Leaky Valves--Carbon Removal

Here is a trick that I learned from my flying days:

Airplane engines are notorious for developing valve deposits and have very stringent compression mandates per cylinder. At $500-$900 per cylinder to rebuild it, any alternatives to get you compression back are welcome.

To get my compression back (or to narrow down a culprit valve that is leaking), we would connect an air line to the spark plug hole. With the piston on TDC, both valves will be closed and this will allow the cylinder to pressurize. Now, with a rubber mallet, "POP" each valve. The air pressure and the spring will both act to close the valve with more force than during operation. A LITTLE AIR WILL DO! START LOW AND WORK HIGH AS LEAKAGE AND DEMAND DICTATE. Works great.


Unlike carb cleaner or oven cleaner--very corrosive, Marvel Mystery oil is very good at softening carbon deposits and is compatible with oil. This is a good thing for that which sneaks past your rings. It also is rubber (seal) friendly.

How to use:

We are after a leaking valve, right? We want the marvel to get to the leak source. The best way to do this is to place the piston on the compression stroke BTDC (slightly). Next, fill the cylinder up with Marvel. Screw in the spark plug.


We all know that fluid cannot be compressed and we have now effectively "hydro-locked" the engine. Therfore, Use a socket on the crank to roll the engine through TDC. If you have a leaky valve, you will compress the fluid and it will squirt past the leak. You may even hear it spray. If you have the intake/exhaust off, you will likely be able to spot the troublesome valve(s) by the leakage. Repeat a few times and let it sit over night. Then, if necessary, repeat the valve staking procedure above. If it is truly a carbon problem, this will correct the problem.

BTDC=Before Top Dead Center

TDC= Top Dead Center

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