I have an 82cd30 cutter with the volvo md7b engine. I've noticed even when idling there is a constant vibration throughout the boat. really became aware of it when checking the mast and saw that the windex was shaking at least an inch or so. felt the vibs in the mast as well. pulled hatchs and inspected engine, felt the engine, didn't seem to be jumping around, checked motor mounts appeared sound. prop. in good shape. will look closely at shaft universal tonight( also whines in reverse) so, as I'am fairly new to the volvo/system do any of you folks have suggestions as to what I should be looking for aside from loose nuts/bolts? how much vibration is normal? i know some is to be expected, but enough to wack the windex around? there is no amp. gauge to read if alt. is charging is this standard on cds? anyone install their own? vibs increase with rpms. bearings,cutlass, u-joint? any help/info would be great, thanks ben
btlandscapers@imagina.com
engine vibration md7b
Moderator: Jim Walsh
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John
Some Ideas
Ben,I have an 82cd30 cutter with the volvo md7b engine. I've noticed even when idling there is a constant vibration throughout the boat. really became aware of it when checking the mast and saw that the windex was shaking at least an inch or so. felt the vibs in the mast as well. pulled hatchs and inspected engine, felt the engine, didn't seem to be jumping around, checked motor mounts appeared sound. prop. in good shape. will look closely at shaft universal tonight( also whines in reverse) so, as I'am fairly new to the volvo/system do any of you folks have suggestions as to what I should be looking for aside from loose nuts/bolts? how much vibration is normal? i know some is to be expected, but enough to wack the windex around? there is no amp. gauge to read if alt. is charging is this standard on cds? anyone install their own? vibs increase with rpms. bearings,cutlass, u-joint? any help/info would be great, thanks ben
We have a '83 with the same engine. I have to say that the Volvo is very, very smooth. She is real smooth at 300 rpm. We have never had any vibration problems of any kind, the engine mounts are the originals. Are yours OEM mounts? Have you payed very close attention to the rubber section of the mounts to be sure they haven't seperated from the metal. Especially important on the Volvo original mounts. When you inspect the motor mounts do you have the engine running and someone at the throttle changing speeds as you watch for excessive movement in the mounts? Put the boat in gear and increase the throttle and watch the engine movement. It should move forward a small amount if everything is okay, if it's excessive you found the problem.
Cutless bearing inspection; have you had anyone dive down and grab the prop (stopped hopefully!) and try to move the shaft side to side?
The coupler is obviously another place to check but my guess is that would be an unlikely location for a problem unless you have a flexible coupler. Is the nut on the heavy flywheel tight and torqued properly? Is the alternator mounting tight?
My hunch would be a motor mount or cutless bearing. Sometimes its hard to see the internally damaged or failing Volvo OEM mount. Your cutless bearing would have to be pretty bad to cause a vibration like you describe at idle.
Is any part of the engine touching anything? Check on the top where the exhaust hose leads aft from the waterlock, make sure it is secured. Make sure the alternator is well clear of the starboard side compartment bulkhead.
That's about all I can think of at the moment, perhaps other people will have some ideas as well. Our CD runs a 100 amp Balmar with a dedicated shunted ammeter that reads in increments of 5 amps.
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Larry DeMers
Re: engine vibration md7b
Ben,
I have a 1983 CD30 with the MD7B also. There is some vibration due to the fact that the original engine mounts are fairly stiff compared to AfterMarket mounts. You will notice resonant peaks and valleys as you increase/decrease the RPM's, and these resonances will be reflected in each item aboard as you work through their resonant point's. The Windex is no exception. At a certain frequency, that length and weighted object will vibrate.
I suspect that the engine mounts may actually be too stiff. This is because the rubber isolators "dry" out over time..they become like rocks. A rock will transmit vibrations readily without much attenuation of the vibration. You may want to think about replacing them with a new mount, which will have a far softer rubber.
The other cause of vibrations commonly experienced in boats is misalignment of the drive shaft. Have you taken a feeler gage to the coupler yet? There should be less than .001 in. difference in the clearances for the 4 sides of the coupler. More than this means the engine needs to be repositioned on the mounts slightly to remove that difference. Misallignmnet of the drive shaft will lead to the cutlass bearing weraing out in 1 year rather than 10 years, so it can be fairly serious if ignored.
The way I have checked the coupler clearance is to remove the retaining screws, and then check all 4 sides of the coupler with the feeler gage. This will give you a good feel for the alignment. Make adjustments as necessary, then replace the screws and any mousing wire locking them in place, and see if that cured the vibrations. If not, I would look at the mounts next.
Cheers!
Larry DeMers
s/v DeLaMer
Cape Dory 30
demers@sgi.com
I have a 1983 CD30 with the MD7B also. There is some vibration due to the fact that the original engine mounts are fairly stiff compared to AfterMarket mounts. You will notice resonant peaks and valleys as you increase/decrease the RPM's, and these resonances will be reflected in each item aboard as you work through their resonant point's. The Windex is no exception. At a certain frequency, that length and weighted object will vibrate.
I suspect that the engine mounts may actually be too stiff. This is because the rubber isolators "dry" out over time..they become like rocks. A rock will transmit vibrations readily without much attenuation of the vibration. You may want to think about replacing them with a new mount, which will have a far softer rubber.
The other cause of vibrations commonly experienced in boats is misalignment of the drive shaft. Have you taken a feeler gage to the coupler yet? There should be less than .001 in. difference in the clearances for the 4 sides of the coupler. More than this means the engine needs to be repositioned on the mounts slightly to remove that difference. Misallignmnet of the drive shaft will lead to the cutlass bearing weraing out in 1 year rather than 10 years, so it can be fairly serious if ignored.
The way I have checked the coupler clearance is to remove the retaining screws, and then check all 4 sides of the coupler with the feeler gage. This will give you a good feel for the alignment. Make adjustments as necessary, then replace the screws and any mousing wire locking them in place, and see if that cured the vibrations. If not, I would look at the mounts next.
Cheers!
Larry DeMers
s/v DeLaMer
Cape Dory 30
I have an 82cd30 cutter with the volvo md7b engine. I've noticed even when idling there is a constant vibration throughout the boat. really became aware of it when checking the mast and saw that the windex was shaking at least an inch or so. felt the vibs in the mast as well. pulled hatchs and inspected engine, felt the engine, didn't seem to be jumping around, checked motor mounts appeared sound. prop. in good shape. will look closely at shaft universal tonight( also whines in reverse) so, as I'am fairly new to the volvo/system do any of you folks have suggestions as to what I should be looking for aside from loose nuts/bolts? how much vibration is normal? i know some is to be expected, but enough to wack the windex around? there is no amp. gauge to read if alt. is charging is this standard on cds? anyone install their own? vibs increase with rpms. bearings,cutlass, u-joint? any help/info would be great, thanks ben
demers@sgi.com