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Discussion Starter · #1 ·
Hey All! Just wanted to get a link up to my newest project...

I bought a '79 CM400t that the previous owner had dismantled some time ago. He had purchased some new parts & tires and had the frame powder coated. The rest came in boxes!

The cafe conversion requires some major subframe mods.......I've been documenting it on youtube. Check it out.......

 

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Welcome to the forum. Great to see another 400 series here. Looks like you're in for some fun.

You'll need a proper Honda Factory Service manual to go with the Clymer picture book.

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Discussion Starter · #6 ·
Quick question.... does anyone know offhand what the stock front and rear sprocket sizes and number of chain links are(were) for the CM400? Thanks
 

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I have been contemplating this frame seat problem on my 450 cm for several months now. I thought about cutting the frame and putting a straight bar design, but seems to lead to a higher rear shock top mounting point and new longer after market shock purchase. Instead I opted to cut the factory seat metal and build a new seat off of that platform. Extremely difficult, but I think I have a unique design vision, and if I can achieve it, I think it will pay off big! It's in my project log link.

 

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Make a run of them, have them upholstered and put them up to auction, there are a few cool seats available for CM400s but none overcome the way the frame design limits (or rather relegates) the bike's cafe racer asperations to mere delusions.

I'd bet they sell out.
 

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Discussion Starter · #14 ·
I have been contemplating this frame seat problem on my 450 cm for several months now. I thought about cutting the frame and putting a straight bar design, but seems to lead to a higher rear shock top mounting point and new longer after market shock purchase. Instead I opted to cut the factory seat metal and build a new seat off of that platform. Extremely difficult, but I think I have a unique design vision, and if I can achieve it, I think it will pay off big! It's in my project log link.

View attachment 247594
I ran into the same issues after I had cut the frame.... problem solved!.... sort of...

 

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Discussion Starter · #16 ·
Looks like you just raised the rear frame swing arm up to the higher shock mounting points. This will lower the rear... and counter act the front fork lowering and racer angle. Not sure how that will look. Probably ok... Might want to lower the front forks a little extra to compensate.

View attachment 247906
Yeah the front forks will be lowered about 2". Not sure If I'm gonna just slide them up the triple mounts or do the proper lowering (shim etc). It will come down to whether or not the clip-ons are above or below the triple tree. I go back and forth on that one

Personally, I think it gives the bike a great stance, we will find out later how it rides :)
 

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Nice work, but what you've done so far raises a couple of questions.
You've got an excellent grasp of the aesthetics, but functionally, I see a couple of problems. Starting with the fuel tank, raising the rear end to align with the seat pan makes for a classic café racer look, but the bike was designed with a sort of chopperesque aesthetic, meaning the tail end of the tank sloped down with the frame. Note the location of your fuel petcock relative to the lowest point on the tank; as it sits now, you'll never be able to drain the tank while it's on the bike, and you'll always run out of fuel before the tank is actually empty. And there will be no way to use what fuel is left in the tank.
It will be a good idea to make room for the rubber biscuit when you go to re-locate the rear tank mount. There's a reason that fuel tanks are rubber mounted.

Now have a look at the angle of the swing arm, and compare it to practically every production bike out there. Note that the normal practice is to have the rear axle sit a few inches below the swing arm pivot when the bike is unloaded. The idea is that the chain is adjusted with a bit of slack that gets taken up as the rear suspension compresses. What you've got now is a swing arm that's barely got any slope to it, before there's an engine in the bike, to say nothing of carrying a rider. Once you add weight, the rear axle will rise above the swingarm pivot. The farther the suspension compresses, the looser the chain will get. This looks like an invitation to having the chain come off over a big bump.

Oh, and you discuss sliding the fork tubes up in the triple clamps to lower the front end. This works just great, up until the front fender or wheel crashes into the bottom of the lower triple clamp under full compression. You can limit suspension travel by installing preload spacers (with possibly shortening the springs as well) so that the springs bind before the wrong parts start hitting each other, but then you open a bucket of worms in terms of adequate sag, spring rate, and damping.

Maybe you intend to address these issues. It'll be interesting to follow your progress.

HTH
 

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Discussion Starter · #19 ·
Nice work, but what you've done so far raises a couple of questions.
You've got an excellent grasp of the aesthetics, but functionally, I see a couple of problems. Starting with the fuel tank, raising the rear end to align with the seat pan makes for a classic café racer look, but the bike was designed with a sort of chopperesque aesthetic, meaning the tail end of the tank sloped down with the frame. Note the location of your fuel petcock relative to the lowest point on the tank; as it sits now, you'll never be able to drain the tank while it's on the bike, and you'll always run out of fuel before the tank is actually empty. And there will be no way to use what fuel is left in the tank.
It will be a good idea to make room for the rubber biscuit when you go to re-locate the rear tank mount. There's a reason that fuel tanks are rubber mounted.

Now have a look at the angle of the swing arm, and compare it to practically every production bike out there. Note that the normal practice is to have the rear axle sit a few inches below the swing arm pivot when the bike is unloaded. The idea is that the chain is adjusted with a bit of slack that gets taken up as the rear suspension compresses. What you've got now is a swing arm that's barely got any slope to it, before there's an engine in the bike, to say nothing of carrying a rider. Once you add weight, the rear axle will rise above the swingarm pivot. The farther the suspension compresses, the looser the chain will get. This looks like an invitation to having the chain come off over a big bump.

Oh, and you discuss sliding the fork tubes up in the triple clamps to lower the front end. This works just great, up until the front fender or wheel crashes into the bottom of the lower triple clamp under full compression. You can limit suspension travel by installing preload spacers (with possibly shortening the springs as well) so that the springs bind before the wrong parts start hitting each other, but then you open a bucket of worms in terms of adequate sag, spring rate, and damping.

Maybe you intend to address these issues. It'll be interesting to follow your progress.

HTH
Old Putz, all valid points, and that's part of the enjoyment of a project like this. Using a CB frame would certainly be more straight forward, but going this route makes me think harder... and ultimately figure out if the mods I'm making are useable in real applications...

To address a couple of things...

The tank as it is right now is level at the bottom, I don't think there will be much fuel that wouldn't reach the petcock, but we will have to see once everything is on. Ultimately a tank swap would be pretty easy..

Once the engine is in and I'm sitting on the bike, I'll see what the swingarm does. The replacement shocks that came with the frame are super stiff compared to what I recall with stock. That makes me worry less, but ultimately a longer shock could remedy things. I've been pondering ordering a new set anyways just to have a bit more adjustability. Another one of those things that ultimately will answer itself as more things come together...

Fully agree about the front forks. Lowered or just slid up the tree, I will have to shim the springs to be tighter. I won't do anything yet until I can ride it and see

Thanks for chiming in!
 

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Discussion Starter · #20 ·
Hey Guys, quick question... on a 450 twin (80something nighthawk - best guess), if I go to pod filters, what jet size(s) seem to work best...

Thanks!
 
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