Mercruiser 7.4L - Testing & Re-Installation


I decided to test run the engine before installing it back into the boat.  The electrical hookup was fairly straight forward and I tapped into the wiring harness connector to simplify the connections.

One of the challenges was to move the engine, now weighing about 1,000 lbs., from the middle of the garage out to the doorway so that it would exhaust to the outside.  I used some dollies to move the engine  and set it up for the test run.  Below is a picture of the engine all set for testing.

Here is a video of the first start up after the ‘re-assembly’ of the engine. (22 MB)

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The leak test after the rebuild showed very good numbers, so that is a good thing.  - the end.

Made on a Mac

Below are the compression test results after the valve job - shown in the column ‘2012’ along with compression results from prior years.  The dark blue line in the graph is ‘after’ and the dotted pink line is ‘before’.  It looks like I fixed the problems with the middle cylinders, but #1 seems just slightly low.  I’ll have to do some leak testing to see if it is a valve adjustment issue.  The ‘2011’ column are the figures before the valve job.

The statistics show a 12 psi improvement in the compression and a much tighter range as shown by the lower ‘standard deviation’.

I also did a leak test prior to putting the engine back in the boat.  Below are the ‘Before” and ‘After’ leak test results.  You can check out the Stringer and Bulkhead Repair pages for the engine installation.