Plug gap and Compression

[craig newton]

Have an older 1984 Mercruiser 5.7L 260hp (repowered 2003) but don't have an owner's manual. Getting 118 -120 psi on the cyl tested so far (six of eight) and all plugs are gapped at 32. Anyone know if these numbers sound right?

 

[alldodge]

Getting 118 -120 psi on the cyl tested so far (six of eight)

If your gauge is accurate then the compression is low, should be closer to 150
Having 6 of 8 at the pressure is worst if the other 2 are even lower

 

[Scott06]

Have an older 1984 Mercruiser 5.7L 260hp (repowered 2003) but don't have an owner's manual. Getting 118 -120 psi on the cyl tested so far (six of eight) and all plugs are gapped at 32. Anyone know if these numbers sound right?

As pointed out 150 is new . Usually you want to be above 125, when it gets down to 105 or so you have a dead cylinder. were these done with a hot engine? Does it run ok or are you hunting down issues ?

 

[Alumarine]

Gap should be .035" but that won't impact the compression test.
You have all the plugs removed, engine warm and throttle wide open when testing?

 

[craig newton]

As pointed out 150 is new . Usually you want to be above 125, when it gets down to 105 or so you have a dead cylinder. were these done with a hot engine? Does it run ok or are you hunting down issues ?

It overheated; enough to melt the impeller. It was running great and continued to after it cooled down. I was trying to find out if it suffered any obvious damage to the block, heads... was the reason for the compression check. 120lbs in 3, 119lbs in 1 and 118lbs in 4. This was done on a cold engine with the coil wire disconnected. Cranking only.

 

[alldodge]

There all within 10% of lowest, and your 120 may be just the gauge. If its not the gauge then the motor will run fine, just not have as much power as when new

 

[Scott06]

It overheated; enough to melt the impeller. It was running great and continued to after it cooled down. I was trying to find out if it suffered any obvious damage to the block, heads... was the reason for the compression check. 120lbs in 3, 119lbs in 1 and 118lbs in 4. This was done on a cold engine with the coil wire disconnected. Cranking only.

You are likely just fine as AD lays out. Likely with a warm engine before doing the test your numbers will come up a tad, but if its running fine dont worry about it.
biggest issue you may run into from an over heat is blowing a head gasket you would see water in the oil.