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Old 02-25-2021, 11:47 AM   #1
JMFL36
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Default New misfire - sticky valves?

Hi guys. My '34 developed a misfire yesterday when I was out for a 20 mile drive. It is noticeable at all speeds, under load and not. I checked all the plugs and none were fouled. It seems to be more noticeable on a cold start and less so when the motor warms up, but never goes away. I notice a bit of smoke from the filler tube which smells like exhaust, so I suspect I may have a sticky valve. I drizzled about 6 ounces of MMO down the carb under fast idle, but still have the misfire. Any advice on what to check next would be appreciated. Here is a link to a 30 second video of the motor running.

https://photos.app.goo.gl/1698PpxL9Xg7jNNX7

Thanks in advance.
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Old 02-25-2021, 12:42 PM   #2
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Default Re: New misfire - sticky valves?

One thing I have done to narrow down the problem is to one by one remove plug wires with the engine running to see which cylinder(s) is acting ugly.
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Old 02-25-2021, 01:37 PM   #3
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Default Re: New misfire - sticky valves?

That miss sounds regular; like one cylinder missing. Removing plug wires as suggested by rbone should affect the idle on all but the bad cylinder. And eventually, it should show up as a wet or sooty plug.
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Old 02-25-2021, 01:40 PM   #4
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Default Re: New misfire - sticky valves?

Do you have a vacuum gauge ? If so see what its reading , see if low and steady or it fluctuates . Check for a leak at the vacuum wiper connectors , and vacuum brake , next i would eliminate each cyl one by one and see if itll tell you which one . Next Id do a compression check on that cyl and on each side of it . If everything is okay idstart looking at fuel or electrical . Your vacuum should be a steady 19-21 if a healthy motor . High mileage may be 16-19 but always a steady needle . A bouncing or dropping needle indicates a sticky valve or dead cyl ( plug , wire , vacuum leak , etc . Good luck . Im a little far from you but willing to help .
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Old 02-25-2021, 02:10 PM   #5
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Default Re: New misfire - sticky valves?

Thanks for the tips guys. I just ran a compression test on all cylinders. All cylinders reported in at around 75 PSI except for #7 which reported in at ZERO. I guess that's the culprit. Any advice on how to un-stick those valves?
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Old 02-25-2021, 06:12 PM   #6
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Default Re: New misfire - sticky valves?

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With the piston at the top of the compression stroke so the stuck valve is off of the cam, go through the spark plug hole and squirt some penetrating oil around the offending valve and hopefully onto the valve stem. Then, after a while, with a screwdriver or rod to the top of the valve, lightly tap with a mallet. With an engine that has been recently in service, the valve should drop right down. Then run some more MMM through the carb while jazzing the throttle up and down.

In the future, add about 4 ounces of MMM to each tank of gas.
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Old 02-25-2021, 08:03 PM   #7
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Default Re: New misfire - sticky valves?

Should I also add some MMO to my oil?
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Old 02-26-2021, 08:05 AM   #8
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Default Re: New misfire - sticky valves?

Pull the plug in that cylinder and you can observe the exhaust valve directly below the plug hole. If that one is sticking open you will be able to see it.
You could remove the intake. You can see the valves in there and might be able to manipulate them up and down.
Squirt some penetrating oil anywhere you can that might get around the valve stems. (down the port for instance).
If you take another movie hold the camera sideways. It comes up bigger on the screen.

Fwiw the only time I experienced sticky valves was in a Y block. I was trying to be clever and was burning some very old fuel. In that motor it manifested itself by bending the pushrod.

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Old 02-26-2021, 09:02 AM   #9
51 MERC-CT
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Default Re: New misfire - sticky valves?

Take a peek into #7 plug hole, you may or may not be able to see something like this.
A burnt exhaust valve spotted after chasing the source of some of the same symptoms.



Attached Images
File Type: jpg burnt.jpg (48.1 KB, 299 views)
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Old 02-26-2021, 02:26 PM   #10
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Default Re: New misfire - sticky valves?

Quote:
Originally Posted by JMFL36 View Post
Should I also add some MMO to my oil?
Modern oil is so good that I do not add MMO to the oil. Without leaded gas, where MMO is needed most is in the fuel to give a little lubrication to the valve shafts. I do include one quart of Valvoline VR-1 in each oil change to provide some zinc to those flat tappets.
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Old 02-26-2021, 04:47 PM   #11
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Default Re: New misfire - sticky valves?

Had 2 sticking exhaust valves #4 and #5 in a 8BA recently. With the exhaust valves in the open position sprayed the stems and guides through the spark plug hole with "Brake Clean" and also MMO. Let them set for a couple of days and tapped them down with a brass punch making sure that the cylinders were on the back side of the cam. I believe the sticking was caused by old gas. Topped the tank off with non-ethanol fuel and some MMO. No sticking since.
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Old 02-26-2021, 06:15 PM   #12
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Default Re: New misfire - sticky valves?

You might try starting the engine at night and looking at the plug wires and distributor cap in the dark. You'd be surprised how much arcing shows up that way.

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Old 02-26-2021, 11:43 PM   #13
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Default Re: New misfire - sticky valves?

Quote:
Originally Posted by 51 MERC-CT View Post
Take a peek into #7 plug hole, you may or may not be able to see something like this.
A burnt exhaust valve spotted after chasing the source of some of the same symptoms.
Had one of these on my 36. Compression was around 30lbs, Bruce L thought that was high from the culprit picture valve. Replaced it with a nice gentleman's help here sending me a good used valve setup.

Exhaust valves are usually the culprit. They receive all the heat and carbon. But sometimes it's the intake valve being burnt from a lean situation. Usually you can figure that out, if it is firing (electrical solid) then it back fires or pops out the carb.

yes you can do a mmo dump down the carb from time to time. It will not hurt. Cheap. I do it just because, once a year as regular maintenance. Seems to work for me so far. I wouldn't say it if it didn't.

When I first read this, the first thing I thought was electrical. But the compression test rules that out. Best of luck!!!

Last edited by Tinker; 02-27-2021 at 12:18 AM.
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Old 02-26-2021, 11:54 PM   #14
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Default Re: New misfire - sticky valves?

If you want to waste a couple bucks and explore your tech side. You can buy something like this. Engine snake camera. (I'm not recommending this one, there are plenty of these types of things nowdays so look around). Doubles as a home colonoscopy (kidding!!! yikes). Again I don't recommend this one. hahaha

https://www.amazon.com/Inspection-Fa...42732349&psc=1




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Old 02-27-2021, 08:23 AM   #15
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Default Re: New misfire - sticky valves?

Thanks for all the advice, guys. Much appreciated. I ran several more compression tests and #7 is definitely the cause of the misfire. I got sporadic compression readings anywhere from 75 to 0 from #7, while all other cylinders reported consistently around 75. I also noticed my plugs, all of them, were somewhat black. So I am suspecting there is some carbon buildup on that exhaust valve stem. I need to lean the carb out once I get everything back together. But first my plan is to spray some brake clean through the plug holes around all the exhaust valves as wife cranks the motor. Then let it sit for a few hours and repeat until I get good compression out of #7. Then repeat one more time, but with MMO instead of brake clean this time. Sound like a reasonable plan?
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Old 02-27-2021, 08:27 AM   #16
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Default Re: New misfire - sticky valves?

I don't know about brake clean, wouldn't you want something that will add lubrication rather than wash lube away? I don't know.

If it is the exhaust valve, you could put something on it and lean on it while the engine is cranked. Make sure it is moving up and returning when it is supposed to.
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Old 02-27-2021, 11:12 AM   #17
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Default Re: New misfire - sticky valves?

Mart, I want to try and clean what I suspect is some carbon on the valve stem first, then lube with MMO after. Make sense?
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Old 02-27-2021, 02:13 PM   #18
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Default Re: New misfire - sticky valves?

I happen to have a scope-cam and took a short video of what I found today while soaking the valves with PB Blaster. Here's a link to that video -
https://photos.app.goo.gl/Sro1BG9P1i9JLNbM9

The sticking valve is the #7 INTAKE valve. When I crank the motor the valve lifts as it should but does not return. With just a little pressure I can push it back down into place. I then hand-turned the motor till the valve was just a little open, and using a 90 degree awl I was able to lift and lower the valve with very little resistance. I can also spin the valve fairly easily.

So I'm assuming I have a broken valve stem or spring. Sound right?
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Old 02-27-2021, 02:34 PM   #19
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Default Re: New misfire - sticky valves?

Any valve that can be pried up that easy has something broken. Probably the spring.
Take the intake manifold off to confirm. Then the head has to come off to fix whatever is broken.
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Old 02-27-2021, 02:34 PM   #20
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Default Re: New misfire - sticky valves?

Horseshoe clip may have come out.
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