Replacing your dry stack muffler

By Scott Flanders on M/V Egret

OK, here's the deal if you own a smaller N or similar dry stack boat and your muffler needs replacing. We replaced Egret's muffler after 8 1/2 years of ownership. We should have replaced the muffler perhaps 2 or more years earlier after looking at it when it came out. I have a theory how the muffler came to be a rust bucket. Over the years we have taken considerable salt spray over the boat deck onto the exhaust pipe. After a long run in heavy spray the stack turns white from salt. When it rains the salt melts and in time it runs down the stack thru the poor seal on the funnel shaped rain guard over the fiberglass stack. When we get a chance we will clean the stack to bright metal then will wrap the joint with a tape we bought locally that will withstand 500 degrees F. While running I used an infrared heat gun and the stack temp at the seal was less than 275 degrees F. Hopefully this will keep salt from running down on top of the muffler and saturating the heat blanket.

Replacing the muffler is a job you can do yourself if you have a helper. You will need a couple tools you may not have but it is no big expense. We used metric sizes even though the muffler is U.S. built. The tools we used are pictured below.

There are three tools that are key. The most important, we had to modify a 26mm open end - closed end wrench (spanner). We cut off the open end leaving the closed end. The overall length of this cut down wrench is 8 3/4" (220mm) from outside the ring at the ring end to the cut off end. This length is key. If its longer it won't get into some of the places it needs to go. This wrench fits the nuts on the flange bolts. The second tool is a 24 - 28mm open end wrench*. You use the 28mm end to hold the head of the bolt for the flange nut. The third tool is a short handle 3lb hammer. You use this to beat the **** out of the cut down wrench to break the nut free. A long pipe slid over the cut down wrench will not break the nuts loose (we tried). Additionally you will need a pair of channel lock pliers, 2 - 14mm/9/16" wrenches, a 1/2" drive breaker bar, a 6" extension and a 28mm socket. Thrown into the mix is a quality Liquid Wrench type product (we used Corrosion Block that works on everything) and a secret product called Anti Bond (available from Anti Bond will save you tons of time as well as the gel coat on your stack removing the stainless trim ring (held in place by 4 - 3/8" bolts and adhesive bedding. Anti Bond turns the bedding loose. We also bought a 50 meter (160') roll of 2" shiny aluminum heat resistant tape to cover everything when we were done. (Don't even think of using duct tape.) And 3 meters (9 1/2') of 2" fiberglass heat shield tape.

  1. Remove the stainless steel grills on both sides of the stack. Loosen the 3 hose clamps that hold the exhaust pipe to the mast brackets, undo the tightening knob on the funnel shaped rain guard then raise the pipe off the muffler tail piece and swing it aside. Re-tighten the lower hose clamp to hold it in place.
  2. Take the time to put old towels around the well under the muffler leading into the engine room to catch the zillion flakes of rust that will come off the muffler when you start removing the heat blankets. THEN!! do the same in the engine room. Cover the transmission, engine and everything around to capture these flakes or you will be VERY sorry. We were just a little sorry but knowing what we know now we would have taken even more time to catch the falling flakes.
  3. Once your stuff is gathered, first remove the heat blankets from around the muffler. Don't worry about the snaps holding the silver finish cover over the blankets, they will disintegrate but its OK. There are 5 major pieces and a few smaller pieces. The 5 are: the large blanket that goes around the muffler cylinder, the flat collars that cover the ends of the cylinder (below the flange), and the flange collars themselves. There are smaller narrow pieces that are wrapped around the pipe above and below the flange you will replace later with 2" fiberglass heat blanket tape. Don't worry about keeping track of where the pieces go, it is simple to reassemble the parts using common sense.
  4. Remove the stainless collars and trim stuff on top of the fiberglass stack. Here is where you use the Anti Bond to break the sealant from under the trim ring. Here is the BIGGGG secret. Take the 4 nuts AND lock washers off the muffler's bottom flange leaving the bolts in place ( break the bolt heads free so they can be taken out) The bolts, nuts and lock washers are good quality stainless steel and will be in perfect shape. The flanges are mild steel and will be in reasonable shape, however the rest of the mess will not.
  5. By leaving the 4 bolts (without nuts) thru the bottom flange you will be able to rock the muffler from side to side so you can remove the stainless steel tail piece** from the top flange (this you will reuse). You will donate a little blood but take your time, bang away with the hammer and you will prevail. Once the bolts have been removed from the tail piece is is all down hill. Have a third person hold the tail piece in place or wire it in place so the two of you can remove the muffler. Take the rust bucket out but do NOT throw it away. Your muffler's measurements and comparison with the new unit are critical.
  6. Reinstall the new muffler as it came out. Again, slip the muffler inside the stack, bolt on the stainless steel tail piece (keeping 4 bolts thru the bottom flange but without nuts while you tighten the top flange nuts), bolt the muffler to the bottom flange.
  7. Reinstall the heat blankets: here is where the silver tape is priceless. This adds another hand. Cut numerous pieces about 4" long and have them handy. As you tightly wrap the blanket bits in place, stick on a piece of tape. It won't hold long term but will get you to the next step. First put the large muffler blanket in place, holding it together with silver tape (only add the silver finish covers at the last). Take two tight wraps of 2" fiberglass tape under and over both flanges holding them in place with silver tape.
  8. Add the flat collars, add the flange collars, then recover everything with the silver finish cover. Tape the whole mess together with silver tape. The silver tape will not hold well to the silver blanket but will stick to itself if you go completely around everything. We used LOTSA silver tape and it isn't going anywhere. It looks good as well.
  9. Reinstall the stainless finish pieces on top of the fiberglass stack and slide the exhaust pipe back on. Re-tighten the three hose clamps holding the exhaust pipe to the stack. Tighten the bottom clamp first, then the top clamp, then the middle. (if you don't tighten in this sequence you'll see why....... as we did)
  10. Shop vac up the rust and take the time to clean the inside of the stack. Clean up and be sure to raid the fridge and shoot at least two beers each. You deserve it!!

Egret's muffler was manufactured by Harco Manufacturing Company in the U.S. The closest muffler number is 824VRS3. This muffler is not an exact replacement but it is close. DO NOT ORDER THIS MUFFLER BY THIS NUMBER!!! This number is to get you close, that is all. Egret's muffler is 32" (810mm) tall, measured from flange outside to flange outside. The flanges are 7 1/2" in diameter with 3/4" holes on 6" centers. This is a U.S. standard flange size and your new muffler must EXACTLY meet this standard as well as the flange diameter, bolt pattern, diameter and overall length. The reason is the heat blankets are custom made to fit your particular muffler.

If your muffler is a different dimension than Egret's it is no biggie. These mufflers are made to order. The manufacturing time is one week. The cost for the U.S. made muffler bought from Harco is $375 in mild steel (what came from PAE) and stainless steel is a little over $1000 (minus taxes and freight). In Egret's case we ordered stainless steel that gives 2-3 times the life. Be sure and order 2 flange gaskets with the muffler.

We ordered Egret's muffler in Launceston, Tasmania from Northern Mufflers. They bought the muffler from Chromend Supply in Melbourne (Daniel). Chromend's phone number is 02 45 88 5089 (in Australia or 0612 45 885089 outside Australia) We paid a little over $1500*** AU for everything including GST (tax) silver tape, 2" fiberglass fire blanket tape, and so on. A mild steel muffler and the rest of the parts plus GST would have cost about $750.

Both mufflers, the original and Chromend's have spark arresters inside. If you order one from Chromend specify a spark arrester. It costs $150 AU more**** but we didn't want sparks and I don't think you do. And one last thing. If the muffler whistles loudly on startup it is installed upside down. Muffler flow is directional so be sure and install the muffler with the flow arrow pointing upward. Egret's muffler's weld on label was mis-marked. Soooo, we got to do it ALL again and WHY I can remember all the details.

So there you have it. Another BU+ (boat unit) gone but it is the price we pay for freedom. It's OK.

*This is also the size for your Lugger motor mounts.

**The stainless steel tail piece is welded on a slight angle. Be sure and mark its fore and aft direction so you don't make a mistake on reassembly.

***Chromend's normal stainless steel muffler is 1.6mm wall thickness. We wanted 2mm (like the tail piece) and negotiated to get 2mm at the same price.

****This is included in the figures we quoted.