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How I replaced a 521 exhaust system

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I used the stock L-16 Y pipe.  they are usually the last piece of a stock exhaust system to rust out, because it is a thicker metal, and the heat of the exhaust dries the water out of it quicker, no water, no rust.

Columbia River calls the part you are looking for a "merge collector"


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I put a L-20-B engine in the truck after I had replaced the exhaust system, the exhaust system was built with a L-16 engine with the 4 into 2 manifold.


When I got the L-20-B engine, I also got the down pipe off that engine.  The 720 down pipe fits the 521 almost perfectly.  I just need to make and put a flange on the down pipe and bolt it up.  I really hope it goes that easy. 

It didn't.


This is the L-20-B downpipe next to the L-16 2 into 1 collector.



This is the flange I put on the L-16 down pipe to attach to the rest of the exhaust pipe.  I did not have an extra flange.  I need to make one.



I did have a piece of 5/16 steel plate.  This is how I made a flange.


I held the flange on the L-16 down pipe on the plate, and marked around it with a Sharpie felt pen.


Found the center of the flange, and center punched it.  The first center punch was not really centered.


Drill an 1/8 inch pilot hole, notice the cup of oil at the top of the picture.  The oil is just old gear lube.  With the 1/8 hole drilled, I then enlarged the hole to 1/4 inch, to make a pilot hole for a hole saw.


The hole saw has a a set screw to hold a 1/4 drill, but the set screw does not really hold the drill secure enough to drill a hole in metal.  But once the 1/4 hole is in place, the hole has only to center the hole saw.  In fact, after the hole saw has started to cut, the 1/4 drill is no longer needed.  I also used a lot of gear oil on the hole saw.  The drill I used on the hole saw is heavy duty 1/2 corded and keyed chuck Milwaukie drill.  A drill press would be even better, but I do not have a drill press.


With the 2 inch hole in the plate, I used a spare piece of pipe up through the 2 inch hole to center the old pipe and flange on the plate, and then to located one of the three  5/16 holes to hold the flange to the other matching flange on the pipe on the rest of the exhaust system.


Here I am drilling the second of three holes to hold the flanges together.  Notice I have the bolt in the first hole to locate the second hole accurately.  I also used the spare piece of pipe to help locate the small holes.


I drilled the third bolt hole, using two bolts in the first two holes to locate the third hole.  With all three holes drilled, I deburred the holes.



Then I bolted the old pipe and flange to the steel plate I was making a new flange with.


and then, a cutting torch to cut the flange from the steel plate.


then I used a 9' angle grinder to smooth the edgers of the new flange, and then smaller grinders to finish the flange more.
More grinding,

and then remove mill scale of the mating surfaces of the flange, and to make eventual welding easier.


This is the pipe mismatch with the exhaust pipe from the 720 truck that the engine came out of, looking up.

This is from the side. 
The down pipe was too low, I put a jack under the 720 down pipe to bend it up.  
I used an old main bearing cap to push the pipe up.


I really did not like the way the whole piece of the 720 down pipe was fitting together to the existing exhaust system on this 521.  I ended up cutting the 720 pipe off just below where it is held on  the exhaust manifold.

I had a 2 inch 90 degree mandrel bend, after deciding it would be easier to use it, I tack welded it to the 720 down pipe short piece and, bolted them on the L-20-B engine.  This is looking from the side.
The straight piece of pipe on the right side of this picture is not welded to the flange I made on Saturday, I bolted the flange I just made to the existing exhaust pipe to check alignment.  Good alignment, looking up.
New pipe elbow tacked to old 720 down pipe.  It ended up too high.
I had to grind out three tacks on the elbow to down pipe, and bend it down slightly.


This is the gap after I adjusted the location of the elbow to match the rest of the exhaust pipe.





Edited by DanielC
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Mklotz70 made L16/18 flanges years ago. I had one for 7-8 years as a novelty item but used it a couple of years ago to join 240sx down pipes to the L16 manifold. The 240sx pipes join under the floor and are quite long. I doubt I could have made a merge collector.







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This is a continuation of an edited post I made above.

I had a good match of the elbow tack welded to the short piece of 720 down pipe, and I just needed a piece of straight pipe to go from the elbow to the existing exhaust system.

I cut a new piece of straight pipe to go between the elbow and the existing exhaust system. 
I am preparing to weld the straight pipe to the new flange.
This is a tack weld joining the straight pipe, and the new elbow.
Tack weld on flange, on one side
Tack welds on flange the other side.

With the downpipe tack welded, I removed it, and welded the flange, straight piece of pipe, the elbow, and the exhaust manifold connection together.  Then grind the welds off, and put it back on the truck.
Other side of the down pipe.


With the downpipe in place, it looked a little too close to the speedometer cable.
I took the transmission end of the speedometer cable off, cleaned the cable, and rerouted the cable outside of the steering column.

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