1941 Desoto Flathead - New member

[Guest flathead1941]

Hello everyone... This is my first post! I recently picked up a 1941 Desoto Custom and I love it. I havent been able to drive it yet because 2 cylinders have no compression, the car has been sitting close to 2 decades. Ive been dropping some marvel mystery oil into them 2 cylinders and rechecking the compression every couple days but still no luck. I think I will be pulling the head to get a better look and to HOPEFULLY free up the valves. Hopefully it fires and purrs after that. I can't wait!

[Guest WEB 38]

Hi I also have a stock 41 Desoto custom It sounds to me that you may have a couple of stuck valves. Good luck with the car If I can be of any help feel free to contact me. Bill

[GLong]

Are the two cylinders that have no compression side by side? If so, it might be a blown headgasket between the cylinders.

Before I'd pull the head, I'd look through the spark plug holes in the head, to see the valves, Squirt some PB Blaster, Kroil, or whatever you like under the open valve, Then, using a piece of coat-hanger wire or welding wire, rest one end of a bent piece of wire on each valve, and rotate the engine by hand. See if the valves travel up and down.. If not, use a skinny prybar, like a bent screwdriver to push the valve down on it's seat. Rotate the engine again, repeat. The penetrating oil and pushing down the valve will usually free them up. I've had a lot of luck using this procedure.

GLong

[Guest flathead1941]

Thanks for the replies. GLong....I did what you suggested, but have a couple questions.... Are the valves directly underneath the spark plug holes? I did rest a piece of coat hanger in each of the cylinders (3 & 5) and they do travel up and down probably 1/2 or 3/4 of an inch maybe, so Im assuming these are the valves. So they do move, just no compression. Im open to more suggestions.

[GLong]

Hi, I'm not familiar with the exact location of the valves on the Desoto engine, relative to the spark plug hole. The valves are off to the side of the piston, the piston travels up and down 3 or 4 inches.. the valves will move up and down about 3/8".

I assume you are using a compression gauge to check the compression? What compression are you getting on the other 4 cylinders?

Valves can be burnt, and need replacement, they can have a chunk of carbon under the valve, keeping it open so it won't seal. The valves can also be badly out of adjustment., so they have no clearance and are held open.. but I find this unlikely, since the rest of the cylinders seem ok.

When you do the next compression check, record the numbers.

The other thing you might try, if there is a chunk of carbon under a valve, you might be able to blow it out of the way by rotating the engine till each valve in the cylinder is open, then blow compressed air in the spark plug hole, the air will go out the intake or exhaust valve depending on which one you have open , this MIGHT blow out some crud and get the valve to seal better.

Can you take a photo of the top of the engine, so we can see the spark plug locations on the head? It would help..

I'd go ahead and start and run the engine for a bit, if the engine will fire up, it might fire on those two cylinders enough to clear any carbon under a valve.

Are the two low cylinders next to each other/? if so, it might be a blown head gasket between the cylinders.

GLong

[Guest flathead1941]

Hi GLong....the cylinders are # 3 and # 5. The compression readings are 75,125,0,75,0,150. Im wondering if the valve that is right under the spark plug in these 2 cylinders are not the stuck one, but the other in that same cylinder maybe? This car has been sitting almost 20 years so I guess this is expected. Too bad cause its a beautiful car. But Im going to go outside, take a picture of the top of the engine, and Ill come in and post it. Thank you.

[Guest flathead1941]

Ok here are some pics.

http://www.juanswebsites.com/flathead1941.jpg

http://www.juanswebsites.com/eng1.jpg

http://www.juanswebsites.com/eng2.jpg

[GLong]

Do you know why the car was put up in storage and not driven?? I'm wondering if it had valve or compression issues and was parked because of those issues.

Looking at the location of the spark plugs, near the ports and valves, I will say that yes, the valves are located under the spark plug holes. But it appears that on some cylinders the valve under the sparkplug is an exhaust valve, and on some it's an intake valve.

Here is another trick I've used a few times.. On the cylinder with zero compression, look in the hole, or use a wire to follow the valve moving up and down. When the valve is down, take a wood dowel or a flat ended punch, and through the spark plug hole, tap on the head of the valve. If there is a chunk of carbon under the valve, often this will break it or crush it to powder, and the valve will be able to seat..

There are lots of tricks to try, but I would try to get the engine to fire.. and see if having it running will blow out what ever is causing the zero compression.

Some times it is just a problem that can be solved with a few tricks. But the other low compression readings from other cylinders tells me that the engine really needs some attention, with the head off. Most likely a valve job.

I rather enjoy the challenge of getting old cars running again, many times they can be put back on the road once the ills and issues that came about from the long storage are fixed.. But if the engine was sick when it was parked, it's still sick..

Have you changed the oil in the engine? this is very important, with all the engine cranking with the starter, you are pumping oil through the bearings, It should be new fresh oil, not the stuff that has been sitting in the engine for two decades. There is a lot of condensation/acids/sludge etc that needs to be drained out and fresh oil added.

Once the oil is changed, put some fresh gas in the carb, reinstall the spark plugs and see if it will start on the cylinders that do have compression.

Once the engine has run for a few minutes, shut it down and check the compression again. I think some of the low cylinders will have recovered some pressure.. If not, then it's time to pull the head and plan on doing a valve job.

GLong

[Rusty_OToole]

Be careful, you can bend a valve if you don't hit it exactly in the center. You might better remove the valve cover and pry down the valve that way. The valve cover is on the side of the engine, under the exhaust and intake manifolds.

I have done this on old motors and the valve should pop or snap down with a little help. Oil it up, turn the engine over and it should soon be working. If it is badly stuck don't force it, better take off the head and see what is the matter.

Incidentally if you need parts Vintage Power Wagons is a good place to get engine parts. The same engine was used in DeSoto, Chrysler, Dodge trucks, and Crown marine and industrial engines 1938 - 1972. So there are still quite a few around.

[GLong]

Yep, if you use a 16oz hammer and whack it hard it could bend the valve.. Hence my terms 'tap' on the valve, and suggestion of using a wood dowel.

If the valve is all the way down, and is held open by ??? something, I think it would be pretty hard to bend it, but hey, if it could happen it will.

I'm thinking it will need the head to come off. The number of rather poor compression readings implies that the valves need a freshing, and who knows what else is needed..

A fiber optic camera through a spark plug hole will tell a LOT. $199 at harbor Freight.

GLong

[hchris]

Hi GLong....the cylinders are # 3 and # 5. The compression readings are 75,125,0,75,0,150. Im wondering if the valve that is right under the spark plug in these 2 cylinders are not the stuck one, but the other in that same cylinder maybe? This car has been sitting almost 20 years so I guess this is expected. Too bad cause its a beautiful car. But Im going to go outside, take a picture of the top of the engine, and Ill come in and post it. Thank you.

Sadly because of the side valve configuration on these engines you wont be able to see or lubricate the valves via the plug hole; but the good news is you can remove the side plate from the engine to access the valves. Unfortunately access is restricted by the exhaust manifold, but you may find by removing the front wheel on that side, you can gain better access through removable panels on the inner guard.

[GLong]

Sadly because of the side valve configuration on these engines you wont be able to see or lubricate the valves via the plug hole; but the good news is you can remove the side plate from the engine to access the valves. Unfortunately access is restricted by the exhaust manifold, but you may find by removing the front wheel on that side, you can gain better access through removable panels on the inner guard.

I went out to the shop, pulled up the hood on my 1941 Plymouth PT125 pickup truck, from the photos of the Desoto engine, they are very close to identical. I removed #2 and #3 spark plugs. Looking down through the spark plug holes I could clearly see the edge of a valve. Using a piece of wire, with a 1" bent end, I was able to feel around, find the edges of both of the valves, the open one and the closed one..

So, the spark plugs are located over the valves, as the Desoto photos show. The access to the valves is very limited due to the small 14mm spark plug holes, and the limited room from the valves to the head..

But, using a piece of bent wire, and a wrench on the crankshaft damper bolt head, the engine can be rotated, and each valve followed up and down.. If the each valve does not move up and down, thien it's stuck, and any of the above mentioned ideas or tricks MIGHT work to lubricate and free up the valve stem/valve guide sticking.

However, I'm thinking that the best thing is to start and run the motor for a few minutes and recheck the compression, if the compression does not improve with plenty of air blowing through the ?? stuck ?? or burnt ?? or held open with crud ?? valves, then the head has to come off and a valve job done..

If this car is to be used a lot, then I'd opt for the valve job anyway.. make it reliable and run as well as reasonably possible.

Best of luck..

GLOng

[Guest flathead1941]

Happy Monday folks..... I did try to tap down the valve directly under the spark plug while it was all the way down as far as it would go, but didn't change anything. I'm trying to get my friend to come over with his fiber optic mechanics "stethoscope" to take a look in the cylinders. I think I'll see Jesus by the time he comes by with it. I might just have to spring for one. I will try feeling the edge of the 2nd valve in those 2 cylinders, (the one not directly under the spark plug), and see if it is not going up and down, or if it isn't going all the way down. I think at this point pulling the head is probably the best option. Ive already got the head gasket for it as well. Ive tried starting the car, but it wont start on just the 4 cylinders. Are valve jobs done with the engine still in the car? I bought the car from a family friend and he said the car had absolutely zero problems when it came to starting and running. He said he parked it one day in his garage almost 20 years ago, and just simply lost interest. I believe him. What I paid for the car was peanuts, and I would've bought it even if he told me it needed an engine because it is clean inside and out. On a brighter note, I just realized this morning that the exhaust and intake manifolds are not bolted to the head, but below the head. That makes it easier. Thanks for the replies guys, I'm probably not going to get to pulling the head til this coming weekend, but and willing to try anything between now and then. Thanks again.

[Owen_Dyneto]

Yes, valve jobs are typically done with the engine in the car, head and valve lifter covers removed. The link, though intended for flathead Packard engines, applies to all such engines including yours. It's not intended as full detailed instructions but may help you understand the nature of the job involved. I'd suggest you find someone who has done this type of work before to guide you if you intended to try any of it on your own.

http://www.packardclub.org/forum/viewtopic.php?f=14&t=862

[ply33]

. . .

I've tried starting the car, but it wont start on just the 4 cylinders. Are valve jobs done with the engine still in the car?

. . .

My when I got my '33 Plymouth (very similar engine) it was hard to start and had a very rough idle. Turns out that it had 50 to 60 pounds compression in four cylinders and 0 in the other two. It was hard to start, but start and run it did. I probably put about 2000 miles on it in that condition before I did a "shade tree" overhaul with the engine in the car on it. So if it is not starting, I'd say that there is something more wrong than two cylinders with no compression.

I the 20s and 30s and maybe later, it was not unusual do do a pretty full overhaul with the engine in the car. If you can find trade magazines of that era you'll see ads for boring machines attached to the top of the block with the block in the car. An engine in the car valve job was a very standard thing to do.

[JACK M]

Since you will have to take the valve cover off to do a valve job anyway, I would be inclined to take the manifold assy off and take a look for stuck valves through the side cover.

Especially since you trust the word of the seller.

Although taking the head off is not that difficult you wont be able to do any adjusting.

[Guest flathead1941]

Well I have spark, fuel, and zero compression on the 2 cylinders. I was thinking "heck Ive had cars start/run before with 2 cylinders down so why wont this one?"..... The common reply I get is "some will start and run, some wont".... So, I will probably start with pulling the head later this week or weekend, see whats going on there, and probably have to pull the side covers as well. But until then, I'm enjoying the challenge. Does anyone know how, and how difficult removing the inner fender panels are? Thanks again.

[JACK M]

You may be able to boost the compression in the four good cylinders by squirting some oil thru the spark plug holes.

Also if the car is roadworthy you may try pushing or towing it to get it to fire off.

Sorry, no advice on the inner fenders. Get a fender cover or blanket to protect the fenders, maybe a step stool will be of some assistance.

[Rusty_OToole]

Back in the day it was common to overhaul the engine in the car. This could include new rings, grinding the valves, and even new bearings.

Check the cylinders when you have the head off. Up to .007 taper and it is permissible to hone the cylinders and install new rings. No boring of cylinders or new pistons required.

Depending how many miles on the car it might be a good idea to hone the cylinders and install new rings when you do the valves. This requires dropping the oil pan which gives you a chance to clean out the sludge and dirt, also a good idea.

Edited May 12, 2014 by Rusty_OToole (see edit history)

[Guest flathead1941]

I tried putting some marvel mystery oil in the cylinders right from the beginning and it didn't improve the compression. I'm definitely going to try to get a look inside the cylinders via the fiber optic tool. Once I do that, then I'll probably have to pull the head. Seems no matter what I see inside the cylinders regarding the valves, chances are the head has to come off anyways..

[hchris]

Well I have spark, fuel, and zero compression on the 2 cylinders. I was thinking "heck Ive had cars start/run before with 2 cylinders down so why wont this one?"..... The common reply I get is "some will start and run, some wont".... So, I will probably start with pulling the head later this week or weekend, see whats going on there, and probably have to pull the side covers as well. But until then, I'm enjoying the challenge. Does anyone know how, and how difficult removing the inner fender panels are? Thanks again.

Before you do any head pulling, as mentioned before you can access the valves via the side covers, pulling the head will only allow you to see the valves; to release them they need to be accessed via the side covers.

So before you go any further can I suggest you get the right front wheel off, remove the inner guard panels (not difficult once you get your head in there) then take off the side covers; now as you spin the engine over you will be able to see if all the valves are opening and closing correctly. Having said that it might be easier to simply remove the inlet / exhaust manifold and get to the side covers that way.

[GLong]

To reinforce hchris's suggestions: the intake and exhaust manifold gaskets are probably in rather poor shape anyway, I'll suggest removing the two manifolds, and then the access to the side/valve covers is really easy.. I think I'd rather do this than remove the inner fender panels. crawling under the fender, looking through the inner fender with the brake drum jabbing me in the chest, me kneeling on the ground or floor, well, I'm thinking I'd rather lean over the fender. Just my creaky old joints would prefer to not be on my knees under the fender.

When you get the valve covers off, you can see the valve springs, watch the lifters move the valves up and down as you trun the engine over..

One last attempt to getting the engine running: Have you tried starting ether, aka: starting fluid? it will fire in a cylinder with much lower compression than gasoline will. Once you get it fired up, it should be much easier to start the 2nd and 3rd times. Is the gasoline in the car fresh, less than a few months old? Modern fuel does not have a very long shelf life.

GLong

[Rusty_OToole]

But you can't take the manifolds out without breaking the joint between the exhaust manifold and pipe. This would be asking for trouble. I would go in thru the fender well first as being a lot less work. Or just take the head off, he has a gasket so what has he got to lose?

[hchris]

But you can't take the manifolds out without breaking the joint between the exhaust manifold and pipe. This would be asking for trouble. I would go in thru the fender well first as being a lot less work. Or just take the head off, he has a gasket so what has he got to lose?

6 of one and half a dozen of the other I guess, if you first remove the head and establish the valves are stuck then you will have to remove the side covers to fix the problem; at this point you are going to have to remove the manifolds anyway. Whereas I am thinking you might be able to lubricate / manipulate a stuck valve via the side cover first without disturbing the head; toss of a coin really.

[Rusty_OToole]

O ya, if you take the head off and find you need a valve job, you definitely should take off the manifolds. I wouldn't take them off otherwise because the bolts are always very rusty, it is too easy to break the bolts and run into problems, plus it is very hard to take the manifolds off then put them back on and get a good seal. I would rather leave them and not take a chance if I could get away with just freeing the valves. But with the head off I think I would do a ring and valve job on general principles.

[c49er]

Those manifolds can be extremely hard to pull off the block if it uses the two long center studs. Done many.

[GLong]

Yep, this is the 'can of worms' that we open when trying to do just one thing to get a car running.

Did Desoto, Dodge, Plymouth use brass nuts on the manifolds like the car makers in the '20's and '30's did? Usually the brass nuts will not sieze to the studs.

You definitiely do not want to complicate the job by breaking any studs in the block..

So with that thought,, I guess I too would suggest looking into removing the inner fender, and finding a way to SAFELY crawl into and under the fender to remove the valve covers.

Have you tried using a spray or two of starting ether while trying to start the engine ?? It might be just enough to get it to fire and run.

Once running, hopefully it will blow out whatever is keeping the valves from sealing.

Story: I once bought a '25 Pierce chassis, pretty complete from the front door posts forward. The engine spun freely: all the valves were stuck OPEN.. I could look through the large 18mm spark plug holes at the valves.. I used the 'spray' and push 'em down procedure. And thankfully the minor rust, and mostly dried old oil and varnish on the valve stems and valve guides was not too stubborn.

I soon had all valves moving, and with a jerry-rigged gas tank, I soon had the engine running.. The challenge didn't end there, I clamped a pair of large vice grips on the steering shaft and put a milk crate on the chassis for a 'seat' and took the now mobile chassis down the drive and back..

Too bak this was so long ago that digital video wasn't around yet, I'd love to have a short video of this adventure..

By the way, after the short drive, the starter cranked the engine so evenly that I took a compression check and I think they were all around 60-65 psi, on that engine, 70 was perfect: it had a 4.5:1 compression ratio.

Can you take a photo of the inner fender on the manifold side? My experience with these engines is limited to the pickup trucks.

Best of Luck,

GLong

[Guest flathead1941]

I knew I wouldnt have time during this week to work on it but I did start getting stuff out of the way to get to the head...The horns, cable to the heater control valve (I think thats what its called, on the back right corner of the head), etc....Probably Sunday I'll pull the head and see whats going on. Maybe Ill try to get it to fire with starting fluid, and Ill take a pic of the inner fender/panel and post it. But Sunday will be the big day.

[Guest flathead1941]

Hi again folks....Well I pulled the head and sure enough 2 valves stuck wide open. Just a gentle tap and they freed up. The one worked flawlessly, immediately it went up and down....The other, when it came back up, stayed up....so a little bit of Marvel Mystery Oil and working it for 15 or 20 minutes completely feed that one up as well so now everything is working as it should. I took the head to the machine shop I go to and they told me the head was slightly warped. He told me he would have to take 10-15,000 off each end.....I guess it was bowed up slightly in the center. So this week I will get it back together and give it another whirl. Do I have to add lead additive to gas? I just thought of that. I guess I should ask if 10-15k off the head is ok?

Thanks for all of your help!

Edited May 20, 2014 by flathead1941 (see edit history)

[Rusty_OToole]

Good show. While you have the head off how do the valves and cylinders look?

No lead necessary. Your car was built at a time when low lead, low octane fuel was the norm. It came stock with hard valves and hardened valve seat inserts.

If you want to be pernickity you can add some Redex, Marvel Mystery Oil or similar upper cylinder lubricant to reduce ring, valve and cylinder wear. It is proven to extend the life of these engines. But is not a necessity.

In very hot weather, if vapor lock is a problem, adding 10% diesel, kerosene or stove oil can reduce the boiling point of the fuel, and does no harm.

Other than that, the lowest octane regular is fine. Your car was made to run on 70 octane or less and the lowest octane today is 87, which is higher than Ethyl when your car was new.

[ply33]

Good show. While you have the head off how do the valves and cylinders look?

No lead necessary. Your car was built at a time when low lead, low octane fuel was the norm. It came stock with hard valves and hardened valve seat inserts.

If you want to be pernickity you can add some Redex, Marvel Mystery Oil or similar upper cylinder lubricant to reduce ring, valve and cylinder wear. It is proven to extend the life of these engines. But is not a necessity.

In very hot weather, if vapor lock is a problem, adding 10% diesel, kerosene or stove oil can reduce the boiling point of the fuel, and does no harm.

Other than that, the lowest octane regular is fine. Your car was made to run on 70 octane or less and the lowest octane today is 87, which is higher than Ethyl when your car was new.

I agree with all the above but would like to add that you should seriously consider replacing the flex fuel hose between the frame and the engine and rebuilding the fuel pump with materials that are resistant to modern gas additives, including and especially ethanol.

[Guest flathead1941]

I didn't take a good look at the cylinders or valves yet. I'll clean it up real good, and take a good close look. Ill probably clean up the valves where they meet the seat, and the seats with sandpaper just to make sure there's no crud on them. The head is actually done, the shop just called me. Is there a head stud kit for these engines. I was just thinking how much easier it would be to drop the head gasket, and head over studs as opposed to not, and using head bolts. Just a thought. Thanks guys for the help, I really appreciate it.

[Guest flathead1941]

I agree with all the above but would like to add that you should seriously consider replacing the flex fuel hose between the frame and the engine and rebuilding the fuel pump with materials that are resistant to modern gas additives, including and especially ethanol.

Thanks ply33...I just saw this after I posted my last post.

[Rusty_OToole]

I wouldn't use sandpaper on the valves or seats. If you scrape the piston tops use a brass scraper to avoid scratching or gouging the aluminum.

Before putting the head on clean the bolt holes with a bottoming tap and blow them clean with compressed air. Ask how much they take off the head, if it is .060 you need thicker washers to stop the bolts from bottoming out.

The old head bolts are fine, they are very strong and will last the life of the engine. Unlike some modern cars where they need to be replaced any time the head is off.

[Rusty_OToole]

If you have a couple of old bolts you can cut the heads off and put them at opposite corners of the engine, to line up the gasket and head.

[Guest flathead1941]

Well here it is. Nicey nice. I started cleaning up the top of the block to start getting ready to drop this on there. The cylinders looked fine...no scratches, gouges and a very small ridge on top. However the valves and pistons look fine but are covered with carbon build up. Should I take the time to get this carbon off the tops of the pistons and valves? I have to still take a better look at the seats too. My initial compression readings were 75,125,0,75,0,150. The 2 with zero I have no idea with what they will have now that the valves are freed up. My friend tells me it still wont fire unless theres at least a compression reading of 90 at each cylinder. Is this true? If it is Ive wasted a lot of time. Thanks for your help.

[ply33]

When I first got my '33 Plymouth it was hard to start and it idled very roughly. But it did start and run and I actually drove it for over 1,000 miles in that condition. When I finally got around to doing a compression check I found about 50 pounds in four cylinders and zero in the other two.

So my experience is that it should start and run with lousy compression, far lower that the 90 your friend says it needs.

[Guest flathead1941]

Perfect ply33! That's exactly what I wanted to hear! :cool:

[Guest flathead1941]

Happy Monday everyone. Ok I cleaned up the valves, checked everything, and put the head back on and put everything back together. I changed the oil, and gave the engine a crank, and she sure sounds like she wants to fire, but I didnt try, I just wanted to make sure I had compression at those 2 cylinders which I do. My last issue is this linkage: mainly this little bracket attached to the spring in the pic. I cant for the life of me remember which way it went, or where it went. I dont know if I have to flip it around, or put it on the other stud on the other side of the bracket....Im just drawing a comlete blank on it, and have no pics, or manual. I did find a service manual on ebay and ordered it, but didnt get it yet. Anyways, help me out guys, please....Thanks!

PS - Therefor I don't know if the spring is attached where it should be.

Edited May 27, 2014 by flathead1941
Added PS (see edit history)

[ply33]

. . . My last issue is this linkage: mainly this little bracket attached to the spring in the pic. I cant for the life of me remember which way it went, or where it went. I dont know if I have to flip it around, or put it on the other stud on the other side of the bracket....Im just drawing a comlete blank on it, and have no pics, or manual. I did find a service manual on ebay and ordered it, but didnt get it yet. Anyways, help me out guys, please....Thanks!

PS - Therefor I don't know if the spring is attached where it should be.

My setup is quite different and I haven't looked that closely at cars that have your style setup. However the slightly curved piece that your spring bracket is attached to is the holder for the bypass oil filter and it seems unlikely to me that a throttle return spring would go through the middle of the oil filter. So I'd say the way you have it now is wrong but I am unable to say what is correct.