jollyroger

HELP!

I am looking at an older boat with pair of Merc 465hp motors, Bravo 1's. The motors have approximately 500 hours on them. Allegedly they were easy hours, guy who owned boat was pretty anal, as the boat itself is in great shape

I need to know more about these motors? What numbers should I be looking for in a compression test. What other tests do I have the mechanic perform?

Woodsy

KNOT-RIGHT

A leak down test would be the best. However if you only do
a compression check look for even compression between
all cylinders. They should be within 10-15 percent of each
other. Simple things like inspecting plugs and fluids.
How the engines run and idle on the water will reveal most of all problems. Engines can sound real nice on the hose.
always run them under load.


Hope this helps
Gerry

HOTTZU98

Find a good shop that can run it on a Dyno you cant hide problems with a dyno run.

jollyroger

THANKS!!

But I have one more question.... I think I understand the concept of a leak down test, pressurize the cylinders and see what happens.

But what are the specifics? what pressure and for how long? Does it require special gauges?

Sorry for the newbie questions... this is my first foray into a twin engined boat and I cannot afford to be hosed...

Thanks again!

Woodsy

FOUNTAINATLAST

They do have a special gauge set-up to test leak down and it will tell you the percentage of leakage in each cylinder. Obviously the valves need to be closed during these tests.

KNOT-RIGHT

1) Remove valve covers
Insert this tool into spark plug hole while noting both rockers are loose on the cylinder. Inject compressed air into cylinder.
Regulate air to about 60 psi on first gauge. The leakage percent will show on the second gauge. With ME?

Repeat the above step to all cylinders
Again you are looking for even readings.

KNOT-RIGHT

The prefered method is above. If that gauge is not available atleast use this. Disconnect ignition coil or better yet pull your
ignition lanyard and insert this into cylinders. Compresion
varies with cam duration static compression so there are no set #,s Again you are looking for even readings Ill guess
in the neigborhood of 150 psi each cylinder.

As I stated above a Good ride in the boat with a Gear head on board goes a long way .Your best diagnostic tool is actually the boat.


Good Luck

Dave_N

Proper compression test and leak-down procedure from Mercruiser service bulletin.