DIY MUFFLER MODIFICATION

DIY MUFFLER MODIFICATION

Sometimes you need to make a modification to a factory engine muffler. This is what I ran into on the DLE-85 for my 1/3-scale DVII. I needed to change from top to bottom exhaust exit.

To begin, drill out the welds for the exhaust exit tube. You need to reuse this tube, so be careful!

This is the basic problem. Nice muffler, but exhaust exit goes the wrong way. Needs to dump the exhaust out the bottom! Also had a small interference problem with the cowl at the front of the muffler.

 

Except for the tig welding, you likely have all the tools required in your shop, drill motor, step drills, files, etc.

This is the basic problem. Nice muffler, but exhaust exit goes the wrong way. Needs to dump the exhaust out the bottom! Also had a small interference problem with the cowl at the front of the muffler.

To begin, drill out the welds for the exhaust exit tube. You need to reuse this tube, so be careful!

Looks kinda rough at this point.

Looks kinda rough at this point.

Smooth out the opening with Dremel tool sanding drum or rotary file in your drill motor.

Smooth out the opening with Dremel tool sanding drum or rotary file in your drill motor.

Drill a pilot hole on the opposite side for the exhaust tube and open it up with a step drill. Make a close fit to make the welding more efficient.

Drill a pilot hole on the opposite side for the exhaust tube and open it up with a step drill. Make a close fit to make the welding more efficient.

Adjust the tube as required ...

Adjust the tube as required …

… and mark it for fit so you can get it welded to the right length later on.

… and mark it for fit so you can get it welded to the right length later on.

Next, find some scrap aluminum to make a cover for the top of the muffler. I found and old battery charger and cut a chunk out with my hole saw. Did a bit of shaping to make it fit the contour of the muffler.

Next, find some scrap aluminum to make a cover for the top of the muffler. I found and old battery charger and cut a chunk out with my hole saw. Did a bit of shaping to make it fit the contour of the muffler.

Nice fit!

Nice fit!

Now you need a way to keep the new part hold in place for welding. A long bolt thru to the opposite side will work. You don’t want to just hand the welder a lot of loose parts and expect him to figure it out.

Now you need a way to keep the new part hold in place for welding. A long bolt thru to the opposite side will work. You don’t want to just hand the welder a lot of loose parts and expect him to figure it out.

And on the opposite side, find a large washer to anchor the bolt to. In other words, the top plate will have to be welded or just tack welded before the exhaust tube. Once tacked, remove this jig and move to the exhaust tube.

And on the opposite side, find a large washer to anchor the bolt to. In other words, the top plate will have to be welded or just tack welded before the exhaust tube. Once tacked, remove this jig and move to the exhaust tube.

Once the top cover is welded, you need to make sure the exhaust tube is straight. A simple plywood jig is bolted to the muffler mounting holes with a guide CA’d to it for alignment. Of course, you do this AFTER the top plate is welded or just tack welded. You will have to be there to do these jigs while the welder is working. No offense to welders, but you are likely going to be the only one who knows how it all is supposed to look. It won’t take long for him to tack things together and you can remove the jigs and let him take his time doing the rest of the welding.

Once the top cover is welded, you need to make sure the exhaust tube is straight. A simple plywood jig is bolted to the muffler mounting holes with a guide CA’d to it for alignment. Of course, you do this AFTER the top plate is welded or just tack welded. You will have to be there to do these jigs while the welder is working. No offense to welders, but you are likely going to be the only one who knows how it all is supposed to look. It won’t take long for him to tack things together and you can remove the jigs and let him take his time doing the rest of the welding.

Top plate welding completed and wire-brushed.

Top plate welding completed and wire-brushed.

Exhaust tube welding completed. The weld may not look quite as clean as the factory welds, but those may be done by a robot or a human welder who does this all day long!

Exhaust tube welding completed. The weld may not look quite as clean as the factory welds, but those may be done by a robot or a human welder who does this all day long!

Another problem was a bit of interference with the cowl on the front of the muffler. You trim off the aluminum with a hack saw as required, make a new aluminum panel or panels, and weld those up too. All this welding ran me $30 but that was WAY less $$$ than buying a new custom muffler!

Another problem was a bit of interference with the cowl on the front of the muffler. You trim off the aluminum with a hack saw as required, make a new aluminum panel or panels, and weld those up too.
All this welding ran me $30 but that was WAY less $$$ than buying a new custom muffler!

Newly modified muffler in its new home. Teflon extension tube dumps exhaust out the bottom of the fuselage.

Newly modified muffler in its new home. Teflon extension tube dumps exhaust out the bottom of the fuselage.

With the cowl in place, engine and muffler are easily seen.

With the cowl in place, engine and muffler are easily seen.

Blacking out the engine and muffler is a plus. To me anyway. A light coat of flat black helps dissipate heat.

Blacking out the engine and muffler is a plus. To me anyway. A light coat of flat black helps dissipate heat.

 

With cowl in place, looks good!


TEXT & PHOTOS BY LANE CRABTREE

Updated: October 6, 2023 — 10:35 AM
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