QSC runs a bit rough at certain revs

[Andre Huizing]

Goodmorning Sailors, This is a question in the category: is this normal?

As long as we have our single QSC490 trawler I have always noticed certain revpoints where there is much more shaking of the engine than others. In our case this is between 800 and 900 and between 1550 and 1850. Especially the latter window is quite noticeable. Up to 1500 revs the engine runs very smooth but beyond that you feel a roughness going through the boat which smoothens again above 1900.

Prop is clean and alignment has been checked recently. This is a full displacement trawler with 1:3 tranny reduction and large/low pitch 4 bladed prop. Maybe it’s just a characteristic of this engine?

Thanks for your input! André

Topic

[Andre Huizing]

Thanks Tony. It certainly looks like it. It seems like some …hole has tried to realign that mount by turning the jamnut against the rubber. Now I have returned the jam nut in it’s proper position the snubber has already recovered a tiny bit. When I shine a light behind it I can see it’s not touching the SS bases anymore…although on ly by a fraction of a mm.

What is the normal life span of these engine mounts (these are 15 yo and 3700 hours)?

Cheers, André

[Tony Athens]

Looks like one mount has totally collapsed (lost its gojo)..    Never did like those mounts with the “cast iron” housings  ( that came with a “green stripe”) on the top of the stud..    As to adjusting them with out checking the alignment–That would be a “no-no” in the normal sense.  

1 user thanked author for this post.

Andre Huizing

[Andre Huizing]

Hi Sailors,

I finally got around to looking into adjusting the engine mounts but still have the question from my last post: Is it possible to rearrange the pressures over the 4 mounts without changing the shaft alignment?

As is clear from the photos above the starboard mounts have the snubber more or less in the middle not touching the bottom nor the top. However the port side mounts look wrong. The rear mount having the snubber touching the bottom and the front touching the mount.

My simple thinking is:

• measure all 4 mount distances between SS base and engine exactly;
• start at the front and increase pressure on port side which will probably lift the engine there but also push the snubber down;
• decrease SB engine height as much as the Port side has risen;
• decrease pressure port side rear hopefully raising the snubber from the SS base but probably also dropping the engine;
• increase SB height by as much as port has dropped.

Does this procedure make any sense? 

Thanks for your input!

Cheers, André

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[Andre Huizing]

In addition to previous answer I did some investigation based on your pointer towards the mounts…and it seems a bit of a mess. Apart from 2 mounts having their jam nut against the rubber instead of upper nut, it looks like the port side mounts are unevenly loaded (see photos) The rear one snubber is touching bottom while the front is touching the mount casting.

last year the shaft coupling has been off and on to replace pss bellow. Then the alignment has been checked and was OK. I have no other indication the alignment is off. Leaves the question how to evenly load the port side mounts without disturbing alignment?

cheers, André 

[Andre Huizing]

Hi Tony, hope these are sufficient? Let me know if not. Curious for your ideas on this!<br />Cheers André 

[Tony Athens]

Post  some good pictures of the engine isolators — Camera level and in plane with the isolators–  18-24″ away–Side view,  and fore or aft views.

 

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