42 DeSoto runs VERY rough, help needed

Ok, I confirmed a few things tonight.

1. I was definitely NOT seeing TDC when I thought I was. By removing the plug over cyl #6, I saw plainly when it came to TDC by putting a cut wire hanger in the hole and watching its position. In the spark plug hole I was monitoring the valve position.

2. Cylinder #6 comes up ON COMPRESSION stroke and gets to TDC when the timing marks line up on the sprockets. My dist rotor is pointing at 2 o'clock in this position.

3. Cylinder #1 comes up ON COMPRESSION stroke and gets to TDC when the CAM timing mark is 180° opposite the mark on the CRANK sprocket.

Is this "180° out" as you mentioned? If so, how is this fixed? Should I confirm that when the marks are opposite and #6 is on compression stroke the timing mark lines up at 0? How can this happen to an engine?

yikes my brain just went "tilt"...

How have you come to determine that #6 is on compression at the point that the marks are across from each other? Are you spinning the engine with the starter and feeling compression past your finger through the plug hole?

Sorry... No, I use the balloon on the compression tester tube trick. When the balloon begins to inflate I know that the piston is coming up on the compression stroke. When #6 gets to TDC, the timing marks on the sprockets are perfectly aligned like I pictured. I can't use the starter since the front of the engine is not bolted down. I have a 1-3/4" socket on the nut connected to the crank and spin it that way.

I'll have to try that someday. I've run a plastic tube off of a modified sparkplug into a bucket of liquid and watched air bubbles but never your method.

So are you getting a literal filling of a balloon, or just an indication that some air is entering? Can you put a balloon on 1 and 6 at the same time?

I'm getting a substantial filling of the balloon so it's gotta be the compression stroke. I don't have the ability to put a balloon on both #1 and #6 at the same time but I did put it on each separately. I found that #6 on compression fills the balloon with the marks aligned and #1 on compression fills the balloon with the CAM mark opposite.

Going to have to ponder a bit.....

Somebody flipped your cam inside out .....

Sorry about misleading you on the timing chain probably jumped. From some of the things you were saying I thought it probably had but obviously was wrong. When #1 is at the top of compression stroke the timing mark should be about TDC and the rotor will be pointing at the #1 wire. If the timing mark is 180 off and the rotor is pointing opposite #1 wire, do this. It is very easy. Pull the dist. up far enough to rotate the rotor 180 degrees and drop it back in. Then see if everything lines up. The dist. only goes in two ways because the shaft is slotted. If you had the dist. out it could have got put back in wrong. Like I said earlier, anytime I take a dist. out I rotate the engine until the rotor points to the firewall so I don't have to remember where it was pointing when I put it back in. Hope this helps.

What has me all perplexed though Les is that the method of finding compression indicates that #6 is on compression when the dots on the timing sprockets are lined up.

That's a near impossibility by all conventional engine setups, unless early DeSoto was timed off #6.

We restored a '38 Plymouth, but it was normal.

I'm confused.

Where are you located, Thom?

I'm in northern NJ Tim. I'm going to go thru everything again and repost my findings and exactly how I came to them. My engine ran good for 2000 miles after a rebuild 20 years ago by a pretty reputable shop. These rough running symptoms began 2 years ago and got progressively worse. Let me go back to the beginning and repost. Thanks all!

The fact that everything was fine for so long and this is relatively recent adds to my confusion.....

Ok, everybody check my reasoning on this......

I've attached an image of the '49 Shop Manual dealing with valve timing. I had to re-read it and throw out all my assumptions of what I thought it was supposed to say....

Everything in that section refers to #6 as being the reference cylinder for lining up the dots on the sprockets, or using the timing marks on the timing cover and harmonic balancer.

So this would mean that we've been fighting conventional timing setup all along, and Thom's finding #6 on compression stroke when the marks line up is how it's supposed to be. It would also seem to make sense, since everything has been fine for the last 18 years or so, and there hasn't been any catastrophic event (right, Thom?) that would change the way the previously functioning engine was set up.

OK everyone, check me on this and make sure I'm not too far off the reservation...

Since this whole exercise started because the quality of the engine's performance was deteriorating, you might check the valve adjustments now and make sure they're within tolerances. That will involve turning the engine through several rotations to adjust all 12 valves.

So I can't find anything specifically in my '49 Shop manual that tells me how to stab the distributor, but based on the image of the distributor cap in the wiring diagram and in conjunction with the text about valve adjustment and finding TDC on #6 I would expect:

Have the timing marks on the sprockets lined up before you put the cover on, and try not to rotate the engine from that point until you're ready to hit the key and start the motor....

Re-assemble the front of your motor and try not to cuss us all out while you're doing it.

When your sprockets are lined up, I'd hope your rotor points in the general area of 2:00/2:30 on your distributor cap as shown in the illustration.

If it's not, you'll need to pull the distributor like Les describes. It's possible that you might need to rotate the shaft for the oil pump so that the distributor gear will align with the rotor pointing where you want it.

Once the distributor is pointing at the #6 position on the cap, set the static timing on the distributor to the point where the points are just about to open.

That should put you back where we were before, however now we're orienting off of #6 instead of #1. Weird.

Check (again) that the spark plug wires are in the right order.

Hear the engine go vroom. (hopefully)

When #6 (the rearward most cylinder) is at TDC on compression, my rotor is pointing directly at 2 o'clock, directly at #6 wire. Correct, nothing catastrophic has happened and the engine turns freely. I rechecked all 6 wires, they're all going to the correct cylinders. It will take me several days to get all this back together (mostly because I need to order a new timing chain cover seal kit) and I'll repost when everything is assembled again.

I have a bad habit of assuming a problem has the worst cause, whether it's a Desoto or my broken dishwasher. When I get everything reassembled I'm going to take a closer look at everything and repost. I still think my problem has an easy fix.

Thanks everyone.

My '42 FSM on the same subject:

OK, line up number 1 at TDC as well as the timing pointer, set point gap about .020 and static time the distributor to TDC.

Replace the condenser with high quality US made part.

Start it up and report back.

Have a good day!
Steve

OH, are you still running 6V positive ground?