Help!!!! No compression in #6 cylinder

[Gordon1987]

I just did a rebuild on my m20 block and my #6 cylinder has 0 compression. Cylinders 1-5 have 160psi compression.

Think it may be a burnt valve because before I took the engine apart I couldnt rev past 2k under load. Now I can.

[Paradox]

could also be a small piece of carbon preventing a valve from closing. Try some seafoam. It might clear it up

[Gordon1987]

I have had friends use seafoam, and they all regret it. Is there an alternative?

[slammin.e28]

I have had friends use seafoam, and they all regret it. Is there an alternative?

This is a first.

Get some BG compression restore then. BG# 109.

Seafoam is awesome, why don't your friends like it?

[Gordon1987]

Where can I get the bg#109...

One of my friends use seafoam and his car had trouble starting for awhile

[slammin.e28]

Lots of indie shops use BG. The one I work at does and we use it with great success. About half way down the page.

I use the MOA in my oil.

Distributor locater.

You also get roadside assistance when you use this stuff...

IDK about other places, but we'll sell the stuff outright. Some places may just do the service for you. Have to ask.

[Adrian_Visser]

Why did you double post this thread?

If you have zero compression in the cylinder don't expect a can of snake oil to fix it.

Seafoam is the real deal for removing carbon deposits though.

Did you replace your rings on the "rebuild"?

Are you sure that you installed them correctly i.e. you staggered the ring gaps and that the end gap is correct?

[Gordon1987]

Yea brand new rings and installed them correctly

[slammin.e28]

Note: I'm going off of the possibility of post #2 being the problem.

I'd do a leak down test and see what happens. Put the tester in the spark plug hole with the piston at TDC compression and see if the air comes out of the intake/exhaust/dipstick tube. That should nail down a burnt/stuck valve or rings installed incorrectly.

Cylinder leakdown test-

While a compression test is a dynamic test (engine moving), a cylinder leakdown test (C.L.T.) is a static test (engine at rest). The compression test measures how much pressure the engine can produce while cranking; in contrast to the C.L.T., which measures how much pressure is lost in the engine. In a C.L.T. the engine is placed on TDC of the cylinder in question and using a similar type of connector as the compression test, we fill the cylinder with pressure. The tester then measures the volume of air needed to maintain a predetermined pressure in the cylinder. This reading is expressed in a percentage. Good cylinder leakdown readings should be below 5-8%.

The great thing about C.L.T. is that it deals with how well the cylinder is sealing and nothing else. The readings are not affected by carbon deposits, cam timing, or even engine cranking speed.

Another great feature of the C.L.T. is the fact that you can hear where the air is leaking out of the cylinder. When a cylinder has high percentage of leakage, first check the oil filler cap. Do you hear a hissing sound? If so, you may have pressure leaking by the rings. Is there air escaping out the exhaust? Is it escaping out the intake system? Then a burned valve may be the problem. If two adjoining cylinders have similar low readings and you hear leakage out the other cylinder, then a failed head gasket may be the problem.

Being able to pinpoint the exact source of the compression loss will tell you where the problem is; and not just that you have one. This knowledge will greatly assist you in the next step… the repair.

[Gordon1987]

Thanks for the inputs...

[Gordon1987]

When using the seafoam to clean the combustion chamber/valves where do u insert the seafoam?

[slammin.e28]

When using the seafoam to clean the combustion chamber/valves where do u insert the seafoam?

I'll dump the whole can in the fuel tank before filling an empty tank.

You're supposed to feed 1/3 into the intake/vacuum system, 1/3 in the fuel, and 1/3 into the oil. There's directions on the side of the can.

[Gordon1987]

Ok

[g.ruff561]

Here's another dumb question, but does anyone have a detailed pic showing exactly which intake/vacumn hose on the M20 engine to use for Seafoam. I have had conflicting information on which hose to use. Thanks in advance for your advice................G.