Frequently Asked Questions: I have an Atomic 4 in my sailboat. I just measured the compression and got 0 for cylinder #1, 80 for cylinder #2, 120 for cylinder #3 and 120 for cylinder #4. I know the zero reading means a stuck valve, but does the 80 reading in the adjacent cylinder mean anything? Any recommendations on a plan of action?

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FAQ: General Information

8. I have an Atomic 4 in my sailboat. I just measured the compression and got 0 for cylinder #1, 80 for cylinder #2, 120 for cylinder #3 and 120 for cylinder #4. I know the zero reading means a stuck valve, but does the 80 reading in the adjacent cylinder mean anything? Any recommendations on a plan of action? - Top

Your instinct that the (relatively) low compression in cylinder two somehow relates to the "0" compression in number one is very astute. Questions concerning the way in which certain findings relate to each other always take me back to my Air Force career in aircraft accident investigation.

We always held strongly to the concept of a single primary cause of accidents. This meant that as findings of various failures and discrepancies emerged during the investigation, we wouldn't rest until we identified the cause and effect of all the findings and arranged them into a specific sequence of events that led to the accident. In this way, one could eventually (by looking further and further upstream in the sequence) discover the single original failure which made a particular accident inevitable.

Applying this rationale to your situation, I can see a possible sequence of events, starting with a partial head gasket failure between the first two cylinders.

We know from historical precedence that head gasket failures typically occur between two adjacent cylinders, that they lead to some lessening of compression, and that they frequently result in cooling water getting into the combustion chambers of the adjacent cylinders.

Whenever a small amount of water continues to enter a cylinder, the likelihood of valves sticking can also be expected to increase, until one of the valves (probably an exhaust valve in the first cylinder in your case) becomes stuck in the open position.

A bit of background information would probably have come to the accident board's attention by this time, which is that engines throughout most of the 1970's had asbestos head gaskets installed by the factory. These were extremely tough gaskets, and they seldom failed catastrophically. They would, however, become more and more brittle, until the constant sequencing of compression back and forth between any two adjacent cylinders eventually led to a miniscule amount of movement between the gasket and mating surfaces of the block and head.

This condition could exist for years as nothing more than a slight reduction in compression in the two adjacent cylinders. However, if this movement between the head gasket and block/head mating surfaces progresses to the point that it intercepts one or more of the nearby cooling water passages, then small amounts of water would be drawn into one or both of the affected cylinders.

With this "suspected" sequence of events giving direction to our investigation, we would, of course, look for supporting evidence. If your boat had crashed into a mountain side, we would have been looking for pieces of the first and second combustion chambers, so that we could inspect them for physical evidence of water damage (rust-colored residue mostly).

Thankfully, your boat hasn't crashed. So, in terms of what to do, two things come to mind:

1) You could decide to make an attempt to free the stuck valve in the first cylinder by inserting a bent screwdriver or "L" shaped Allen head wrench in through the spark plug hole and pressing on top of the valve.

If you're able to free the valve, you could squirt Marvel Mystery Oil into the first two spark plug holes and try to restore the condition of the first two cylinders to that which existed prior to the valve sticking. If compression readings continue to reflect 120 psi in the last two cylinders and 80-ish in the first two, you would have additional evidence that a head gasket might be the cause.

2) If you're unable to free the valve, you'll likely have to remove the head. With the head removed, you'll be able to free the valve more easily, and you can inspect the first two combustion chambers for water indications.

With the head removed, you'll also be able to determine whether or not you had a hard, brittle asbestos head gasket, and (more importantly) whether the part of the gasket between cylinders one and two came free from the block and head quite easily - while it had to be scraped off the rest of the block with considerably more effort. - Updated: December 4, 2003

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8. I have an Atomic 4 in my sailboat. I just measured the compression and got 0 for cylinder #1, 80 for cylinder #2, 120 for cylinder #3 and 120 for cylinder #4. I know the zero reading means a stuck valve, but does the 80 reading in the adjacent cylinder mean anything? Any recommendations on a plan of action? - Top: Your instinct that the (relatively) low compression in cylinder two somehow relates to the "0" compression in number one is very astute. Questions concerning the way in which certain findings relate to each other always take me back to my Air Force career in aircraft accident investigation.

We always held strongly to the concept of a single primary cause of accidents. This meant that as findings of various failures and discrepancies emerged during the investigation, we wouldn't rest until we identified the cause and effect of all the findings and arranged them into a specific sequence of events that led to the accident. In this way, one could eventually (by looking further and further upstream in the sequence) discover the single original failure which made a particular accident inevitable.

Applying this rationale to your situation, I can see a possible sequence of events, starting with a partial head gasket failure between the first two cylinders.

We know from historical precedence that head gasket failures typically occur between two adjacent cylinders, that they lead to some lessening of compression, and that they frequently result in cooling water getting into the combustion chambers of the adjacent cylinders.

Whenever a small amount of water continues to enter a cylinder, the likelihood of valves sticking can also be expected to increase, until one of the valves (probably an exhaust valve in the first cylinder in your case) becomes stuck in the open position.

A bit of background information would probably have come to the accident board's attention by this time, which is that engines throughout most of the 1970's had asbestos head gaskets installed by the factory. These were extremely tough gaskets, and they seldom failed catastrophically. They would, however, become more and more brittle, until the constant sequencing of compression back and forth between any two adjacent cylinders eventually led to a miniscule amount of movement between the gasket and mating surfaces of the block and head.

This condition could exist for years as nothing more than a slight reduction in compression in the two adjacent cylinders. However, if this movement between the head gasket and block/head mating surfaces progresses to the point that it intercepts one or more of the nearby cooling water passages, then small amounts of water would be drawn into one or both of the affected cylinders.

With this "suspected" sequence of events giving direction to our investigation, we would, of course, look for supporting evidence. If your boat had crashed into a mountain side, we would have been looking for pieces of the first and second combustion chambers, so that we could inspect them for physical evidence of water damage (rust-colored residue mostly).

Thankfully, your boat hasn't crashed. So, in terms of what to do, two things come to mind:

1) You could decide to make an attempt to free the stuck valve in the first cylinder by inserting a bent screwdriver or "L" shaped Allen head wrench in through the spark plug hole and pressing on top of the valve.

If you're able to free the valve, you could squirt Marvel Mystery Oil into the first two spark plug holes and try to restore the condition of the first two cylinders to that which existed prior to the valve sticking. If compression readings continue to reflect 120 psi in the last two cylinders and 80-ish in the first two, you would have additional evidence that a head gasket might be the cause.

2) If you're unable to free the valve, you'll likely have to remove the head. With the head removed, you'll be able to free the valve more easily, and you can inspect the first two combustion chambers for water indications.

With the head removed, you'll also be able to determine whether or not you had a hard, brittle asbestos head gasket, and (more importantly) whether the part of the gasket between cylinders one and two came free from the block and head quite easily - while it had to be scraped off the rest of the block with considerably more effort. - Updated: December 4, 2003

[e-Mail the FAQ's] - [Search our FAQ's] - [Question Not Answered?]