Being new to owning a boat with a Diesel, My 3HMF similar to 3GMF shakes quite a bit at around 1100 to 1600 RPM. So much so that it bangs the shaft on the stern tube. But when your at any other RPM it is fine. I've been told by a couple people that this is normal. My question is, Is this normal? Or would a better alignment solve the problem? Thanks for the help, Doug
- Status
- Not open for further replies.
Have you motor mounts checked.
Doug: Yes, these are NOT the smoothest running engines in the world but I would not think that you should be getting that kind of vibration. I would have the motor mounts checked out. If they are OK, then you may think about having a qualified Yanmar specialist check out your engine. Suppose that it could be something like an injector problem too.
Doug: Yes, these are NOT the smoothest running engines in the world but I would not think that you should be getting that kind of vibration. I would have the motor mounts checked out. If they are OK, then you may think about having a qualified Yanmar specialist check out your engine. Suppose that it could be something like an injector problem too.
T
Tom Schlagel
Shaft Alignment Needed!
Doug, I assume that you are in gear when you notice this vibration. Has the shaft been aligned recently? Have a professional align your prop shaft to the engine - it's only about 1 hour's labor so it's not very expensive. We have it done every other year or so and it takes care of most of the vibration.
Doug, I assume that you are in gear when you notice this vibration. Has the shaft been aligned recently? Have a professional align your prop shaft to the engine - it's only about 1 hour's labor so it's not very expensive. We have it done every other year or so and it takes care of most of the vibration.
S
Stevec
2 votes for a bad motor mount
When it starts shaking, go below and physically observe the motor mounts. I have a 37 and the starboard rear mount could be seen 'vibrating' about an inch while the other 3 did not show any apparent movement. $100 later and an hour of my time did the trick. The actual movement of the engine up/down caused the shaft to bang against the stern tube. When the engine was not running all the mounts appeared to be OK.
When it starts shaking, go below and physically observe the motor mounts. I have a 37 and the starboard rear mount could be seen 'vibrating' about an inch while the other 3 did not show any apparent movement. $100 later and an hour of my time did the trick. The actual movement of the engine up/down caused the shaft to bang against the stern tube. When the engine was not running all the mounts appeared to be OK.
P
Paul Akers
Happened to me once.
I have a 3HM35F in my '88 L37 and I once had that problem at lower rpm's. The shaft was realigned and solved the problem.
I have a 3HM35F in my '88 L37 and I once had that problem at lower rpm's. The shaft was realigned and solved the problem.
G
Gordon Torresen
Shaking and alignment
Alignment of the shaft to the engine does not cause vibration of itself. If the reversing gear flange runs true AND the shaft coupling runs true to a straight shaft, it will not generate vibration. Aligning the shaft to the engine is a misnomer. The shaft is fixed to the boat by the cutless bearing and the stern tube. This is where alignment must start. With the shaft disconnected from the engine, position it in the center of the tube. This can usually be done by flexing the stuffing box hose up and down and sideways. You will feel the shaft hit the tube. Then approximate the center of all this motion and that is where the shaft belongs. Next you align the engine to the shaft - while keeping the shaft in its proper location. This is done by adjusting four motor mounts, any three of which will support the engine. You must assure that the weight of the engine sits equally on all four mounts, not easy. If any one of the top adjusting nuts pulls down on its mount, the loads of the other three are affected. To respond more directly to your post, every piece of rotating machinery has what is known as "a critical speed", where its vibration is the greatest. Balancing techniques can control the RPM at which the maximum vibration is experienced. Your vibration and a certain speed may be its manifestation. The shaft slapping the inside of the tube may well be because the shaft was not properly centered in the tube when the engine was adjusted. This has not ruled out defective motor mounts. Mounts are generally good until the rubber starts to take leave of the steel. This can usually be found by prying them about while looking at the interface. Again, if the load is not equally on all four, the mounting "system" can be considered defective. Consider too, these floppy mounts keep the engine noise out of the hull but what happens when you put that engine in gear and change throttle settings. Look at it!
Alignment of the shaft to the engine does not cause vibration of itself. If the reversing gear flange runs true AND the shaft coupling runs true to a straight shaft, it will not generate vibration. Aligning the shaft to the engine is a misnomer. The shaft is fixed to the boat by the cutless bearing and the stern tube. This is where alignment must start. With the shaft disconnected from the engine, position it in the center of the tube. This can usually be done by flexing the stuffing box hose up and down and sideways. You will feel the shaft hit the tube. Then approximate the center of all this motion and that is where the shaft belongs. Next you align the engine to the shaft - while keeping the shaft in its proper location. This is done by adjusting four motor mounts, any three of which will support the engine. You must assure that the weight of the engine sits equally on all four mounts, not easy. If any one of the top adjusting nuts pulls down on its mount, the loads of the other three are affected. To respond more directly to your post, every piece of rotating machinery has what is known as "a critical speed", where its vibration is the greatest. Balancing techniques can control the RPM at which the maximum vibration is experienced. Your vibration and a certain speed may be its manifestation. The shaft slapping the inside of the tube may well be because the shaft was not properly centered in the tube when the engine was adjusted. This has not ruled out defective motor mounts. Mounts are generally good until the rubber starts to take leave of the steel. This can usually be found by prying them about while looking at the interface. Again, if the load is not equally on all four, the mounting "system" can be considered defective. Consider too, these floppy mounts keep the engine noise out of the hull but what happens when you put that engine in gear and change throttle settings. Look at it!
S
Sam Lust
Bravo!!!
That is the most lucid and succinct discussion of engine alignment I read. A note on this era of Hunters from my experience Next time your boat is out of the water check the relationship of the stern tube to the cutless bearing strut. On my 33 I discovered that the stern tube is installed slightly out of line. This is not a big deal by any means except that it effectively narrows the passage for the shaft and makes alignment even more critical. With my previous engine, a 2GM, the shaft would slap during acceleration, deceleration and at certain steady states. With my 3GM30F, I only get slapping when I throttle down very abruptly. The 3GM is that much smother. Once I know the shaft is as centered as possible in the tube I choose to ignore the slap as I've yet to observe any damage. When the shaft was out it checked out dead true at the prop shop.
That is the most lucid and succinct discussion of engine alignment I read. A note on this era of Hunters from my experience Next time your boat is out of the water check the relationship of the stern tube to the cutless bearing strut. On my 33 I discovered that the stern tube is installed slightly out of line. This is not a big deal by any means except that it effectively narrows the passage for the shaft and makes alignment even more critical. With my previous engine, a 2GM, the shaft would slap during acceleration, deceleration and at certain steady states. With my 3GM30F, I only get slapping when I throttle down very abruptly. The 3GM is that much smother. Once I know the shaft is as centered as possible in the tube I choose to ignore the slap as I've yet to observe any damage. When the shaft was out it checked out dead true at the prop shop.
- Status
- Not open for further replies.