I’ve been diagnosing a weird issue in my 1950 Lincoln Cosmopolitan and I think I’ve found the problem, for better or worse. It has a bad misfire on one cylinder, that is practically constant. Doing a compression test the cylinder is MUCH lower, approximately one third of the psi that the other cylinders are reading. I put oil in the cylinder, no change. I listened close at the exhaust, and while cranking I hear it hiss. So the exhaust valve must not be sealing well and that’s what’s causing my issues. The engine seems super healthy otherwise, doesn’t smoke or even tick And is basically a barn find car that has to my understanding, not been running for particularly long, but has been driven around a bit. To be completely honest, this car was cheap, and I don’t have the time or skill set or budget to tear down this 337 engine to fix this valve. I know that there is a correct fix for this, but I need a fix that is cheap and dirty so to speak lol. Are there any quick fixes or things I can try to make this valve seal correctly, or do you think it’s possible it will fix itself on its own? I wish I could fix it the right way, but my budget is not going to allow that for a while. Even if it’s not fixed, Would it damage the car to drive it around like this? Other than sounding annoying, it really doesn’t drive bad at all. Thanks for any help you can give me!
Tried and true 'Medicine' For flathead valve action, has always been 'valve top' oil. The most used and sworn by oil is Marvel Mystery Oil. Some in the gas and some in the sump.. Read the directions on the bottle. Back when, every brand of gas and oil offered there own valve top oil. Marvel has survived the ages and cured many a sticking valve. The need of it, I always like to point out, is that, unlike OHV motors, that get oil bathed on the valves from above, for gravity to supply oil to the valve stems, flatheads have fire, from above, to bathe in. Consequently they need the help of lube mixed into the fuel supply.
My flathead sat for 14 years without being cranked and had a sticky valve in it. All I did was put some miles on her and the problem has gotten a lot better. I usually do not promote quick fixes but I remember my granddaddy saying that Marvel Mystery Oil was a go to for something like that before you break into the motor. You can add it to the fuel and oil and it should help with the problem. I did change the oil and put fresh gas into the car before driving but didn’t add anything else to the mix and it’s running better.
If you’re careful and meticulous in clean up, pull the head. Pull the valve, if not burnt, clean up the seat and lap the valve to the seat. Also, what is your location? There’s a reason I ask…
I agree that Marvel Mystery oil could loosen a stuck valve and I wouldn’t hesitate to try it but if the valve face and seat are burnt or pounded out. Nothing in a can will fix that. Here’s hoping to a sticky valve guid.
I’ll PM you later today (night shift then some things to do when I get up) might be your evening time.
I’m hoping it’s carbon buildup. I would imagine that the valve train would be making some funky noises if a valve was damaged enough from being burned to do this much. In the case of this engine though, It runs so smooth you can’t even hear the valve train unless you have your ear against the engine
So before you dig into it, you need to diagnose it. Pull the plugs ( all of them. Makes it easier). Bring that cylinder to TDC. Find/make an adapter that screws in the spark plug hole that you can connect to compressed air. Put some air into the cylinder. Start with low pressure. Listen to where the air is going, ie. Crack open the throttle, put your ear to it. Then check out the exhaust pipe. Poor man’s “leak down” test. If air is coming through the intake or exhaust, then pull the head and see if the valve is seating or not. If it seats, then pull the valve.
Another way to see if it’s an exhaust valve is take a dollar bill and hold it near the exhaust pipe and if it sucks in then you know it’s the exhaust valve. WARNING be sure to pinch it tight because it will eat it and get hung up in the muffler and drive you nuts having to listen to it!!
I’m certain it’s the exhaust, I can hear it hiss out the side dump straight pipes when it’s cranking over.
Couldn’t the valve be too tight? Not enough lash. Seems like pulling the intake and checking that might be a good first step, assuming it is leaking from the exhaust.
I wouldn’t think k it was too tight, from what I can tell, this engine is largely original and untouched from the factory. On top of that, wouldn’t it also be making a clicking noise? I imagine if the valve was hitting something or too tight, it would be ticking louder than the other valves, but all the valves are practically dead silent.
Okay, found out good news. This engine sat from 1977-2014 locked up and in a barn, and has had less than 100 miles driven on it since it was revived then. That could explain the valve and driving it might bring it right back. Though the fact it was torn apart in that barn does make me question why however.
So been sitting, as mentioned before, best guesstimate is a sticky valve. Thing is, the head should come off and use your favorite concoction to lube/spray the stem, then light taps down on it, rotate the engine and repeat over and over so the valve moves freely. I’d be hesitant to “add to gas and oil and drive it” as if it get very close to the seat, say a somewhat of a decent but not proper seal, those hot gases have to go somewhere and may cause a valve issue. I know many have done it, just not what I’d do. But I’m just a guy in the corner!
Too tight would be quiet too. What I mean is that the valve stem doesn’t have any or enough clearance with the lifter. Basically adjusted too tight. Holding the valve open.
Very well could be. I don’t know about the 337c but if there’s a side cover to access the valves, should be evident with feeler gauges with the valves closed. Ie 40 thou clearance, or in spec, etc
Well, here's a story that may or may not have any relevance to your situation. Back in prehistoric days, '63. '64, in Honolulu, my pal had a '33 Plymouth that showed 2-3 psi of oil pressure on a good day and had a valve that hung every 30 or so miles. We got very good at popping a side cover and freeing the valve with a screwdriver and a sailors litany of curses. One day while buying gas we put a can of STP in it. The oil pressure immediately jumped to 25 or so and never dropped below 15 again and the valve freed itself in fifteen minutes and never stuck again. Would this help your engine? Who knows? But trying it would be cheap and easy.
Checking with the spark plug out, both valves seem to be moving perfectly fine, so that means it must just not be sealing correctly rather than getting stuck.
X4 on the MMO question, did the 337 come with adjustable lifters? most flat head of the day engines didn’t
I think the Lincolns had hydraulic lifters. EDIT : I checked it out, and the Lincoln 337's had hydraulic lifters. This adds a new factor to the equation. The 337's used in the big Ford trucks had solids.
This is a good suggestion. I got an OT pickup cheap because it was running on 7 cylinders. Compression test yielded similar results to OP... Backing off the preload on the exhaust valve brought the compression up enough that it ran normally. There was more going on in there I found when I pulled it apart, but I drove it for about a year like that.
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