[C320-list] Engine vibration at low RPM. 3GM30

[Brahmany Kite]

As per previous poster said. If you don't know a doctor ha ha a long
screwdriver, metal through type a little better. Fat end to the ear. Don't
recommend putting anything on rotating equipment. Some shafts will rattle
or knock even in neutral. Yanmar are quite adamant to use their 75 and 100
mounts. I did ask if they had stiffer ones but they wouldn't budge in the
originals. At the recommended 825 RPM the 3ym hops around a bit especially
when cold. To many RPM the Kanzaki will clunk into gear (not good) So
engine hull tube alignment and cutlass bush condition makes a huge
difference. From the cockpit a rattly shaft can sound like the props
falling off. Sound and water thing!!!

Someone here will know this: Did Catalina increased the shaft size at some
point to1 inch? If so,did they increase the size (id) of the hull tube?.
Cheers



On Sat, May 16, 2015 at 3:09 AM, Elizabeth Schwartz <
schwartz781 at optonline.net> wrote:

> Ahoy.....use the screwdriver as a stethescope.....a long one in this
> app....it will magnify any noise when held up to machinery......the but end
> to your ear....Joe...#245
>
>
> On Fri, May 15, 2015 at 08:36 AM, Marek Fluder wrote:
>
>  Brahmany,
>> Can you elaborate on the "screwdriver trick"?
>> Sounds like some interesting diagnostic.
>>
>> Marek
>> #1028
>>
>> On Thu, May 14, 2015 at 5:49 PM, Brahmany Kite wrote:
>>
>>  The shaft contacting the stern tube is a source of vibration also as
>>> there
>>> is not much clearance. Especially if there is misalihnment. On one boat i
>>> found the gland body pushed too far on astern through the hose and
>>> bumping
>>> on the inboard end of the stern tube. Yanmar mounts are soft as you know
>>> and small clearances dont help. Under load the engine will twist slightly
>>> sometimes allowing shaft contact as well. The old screwdriver end held to
>>> the ear trick will help find the source. Just a thought.
>>> On 14/05/2015 10:28 PM, "Graeme Clark"  wrote:
>>>
>>>  Jeff
>>>>
>>>> New mounts fitted as the  rear starboard original had become disbonded
>>>>
>>> due
>>>
>>>> to a diesel leak onto the rubber. They were 18 years old original to the
>>>> boat, anyway!  All the correct spec mounts in the correct place!
>>>>
>>>> BUT -  they aren't Yanmar mounts. They are made by a  company called R&D
>>>> as a direct replacement and I chose them because the design protects
>>>> against a  similar problem as they are shielded and the rubber is
>>>>
>>> inserted
>>>
>>>> into the mount not bonded to it.
>>>>
>>>> There is a page on the Yanmar site about using non-Yanmar mounts and it
>>>> does mention that “other makes’ can be stiffer which increase vibration
>>>>
>>> at
>>>
>>>> lower rpms.
>>>>
>>>> The tacho is spot on, calibration, (I have a laser tachometer that I
>>>> used
>>>> on the crank pulley to check). So at 1000 rpm its in fine form, at 800
>>>>
>>> its
>>>
>>>> shuddering away!
>>>>
>>>> One thing someone else suggested was to check that with higher amplitude
>>>> vibrations it is possible that some part of the engine actually touches
>>>>
>>> the
>>>
>>>> boat; I’ll have to check next time I am on board.
>>>>
>>>> So really my question is whether it is normal for the engine to shake
>>>> around a lot at low revs, rather than for the boat itself to shudder.
>>>>
>>>> The other thing I am unsure of is how the governor works - mine
>>>> maintains
>>>> a set RPM when the boat is out of gear or if the boat is in gear, but
>>>>
>>> when
>>>
>>>> you transfer from neutral to forward gear, obviously the engine comes
>>>>
>>> under
>>>
>>>> load, and the rpm drops requiring more throttle.
>>>>
>>>> I don't know if this is expected behaviour or not?
>>>>
>>>> Thanks
>>>>
>>>> Graeme
>>>>
>>>>
>>>>
>>>>
>>>> On 13 May 2015, at 23:24, Graeme Clark  wrote:
>>>>
>>>>  Hi,
>>>>>>
>>>>>
>>>>> It depends.  Do you feel boat vibration, or are you just seeing the
>>>>>
>>>> engine
>>>>
>>>>> "rocking" in its mounts?  If you feel the boat shuddering, then this is
>>>>>
>>>> not
>>>>
>>>>> normal, and *usually* indicates that the idle is too low.  If the
>>>>>
>>>> engine
>>>
>>>> "looks" like it's vibrating a lot in its mounts, that's probably ok as
>>>>>
>>>> long
>>>>
>>>>> as the prop shaft isn't bouncing all over. Some shaft movement is to be
>>>>> expected at idle however.
>>>>>
>>>>> The engine is supposed to oscillate (rotate/rock side to side) in line
>>>>>
>>>> with
>>>>
>>>>> the prop shaft.  (imagine the prop shaft extending through the engine
>>>>>
>>>> and
>>>
>>>> out the front and attached to fixed mounts at both ends. The engine
>>>>>
>>>> will
>>>
>>>> pivot side to side around this shaft, more so when at a low idle, and
>>>>>
>>>> when
>>>>
>>>>> revved up, it should appear to be much more stationary).  The Yanmar
>>>>>
>>>> rocks
>>>>
>>>>> quite a bit at idle, but gets more smooth as you increase the speed.
>>>>>
>>>>> So, if the tach reads 1000 and you feel the boat shuddering, the idle
>>>>>
>>>> is
>>>
>>>> too
>>>>
>>>>> low and your tachometer is probably reading a little high. Increase
>>>>>
>>>> the
>>>
>>>> idle by adjusting the governor (on the cable right below the engine
>>>>>
>>>> mounted
>>>>
>>>>> fuel filter).  If the tach is correct and it only smooths out (stops
>>>>> shuddering) at higher RPM, your engine mounts may be shot.  Another
>>>>>
>>>> thing to
>>>>
>>>>> notice is if you rapidly back the throttle down to idle position and
>>>>>
>>>> the
>>>
>>>> engine shudders or nearly stalls then again, your idle setting is too
>>>>>
>>>> low.
>>>>
>>>>>
>>>>> Cheers!
>>>>> -Jeff Hare
>>>>> #809
>>>>>
>>>>
>>>>
>>>>
>>>
>>