Exhaust pipe threads

[kylev]

I am cleaning up my Exhaust manifold and the threads where the pipe screws in are pretty dirty. Does anyone have a tap that I could rent or buy or know where I can purchase a single 1 1/4" NPT tap?


Also is it ok to just go ahead and run a tap on it to clean the threads?

Thanks

[Paul_NJ]

A pretty effective way to clean up those threads without buying a tap is to take a pipe nipple of the same size, and cut kerfs with a hacksaw at right angles to the threads. Turn the nipple into the manifold with a pipe wrench. Unless the manifild threads are really bunged up, this trick will do a decent job cleaning them out.

[Paul_NJ]

Also, I seem to recall the exhaust pipe on the Cub is 1" NPT, not 1 1/4" NPT

[John *.?-!.* cub owner]

According to my parts book, the change from 1 inch to 1 1/4 inch was made at engine serial number 312390.

[parts man]

If the manifold is off the tractor you can take it to a plumbing shop, they should have a tap.

[kylev]

Ok what I have is a 1 and 1/4 inch hole. I looked at the threads and they are way to messed up to tap. So I dropped it by my cousins machine shop and what he said he would do is machine the hole out smooth then make a bushing to insert into it and brase it in the manifold. Then he will tap it with a 1 inch npt tap. He didnt have a 1 and 1/4 to tap it with and he said it wouldnt have done much good anyway since the threads were so badly messed up. Having that said I am assuming that going to 1 inch will not restrict the engine much since they have made 1 inch manifolds for earlier engines... Is this correct?

[Eugene]

Probably to late now.

Why not thread in the 1 1/2 inch exhaust pipe. Then drill and tap through the side of the manifold and exhaust pipe. Then install a bolt. Allis Chalmers did that on some of their manifolds.

Second choice. Thread in then braze in an 1 1/2" nipple. Use an 1 1/2 " to 1 1/2" coupling to thread on the exhaust pipe.

You probably won't notice a significant loss of power with the reduced exhaust size pipe.

Eugene

[Paul_NJ]

Pipe sizes are nominal. The OD of 1" pipe is 1.3"; the OD of 1-1/4" pipe is 1.66". If your manifold female thread measures approx 1-1/4", then what you originally had in there was a 1" pipe.

[Matt Kirsch]

As a general rule, when they measure PIPE, it's by the inside diameter because that's the one that's important for flow. Your typical 1" iron pipe will measure approximately 1" inside. Note that I said approximately.

TUBING on the other hand, is measured by the outside diameter, I believe. That's because tubing is structural, and the outside measurement is the one that's important.

[John *.?-!.* cub owner]

Kyley, you never did state which model and year you are working on. Teh lkater ones had the larger manifold, with teh Zenith carb, as well as a modified camshaf, stepped pistons, adn modified head. h
This set up gave more hp and rpm, and therefore required the larger manifold openings. The differenced may not be large, but if you work it hard, would be noticeable. Teh difference between the 2 is approximately 20% in ctha ability of the pipe to carry exhaust gas. 3.14 square area cross section versus 3.83.

[Ron L]

Pipe sizes are nominal. The OD of 1" pipe is 1.3"; the OD of 1-1/4" pipe is 1.66". If your manifold female thread measures approx 1-1/4", then what you originally had in there was a 1" pipe.

Kylev. The above is correct. It's probably too late since to gave it to a machine shop. But remember, the tap is tapered. And, you could have went a little deeper to clean the threads up (or had the shop do it). My manifold threads looked shot, so I just tapped it deeper. Worked great - And, it did not leak.

[Ron L]

Here's a couple pics for your info .......... (This was almost two years ago, and she's still holding strong)

BEFORE:


AFTER:

[kinelbor]

Check your math John.

3.14*(0.5*0.5) = 0.785 square inches
3.14*(0.625*0.625) = 1.226 square inches

0.785/1.226 = 0.64(100) = 64% larger opening between 1" and 1 1/4"

[Bus Driver]

Ron is right. Pipe threads taper 3/4" per foot. Just a couple of turns of a tap cuts considerably deeper. It is the easiest thing to try first. Everything else is Plan B.

[beaconlight]

I have cleaned them up with grooves ground in pipe to make it fluted like a tap with quite success. It was on a C with vertical exhaust. The old threads looked all gone but they cleaned up enough and the tapered pipe threads went in far enough to hold well for over 10 years that I know of. My neighbor died and his family sold the tractor. I used it quite often too. That was before I got my Low Boy. George had a Woods belly mower on it. I had trouble with the mower a couple of different times. The first time the Fibre slip washers wore through. There not a Woods dealer near Oneonta so I replaced them with hand cut leather washers. It worked fine. Another time the bearings in one of the spindels went bad. I was headed home and again no dealer so I juru rigged the spindle from a riding lawn mower in it's place. I called George in Connecticut where he lived so he would know. He said not to worry there was a dealer in Connecticut near where he lived. I offered to pay for the parts. Even at that it was cheap rental. George had the Radiator lose a couple of tubes one time and I cleaned and soldered them for him.
George was Highway Super in his town in CT. He is the one taught me if you are on a slope sideways, never turn up hill. Ride it down, it may be scary, and build up speed, the engine holding back and or brakes may make the tires skid but you will not flip over. It came in handy to know what to do once. Don't ask.

Bill