289 Low Compression on Two Cylinders

[LeeFred]

A couple of weeks ago, my 289 started running poorly practically overnight. One day, ran fine...next day, go out for breakfast, and can't hold idle at stoplights, etc. The carburetor is a 600 Holley. I figured it had to be a vacuum leak, and checked all over the intake, but no luck. Even switched out carburetors, but no change. I figured I'd check the compression, and six of the cylinders were at 175-180 on the gauge. However, cylinder 2 was at 120, and cylinder 5 was at 105. I squirted oil in the spark plug holes on these two cylinders, and the compression went up - 140 on #2, and 120 on #5. It appears it could be bad or worn rings, but overnight? I pulled the heads and checked the valves, and this is what I found. This is the intake valve from cylinder #5.

[LeeFred]

In comparison, this is the intake valve from cylinder #6.

[LeeFred]

Here are pics of the intake valve from cylinder #2.

[LeeFred]

In comparison to #2, here is the intake valve from cylinder #1

[Roddster]

Intake valve deposits. Really looks normal. But time to check the valve guides for wear. You might end up doing valve guides and a valve job. But, this isn't why the engine is running bad. There are other things to look into. Two fouled plugs also? Weak coil? Stuck piston rings? Worn cam lobes?.

[LeeFred]

Roddster - the only plug that was fouled was the #2 plug, the others looked "normal" and alike. I pulled the pistons out of #2 and #5 - what would be the symptom of a stuck ring? They're moving freely now that the pistons are out of the block, and the pistons don't show any sign of crud buildup, scuffing, etc. The cylinder walls aren't scored or appear to be damaged in any way. Quite perplexing!

[65 fstbk]

Too late but it is an internal intake leak?