Attention: TDR Forum Junkies 
Mike Ellis
TDR MEMBER
Thanks for the good suggestions on the install folks! I had to wrestle with it a bit, but after Mark Holmes at Bigfoot verified they do indeed put a clamp on the tailpipe-muffler outlet joint I came up with a scheme that worked pretty well. For those who might run into the same scenario down the road, I will post the details.
*********************
Camper - Bigfoot 2500 10. 6, 1997 vintage
Generator - Onan 2500 Microlite
Install Notes
1. On my generator, the muffler outlet is up inside the generator itself and the compartment is very tight. Raising the generator up on shims (1st thing I tried) to the roof of the compartment didn't give enough room to do the install - see first thread for pics of compartment and the basic problems:
https://www.turbodieselregister.com/forums/showthread.php?t=125654
2. Mark at Bigfoot assured me the install could be done through the duct, if necessary the duct can be unscrewed and dropped down for a bit more room (it is a sheet metal sleeve). Apparently some folks can indeed get their hands into the duct, in my case this was a no-player. A picture of the duct with pipe installed gives you an idea of how much room you have left for your hands.
3. When you get the tailpipe kit from Onan or your RV dealer, it will likely be UNSLOTTED like mine. In fact, the original tailpipe on my camper was unslotted and had just been "slip fit" with some goop over the muffler outlet - hence the ease with which it came out. If your pipe is unslotted, take it to the muffler shop and they will cut slots in it for a few bucks. The first place I took mine to told me to pound sand, but the guys at the 2nd place did it for free. Don't let the kit fool you, the pipe is indeed supposed to clamp on to the muffler outlet, without slots you won't get much clamping accomplished without one HECK of a lot of grunting.
4. My tailpipe kit had a pipe that was necked down, if you had a pipe that was the same smaller diameter all the way down it would give you a bit more room in the duct. If I had to do it again, I wouldn't bother buying a kit, I'd just go get the smaller diameter pipe at a muffler shop and have them bend it and slot it from the get-go.
5. Unless you have the proverbial skinny ape-like arms :-laf you will benefit from unbolting your generator and moving it toward the back right corner of your gennie compartment. This will put the pipe near the edge of the duct and give you max room for wrenching.
6. After slotting, I prepped my pipe by gooping the slots thoroughly with high-temp Permatex "Ultra Copper" copper-filled silicone. I then folded several thicknesses of heavy duty aluminum foil and made strips that I stuck inside the pipe to cover the slots and prevent leaks. I folded the foil over the top, then used some stainless steel tape to hold it down and cover the slots on the outside - wanted to try and minimize chances for leaks. Since this tailpipe is post-muffler, there shouldn't be enough pressure to raise a concern but what the heck. The clamp is then installed on the pipe, a good layer of the silicone applied inside the neck for further sealing, then the pipe is stuffed up into the duct and slid over the muffler outlet. May have to spread the tailpipe a bit to get it to go on, the slotting makes this easy to do.
7. The duct itself is nearly 14" long, so once the tailpipe and clamp are up in there, how do you reach the bolts? Some installers can reach up into the ducts, but if you have beefy mitts like me you need a wrench on a long handle. A box wrench or open end might work here if you have the patience of Job, or a socket wrench if you have one with a REALLY skinny head and socket. The best approach is to get one of those ratcheting box wrenches. Important note - you need one that has a fine-tooth ratchet, like the Craftsmen variant. Give the length of the handle you will have to use, and the width of the duct in which you can swing it, a coarse-tooth ratchet will very likely not be able to index with such a short swing.
The Craftsman wrench I used has 72 teeth per rev, so even a tiny arc of motion will let it ratchet. Even with this I was able to get only about 1 click per swing, but that was plenty to get the job done.
8. I used a LONG socket extension for my wrench handle, and held the wrench on with 3 stainless steel hose clamps. This made a rigid assembly that worked fine for wrenching the clamp. Tie wraps might work in a pinch, but might flex enough to make wrenching a problem. Go with the hose clamps.
9. The actual installation took less time than doing this write-up, but I had a couple of false starts along the way. First, trying to do it in daylight is a pain in the butt - the bottom of the camper is very white, and your daylight-adjusted eyes can't see into the $%^&!!! duct very well. Trying to hold a flashlight, a tailpipe, and a wrench while trying to peer up into that duct is a massive exercise in frustration. Do it the easy way - wait until the sun goes down, or do it indoors. I happened to have my camping LED headlight which puts the light right where you are looking, doing it after dark was far far easier.
10. Once you get the pipe in place and start wrenching, you will be there for a while so make yourself comfortable
*********************
Camper - Bigfoot 2500 10. 6, 1997 vintage
Generator - Onan 2500 Microlite
Install Notes
1. On my generator, the muffler outlet is up inside the generator itself and the compartment is very tight. Raising the generator up on shims (1st thing I tried) to the roof of the compartment didn't give enough room to do the install - see first thread for pics of compartment and the basic problems:
https://www.turbodieselregister.com/forums/showthread.php?t=125654
2. Mark at Bigfoot assured me the install could be done through the duct, if necessary the duct can be unscrewed and dropped down for a bit more room (it is a sheet metal sleeve). Apparently some folks can indeed get their hands into the duct, in my case this was a no-player. A picture of the duct with pipe installed gives you an idea of how much room you have left for your hands.
3. When you get the tailpipe kit from Onan or your RV dealer, it will likely be UNSLOTTED like mine. In fact, the original tailpipe on my camper was unslotted and had just been "slip fit" with some goop over the muffler outlet - hence the ease with which it came out. If your pipe is unslotted, take it to the muffler shop and they will cut slots in it for a few bucks. The first place I took mine to told me to pound sand, but the guys at the 2nd place did it for free. Don't let the kit fool you, the pipe is indeed supposed to clamp on to the muffler outlet, without slots you won't get much clamping accomplished without one HECK of a lot of grunting.
4. My tailpipe kit had a pipe that was necked down, if you had a pipe that was the same smaller diameter all the way down it would give you a bit more room in the duct. If I had to do it again, I wouldn't bother buying a kit, I'd just go get the smaller diameter pipe at a muffler shop and have them bend it and slot it from the get-go.
5. Unless you have the proverbial skinny ape-like arms :-laf you will benefit from unbolting your generator and moving it toward the back right corner of your gennie compartment. This will put the pipe near the edge of the duct and give you max room for wrenching.
6. After slotting, I prepped my pipe by gooping the slots thoroughly with high-temp Permatex "Ultra Copper" copper-filled silicone. I then folded several thicknesses of heavy duty aluminum foil and made strips that I stuck inside the pipe to cover the slots and prevent leaks. I folded the foil over the top, then used some stainless steel tape to hold it down and cover the slots on the outside - wanted to try and minimize chances for leaks. Since this tailpipe is post-muffler, there shouldn't be enough pressure to raise a concern but what the heck. The clamp is then installed on the pipe, a good layer of the silicone applied inside the neck for further sealing, then the pipe is stuffed up into the duct and slid over the muffler outlet. May have to spread the tailpipe a bit to get it to go on, the slotting makes this easy to do.
7. The duct itself is nearly 14" long, so once the tailpipe and clamp are up in there, how do you reach the bolts? Some installers can reach up into the ducts, but if you have beefy mitts like me you need a wrench on a long handle. A box wrench or open end might work here if you have the patience of Job, or a socket wrench if you have one with a REALLY skinny head and socket. The best approach is to get one of those ratcheting box wrenches. Important note - you need one that has a fine-tooth ratchet, like the Craftsmen variant. Give the length of the handle you will have to use, and the width of the duct in which you can swing it, a coarse-tooth ratchet will very likely not be able to index with such a short swing.
The Craftsman wrench I used has 72 teeth per rev, so even a tiny arc of motion will let it ratchet. Even with this I was able to get only about 1 click per swing, but that was plenty to get the job done.
8. I used a LONG socket extension for my wrench handle, and held the wrench on with 3 stainless steel hose clamps. This made a rigid assembly that worked fine for wrenching the clamp. Tie wraps might work in a pinch, but might flex enough to make wrenching a problem. Go with the hose clamps.
9. The actual installation took less time than doing this write-up, but I had a couple of false starts along the way. First, trying to do it in daylight is a pain in the butt - the bottom of the camper is very white, and your daylight-adjusted eyes can't see into the $%^&!!! duct very well. Trying to hold a flashlight, a tailpipe, and a wrench while trying to peer up into that duct is a massive exercise in frustration. Do it the easy way - wait until the sun goes down, or do it indoors. I happened to have my camping LED headlight which puts the light right where you are looking, doing it after dark was far far easier.
10. Once you get the pipe in place and start wrenching, you will be there for a while so make yourself comfortable
