42 DeSoto runs VERY rough, help needed

No question is insulting. I appreciate the help!
I'm counting cylinder #1 as closest to the radiator.

I checked the compression several months ago and they were all good and very consistent, about 100 PSI on every cylinder if I remember. The engine has less than 5000 miles on it since a rebuild 20 years ago.

Just to be sure though, I'll check it tonight again and repost the findings.

Is it weird that #1 and #6 are not both up at the same time? Not even close.

I hesitate to jump in here because Tim is doing a good job and I don't want to confuse things. But, looking at your earlier comment when you said with #1 at tdc the rotor is pointing at #2 which is almost opposite where it should be. This sounds like either it was at tdc on the exhaust stroke or the distributor is in backwards. I would go back to the "finger in the spark plug hole" to make sure the #1 cyl. is coming up on the compression stroke, then rotate the piston up to tdc and check the position of the pointer. It should be at TDC. Then look at where the rotor is pointing. If the rotor is pointing opposite #1, the distributor is backwards. I wouldn't be concerned about the location of any other cylinders because it really isn't relevant. Timing is determined by #1 cyl.. My turn for a stupid question. When you had the distributor out you did make sure it was put back in with the rotor pointing the same way? I always rotate the engine until the rotor is pointing toward the fire wall before taking the dist. out so I don't have to remember where it was pointing when I took it out. Also, are you getting any backfiring while it is trying to start? That would indicate a timing problem. Hope I didn't confuse everyone.

Hello,
I went back, and read the very first post, from the author.

This is what I think..............

I am the 1952 Desoto Technical Adviser. What I am proposing, I know is true with the 1952 model. There is an Oilite filter, inside the fuel tank. After 60 + years, they tend to plug up.
I do not know for sure, if the 1942 model has this. This information can be found in sales brochures, Ross Roy books, and parts books. Mine do not go back far enough.

The reason I think it might be plugged, is that it started getting worse over time.

It lays flat on the bottom, inside the fuel tank.

Easy way to unplug it, is to disconnect the fuel line at the tank, and shove a small diameter, somewhat flexible rod through the hole towards the tank, long enough to get to the middle of the tank.

It will pierce the filter, and at the same time, stir up any sediment, and chunks of whatever might be in there. However, you still have a fuel filter before the carb. that will stop them.

If it runs good for a while, then starts running badly again..........you know that the carb. filter is now plugged. Time to remove the tank, and really clean it out.

If it ran good once before, and the timing had not changed, this COULD be the problem.

Good luck!

Mark Waite

I think 1 and 6 are coming up at the same time, but you won't feel compression on them both because one of them would be on it's exhaust stroke and the exhaust valve will be open while the piston is traveling up.

If you could find 6 fingers to be in each cylinder, you should feel compression to match the firing order 153624 as the engine spun.

It still concerns me that you say that the pointer on the timing cover isn't pointing at 0 when #1 is at TDC. It's possible that your harmonic balancer has spun, but the car should still run on static timing.

So, when you get back to it, my next step would still be to get #1 on TDC, locate the position of the rotor and put #1 plug wire there. Then, in clockwise direction, put the rest of the plug wires in the order 53624. Locate the distributor to a position of the points just about to open, and give it a try.

Reading my '49 shop manual, it says there's a fitting over the #6 cylinder in the head which you can remove, and if it's the same for your '42, you can put a small wire (like a welding rod, or similar) down that hole and rest it on top of the #6 piston. It should be coming up at the same time as #1 is coming up on compression. As soon as you know #1 is on compression, you can continue to rotate the engine slowly by hand on the fan blade and belt until the wire stops coming up. As soon as it stops, you would be pretty accurately at TDC

Tom,
If you go back through your stack of DeSoto Adventures, you'll find an article about ignition coils and how to test them.
The article is in the March-April 2014 issue (Volume29, Number 2) starting on page 7 and continued on page 20.

Best of luck and best regards,
Geoff

Mark- I think I read that the tank filter began in 1948. Mine has full fuel flow, no problem there anyway.

Les- You might be right (but see below) about the distributor being 180° off. It was early winter when I took the distributor out and reinstalled it. I'm pretty sure I did it correctly but not 100%.

Tim- I also read about the fitting over #6 but didn't bother. To see the location of each cylinder, I've had all six spark plugs out so I monitor piston travel that way with a short dowel in the hole.

I just re-evaluated everything I did, redid the compression test, and tried to find TDC again. Here's how I checked compression: With all plugs out, I attached my gauge to each spark plug hole separately and cranked the engine about 5 times with the starter. I got 1=45, 2=80, 3=100, 4=95, 5=100, 6=73. Several months ago I got a very consistent reading among all cylinders of 100 PSI.

I also noticed that my 0° timing mark DOES appear at a 7 o'clock rotor position, but only EVERY OTHER time the 0° mark appears at the timing pointer. This wasn't something I realized. This makes me think the dist is in properly (not backwards).

The finger-over-the-hole to find the compression stroke wasn't doing it for me so I tried another method I read about. I used my compression kit but instead of the gauge, taped a small balloon to the end tester hose. As soon as I saw the balloon starting to expand, I knew I was at the compression stroke. I watched the timing marks and gently rotated the engine to 0°. Shouldn't this 0° mark be TDC #1? The #1 cyl was still down at this point. Shouldn't the cylinder be physically at the top of the stroke? When I bring that cylinder to the top, the timing marks are nowhere to be seen. Can this still be an indication of a distributor in backwards?

When I say the distributor might be "backwards" I actually mean it might be 180 degrees off because it will only go in two ways.

I think it has probably jumped time. The #1 piston should be at the top when the pointer is on 0 degrees. It would also account for the variation in compression because the valves are opening at the wrong time so some would open before the piston gets to the top giving a low compression reading on some cylinders. Also, you said the problem was gradual. If the timing chain jumped one tooth I think it would still run but rough. Then if it jumps another tooth or two it probably wouldn't run at all. That is my "guess" for what it is worth.

You could squirt some oil in the cylinders and see if your compression comes back, but I'm concerned that Les may be right and the timing has jumped.

I think I know the answer to this question.... but is there an "easy" way to confirm if the timing chain has jumped?

The fact that the #1 piston isn't at the top when the pointer is on TDC is enough to convince me it has jumped. To know for sure, take the timing chain cover off and rotate the engine until the marks (a dot) on the gears align. They will come together when the mark on the crankshaft gear is at the top and the cam shaft at the bottom. If they don't align it has jumped. It is a bit of work to get the cover off but if it has jumped you would have to do it anyway.

And you might start hunting a source for a new new chain/sprockets in the event you need them...

http://www.oldmoparts.com/parts.aspx

http://www.robertsmotorparts.com/store/

http://egge.com/

Thanks everyone for your help!
I have experience repairing almost everything except for a timing chain. My FSM hardly mentions a repair and replace procedure. I know where it is and can probably do it without a repair procedure, but would be more comfortable with a written manual on the subject. Is there an online procedure or manual I can source for it? Maybe an old MOTOR repair manual? Where can I look?

I'm not going to be of any help with this issue. But what I'm really hoping for, after the problem finally gets fixed, is that one of you guys will write all of this up as an article for the club's magazine! I think it would make a great article, and would probably be very helpful to other club members. (And throwing in a few photos wouldn't hurt either.)

Bill Noble

I will definitely do that Bill! Great Idea. Tonight I took out the hoses and radiator. Will I need to remove the engine to change the timing chain? The bolts are behind the front engine support. Can the engine be supported from the bottom and the support removed that way? I have an engine crane but my 440 is on it waiting to go into my Imperial!

I would probably look at it and consider that a floor jack with a piece of 1x8 or something to distribute the lifting point could raise the engine enough to allow you to get the front of the motor off.