Testing of Switch Box and Engine Block

[Wiggy]

I've stripped a 1977 Merc 20hp as it was only running on one cylinder (stripped as I needed some of the parts for my other motor). Occasionly the motor would run on both cylinders but after five minutes (or when it was warm) it would only run on one again.<br /><br />Now I'm 100% sure it either the Switch Box or Engine Block that's the culprit. But how can I test them when they're seperate (not attached to the motor)?<br /><br />Can a cold compression test on the block give a 100% safe result?

 

[WillyBWright]

Re: Testing of Switch Box and Engine Block

You should've diagnosed the problem before you took it apart. An invisible hairline crack in the block is all it takes to make hours of work and lots of money in parts a total waste. I dunno, can you mangaflux aluminum? A compression test wouldn't detect it unless there was a gaping hole you could see anyhow.<br /><br />The switchbox can only be tested with an intact ignition system. You test output and can't do that unless things are put together.<br /><br />At this point, I'd consider that motor as nothing more than a source for parts.