Join Date: Feb 2010
Location: Narragansett Bay
Thanked 224 Times in 209 Posts
Rep Power: 7
Re: Compression test 2GM20F
According to Mr. Google, your motor is rated at 3400 rpm for continuous use. That's just the rpm you should not exceed for lengthy periods. Wide Open Throttle rpm should be 3600 rpm. It really sounds like you've been over propped for a long long time, if these were the rpms you were getting years ago. If you don't correct that, things will get worse and your repairs with be for naught.
However, clogging the exhaust elbow to the point of stoppage and running the oil low for 500 nm had to have done some damage. It's just hard to tell what exactly. I would even wonder if water flushed back into the cylinders with that elbow stoppage. However, other than the low compressions, you have no unusual starting, smoking or noises. That either defies reality or is a testament to just how tough these motors really are.
With the limited experience you describe, I suppose it's possible you don't know they are unusual and it might be wise to get someone aboard to take a look/listen to help you diagnose.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.