The Exhaust Elbow Blues

Our trawler is powered by a single Lehman 120. These are classic engines found in thousands of vessels throughout the world. They are extremely reliable, durable and simple to work on. They will chug along at low rpms for thousands hours. They do have two peculiar traits though.

One oddity is that you have to change the oil in the injector pump. The other is that the exhaust elbow is guaranteed to fail at around five years. It’s cast iron. It has saltwater passing through it. It rusts out eventually and develops a hole in it. This is usually on the bottom where you can’t see it developing.

Our is well over five and overdue to be replaced. I noticed a lot of rust below the elbow, collecting on the heat exchanger. I ordered a new elbow along with a gasket and new bolts. There are only four bolts. No big deal, right?

As with many boat jobs, something that should take an hour or two has stretched out over three days now. The job still isn’t finished. Here’s the old one, finally removed. It had a pin hole surrounded by rust. That is – until I beat the living daylights out of it with a hammer.


Notice the bottom right bolt hole. That bolt refuses to come out. I couldn’t fit a socket on it, until I made the large hole with my trusty hammer. Who knew there were so many uses for a hammer on a boat? Day one consisted of removing three bolts, then cussing at the fourth for a few hours.

Day two consisted of acquiring special sockets for extracting pesky, slightly rounded bolts and trying again. Nope, nope, and nope.

Day three consisted of acquiring a torch (Mapp Gas), and heating the stubborn bolt. Still nope. The local mechanical guru in Boot Key Harbor (Diesel Don), attempted to cut out around the bolt with a Dremel Tool and a tungsten carbide bit.


Almost worked. No cigar. We did manage to get some penetrating oil into the threads at this point. We waited over a beer, then tried the socket again. PLING! Broke the head off the bolt. Bottom right, now painted red:


The only good thing is that it didn’t break off flush with the exhaust manifold. I’m soaking it in Sea Foam Deep Creep overnight. We’ll see what day four brings.

Meanwhile, the new elbow waits patiently to be installed:


The day a boat repair/project goes simply and smoothly and faster or easier than anticipated . . . well, when pigs fly, hell freezes over, etc.

11 thoughts on “The Exhaust Elbow Blues

    1. george smith

      I think I would replace the bolts with studs and nuts. That will make the next elbow change much less of a pain in the backside.

  1. Jack

    Screw a nut partly on the stud then weld in the inside of the nut.
    Thread two nuts on the stud then jam them.
    Use a stud remover tool.

    You may have to drill it out. If so use a reverse drill bit.
    Good luck.

  2. sDee

    That cast iron elbow brings back childhood memories of working with my dad on his Owens with a raw saltwater cooled, cast iron, engine. I mustered enough skills to put my way through school working on saltwater assaulted outboards. For what it is worth…

    If you think its gonna break off, or its gonna be a bear to drill out, or if one has already broken off, stop and try…
    – Apply heat: MAPP “may” work but ox-acetylene is really the only way to get enough expansion/contraction.
    – Penetrating oil
    – Use a hand held impact wrench and hammer. The action helps break loose the corrosion but first impact counter clockwise, then back clockwise. Use this bi-directional action even after it starts to come loose to keep the threads from jamming.

    If it breaks off, you can try using the ox-acetylene and penetrating oil again with vice grips. But be prepared to dill and use an extractor and also likely…. expect to drill/tap a new hole. Have these tools on board.

    My father ( who spent WWII in the engine room of a supply ship) ALWAYS removed studs and replaced them with a high grade stainless steel bolts when he had something apart.

    Finally – all threaded fasteners on a boat need a heavy coating of Permatex Anti-Seize when replaced. It serves as a lubricant, corrosion protection, and a sacrificial anode in salt environments.

  3. rotten ralph

    I’m not knowledgeable about salt water corrosion but instead of replacing a known inferior part with another inferior part, wouldnt it be better to fabricate one out of stainless steel?

  4. Randy

    Just started reading your blog. If you replace steel bolts with stainless, your asking for trouble with electrolsis. Left handed drill bit (same tap drill size.) is the hot ticket. Just remember not to pick one up to drill a standard hole!


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