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post #1 of 5 Old 04-06-2014 Thread Starter
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yanmar 2QM20 to 3GM30F repower

Hello - I have a '79 C&C 34 with a trusty 2QM20 and have the opportunity to "upgrade" to a well maintained and conditioned 3GM30F. Primary interest is the 30 is freshwater cooled, smaller, lighter and a bit more power. I think I have a handle on the bed spec dimensions, the 30 has a bit smaller footprint. Wondering if anyone has done this repower with these models before and can offer and advise or other considerations. The 30 comes with a 2.61 transmission, so I will need a new prop. I think the exhaust set up is similar.. etc, etc;
Many thanks!
ps. still snowbanks here is Portsmouth NH...
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post #2 of 5 Old 04-06-2014
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Re: yanmar 2QM20 to 3GM30F repower

Besides the footprint itself, be sure to check side clearances up high - alternators/belt pulleys may be in different spots?.. the shaft coupling position vs engine mounts may be slightly different too, will the original shaft fit?

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ps. still snowbanks here is Portsmouth NH...
Yuck....

Ron

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post #3 of 5 Old 04-06-2014
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Re: yanmar 2QM20 to 3GM30F repower

Our C&C 32 was upgraded from it's original A-4 to a 3GM30F. The shaft was replaced from it's original 7/8" to a 1" diameter shaft and a fixed 3 blade prop of an unknown size. The motor itself is a tight fit and is difficult to work on.
Ours is fresh water cooled.
Other than the engine mounts, the fuel tank and the shaft, there were no further modifications.
However, the exhaust outlet was not changed and it is smaller by 1/2". It does not seem to cause any problems. The engine has almost 600 hours on it and has run flawlessly for 6 years now.
It's a bit over powered but it is nice to know that I can travel through some of our Gulf Island passes with the tide running and make it. It will cruise all day long at 7 knots and 2700 rpm.

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post #4 of 5 Old 10-23-2014
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Re: yanmar 2QM20 to 3GM30F repower

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Originally Posted by Dog Ship View Post
Our C&C 32 was upgraded from it's original A-4 to a 3GM30F.
It's a bit over powered but it is nice to know that I can travel through some of our Gulf Island passes with the tide running and make it. It will cruise all day long at 7 knots and 2700 rpm.
Interesting. I have a C&C 32 I am considering re-powering, I find the Yanmar that's in the boat just doesn't have enough power for 'cruising'. You are the second owner I have come across with a 30HP. I was thinking 25 but maybe I am setting my sights too low.
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post #5 of 5 Old 10-25-2014
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Re: yanmar 2QM20 to 3GM30F repower

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Originally Posted by markstoport View Post
Interesting. I have a C&C 32 I am considering re-powering, I find the Yanmar that's in the boat just doesn't have enough power for 'cruising'. You are the second owner I have come across with a 30HP. I was thinking 25 but maybe I am setting my sights too low.
The prop is probably more important than a few more horsepower. Make sure you have a correctly sized prop before considering an engine change. The important thing is the thrust developed by the prop, not the power produced by the engine. Delivering more power to an undersized prop will not help anything.
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