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| Gray Marine 491 Sea Scout evaluation |
| Author |
Message |
    
Donovan (Donovan)
| | Posted on Tuesday, September 10, 2002 - 04:02 pm: | 
|
I am considering purchasing a '65 Alberg 30 equiped with the original Gray Marine 491. The boat has been very well maintained and the engine appears to be in good order. I want to evaulate the motors current condition. What steps should I take to get a good idea of the condition and reliabilty of the motor. I was planning on doing a compression test. What tolerances should I be looking for. The boat is out of water, but the owner claims the engine runs well.
Thank you in advance for your thoughts. |
croozertoo
| | Posted on Tuesday, September 10, 2002 - 09:27 pm: |
|
Look at each plug as you remove them for the test. Unless they've been very recently replaced, that will give you a clue to each cylinder's health. Can't give you an exact PSI to look for, but I'd be wary of numbers less than 120. Even then, the most important thing is that all cylinders are with 10% of each other.
A 6 or 8 cylinder engine can run very well with one or even two moderately low cylinders, especially a big, low RPM marine engine. If you find a low cylinder, do a wet test to determine if valves or rings are at fault. A leak-down test is also good if you can do one.
Google can find you plenty of sites on the web that describe both tests. One last thought, pay special attention to the exhaust manifold - ask the owner if he has replaced it recently or if he knows how old it is.
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Donovan (Donovan)
| | Posted on Tuesday, September 10, 2002 - 10:36 pm: |
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Does the manifold question indicate overheating problems? |
croozertoo
| | Posted on Wednesday, September 11, 2002 - 06:34 am: |
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Not necessarily, but they tend to rust from the inside out, allowing water to enter the cylinders. A motor this old should have had several replacements. If it's original, it will need to be replaced for sure.
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