RC380 custom (from 1974 CL360)

Untame

Untame

Well-known Member
Joined
Dec 18, 2023
Total Posts
64
Total likes
53
Location
La Crosse, WI
I picked up this bike from my wife's uncle. It has been sitting in a barn for the last 30 years. He would only take $25 for it (no title). Most of the parts are being disposed of -- only going to use the frame, motor, forks, and wheel hubs/brakes.

I am building it out in the style of the 1967 RC174 - not a replica, but a homage (general shape and colorway). Full fairing from AirtechMoto (AJSM7) with Gustafson low profile windshield.

Bored out with GS850 pistons for 378cc. I'm calling it the "RC380" (rounding up, because Honda rounded up 356cc to CL360). Frame is stripped down and most tabs shaved off (I am going to 3D-print accessory mounts as needed). Original carbs have been restored by CrazyPJ. I have gone through the entire engine/gear box including bead-blasting all of the cases. Assembly is in process, but I am waiting on copper base/head gaskets from Copper Gaskets Unlimited (.063 base for zero-deck, and .042 head with 69.5mm gasket bore -- cylinder bore is 68.9mm) and Bore-Tech heavy clutch springs.

I've been updating a thread at DTT, but there isn't a lot of feedback there, so I thought I'd try here to see if I get more input. This is my first bike build, so I appreciate advice.

About me... I'm 49 years old, the father of 4 daughters (empty nest T-minus 2 years). Never ridden a motorcycle before (except a minibike). Been a R&D mechanical engineer in the diary industry for the last 10 years. Before that I spent 4 years working as the "Resident Engine Artist" for a custom car builder (exotics like, Ferrari, Bugatti, Delahaye, Tojeiro...), and before that I was a Baptist pastor for 9 years.

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Here is a current status photo (my bike is in the foreground, the other is my daughter's project - a 1981 Suzuki GN400 café racer):

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I ran into a conundrum last night assembling the clutch side of the motor. I have this thick steel washer/bushing. Obviously a precision part for a specific application, but I can't for the life of me figure out where it goes. I had bagged it up with the hardware for the gear that drives the oil pump, and it loosely fits on that shaft, but there is already a thin washer there, and the HSM doesn't show this piece in any of the diagrams. I even wondered if it got misplaced from the other side of the motor or the top end, but none of the (blurry) diagrams show this piece.

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Also, I was wondering if this wear is acceptable, or should it be replaced (if that is even possible to find one):

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Untame said:
Also, I was wondering if this wear is acceptable, or should it be replaced (if that is even possible to find one):
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I can't personally speak to the bottom end of a 360 as I've never had one apart myself, but that level of wear on a shift detent roller would be a problem for most of our twins that use detent rollers like it (the DOHC 450 specifically would have serious issues going from 2nd to 3rd with one in that condition). I'd imagine if anyone had encountered it, @crazypj would have and I'm sure he'll be along.
 
Fairing is on order (7 week lead time).

Seat has been ordered with custom paint for the rear cowl (Traffic Red) -- should be here in about 3 weeks. I want to cut an upswept angle on the seat cowl, but I don't want to damage the new paint, so I'll see what looks possible when I get it.

I have the fuel tank in bare steel (needs to paint Traffic Red), and I was able to get OEM vintage tank decals from Japan to match the RC174. New aluminum rims and spokes from 4into1 (need to rebuild the hubs and lace them up... will start on this after frame work is finished for the fuel tank and seat).

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ancientdad said:
I can't personally speak to the bottom end of a 360 as I've never had one apart myself, but that level of wear on a shift detent roller would be a problem for most of our twins that use detent rollers like it (the DOHC 450 specifically would have serious issues going from 2nd to 3rd with one in that condition). I'd imagine if anyone had encountered it, @crazypj would have and I'm sure he'll be along.
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I'm wondering if it is even possible to find an NOS part. If not, I'll need to think of a fabricated solution.
 
Untame said:
I'm wondering if it is even possible to find an NOS part. If not, I'll need to think of a fabricated solution.
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If you have access to a lathe, you can turn down a new shaft for the roller and peen the end of it. The roller wheel itself is harder metal than the shaft and generally doesn't wear, at least not on the 450. VHT member @12ozPBR makes replacements for the large detent roller on the 450 but he's not done a 360, and frankly I'm surprised that we've never seen anyone with a problem on a 360 AFAIK. It might not be as big an issue with the 360 but that roller looks pretty sloppy.
 
ancientdad said:
If you have access to a lathe, you can turn down a new shaft for the roller and peen the end of it. The roller wheel itself is harder metal than the shaft and generally doesn't wear, at least not on the 450. VHT member @12ozPBR makes replacements for the large detent roller on the 450 but he's not done a 360, and frankly I'm surprised that we've never seen anyone with a problem on a 360 AFAIK. It might not be as big an issue with the 360 but that roller looks pretty sloppy.
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It actually feels gritty -- doesn't want to roll well.
 
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Untame said:
Thanks for linking me up with this! Got one on order.
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I'm always concerned about the shipping costs between suppliers (I'm budget-conscious all the time), the price is less for the one from CMSNL but hopefully their shipping isn't too high. DSS has a flat $10 fee for smaller parcels IIRC.

You did look at the link about identifying and locating parts in my Welcome Package, right? Many good suggestions there.
 
crazypj said:
If you didn't get a reply about thick steel washer, it fits on oil pump pick up to compress o-ring.
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I figured you'd know what it was for. I've done so little to any 360 that I wasn't sure it was even from the bike, thanks for the clarification.
 
bilbikek411 said:
Untame,will you build a custom 2 into 2 exhaust in similar design to the RC174 ?
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Not sure what you mean. Isn't it 6 independent pipes?

I thought about an x-pipe for flow, but decided it might change the vacuum signal to the carbs too much. I'm planning to just use CB360 pipes.

For mufflers I like the sound of Cone Engineering reverse cones. Going to be black to match the aesthetic.
 
Untame said:
Not sure what you mean. Isn't it 6 independent pipes?

I thought about an x-pipe for flow, but decided it might change the vacuum signal to the carbs too much. I'm planning to just use CB360 pipes.

For mufflers I like the sound of Cone Engineering reverse cones. Going to be black to match the aesthetic.
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Ok, wanted to hear your exhaust concept for the 360.

How has this project been looking to you lately;' back burner' ?
 
bilbikek411 said:
Ok, wanted to hear your exhaust concept for the 360.

How has this project been looking to you lately;' back burner' ?
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Actually, been waiting for parts. Got the detent roller, copper gaskets, and HD clutch springs this week, so today I did more assembly. I got finished up through the camshaft.

Pistons zero-deck nicely.

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bilbikek411 said:
Ok, wanted to hear your exhaust concept for the 360.

How has this project been looking to you lately;' back burner' ?
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On the mufflers, I plan to pitch them upwards toward the rear wheel hub. Something middlin compared to the three mufflers on each side of the RC174.
 
Got it back together. Still need to set the valve lash.

I installed a used Pamco electronic ignition that someone on the forums generously gave me.

I have no idea what it weighs, but... when I move it I find myself wondering what a hernia feels like.Screenshot_20241013_203711_Gallery.jpg

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Time to restore these and get the new rims laced up.

Still waiting for the new seat so I can work on finishing the frame (fitting tank and seat).

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The aluminum has some patina from where the oxidation was, but I like it. Gives it character that speaks to its age. I didn't want it to look new. It will look vintage.
 
Untame said:
The aluminum has some patina from where the oxidation was, but I like it. Gives it character that speaks to its age. I didn't want it to look new. It will look vintage.
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Sometimes I use a quality small blue plastic handle(Weiler) brass brush on blasted aluminum like that and detail it;the brass color of the bristles give a gold tint which I like.
I've also used a medium grade steel wool which polishes it just a bit.
 
bilbikek411 said:
Sometimes I use a quality small blue plastic handle(Weiler) brass brush on blasted aluminum like that and detail it;the brass color of the bristles give a gold tint which I like.
I've also used a medium grade steel wool which polishes it just a bit.
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In the past I've darkened bead blasted aluminum with phosphoric acid (spray bottle), rinsed it, and sealed it with Cerakote. Gives it a medium gray concrete color.
 
Something I want to mention for posterity's sake, I expanded the first loop of the spring under the modified oil transfer piece. I did this for two reasons: to ensure a positive seat on the smaller modified rim, and to make sure the spring wire was not interfering with full flow.

This much expansion was enough to eliminate any clearance between the spring and the inside wall of the oil transfer piece.

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For those of you keeping score at home...

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Probably going to be in the $3,500-$4,000 range to get this done. Right now my motorcycle fund is tapped out... need to spend time reworking the parts I have and save up some $$$ for future parts.
 
Untame said:
For those of you keeping score at home...

View attachment 38285

Probably going to be in the $3,500-$4,000 range to get this done. Right now my motorcycle fund is tapped out... need to spend time reworking the parts I have and save up some $$$ for future parts.
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You may need to put your motorcycle project on hold for a while;parts $ add up.
 
I feel your pain, I have close to $10k invested in my 450 including the $1900 purchase price, $2500 in the engine alone. It adds up quickly, and at some point you just have to ignore the total and push toward the finish line.
 
bilbikek411 said:
You may need to put your motorcycle project on hold for a while;parts $ add up.
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I have a lot of refinishing and restoration work to do -- time stuff, not dollar stuff. Still waiting for the seat (next week or so?) and the fairing / windshield. I won't be able to do much with the fairing right away, but I wanted to get one ordered ASAP. Once I have the seat I can work on my fuel tank location.

Next spend will need to be a seat loop. I'm having a hard time finding 205mm loops (planning on upswept, but that will require reworking the bottom of the seat cowl).
 
ancientdad said:
I feel your pain, I have close to $10k invested in my 450 including the $1900 purchase price, $2500 in the engine alone. It adds up quickly, and at some point you just have to ignore the total and push toward the finish line.
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How long did that take you start to finish?
 
Untame said:
How long did that take you start to finish?
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Total time for the overall (first) build, about 6 months, but then in its first 3 months running and riding I had to chase a big oil flow problem (accidentally of my own doing) that ruined a few engine parts, followed by a couple of cracked rear fender mounts (fabricated replacement mounts we made for the aftermarket fender that were not up to the task as expected, combined with over-zealous weld cleanup). So after 3 months together in mid-2017, it all came back apart and was apart for almost a year. During that time my longtime friend and welder/fabricator, who had helped me with all the original frame work, sadly had a stroke and lost the use of his right side. It took me a few months to find a decent welder to help with the newly-revised rear fender mounts that Mike welded in for me literally days before his stroke, then the re-powdercoating of the frame after the welding was done (which also had to be done twice as the shop got sand in the first effort that time around), and finally a successful full reassembly in mid-2018 for good and it's been together ever since. Here's the build thread if you feel like doing some reading, LOL

CL450 project reboot, street-legal this time

This attempts to be a synopsis of the nearly 500 posts of my "little red monster" build from another forum long ago... original build thread is here if anyone is interested. CL450 project reboot, street legal this time When I was 19, I built a CL450K5 into a modified class drag bike Ever...
www.vintagehondatwins.com www.vintagehondatwins.com
 
Untame said:
For those of you keeping score at home...

View attachment 38285

Probably going to be in the $3,500-$4,000 range to get this done. Right now my motorcycle fund is tapped out... need to spend time reworking the parts I have and save up some $$$ for future parts.
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I find it much easier to right click on the "running Total" cell and hit "Clear Contents". Kidding, sort of - I also list vendor where possible, particularly for planning when you're researching ahead of time.
 
My plan is to keep the total restoration costs in my memory..... mmm.... what did I have for breakfast again. That's the engineer side of you, plus being fiscally responsible for sure. Even inexpensive bike buys add up when you just doing a normal refresh, so nothing custom like your very interesting project.
 
Flyin900 said:
My plan is to keep the total restoration costs in my memory..... mmm.... what did I have for breakfast again. That's the engineer side of you, plus being fiscally responsible for sure. Even inexpensive bike buys add up when you just doing a normal refresh, so nothing custom like your very interesting project.
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I've got a lot of the upcoming expenses already planned on another worksheet along with vendor. I then prioritize my next purchases from this list depending one where I am in the project. I have listed at least another $1,200 in expenses, and I'm sure there is going to be about $500 in odds and ends to get it done. Originally my idea was to pick up a cheap Japanese bike to build a cafe racer for under $1,000. But I started dreaming...

In the end, I'll own a bike that nobody else has. But more importantly, I'm paying for the joy of the restoration process, which I truly enjoy as a hobby. I honestly think I'll enjoy building this bike more than riding it.
 
Untame said:
n the end, I'll own a bike that nobody else has. But more importantly, I'm paying for the joy of the restoration process, which I truly enjoy as a hobby. I honestly think I'll enjoy building this bike more than riding it.
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Mine was something that rattled around in my head for decades, and I knew when I started that it wouldn't be sold until probably after I'm long gone. You do it for the result you want, and once you go down that rabbit hole there's no turning back. But it's also something you can stare at later and know that it is just what you wanted it to be, and remember every single piece you touched to get it there.
 
Disassembled and washed up the wheel hub halves. The HSM isn't much help with the bearings. They are still in there... for now.

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