Re-installing power chamber and adding sportster mufflers

RocketMan

RocketMan

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Hey everyone,

Some background - I bought a 1980 CM400T with some ugly cafe cone mufflers and straight pipes. I noticed the bike doesn't run super well (popping, low-power), and did some research. Everyone seems to say the power chamber is necessary on the bike, so I snagged a stock one.

So here's the issue - I have some Harley sportster pipes to replace these ugly cafe pipes with, and I'm stumped. Both the power chamber AND the pipes have the same flange, meaning I can't connect them. There doesn't seem to be enough room on the inside of the power chamber to slide some stainless steel connection pipes, which I have. There's some pics of both parts attached for context. Now go easy on me, I'm not a mechanic and this is my first bike - I know enough to keep me afloat, but not enough to answer this question myself.

My question is - can anyone help me figure out how to connect these pieces? I've seen that this is a pretty common mod, and yet I can't find any details about installation.

IMG_2246.jpegIMG_2247.jpeg
 
1st review this parts fiche https://www.partzilla.com/catalog/honda/motorcycle/1980/cm400t-a/muffler
The primary pipes insert into the power chamber and are sealed by number 13. The clamps for the pipes are special pieces, they have tabs that go over the ridge on the pipe on the front and fit into grooves on the chamber. This keeps the power chamber secured firmly to the pipes.
The mufflers are set up the same way, looking at the muffler picture there may not be enough inlet pipe to work with so an extension may be needed.

PS: my replies may be slow as I'm still recovering from surgery
 
Thanks for this answer, Jim - so I'll need to get those exhaust gaskets and clamps and we should be in business. Do you know where I can get some extensions? I suppose I'd need to get some extra gaskets for both sides of the extension pipe if needed - could I get any old stainless steel pipe extensions from the auto shop? Any diameters that would fit the gaskets best?

Hope you recover soon!
 
You'll need 2 each of #13 and #14. I'd look at eBay to see if you can find the correct clamps rather then buy them from Honda, regular type muffler clamps don't work well and are ugly as sin.
Once you have the seals you can see how the mufflers will fit in the chamber, auto part stores carry short muffler pipe pieces so that's an option but might be better to go with a muffler shop and have the extension welded to the muffler. In any case you'll want to hold on that until you get the pipes and chamber mounted up so you can see where the mufflers need to be set, which will be the final call on and extension.

Something happened with my ear last night, made a horrific Snap followed by intense pain BUT now the pain is less than prior, I slept for over 10 hours and on the right ear. The surgery was replacing the right Cochlear Implant which was failing. Feel so much better today.
 
2 of each, #13 and #14. Got it. Luckily, I was able to salvage the rear clamps off of the old, rotting power chamber and exhaust pipes, so I can cross those off the list. Just need two front clamps.

Anywhere I can get the gaskets for a bit of a better price? I don't mind shelling out the cash for the exact fit, of course, but I wonder if there's something readily available and universal I could go get somewhere. I'd like to try that option before getting everything welded together. I also have the extensions already, so once I have the gaskets I have a feeling everything will fit, but we'll see.

Sorry about your ear - I hope it gets well soon, that seems like it would be awful. Take it easy and hopefully it'll improve
 
Found some on eBay, along with 4 OEM clamps. https://www.ebay.com/itm/294865101191

I'm hoping this all works out, if it doesn't maybe I'll just tune the carbs for straight pipes in the meantime and bring it to an exhaust shop. I just feel I could be getting so much more out of the bike.

Again, I'm decently inclined on repairs and installations, so this shouldn't be difficult, but I always like to have a backup plan.
 
I hope you will check the carburetor jetting when you have your power-chamber all hooked up;plug check for color of the center electrode porcelain.
I had run too lean in the past;it turns out when I ran it richer later that it was covering-up a problem of a worn set of needles and needle jets too,as the fuel was not atomizing in an optimum ratio.
 
bilbikek411 said:
I hope you will check the carburetor jetting when you have your power-chamber all hooked up;plug check for color of the center electrode porcelain.
I had run too lean in the past;it turns out when I ran it richer later that it was covering-up a problem of a worn set of needles and needle jets too,as the fuel was not atomizing in an optimum ratio.
Click to expand...

Definitely will be doing that - the owner said it had stock jetting from when he originally removed the power chamber and never replaced it. He seemed trustworthy, however it doesn't hurt to check his work ;)
 
Hey again, everyone!

OK so I've got the clamps and the gaskets. The gaskets don't seem to fit the power chamber's ports very well. Any tips for getting everything settled? Would a heat gun work to get me get everything connected?

Thanks in advance!
 
RocketMan said:
OK so I've got the clamps and the gaskets. The gaskets don't seem to fit the power chamber's ports very well. Any tips for getting everything settled? Would a heat gun work to get me get everything connected?
Click to expand...

You didn't say if the gaskets were too small, too large, or the ports are out of round. You may have to scrape the old gasket out, it does a good job imitating metal sometimes.

For too small, or out of round, an exhaust pipe expander is the solution. The smallest commonly available is 1-1/8" at its smallest, which should work.

I don't have this one, but it looks just like mine:
https://www.amazon.com/Small-Tail-Expander-Exhaust-Muffler/dp/B01HLUVHQM

I use my Knipex Pliers Wrench for straightening the petals:

https://www.amazon.com/Tools-86-03-125-SBA/dp/B00OYQ2YOG
 
Ah yes! Slightly too large - my bad. They don't quite fit into the ports. Any advice on gaskets that are too big? I'll check to see if there's any extra gasket material stuck in the ports.

Thanks for the pipe expander tidbit of information, that will definitely be helpful for the future.
 
RocketMan said:
Ah yes! Slightly too large - my bad. They don't quite fit into the ports. Any advice on gaskets that are too big?
Click to expand...

The gaskets are sized to fit into the power chamber ports. If they don't, either the ports have been shrunk by clamps, and need the expander (like the one I linked), or there is gasket material in there that needs to be cleaned out.
 
Oh got it - I misunderstood, thought you meant expanding the gasket (which now that I think about it, doesn't make sense). I'll try that out, thanks for the advice!
 
I've used the expanders to get ovals round but smaller, sharper dents I hammered out with a ball peen using a large thick galvanized waterpipe for a inside anvil. I forget the size and may have added some sheet metal to keep it tight. It came out great.

Is the inner diameter of the gasket snug to the header pipe? If so your good. If it's still to big around after you get the chamber ports all nice then you could file or belt sand the gasket outer some. Get a small gnarly wire wheel to really get the rust layers out of the chamber ports.
 
KenCM450 said:
The gaskets are sized to fit into the power chamber ports. If they don't, either the ports have been shrunk by clamps, and need the expander (like the one I linked), or there is gasket material in there that needs to be cleaned out.
Click to expand...

I find that the four 'petals' on the 2 outlet ports of the power chamber are usually compressed/bent-in from previous tightenings with the clamps and that area needs to be expanded open to fit new factory gaskets.
 
KenCM450 said:
You didn't say if the gaskets were too small, too large, or the ports are out of round. You may have to scrape the old gasket out, it does a good job imitating metal sometimes.

For too small, or out of round, an exhaust pipe expander is the solution. The smallest commonly available is 1-1/8" at its smallest, which should work.

I don't have this one, but it looks just like mine:
https://www.amazon.com/Small-Tail-Expander-Exhaust-Muffler/dp/B01HLUVHQM

I use my Knipex Pliers Wrench for straightening the petals:

https://www.amazon.com/Tools-86-03-125-SBA/dp/B00OYQ2YOG
Click to expand...

Thank you for exposing me to another expensive tool I did not know about :)
 
ausman1000 said:
Thank you for exposing me to another expensive tool I did not know about :)
Click to expand...

The Knipex? You're welcome!

It is great for working with metal. It has enough leverage to flatten things out just by squeezing. The jaws are smooth, so it doesn't chew up the finish. It also makes a fabulous plumber's tool.

I have 5 now, in all sizes, one I carry in my Honda Valkyrie tool roll.
 
Alright, so an update - this is a slow-moving project for me.

I called my local muffler shop, they work on bikes. They're willing to help me out in getting everything together if I can't quite figure it out myself, but I'm determined.

It turns out that the old gaskets were still wedged into the power chamber, just like Ken said - I used a pick to scrape them all out. Now that I have them out, I need to pop some new gaskets in there, as well as the pipes, and pipe extenders. I also bought an exhaust pipe expander just in case - thanks again for that recommendation.

Going to attempt this later, then next up is a VT750 headlight swap. But we'll see how the exhaust goes, I'm not trying to get ahead of myself here. I'll keep everyone updated, as I know we're all heavily invested :lol:
 
Glad you're making progress, and I deeply understand the nature of slow-moving projects. I'm putting together an after-the-fact project log for this site, and shake my head on how long it took me to fix my bike. fix.

The wedged gaskets were fresh in my mind because I just dealt with that 2 months ago. The fact that they are painted a metal color doesn't help, at first I thought they were part of the power chamber.
 
I feel every project of mine is a slow moving one, but the results always come. As long as the bike is rideable in its current state and not spending most of its time in the garage, I consider it a win. This is just to make it run a little nicer :)

Good tip - I'm not sure why they painted them with a metal texture. Doesn't make much sense to me in terms of removal
 
RocketMan said:
I feel every project of mine is a slow moving one, but the results always come. As long as the bike is rideable in its current state and not spending most of its time in the garage, I consider it a win. This is just to make it run a little nicer :)

Good tip - I'm not sure why they painted them with a metal texture. Doesn't make much sense to me in terms of removal
Click to expand...

I just got my generic 38x45 mm graphite sleeves ordered by size on ebay and they were cheap. Onward with my 305 exhaust project.
I wanted to share how I used a thick walled hunk of galvanized water pipe as an anvil inside to bang all the dents out of the power chamber flanges and get them really round again. It was well worth it and everything slid together pretty nice. Also, I was careful not to overtighten the clamps when it was done, like so many seem to do.

Very cool that you still have a power chamber.
 
So I found out my problem - I've looked into several other posts on this topic, and it seems a lot of people used mufflers from a Dyna, and I got mine from a sportster. The dyna mufflers seem to slip right into the outlet of the chamber, whereas the sportster ones are the same size. The coupling seemed to be a bit loose, so I opted into taking this to my local muffler shop to attach the mufflers onto the back of the chamber. I like the look of the thicker sportster mufflers, so I'm okay with it.

It was worth a shot to do the work myself, but at the end of the day, it made more sense for me.

Thanks for all of your help!
 
Glad you got it figured out. Be sure to post some pictures of the results for the benefit of others later.
 
100% - They're going to do some welding magic and I'm sure it'll turn out great.

Can't wait for my bike to make its forum debut
 
Alright y'all, here we have it.

First on the list was getting this bike running well. Now, to tackle the awfully un-ergonomic buckhorn bars and headlight. Here's a video of it running:


20241.jpg
 
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Thanks, Jim!

I have a set of bars that look similar to that. I need to figure out how to route the throttle cable, it was giving me some trouble the first time.

Appreciate the info about Speedmotco.

And thanks, Ken! I am too
 
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