Leak down numbers-feedback

[poboy427]

I have been fouling plugs all the way around and had been pursuing the possibility of leaking intake gaskets. Before pulling the intake and resealing I ran a full leak down today as I was nervous about the bad experience I had with my 660 carbs and feared I washing out the rings.

On my leakdown gauge all my numbers fall well into the "Low" scale on my gauge. 40% is the start of the moderate leak scale. I only have 119 miles on the engine so I am thinking that my best numbers indicate that the rings in those cylinders have seated and the double digit numbers indicate cylinders that have not yet seated.

If the new intake gaskets don't stop plug fouling then I think I will look again at my MSD distributer-rotor phase maybe. I have had 2 ignitions, 3 caps and 3 sets of wires. Running cheap Autolite 45 plugs for now until I get this sorted. Perhaps Autolite 47 would help. The car idles pretty good but the plugs drop out fairly fast when running down the street.

Someone also mentioned running a ground cable from the engine directly back to the battery.

Open to all feedback.

Thanks Ray

[poboy427]

Forgot to post my numbers:

Cyl 1-8%
2-5% This bank fouls sooner and pushes fuel/oil vapor (raw mostly)
3-5% All plugs were uniformly oil/fuel fouled out. Oily to the touch.
4-23%

5-32%
6-12% This bank fouls later and really does not put out much.
7-21% Pipe is dark though.
8-5%

Thanks for any input
Ray

[undy]

I think I remember in another thread you're running Dove heads and I'm assuming intake too. If so, you might have a mis-match on the heads to intake. I'm running a Dove Tunnel Wedge intake bolted to a set of CNC'd MR Eboks. I had to have work done to Dove's intake by my local macinine shop to render it useable. It required re-cutting the intake faces. The reason I'm mentioning that is if your intake/head surface mating area is not right you would have the right conditions for an oil sucking intake leak, hence the plug fouling.

I'd wait another 4 or 5 hundred miles and run a new compression test..

[RICK LAKE]

poboy427 Ray you have a PM Rick. I have CSX #58 and CSX#428 blocks, we are neighbors

[ERA Chas]

Ray,
Any progress on this problem to date? Curious about the intake leak possibility.

[poboy427]

Still working on the whole deal. I will post results when I know more.

Ray

[Rick Parker]

The manifold mismatch will not have any affect on leakdown %'s. Leaking valve seats (hissing heard through carb) or rings (hissing heard through breather/valvecover opening) are the tell tale signs of potential problem. Pressurize from a source at 100 PSI through spark plug opening and read the pressure on secondary pressure gauge. The difference between the two gauges is interpreted as your loss in %. It has nothing to do with what the compresssion ratio is, only the condition of valves and rings. The test assumes head gasket is uncompromised. Do it on a thoroughly warm engine. Do one bank, then rewarm the engine for the other side. 2% - 5% or less is target.

[mr0077]

Poboy, a couple of things...Do you have a conventional dual-gage leakdown tester? If so, what were the actual readings (like 95/100 or 112/120, lbs air pressure in vs lbs sir pressure held)? And even though it is a bit of a challenge, each cylinder needs to be tested at TDC or you won't get good readings. The ratio of the two readings is your percent leakdown. Rick is right that the leakdown tests only the sealing of each individual cylinder...rings, valves and head gasket. Additional note, a leaking exhaust valve can be heard as a hiss through the exhause pipe(s).

Secondly, if/when you pull the intake, check the ports for oil. If you have oil on the walls of the ports in the heads but not on the mating intake runners you almost certainly have an intake gasket leak. If the intake and ports are dry (of oil), you've got something else going on...bad valve guide seals or rings cracked or not seated.

Let us know what you find.

[Rick Parker]

mr007

I went brain dead re the exhaust valve .......DUH!