ENGINE RUNNING ROUGH - FLANGE COUPLINGS (plus exhaust riser)

[Stu Jackson]

A few weeks ago I had replaced my 18 year old exhaust riser and installed a new
3 inch heat exchanger on our 1986 boat.

About a week after that, we noticed that the engine was running rough.  There
was more vibration than we had ever experienced, at every different throttle level,
and the engine seemed to be very rough at idle, which dropped from 800 to 600
rpm on the tachometer.

Yesterday, I dove into the aft cabin access "hole" and checked things out.

Imagine my surprise when I found two of the four bolts and nuts that connect the
transmission coupling to the propeller shaft coupling sitting, rusted, on the hull just
below the coupling flanges.  One of the remaining two nuts and bolts were loose.

I purchased new bolts and nuts and reinstalled them today.  I also noted that the
bolts were inserted from the aft side going forward, which made starting the nuts
on the forward side quite difficult.  It wasn't until I got home that I considered
trying to install the bolts from forward so that the nuts could be started from the
side I could see, although I don't know if there is enough space to do that.

I most also should have put some light or medium Lock Tight on the bolts.  Any
input about whether or not this is a good idea?  I'll be sure to check them regularly.
(Only, and not valid, excuse, was we had a bunch of stuff in the garage during
the summer.)

Engine hours: 1417.  Bolts were 3/8 inch hex nuts FINE THREAD, about an inch or an inch and
a half long.  Maybe not a bad idea to have some spares.

So, in addition to engine alignment, stuffing box stuff and other weird noises, be
sure to check your flange nuts and bolts on a reasonably regular basis.

Trial run showed all is well, now.

Stu

[Ray & Sandy Erps]

Stu,
I was hoping someone else would ask the question, because it sounds stupid, but what's your theory on why the loose coupling bolts would cause the engine to idle rough?  I could understand some extra racket and vibration while underway, but I haven't made the connection yet to a rough idle.  

On the new bolts, I think some loctite would be a good idea, or at least some new lock washers or maybe lock nuts.  I'd go with fine thread #8s too, not those cheap grade 5 bolts.  
Ray

[Stu Jackson]

Ray,

I may have been somewhat incorrect in my description, I should have said running rough at low rpm.  You're right, it did fine in idle.

I'll have to go back and see if I can get the bolts in from the front, try lock washers, locktite, or nylock nuts.

Oh, well, at least I know I can still fit in there, although my sides are starting to give me grief today, that's one rough hard edge at the "hole."  :)

Stu

[Mike and Theresa Vaccaro]

The coupling bolts should be attached with the appropriate locknuts and properly torqued (i.e., installed with a torque wrench).  If your coupling is equipped with studs vs. bolts, the studs should be installed using locktite.

There are different styles of locknuts, the most common usually being those with a nylon insert.  These may or may not be appropriate depending on the coupling dimensions and the clearance between the coupling and the transmission.  Also, can't comment on the appropriateness of installing this type of nut on a non-static (i.e., moving) assembly.  Typically, this type of assembly would use an all-metal fastening system, a good example of which is a "low-profile" nut that uses an eliptical vs. round hole.  

The best bet is usually a direct replacement--i.e., using identical parts.  That way, there's no engineering involved.  Hopefully the engine, transmission or coupling manufacturer can provide specs.

If you are doing your own engineering, keep in mind that torque values are different for lubricated vs. non-lubricated threads.  Also, if you replace the stock, all-metal coupling with a flexible coupling, or use a "drive-saver," be careful not to use any lubrication or cleaning product that would threaten the integrity of the rubber.  With this type of installation, the best bet is to periodically loosen and retorque the nuts to prevent corrosion.  

A self-locking fastener can be reused, but if in doubt it should be replaced.  A good rule of thumb is that it can be reused once safely--but a simple test is to thread it and if you are unable to do it by hand (you shouldn't be able to hand-tighten a self-locking fastener), it should be safe for re-use.

Hope this helps!

Mike

[Stu Jackson]

I found another one of those four nuts had backed off yesterday.

There is simply not enougoh room to get a lock washer OR a nylock on the fine threaded nuts.  Regular thread nuts do not have enough shaft sticking through to work either.  I haven't seen fine thread nylocks, either.

I keep putting LockTite on them, and keep checking them.

Just another reminder.

Nice part:  they seem to fly off and then drop right behind the coupling!   

Engine hours now:  2094

[Roc]

Stu,
My coupling bolts are inserted from aft to forward.  I have a lock washer and not a nylon lock nut.  There is no Loc-tite.  In order to tighten them, I need to spin the shaft so the nut is away from the trans box.  This lets me put a wrench on it.  This is how the marina set it up when they installed the flexible coupling several years ago.

[Ron Hill]

Stu : Go to a "fastener" store in your area (I'm sure that there is one) and get a "thinner" thin style self locking nut!  You might also reverse the side the nut is on.  A few thoughts.   

[sailingdolphin]

Stu- how much and where did you get your 3" HX? I just checked on a price and it was $523.00 I said no thanks I will keep the 2". If I can find one for a decent price I will do it.

[Craig Illman]

Doug - Google "299835 exchanger", you should find something for $342 or below

Craig

[Stu Jackson]

In 2001 I paid $300 for it, local SeaPower Universal dealer.

[canuck]

I painted the coupling with a rust prevetitive paint. Keeps the rust down and any movement can be detected during normal maintenance and inspection.
The flange on the crankshaft has been safety wired as well.
2004 MkII #1678

[Tom Glennon]

Stu: I need to replace my exhaust pipe on my 87 with an M25XP.
I disconnected everything, and unwrapped the covering, to expose black pipe.  It looks like it is in really good condition, with the exception of the two holes in the area of the weld where the water is injected.  I was thinking of just making up a new exhaust pipe out of the black pipe, and have a machine shop fabricate the last piece for the small tube for the water injection.  Did you make your own, or did you get it from Catalina?
I kknow they offer a stainless replacement, but a mechanic I know said that stainless is not the way to go, that the black pipe is just as good.  Your thought would be appreciated.
Thanks, from Buzzards bay!

[Steve McGill]

Tom,

I am sure Stu will reply to your post, but till then.....................

The following post will help along with any search for "exhaust riser"

http://c34.org/bbs/index.php?topic=3945.0

Many folks have had the entire riser reconstructed by a local shop. I just received mine back from CY.
The total cost was $196.00 US. It is out of stainless steel and fully covered. I will post new pictures to the above post when I reinstall mine. I did have to resend it back to CY since the new flange needed an adjustment of about 20 degrees in relation to the pipe. The folks at CY paid for this shipping both ways.

11 weeks until I splash for spring

Steve

[Stu Jackson]

Tom

I ordered mine from Catalina.  Steve's link is the one I'd have sent you to, thanks Steve.

The discussion has been going on for years.   

Mine's been there since 2003 and is still working at the weld at the nipple, although I do have to unwrap and check for some blow-by, which I discussed in an earlier thread.

Tom, the downside of re-using the old one is that the damage is coming from the inside out, so I'm not sure how you know it's in good condition.  Age?

Given the long discussion in that referenced link, there are so many ways to do it that I can't recommend a "best" way.  I did mine as easily as I could through CY, maybe I could have found a local shop down the street from my boat, but I didn't look.

By the time all is said and done regardless of what you use, other than NOT using galvanized, you're looking at a piece of pipe with a shelf life of from five to ten years (although my original one seemed to have lasted from 1986 to 2003!!! - maybe the PO actually did have it replaced once before...).

SOME LATER DISCUSSIONS WITH PICTURES:  http://c34.org/bbs/index.php/topic,4300.msg24854.html#msg24854