Catalina 28 engine exhaust

[jansan]

Having hauled out the original 1991 M3-20 Universal engine and gearbox ( to replace a defunct g/box ) from a Catalina 28 ( engine approx. 850 hrs ) several issues have arisen which may be of interest to the sail boat community.

Firstly. I`ve always had to keep a close watch on the water coolant temp. when pressing hard into anything above a F6 butit`s never been too much of a problem as long as I kept to around the 2000 rpm mark accepting that slower progress was inevitable. On close inspection I found that the heat exchanger cooling tubes were virtually all blocked up !! Couldn`t believe just how bad the blockages were ( there`s approx. twenty of them ) --------- more or less had to " drill " them clear.Each tube had roughly two-three inches of hard packed sediment/gunge.

Then ----- in order to get the engine out I had to disconnect the exhaust pipe from the engine manifold, which also involved loosening various hoses. ( I had decided to renew the rubber hose where the seawater rejoins the exhaust pipe). In the course of this procedure I found that the exhaust pipe was more or less completely fractured at the point where the seawater cooling pipe rejoins the exhaust ( not normally visible as it is hidden behind a panel in the heads ).

The most disturbing issue here was the now broken pipe revealed that the internal diameter of the exhaust pipe was so coked-up it was reduced to about one inch. As I had never been able to achieve anything like the claimed limit of 3600 rpm for the engine -------- could this be the reason ?

Anyone out there had similar problems ? Anyone had difficulty getting upto the 3600 rpm limit of the M3-20 Universal ?

Would appreciate any comments.

 

[jerry]

I have a 1991 Cat 28 M3-20. I get about 6.5 kn at 2200 rpm which is the hull speed. anything above 2500 the soot is too much. The temp guage stays rock steady at 165. have about 500 hours on the engine. I figure my tach is probably off since I reach hull speed ok. Also, I have never checked the prop for proper pitch so I really don't expect the the engine to be running at peak efficiency. I sail in fresh water only.

jerry

 

[jansan]

I have a 1991 Cat 28 M3-20. I get about 6.5 kn at 2200 rpm which is the hull speed. anything above 2500 the soot is too much. The temp guage stays rock steady at 165. have about 500 hours on the engine. I figure my tach is probably off since I reach hull speed ok. Also, I have never checked the prop for proper pitch so I really don't expect the the engine to be running at peak efficiency. I sail in fresh water only.

jerry

Hi Jerry --- presumably you have the 12 inch two bladed prop fitted as standard ? Have you ever been knocked back from max. hull speed to 1 or 2 knots from the effect of a large wave ? I am wondering whether this exhaust problem I`v been having means I haven`t been getting full engine power through to the prop. I am attaching a couple of photos of the inside of the pipe just to illustrate how much the internal bore has been reduced.

regards Sandy

 

[Stu Jackson]

Pipe deterioration

In all the years we've been sailing and in our building engineering business practice, we keep noting that pipes deteriorate FROM the inside OUT. This is not to be unexpected. The corrosive nature of the mix of the hot exhaust gas with the cooler raw water exhaust is a pretty noxious combination. Many have reported a five year life of exhaust risers, some of us have gone 12 or more years with over 200 engine hours per year. I recall about 1500 engine hours on our riser, although I don't know if the PO had ever replaced it, but there's no eveidence that hever did. It's not a car and it's not a tractor either, even though some of us actually have tractor engines in our boats! Maine Sail just posted a very good "How To" on heat exchangers this week. That's what's been making your engine overheat. I'd check with your C28 Association to see if your prop is one of the ones recommended for use with your boat and engine - there are usually a few choices in blades and pitch - but the diameter is limited by the clearance between the prop and the hull.

 

[jansan]

In all the years we've been sailing and in our building engineering business practice, we keep noting that pipes deteriorate FROM the inside OUT. This is not to be unexpected. The corrosive nature of the mix of the hot exhaust gas with the cooler raw water exhaust is a pretty noxious combination. Many have reported a five year life of exhaust risers, some of us have gone 12 or more years with over 200 engine hours per year. I recall about 1500 engine hours on our riser, although I don't know if the PO had ever replaced it, but there's no eveidence that hever did. It's not a car and it's not a tractor either, even though some of us actually have tractor engines in our boats! Maine Sail just posted a very good "How To" on heat exchangers this week. That's what's been making your engine overheat. I'd check with your C28 Association to see if your prop is one of the ones recommended for use with your boat and engine - there are usually a few choices in blades and pitch - but the diameter is limited by the clearance between the prop and the hull.

Hi Stu

Just to clarify the issues regarding the exhaust riser pipe problem. The pipe does not appear to have fractured through corrosion as the " coking " of the pipe internally seems to be a carbonised deposit --------- rock hard at the point where the seawater enters the system and progressively softer above it. At the point where the steel pipe ends and enters the hose leading out of the hull the internal diameter of the pipe is as new.

I suspect that the pipe has fractured at this point due to hot and cold cyclical stress ?. The fracture appears clean without any evidence of a mechanical or corrosive cause.

It would seem that anyone with a Catalina Mk1 with the Universal M3-20 and around 900 hours on the engine would be well advised to check out this part of the exhaust system. My exhaust pipe was obviously leaking fumes un-noticed behind the panel in the heads compartment ------ who knows for how long ?

There is a definite health risk/ issue here.

 

[Stu Jackson]

Yup, that's how they break

Here is our old one (2003) showing the break, which tend to occur where the nipple meets the riser. 900 hours is pretty good. Somewhere, the boat builder's could do a better job of pointing this out to boaters. It's one of those out of sight out of mind things. Our car exhaust systems do not have this type of corrosive mixture and people mistakenly think they're the same. Plus, it's so damned hard to get the bolts to the manifold off that...

And it's not only your boats, it's everyone with a diesel engine on a boat.

 

[jansan]

Here is our old one (2003) showing the break, which tend to occur where the nipple meets the riser. 900 hours is pretty good. Somewhere, the boat builder's could do a better job of pointing this out to boaters. It's one of those out of sight out of mind things. Our car exhaust systems do not have this type of corrosive mixture and people mistakenly think they're the same. Plus, it's so damned hard to get the bolts to the manifold off that...

And it's not only your boats, it's everyone with a diesel engine on a boat.

Stu

I notice that your`s broke exactly as mine did ------- just above where the seawater pipe enters the exhaust. Surely there has to be a better way of engineering this arrangement ------ perhaps a " sea-water jacket " welded around the pipe and then running the seawater into the muffler chamber via another hose. This separates cold seawater and hot exhaust gases from inter-reacting

I assume the way it is done at present is to allow a rubber hose to join a potentially hot exhaust pipe

Would welcome any thoughts

 

[Stu Jackson]

Figure out the "system"

I agree, they almost always break there. But the reason they make it this way is that you have to consider the options: the cost of mufflers would go WAY up if they had to make them out of stronger thicker material than the simple fiberglass ones currently employed. Unless the cooling water mixes with the hot exhaust gases BEFORE they hit th muffler, the muffler's gotta be made MUCH heavier.

Like everything else in boating, it's a trade-off.

Remember, we have tractor engines in our boats. The old dry exhaust has to be modified to get a wet exhaust with the HX raw water mixing with the exhaust gases.

Except for the absolutely horrible job necessary to get the bottom nut off the stud in the exhaust manifold to remove the riser, it's not so hard to do once you recognize it is a REPLACEMENT part, not a car exhaust system which lasts much longer. Also, like anything else on a boat, once you do it once, it's always easier the second time around! Tell my knuckles that...

Also, leaks do develop outside of the nipple area. The most common is blow-by the threads where the riser screws into the exhaust manifold flange. Muffler patch paste is recommended for that joint.

 

[Stu Jackson]

You may also be interested in this

http://www.c34.org/faq-pages/faq-hump-hose.html

 

[jansan]

http://www.c34.org/faq-pages/faq-hump-hose.html

A facinating read. Thanks for the link.

 

[Stu Jackson]

You're welcome and good luck

with your riser. The hump hose would help your muffler lip. Feel free to wander around our C34 website, many systems are the same. The C36 'site is also a great resource.