engine oscillations

[jstoesz]

I have owned my C34 for 8 months, and I live aboard it.  I absolutely love the boat, especially as it is my first keel boat.  I know that this is a bit rediculous for some, but I am a fairly adventurous person and adept with mechanical systems. 

I have been able to remedy many of the small problems with my particular vessel, but then next one is slightly more complicated. 

I have decent engine vibration oscillations which changes in frequency with rpm.  The engine/hull shaking oscillates with rpm.  There is no obvious loss of power or rpm with the oscillations of vibration, but it is somewhat annoying. 

The engine mounts on my diesel do not look very pliable, and clearly are original to my 1988 hull.  They have some corrosion, but do not look structurally compromised.  So my first suspicion is with the engine mounts.

My second suspicion is with the shaft alignment.  I have no idea if it is properly aligned.

My third suspicion is with the stuffing box.  It is a traditional stuffing box with flax packing, I think.  It does not drip or at least no much at all.  Although enviable by some, this does not seem typical, or acceptable considering the design. 

My forth suspicion is with the 25xp diesel.  I wonder if all 3 cylinder engines have this imbalance, and I am annoyed with something unavoidable for a 20 year old diesel.  I must state that the engine seems to run very well, starting up with no trouble what so ever. 

Any help would be appreciated...hopefully this problem has not already been addressed, and I will not receive the all to common pointing to the search engine.  I do not want to change my mounts, but that seems to be the most likely culprit. A step by step check list would get me motivated to solve this problem.

[Michael Shaner]

Dude, I think you have created your own step by step check list... Perhaps a prop issue?

Welcome, and join the Association! (if you haven't already)...

[Ken Juul]

Are you seeing the engine move or just feeling the vibrations?  If it's the whole boat it could be prop, shaft, alignment, engine mounts or loose engine covers/boarding ladder amplifying the noise.  If it's just the engine could be the mounts, dirty injectors, or alignment. It is probably not the stuffing box.

Lots written about how to change the mounts.  Other than the awkward positioning, not hard to check the alignment.  While doing the alignment, disconnect the coupler and spin the shaft, that may help determine if the shaft is bent.  As far as the prop, a diver or pull the boat.

The engine idles smoothest at 900-1000, if you pull it back too far it really doesn't like it.  There is also a harmonic (at least on my boat) in the 1600-1700 range.  I just try to avoid those areas.

[Ted Pounds]

I would suggest the replacing the mounts.  The rubber does tend to harden-up over time.  Get yourself some Vetus K50's or K75's.  You'll notice a big difference.  You'll have to do an alignment after replacing the mounts so that kills two birds w/ one stone.   If you have the vibrations when in neutral then you know it's not the drive train.  If the PO used dripless packing in your stuffing box then it shouldn't leak.  If it's conventional flax then it should leak a couple drops per min when underway.  I highly recommend the Gore dripless packing. 

[Stu Jackson]

In addition to the obvious items discussed above, and BEFORE you go spending any $$

1.  check the coupling bolts between the transmission and prop flanges (they're fine thread bolts on ours)

2.  check the lag bolts on the engine mounts themselves

Both of these cause serious vibration.  We have a 1986 with what I would call literally "solid" engine mounts, which I have learned to live with until I get strong enough to lift up our little tractor engine and put in K75s.  

These two items have always been the source of any vibration for me.  After all, it's a three cylinder tractor engine...

And, welcome. 

[Jon Schneider]

If you decide that it's the engine mounts, alignment, or injection pump, go to the "Engine" topic in the knowledgewiki to read the great project articles there.  (www.c34.org/wiki)

[Albreen]

I have only one sailing season (and a short one at that here in Vermont) with the '87 C34 I purchased last spring. This is a great boat - echoed by everyone and everything I read on this forum. My pre purchase survey indicated that I pull the shaft back from the coupling to check its condition, renew the stuffing box, align the shaft and either replace the flexible tube (?) and clamps or install a dripless unit. So, this thread is very relavant and I've been pouring over the great information in the tech notes. Regarding Ken's commented about the harmonic on his C34 - its present on my '87 too and when I drive thru the mooring field at these rpms, I'm sure it can be heard by everyone with their sundowners. :-) I wasn't sure if this was a normal sound or not but based on Ken's comment, completing any of these recommendations by the surveyor will not change this. Is this true? I guess I was hopeful it would go away.

[Stu Jackson]

Our experience has been that ALL engines have their own specific and individual harmonics.  Ken covered it well and described it. Dare I suggest doing a search on "harmonics" and read up some more?

[Albreen]

Ah..........I was looking strickly in the Tech Notes and Projects - there is more "harmonics" info. to be found in a Forum search. Thanks, Stu - please do dare more often!  I'll read up more at home tonight.

[Stu Jackson]

You're very welcome.  This is why I keep the GUIDE as a sticky - it explains ALL of the resources available here.

[Ron Hill]

jsto : I'll guess that in your 1988 C34 you have a number of problems:
1. The engine mounts need to be changed (Vetus K50s in front & K75s rear or all K75s)
2. The injectors are partially clogged/bad spray pattern and need a cleaning rebuild/new ones
3. The engine alignment is off, but do those items above before you align.
4.  You may want to conside the Gore Drippless packing
5.  A 3 cylinder will run as smooth as a 4,5,or 6 cylinder if all is right "inside"

[jstoesz]

Wow, you guys are awesome...one day and 9 posts.

I fear the mounts, but I was hoping you all would tell me it is completely normal and drink a beer. 

I think I will check the alignment/coupling first, because that is at least free.  Then I may get ambitious with the injectors or mounts.  Is the injector problem likely, or off chance? 

[Jon Schneider]

I don't have a ton of experience with injectors, but, logically, I would think that an injector problem either starts off badly at low RPMs and with increased pressure gets better or the opposite.  I can't see how the problem would manifest itself as in a sine curve fashion.  And as others have said, you can check to see if the problem relates to alignment by simply putting the engine through its paces in neutral.  But, BTW, it's very likely that it is slightly out of alignment, because, unless the PO was someone like Ron, he probably hadn't had it checked in a long time.  Still, I don't think that's the problem.  It's the mounts in combination with some other mysterious demon (new mounts will actually only hide the problem, which is okay because it's probably not anything serious).

[Ken Juul]

Most peoples experience shows it is about the same price to rebuild your injectors as it is to buy new ones.  Provided you buy from Kubota, not Universal.  So most buy new, then rebuild the old at their leasure for spares.  Before you go that route you might want to run some Injector cleaner through the system.  Couple ways to do this, one is to drain your Racor and fill it with injector cleaner.  This will give a concentrated initial rush tapering off as the cleaner gets mixed.  I prefer to put a full bottle of Techron in a gallon container.  Fill it up with diesel, stick the input line to the electric fuel pump in and run the engine till it's empty.  Generally do this when I'm changing the racor, so I have the system apart and need to bleed it anyway.  Seemed to help the first time, now that I'm trying to keep them clean, don't notice as much change.

You are probably using low sulpher fuel, a cetane boosting additive is highly recommended.  Most of them have a cleaner as part of the chemistry.  The additive also helps keep the system clean in the long run.

[Mike and Joanne Stimmler]

Ron has reccomended a product in the past that has worked very well for me. It's called PS (power service) diesel fuel supplement and it works as both a cetane booster and an injector cleaner. It's very innexpensive and is available at most auto parts stores It's good to use routinely when you get fuel but you can also use it as Ken suggested to put directly in your racor filter as I do each time I change it. This product is also widely used by truckers so you will also see it at truck stops.

Another cheap alternative before you spend the big bucks.