Finally got the chance to launch and conduct sea trials on my 85' Hunter 28.5 purchased in January. My main concern is the clattering sound in the engine/drivetrain when engine revs are pushed past the 2500 rpm mark. Is this normal? What rpm/speed range is the Yanmar 2gm20 usually operated at? I had the boat surveyed before launch, and all seemed well with the prop/ support shaft and bearing. I also installed new anodes tightly, in the same location as the old ones. If this is a problem, any thoughts on what's causing it, and possible cures. Hope get feedback ASAP as I haven't signed off on the mechanicle holdback on the deal as yet. Thanks Eric
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Marc Honey
Yanmar
My 87 28.5 seems to run the smoothest around 1800 - 2200 and 2800 rpm. I often run it at 3200 rpm for awhile to make sure it gets up to temp. It vibrates a bit around 2900-3100, but smooths out at 3200. Need to check engine/shaft alignment. Also I'd check-out all motor mounts. Good luck.
My 87 28.5 seems to run the smoothest around 1800 - 2200 and 2800 rpm. I often run it at 3200 rpm for awhile to make sure it gets up to temp. It vibrates a bit around 2900-3100, but smooths out at 3200. Need to check engine/shaft alignment. Also I'd check-out all motor mounts. Good luck.
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Wally Boggus
Yanmar
I have the same motor in a Beneteau 281 presently and my experience is exactly the same as Marc's. The motor is very reliable if you feed it good fuel and additives but it does vibrate the hull within certain rpm ranges. However, I have never experienced any mechanical clatter that you describe. I would check the condition of rubber on the motor mounts as any metal to metal contact there would create alot of racket. Also, check that the motor is propery positioned on the mounts (refer to the yanmar manual).
I have the same motor in a Beneteau 281 presently and my experience is exactly the same as Marc's. The motor is very reliable if you feed it good fuel and additives but it does vibrate the hull within certain rpm ranges. However, I have never experienced any mechanical clatter that you describe. I would check the condition of rubber on the motor mounts as any metal to metal contact there would create alot of racket. Also, check that the motor is propery positioned on the mounts (refer to the yanmar manual).
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Stephen Ostrander
2GM20
You have to remember that marine diesels aren't the smoothest engines in the world. This is a 2 cylinder engine and they do tend to vibrate. As the previous posts mentioned, there are several things to check: 1) Prop is balanced, not dinged or bent. 3- blades are smoother than 2-blades. 2) Shaft is straight and true, and aligned with engine. 3) Cutless bearing is not worn or loose. 4) Motor mounts are tight, not worn.
You have to remember that marine diesels aren't the smoothest engines in the world. This is a 2 cylinder engine and they do tend to vibrate. As the previous posts mentioned, there are several things to check: 1) Prop is balanced, not dinged or bent. 3- blades are smoother than 2-blades. 2) Shaft is straight and true, and aligned with engine. 3) Cutless bearing is not worn or loose. 4) Motor mounts are tight, not worn.
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Bob England
Shaft centering and alignment
A couple of other people have reported problems when the shaft is not centered properly in the stern tube. At certain RPMs, the prop shaft can actually bang on the bottom of the boat. Poor alignment makes this worse.
A couple of other people have reported problems when the shaft is not centered properly in the stern tube. At certain RPMs, the prop shaft can actually bang on the bottom of the boat. Poor alignment makes this worse.
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Tom Long
Prop shaft
Definitely check out the prop shaft alignment and the coupling between the transmission and shaft. Two years ago we had to replace the shaft and coupling because the coupling had loosened and scored the shaft to the point where we had significant vibration at certain rpm's. It was about a $900 bill.
Definitely check out the prop shaft alignment and the coupling between the transmission and shaft. Two years ago we had to replace the shaft and coupling because the coupling had loosened and scored the shaft to the point where we had significant vibration at certain rpm's. It was about a $900 bill.
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Eric Grant
RE: 2 GM 20 Replies
Sounds like theres a common thread to most of the replies to my posting. Will check engine mounts/alignment and prop shaft coupling, as Cutlass bearing and prop seem to be in good shape. Thanks to all respondents once again for the quick, informed replies! Regards Eric
Sounds like theres a common thread to most of the replies to my posting. Will check engine mounts/alignment and prop shaft coupling, as Cutlass bearing and prop seem to be in good shape. Thanks to all respondents once again for the quick, informed replies! Regards Eric
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Ernie Rodriguez
Perfect Pitch Propeller
Cruising Design, Inc. (CDI) makes a two bladed prop designed just for the Yanmar 2GM 20 engine. You may want to check it out. Visit their web site at www.sailcdi.com.
Cruising Design, Inc. (CDI) makes a two bladed prop designed just for the Yanmar 2GM 20 engine. You may want to check it out. Visit their web site at www.sailcdi.com.
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doug
From Experience........
All the things mentioned in the previous posts are possibilites. In our case it was the shaft literally slamming into the stern tube. It should be perfectly centered. From under the boat, if you have your shaft out you would be able to notice wear on tube's inner edge. This engine vibrates the boat to the point of rattle at a couple of rpm ranges. I have talked to 3 Yanmar dealers and this is indicative of this 2 cyl. engin. Find the smooth numbers and stick with them. For smoother ride, on next major haulout, this is how (without a ton of money you can really decrease vibes). 1) replace shaft (go stainless and get from Hunter..much cheaper)if you can afford to. 2) put flexable flange coupler in. PYI in seattle makes a great one. 3) Go three blade if you can afford to. I would recommend campbel sailor if you can't afford lower drag folders and feathering. Theirs is just a touch more drag than standard 2 blade and around $400.00. While your at it a new cutlass bearing (cheap from Hunter parts in FL)and a PYI dripless seal to top her off. Whole deal around $1,000 (figured food and beer into that figure). Have fun! Doug
All the things mentioned in the previous posts are possibilites. In our case it was the shaft literally slamming into the stern tube. It should be perfectly centered. From under the boat, if you have your shaft out you would be able to notice wear on tube's inner edge. This engine vibrates the boat to the point of rattle at a couple of rpm ranges. I have talked to 3 Yanmar dealers and this is indicative of this 2 cyl. engin. Find the smooth numbers and stick with them. For smoother ride, on next major haulout, this is how (without a ton of money you can really decrease vibes). 1) replace shaft (go stainless and get from Hunter..much cheaper)if you can afford to. 2) put flexable flange coupler in. PYI in seattle makes a great one. 3) Go three blade if you can afford to. I would recommend campbel sailor if you can't afford lower drag folders and feathering. Theirs is just a touch more drag than standard 2 blade and around $400.00. While your at it a new cutlass bearing (cheap from Hunter parts in FL)and a PYI dripless seal to top her off. Whole deal around $1,000 (figured food and beer into that figure). Have fun! Doug
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