1950s '55 Eldorado - Sticking Inlet Valve

[Lockhouse]

Hi All,

I've got a suspect sticking inlet valve on my '55 Eldorado. Standard 331 with Dual Rochesters.

Idle, mixture and timing are all OK. Plugs and HT leads are new.

What started out as a "lazy" valve occasionally missing has now backfired through the carb a couple of times so seems to be getting worse.

I've just added some petrol additive to see if that helps but assuming the worse, what's the best course of action? I was thinking doing a compression test to identify the cylinder but not sure how to proceed after that. Everything else seems absolutely fine.

Best regards,

Andy


 




 

[Jeff Rosansky CLC #28373]

I'd think a compression test would only help if it is stuck at that time. If it isn't I'd think it would show the same as the other cylinders.
I am a minimally evasive kind of guy. I would do what you're doing with an additive. Everyone has their own magic potion, but I use Marvel's.
For what it's worth, people use Marvel's in airplane engines too. It cleans the guides and prevents morning sickness.

[Lockhouse]

I'd think a compression test would only help if it is stuck at that time. If it isn't I'd think it would show the same as the other cylinders.
I am a minimally evasive kind of guy. I would do what you're doing with an additive. Everyone has their own magic potion, but I use Marvel's.
For what it's worth, people use Marvel's in airplane engines too. It cleans the guides and prevents morning sickness.

Thanks Jeff - we don't have Marvel here in the UK but we have something close. Would you add to fuel, oil or both?

[Big Fins]

A close product may not do the same job. See if you can compare the chemical makeup of both products.

https://marvelmysteryoil.com/     Not sure if you could obtain this in the UK. Shipping may pose a problem.

But, personally, I would use it in both the fuel and crankcase.

[Big Fins]

Here is the Safety Data Sheet on the product. Not sure it will help, but, here it is.

[James Landi]

Andy,

Get yourself a vacuum gauge, carefully read the instructions, and you'll have substantially more information about the overall condition of your engine.  By simply "teeing" into the intake manifold vacuum nipple, you'll know if you have a misfiring cylinder due to a stuck or burnt valve, you'll have other essential readings regarding the health of your engine .  The vacuum gauge is an essential tool for diagnosing engines. 

Many of us make the mistake of starting and idling our engines without getting them up to operational temperatures. This practice causes heavy condensation to rain down internally, especially on the valve train.. and often causes valve stems to rust and get stuck in the valve guides... If after performing a vacuum gauge test, you note an intermittent misfire along with a rattling sound, then you have this stuck valve condition. Starting, idling and stopping the engine only exacerbates the amount of water raining down on the valve train.  So you may have to remove the valve covers to investigate and identify those issues.

[Jeff Rosansky CLC #28373]

Thanks Jeff - we don't have Marvel here in the UK but we have something close. Would you add to fuel, oil or both?

I add to both. But in this situation, oil would be the best bang for your buck. Need it to slowly, and gently clean up in there.

[Lockhouse]

Thanks for the replies - will be carrying out further tests over the next week or so and will report back.

[1959Fleetwood]

Hello Andy, Let me throw in my five cents. A compression test with a cold engine is something to start with. To determine if low compression is due to a sticking or leaking valve or to a bad piston or rings you can spray oil on top of the piston. If the reading with oil is higher then the first test without oil then you have a worn out piston or rings. If the test with oil is the same as in the first test then you have to determine witch valve is leaking/sticking. The second test you can perform is a cylinder leak down test. You have to make a test nipple that you can screw in the spark plug hole. Connect a hose with a pressure regulator to that nipple. Make sure that the piston in the cylinder you want to test, is at top dead center with both valves closed. Now you can turn up the pressure regulator gently to allow compressed air into the cylinder. 29 PSI max will do the trick.
Now if you hear escaping air in the carburetor you know that the intake valve is leaking/sticking. On the other end when you hear the same noise at your tail pipe you know that an exhaust valve is leaking.
Hope this helps to solve your problem.

Matern Harmsel
CLC 15331