched timing chain, my engine has been running great. Mileage is normal and power is great.

 

I have replaced a few timing chains in my day, and my procedure has always been to “pop” off the timing cover (because it just pops right off easy, right?), turn the crankshaft until the timing gear dots align next to each other, pull gear and chain, replace them making sure the dots align.

 

 

The weird thing is, on my Jeep when I align the timing gear dots, my dizzy is off 180° (rotor sits at #6 position)

 

 

In this alignment, looking at the position of the Crankshaft from below, the #1 cylinder (front of Jeep) it appears to be Top Dead Center (TDC).

 

 

 

Since it runs fine in this condition, I am trying to decide if I want to fix, or just run it. I am leaning toward "fixing" as this has caused confusion in the past. When I swapped out my distributor and started indexing it last year, I discovered I had to rotate the distributor 180° to get the engine running but didn’t exactly know why and since it ran fine, I just shrugged my shoulders and ran with it.

 

Here is how it is currently timed

 

Turning the crank so the distributor is in the #1 position, the #1 cylinder is at Bottom Dead Center (BDC) and the crank timing gear dot is on the opposite side of the gear, but in alignment (180° off)

 

 

Dizzy Position

 

 

Crank Position

 

 

From what I can surmise, I think I have two things 180° out of rotation.

1.       Crank Shaft

2.       Distributor (to compensate for the Crank being out of timing)

 

Mystery questions:

How did/does my engine even run with the existing timing condition?

Is it firing in reverse order?

Does it matter?

I think the double 180° reversals are like a double negative, they cancel each other out and get it into correct timing. But it makes my head spin trying to figure it out.

 

DISCLAIMER: This is how I got the Jeep.  There was one bolt missing from the timing cover, so I suspect somebody in the past screwed this thing up when they replaced the timing ger set (?).

 

Since this is still all pulled apart, I’d like to fix it, BUT it is working, so I am trying to decide if I want to risk making matter worse or get it straightened out while its accessible, so here is where I need your help.

 

I am pretty sure I can fix this by:

From it's current condition, rotate the crank, so the dots align (to get the cam gear in correct position) this will put the crankshaft into BDC. Next step would be removing the timing gearset, rotate the crank so it sits at TDC, replace the timing gearset, ensuring the dots align next to each other. At this point the distributor should still be at #6 position so I will need to pull it out, rotate it 180° then make sure it is indexed properly. (I still have my cut cap from when I did this before).  Does this seem like the correct sequence to y’all?

 

Before I try to “fix” anything I ask the forum to back check my understanding of timing.

Please confirm that if these conditions are met that my timing should be sound (or at least set to zero)

 

1.       Both timing gear dots are next to each other

 

 

2.       Distributor is in #1 rotation/position

 

 

3.       #1 (front) cylinder is set at TDC

 

 

Final question: Does it matter if TDC is in the compression stroke, or exhaust stroke when I set the timing? I think it doesn't matter since anytime the dots align, the distributor will be at #1 index. Since one stroke of each cylinder is firing (compression) and the other is exhaust (non compressing) the ignition should sort this out on it’s own but I want to be sure before proceeding.

 

I know it’s early in the day and there are lots of 180°s here, so I appreciate your help. I do want to make this right before I button it up because hate leaving issues unresolved, especially since I can easily fix this now while I have it all apart!

 

Thanks in advance I look forward to your answers!

[Ωhm]

Yes, you can have the valvetrain off 180°, making the Distributor off 180° and the engine will run just fine, but now your SYNC signal is off 180°. Some will say the SYNC signal will correct itself every time you START and RUN your engine if that what you want.

 

2 hours ago, Big_Mark said:

Does it matter if TDC is in the compression stroke, or exhaust stroke when I set the timing?

 

Yes. TDC has two meanings. With timing you're looking for TDC during the Compression↑TDC↓Power stroke.

[Big_Mark]

Thanks @Ωhm 

Since I know there is a deficiency I am going to correct it otherwise it will eat at me.

To make sure I'm on the correct stroke at TDC I am going to pull of the valve cover so I can make sure #1 is compressing by visually inspecting the valve/rocker positions.

Oh the joys of being a Shadetree mechanic!. 

 

 

[Ωhm]

3 minutes ago, Big_Mark said:

Oh the joys of being a Shadetree mechanic!. 

 

[Big_Mark]

After pulling the valve cover, I’ve determined by observing the valve position and stroke based on the position of the distributor all is correct. if anything is 180 off, its the cam pin/sprocket . To rotate that would require switching the set pin to the other hole. That sounds like a recipe for disaster so I’m just going to run it as is. Afterall it works fine.

Maybe it was margarita Monday when my engine was assembled?

 I definitely overthought this whole process 

 

 

[BlueDove91]

Big_Mark 

I just finished changing the timing chainset on my '91 4.0, and I encountered the same situation that you have laid out here. I had TDC at #1 plug with pressure test, timing cover/balancer lined up at zero mark, and rotor at the #1 position. When I pulled the cover and matched my new gears to the ones I had just pulled off...the cam gear timing mark was at 10o'clock -- 180 AWAY from where it should be.  Turning the cam gear only (chain off) to align with the crank gear's mark put my rotor at #6 position. 

 

It was my first time trying this repair...and as you can imagine, all of the available information online is telling me one thing, and yet I'm looking at a completely different situation -- it was pretty confusing, and nerve-wracking. Not to mention the thought of putting it all back together, only to have to do it over again. 

I just finished the project a few hours ago, and have been feeling nervous that I'm going to go driving tomorrow and discover I messed something up. I did take a quick test drive up the block. Seemed pretty normal. Although I'm noticing new little noises that I'm not sure are actually new or are just my paranoia...lol. 

 

Anyway -- it is reassuring to find your post. 

Thank you for the detailed explanation and walk-through with pics. 

Funny enough, I ended up coming to the same conclusion -- it was running fine before, best to leave it how it was. And I also noticed the alternate hole for the cam pin, and questioned whether it was just a matter of maybe a mechanic (or the factory?) having used the opposite pin hole, and so my cam gear seats in with the mark OPPOSITE to what everyone else's does. 

 

I'm curious -- have you had good results since this post? Ever have to circle back and redo the timing again?

[Gojira94]

I've seen this question come up time after time after time in the SBC world. The dots are for ease of lining things up when clocking cam and crank together. 6 and 12 is easier to see if you're off a tooth than at 12 and 12. Dots at 6 and 12 is the companion cylinder of #1 firing, not #1. In the SBC world, once the timing is set and the engine spun to #1 firing/ TDC, the dots are at 12 and 12. Dots together in a SBC are #6 firing, as 1 and 6 are both at TDC at the same time. Just so happens 1 and 6 have the same relationship in the AMC/Jeep/Chrysler I-6 engines. Crank rotates 2x for every 1 revolution of the camshaft...

[BlueDove91]

Sorry Gojira...

You lost me there 😅

I need it dumbed down...basically novice level here, as I know only as much about this stuff as I've had to do on my own MJ. And I keep it pretty simple...mostly stock, daily driver, maintain as needed. 

 

Good news is -- I drove around town today and all seems great. She seems to run a little tighter, smoother, and quieter than before. No weird noises or issues. 

[Gojira94]

If the crank and cam gear weren't (visually) tilted at an angle to each other, but directly above and below one another...

 

With the crank gear dot at 12:00 + cam gear at 6:00, both #1 and #6 piston are at top dead center, with #6 firing, #1 on exhaust stroke.

With the crank gear dot at 12:00 + cam gear at 12:00, both #1 and #6 piston are at top dead center, with #1 firing, #6 on exhaust stroke.

 

While one cylinder is firing, its companion is on the exhaust stroke. This is true for cylinder pairs 2&5 as well as 3&4, but only 1&6 have the 12:00 & 6:00 relative positions we use to "time" the engine.

 

So... when we pop in the distributor, with #1 at TDC, firing, the dots are 12:00 cam gear and 12:00 crank gear, but hidden behind the timing cover. If you install the distributor with the timing cover off, and dots at 6:00 and 12:00, you're installing it 180* out.

[BlueDove91]

On 5/1/2025 at 9:37 AM, Gojira94 said:

If the crank and cam gear weren't (visually) tilted at an angle to each other, but directly above and below one another...

 

With the crank gear dot at 12:00 + cam gear at 6:00, both #1 and #6 piston are at top dead center, with #6 firing, #1 on exhaust stroke.

With the crank gear dot at 12:00 + cam gear at 12:00, both #1 and #6 piston are at top dead center, with #1 firing, #6 on exhaust stroke.

 

While one cylinder is firing, its companion is on the exhaust stroke. This is true for cylinder pairs 2&5 as well as 3&4, but only 1&6 have the 12:00 & 6:00 relative positions we use to "time" the engine.

 

So... when we pop in the distributor, with #1 at TDC, firing, the dots are 12:00 cam gear and 12:00 crank gear, but hidden behind the timing cover. If you install the distributor with the timing cover off, and dots at 6:00 and 12:00, you're installing it 180* out.

 

Interesting. Thanks for re-explaining that. I didn't deal with installing the distributor...it was in its current position since before I owned the truck. 

So-- 

#1 TDC compression + #6 exhaust is what I had mine on, then. Which is the correct combination. 

And according to your explanation, the way my timing marks were when I found them (10 oclock and 10 oclock, or in your terms 12 oclock and 12 oclock) is normal for that firing position, while also having the rotor at position 1. 

 

What confused me was: all of the info I found instructed me to align the cam mark (while the TC is off) facing the crank mark. AND that the rotor should be at position 1 with the marks facing each other. Then to reassemble sprockets together with chain.  Which, according to your explanation, would have resulted in #1 compression + #6 compression. 

Not good. 

 

I'm still confused as to why all the generally available info didnt align with my experience. 

But just glad that what I did worked.   

 

 

[Gojira94]

17 hours ago, BlueDove91 said:

What confused me was: all of the info I found instructed me to align the cam mark (while the TC is off) facing the crank mark. AND that the rotor should be at position 1 with the marks facing each other. Then to reassemble sprockets together with chain.  Which, according to your explanation, would have resulted in #1 compression + #6 compression. 

 

I'll just say this last piece on it-

 

Getting the timing gears set up has absolutely zero to do with installing the distributor, which is typically a much later step in engine assembly. The dots are to help line up the cam/ crank relationship when assembling the shortblock. If, due to age/ wear/ fatigue, the timing chain skips a tooth, that certainly will affect (severely retard) distributor timing, as it's driven by the cam.

 

By the time we're installing the distributor, the timing cover is on and the dots are out of sight. So we use the timing tab marks, plus other supplementary methods to determine if we're on #6 or #1. Suck, squeeze, bang, blow. Putting your thumb on the spark plug hole of #1 and turning the crank tells you whether it's sucking or squeezing as it approaches TDC/ timing tab at 0*. We need #1 squeezing air/fuel, preparing to fire as it nears TDC to install the distributor. While #1 is squeezing (air/fuel), #6 is blowing (exhaust out). That's why they're both at TDC at the same time. The difference is what the valves are doing.

 

A word on spark advance-

 

We need to light the fuel/ air mixture some number of degrees of rotation before TDC because it takes a measurable amount of time for the mixture to burn. We want the peak of the energy from that burn to occur just after TDC, so the maximum possible amount of energy from it pushes the piston downward. That ideal point of finishing the burn completely varies by engine combination, but average naturally aspirated is about 12-14* after TDC. This ideal point after TDC is referred to as MBT (Maximum Brake Torque). Less efficient head combustion chambers need more time to complete the burn, so we light them earlier with more spark timing advance. More efficiently designed chambers burn more quickly and need less lead time to finish the burn by the MBT point. Our heads (every AMC/Chrysler inline 6 factory head) are not very efficient, and require a fair amount of timing advance to hit that 'finish at MBT' goal. Which really underscores the importance of Cruiser54's distributor indexing lessons.