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CL350 Vintage racer project

Emlupi

Veteran Member
Joined
Sep 9, 2024
Total Posts
389
Total likes
517
Location
CT
Hello all,
So, I’ve had the itch to give vintage racing a go for awhile now and have decided to quit messing around and get on with it. The organization I am going to join has a spec Formula CB350 class which runs basically stock machines with a handful of modifications allowed. Seems like the best way to get involved as these bikes are plentiful and relatively easy to work on.
Anyway, I found a likely donor (‘73 CL350K5) and dragged it home. I’ve stripped it down and have begun disassembling the engine. The bike is showing 7888 miles on the odometer and has obviously been sitting neglected for many years. The PO had video of it running, although roughly. The frame, swingarm, hubs, etc. are dirty and rusty but look solid enough to build on. So, I’m tearing into this thing and hoping for the best.
As I stated, this is a spec class for mostly stock bikes so I’m not looking to build a MotoGP racer. I’m looking to build a good, reliable bike with all the legal mods to get me on my way.
Looking forward to leaning on the knowledgeable types here to keep me on the path.
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I didn’t get very far with the engine, yet. Time is limited. I got the cylinder head cover off and the rockers/spindles removed. Don’t really know what I’m up against yet but didn’t see any glaring nightmares in there.IMG_6025.jpeg
 
If you don't have the FSM for it, you should get it now and review engine disassembly. The concern is for tension on the cam bearing covers when removing them prior to removing the cam sprocket bolts after rotating the engine to the point where no valves are open, in order to relieve any pressure from rocker arms opening valves.

Get the FSM here:

Honda CL350 SL350 CB350 Factory Service Manual Searchable.pdf

drive.google.com drive.google.com
 
ancientdad said:
If you don't have the FSM for it, you should get it now and review engine disassembly. The concern is for tension on the cam bearing covers when removing them prior to removing the cam sprocket bolts after rotating the engine to the point where no valves are open, in order to relieve any pressure from rocker arms opening valves.

Get the FSM here:

Honda CL350 SL350 CB350 Factory Service Manual Searchable.pdf

drive.google.com drive.google.com
Click to expand...
Yeah, I have the FSM on hand and have watched some videos on disassembling. I left the two cam boxes on the sides to support the cam while I rotate the engine to remove cam sprocket bolts. I took the rockers and spindles out already. I am going to rotate the cam sprocket and remove bolts next but still need to remove seized screws from stator cover. Any tips to save headaches are always appreciated and welcome.
 
Emlupi said:
Yeah, I have the FSM on hand and have watched some videos on disassembling. I left the two cam boxes on the sides to support the cam while I rotate the engine to remove cam sprocket bolts. I haven’t gotten to that stage yet, still need to remove seized screws from stator cover. Any tips to save headaches are always appreciated and welcome.
Click to expand...
The concern is always for removing the cam bearing covers without stress on them (IOW, forcing them off) and the 90° past LTDC on compression stroke is the point on the 350 where all valves are closed so there's the least tension on the camshaft. Though there are a lot more good used 350 engine parts still out there, it is a finite supply and NOS is really expensive in most cases.
 
Emlupi said:
and have watched some videos on disassembling.
Click to expand...
Do yourself a big favor early in this process and ask here before putting too much credence in videos. Here's a good example of why, from one of the most popular sources

450-1.jpg

That video has been taken down and since replaced, but you get the idea of how so often "a little knowledge is a dangerous thing" and ends up being published for the world to see and take as a proper method.
 
Ok, point taken. The cam boxes came off without any drama, I didn’t have to fight them and didn’t have any unusual tension while sliding them off. Maybe I got lucky with crank position when I did it.
Now with the rockers and spindles removed, there’s no stress or tension on the cam so it should be a simple matter of rotating the cam sprocket to the proper position and removing the bolts, paying attention to the position of the two dissimilar bolts. Correct?
 
Emlupi said:
Ok, point taken. The cam boxes came off without any drama, I didn’t have to fight them and didn’t have any unusual tension while sliding them off.
Now with the rockers and spindles removed, there’s no stress or tension on the cam so it should be a simple matter of rotating the cam sprocket to the proper position and removing the bolts, paying attention to the position of the two dissimilar bolts. Correct?
Click to expand...
Yes, and I'm not trying to beat you up about it either. We just like new members to be aware of the easy pitfalls and misinformation we've seen on the internet so they can avoid them. We have a collective 100+ years of Honda dealership knowledge here among all active veteran members and happily share it to help members get things done the right way. And I, for one, am passionate about debunking all the backyard-level videos out there that purport to be 'correct'. Videos can be good to get a visual of the components though, just be sure to ask if anything is the least bit unclear. This forum is self-funded, we're all volunteers, and we're here to help.
 
Very cool, thanks.
Ok, here’s one for you, I have read a bunch about the top end oiling problems at higher RPM and the mods that people are doing to alleviate this. Is this a recommended step to take?
 
Emlupi said:
Very cool, thanks.
Ok, here’s one for you, I have read a bunch about the top end oiling problems at higher RPM and the mods that people are doing to alleviate this. Is this a recommended step to take?
Click to expand...
VHT member @crazypj has a thread on the mod for the 350, 360 and DOHC 450 that increases flow from the centrifugal oil filter. VHT member @Jays100 has already developed an improved gear-type oil pump for the 450 and is in the latter stages of development on a similar pump for the 350 engine as well.

CB350 oil transfer piece - with pictures (also applies to CB250)

Hi all, Was sent a set of 350 carbs to modify plus, the oil filter cover. Actually took measurements of this one as the clearance between sliding oil transfer piece and delivery to filter seemed smaller than usual? Anyway, oil delivery hole to centrifugal filter varies between 0.250" and 0.280"...
www.vintagehondatwins.com www.vintagehondatwins.com
 
90% of your horsepower comes from the head. I'll suggest sending the head to Chris with a list of "legal" mods so he does everything by their book.
www.facebook.com

Schumann Motor Works | Milwaukie OR

Schumann Motor Works, Milwaukie, Oregon. 615 likes · 28 talking about this · 5 were here. Specializing in vintage motorcycle cylinder head services and custom valve train components.
www.facebook.com www.facebook.com
The screws holding the covers on plus other areas are JIS, not Philips. Vessel makes some nice screwdrivers and you'll probably need impact driver bits #2 and #3
Attention to detail in building the engine and bike will reap rewards
 
Emlupi said:
Very cool, thanks.
Ok, here’s one for you, I have read a bunch about the top end oiling problems at higher RPM and the mods that people are doing to alleviate this. Is this a recommended step to take?
Click to expand...
Absolutely would do, just make sure the mod is rulebook compliant. I know a lot of the CB/CL 350 rely on using an SL oil pump.
 
This will be good for me and my still novice 350 motor skills.

I'm sure you'll share whatever mods are acceptable for this project.
 
Any modifications other than those listed below are not permitted. Output shaft seal retainer mandatory.
1. Approved models: Honda CB/SL350, CL350/360, CB/CD/CJ360
2. Engines: Stock, the following modification are permitted:
a. May replace the stock cam tensioner with a slipper style cam chain tensioner.
b. May use aftermarket replacement pistons, teflon ‘buttons’ and valves of OEM size and materials. Valve guides of any material permitted. Changes to OEM valve configuration (i.e. multi-angle valve grinding) prohibited.
3. Carburetion: Stock or aftermarket Mikuni VM type, maximum 26mm allowed, air boxes may be removed or modified. Carburetor jets may be changed. Choke plates may be removed. Carburetors from any approved model are permitted.
4. Exhaust: System may be changed.
5. Gearing: External gearing changes permitted.

These are the engine mods allowed in the rulebook. As you can see, very limited. Are people doing more than this?…….well, who really knows. I’m not looking to build a sleeper or a cheater. Like I said earlier, just want to put it together correctly and have a solid, reliable engine.
I will have to contact the director and ask about oil mods. By the letter of the rules, it’s not on the list so is not permitted.
 
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LongDistanceRider said:
90% of your horsepower comes from the head. I'll suggest sending the head to Chris with a list of "legal" mods so he does everything by their book.
www.facebook.com

Schumann Motor Works | Milwaukie OR

Schumann Motor Works, Milwaukie, Oregon. 615 likes · 28 talking about this · 5 were here. Specializing in vintage motorcycle cylinder head services and custom valve train components.
www.facebook.com www.facebook.com
The screws holding the covers on plus other areas are JIS, not Philips. Vessel makes some nice screwdrivers and you'll probably need impact driver bits #2 and #3
Attention to detail in building the engine and bike will reap rewards
Click to expand...
Yes, sir, Schumann is already on my list. I am well aware of the JIS vs Phillips vs Posidrive screwdriver confusion. I have a ‘72 Honda CB750 and a ‘67 Triumph Bonneville TT Special. I’m fairly well versed in SAE, Metric, Whitworth, JIS, you name it.
To be honest, for something like this where originality counts for squat, I prefer to use Allen screws. Less chance of buggering up screw heads, if used properly of course.
 
Interesting that the rules mention material of the valves. Schumann made stock size titanium valves for my 450 head. Also interesting that they limit you to 26mm carbs when the stock Keihin carbs for the 350 are 28mm.
 
I just gotta say, I love this site already. I went to the “other” place and posted threads and all I got was crickets 🦗.
 
Emlupi said:
I just gotta say, I love this site already. I went to the “other” place and posted threads and all I got was crickets 🦗.
Click to expand...
Yep, we left the corporate-taken-over environment behind and brought as many as we could to our new, ad-free and self-owned version in June of 2020. That place has averaged about 10 posts a day for a while now, with a low level of long-term experience there as well.
 
I think the organization is trying to keep the class from turning into a money war. It’s there for guys like me who are trying to get involved without having to sell a lung to do it.
You can mod up your bike as much as you want but you will have to bump up to another class to run it.
 
Emlupi said:
I think the organization is trying to keep the class from turning into a money war. It’s there for guys like me who are trying to get involved without having to sell a lung to do it.
You can mod up your bike as much as you want but you will have to bump up to another class to run it.
Click to expand...
Yeah, and while it makes good sense for privateers, it makes me wonder why their carb spec would be smaller than OEM. But hey, if they're all running 26s then the playing field will be level.
 
What ignition do you plan to/be allowed to use? Did you plan to run total loss and remove the alternator?
 
I am looking to get involved just because I really enjoy it. It’s alot of fun to watch riders out there on the old racers, two strokes, sidecars, and whatnot. I’m too old to be out there on a a Superbike, even a vintage one. I have a 2020 Triumph Street Triple 765RS that I run track days on if I want to scare myself 😃IMG_5580.jpeg
 
ancientdad said:
Interesting that the rules mention material of the valves. Schumann made stock size titanium valves for my 450 head. Also interesting that they limit you to 26mm carbs when the stock Keihin carbs for the 350 are 28mm.
Click to expand...
Chris made some SS valves, I have a set but didn't use them yet.

Maybe it's only the Mikunis that are limited to 26mm.
 
I was thinking about something like PVL, ditch the battery and alternator. Ignition is unrestricted.
 
Emlupi said:
I was thinking about something like PVL, ditch the battery and alternator. Ignition is unrestricted.
Click to expand...
It's a good choice and the rotor is significantly smaller too IIRC, though I've only seen them in pictures. Pretty sure the Team Hansen 450s ran them too.
 
5.6.4 Formula CB350
A spec class for near stock Honda CB350s and CB360 Twins.
With the creation of this class, Honda CB350’s will no longer be eligible for Period 1-350GP, but are eligible in Formula CB and Lightweight Supervintage. All Formula CB races will be run with 350GP. Any modifications other than those listed below are not permitted. Output shaft seal retainer mandatory.
1. Approved models: Honda CB/SL350, CL350/360, CB/CD/CJ360
2. Engines: Stock, the following modification are permitted:
a. May replace the stock cam tensioner with a slipper style cam chain tensioner.
b. May use aftermarket replacement pistons, teflon ‘buttons’ and valves of OEM size and materials. Valve guides of any material permitted. Changes to OEM valve configuration (i.e. multi-angle valve grinding) prohibited.
3. Carburetion: Stock or aftermarket Mikuni VM type, maximum 26mm allowed, air boxes may be removed or modified. Carburetor jets may be changed. Choke plates may be removed. Carburetors from any approved model are permitted.
4. Exhaust: System may be changed.
5. Gearing: External gearing changes permitted.
6. Frame: Stock frames and swingarms only, the following
modifications are allowed:
a. Frame tabs may be removed.
b. Non-structural tabs may be added to facilitate mounting
of footpegs, steering damper, seat and gas tank.
c. Swingarm bushings may be changed to aftermarket types.
d. Frame seams may be welded. No bracing allowed.
e. Tapered bearings in steering head permitted.
f. Frame and/or swingarm from any approved model permitted.
8. Forks: 35mm maximum fork tube diameter.
9. Brakes: Mandatory drum brakes front and rear. Aftermarket brake
shoe linings permitted. Complete OEM front end (forks, triple trees,
disc, calipers and master cylinder) permitted.
10. Clip-on handlebars permitted.
11. All street equipment must be removed. May retain stock fenders. 12. Ignition system: Unrestricted
13. Bodywork: Fairings prohibited, aftermarket seats, fenders
and gas tanks permitted.

Here are the class-specific rules.
 
In addition to the output seal retainer (which rarely happens on a 350, in fact I've never personally seen one get blown out of the bottom end) you should make a clutch rod seal retainer. The 350 is far more famous for blowing that one out and losing all the oil in less than 10 seconds.
 
Emlupi said:
Any modifications other than those listed below are not permitted. Output shaft seal retainer mandatory.
1. Approved models: Honda CB/SL350, CL350/360, CB/CD/CJ360
2. Engines: Stock, the following modification are permitted:
a. May replace the stock cam tensioner with a slipper style cam chain tensioner.
b. May use aftermarket replacement pistons, teflon ‘buttons’ and valves of OEM size and materials. Valve guides of any material permitted. Changes to OEM valve configuration (i.e. multi-angle valve grinding) prohibited.
3. Carburetion: Stock or aftermarket Mikuni VM type, maximum 26mm allowed, air boxes may be removed or modified. Carburetor jets may be changed. Choke plates may be removed. Carburetors from any approved model are permitted.
4. Exhaust: System may be changed.
5. Gearing: External gearing changes permitted.

These are the engine mods allowed in the rulebook. As you can see, very limited. Are people doing more than this?…….well, who really knows. I’m not looking to build a sleeper or a cheater. Like I said earlier, just want to put it together correctly and have a solid, reliable engine.
I will have to contact the director and ask about oil mods. By the letter of the rules, it’s not on the list so is not permitted.
Click to expand...
I'm thinking the 26mm restriction is to the aftermarket Mikunis only - maybe just oddly worded?

I like those restrictions, it really does make it less of a bank account race and more about the build and rider. There's only so much you can do with intake and exhaust. After that it's weight reduction and playing with timing and rudimentary tuning.
 
This engine is coming completely apart for thorough inspection, cleaning, and rebuild, step by step. I don’t want to spend my afternoon in the paddock ripping the bike apart because I skimped out on something. The only thing I know about this bike is that it sat in the corner of a garage for years unloved and neglected. It only has 7888 miles on it but I don’t know if they were hard miles or what?
 
ancientdad said:
In re-reading it, could be.
Click to expand...
Yeah, the wording is kinda funky, I believe the 26mm restriction is for the Mikuni VM’s. If you have stock carbs you can run them as is.
I’m also intending to at least upgrade to 360 forks so I can run emulators in them. The rules allow 35mm so I could do a swap with a set of CB500 forks but that would gets into geometry changes, possibly spacers to get the hubs to fit correctly, etc. Not sure if I want to dive in that deep but I will definitely consider it.
 
Emlupi said:
It only has 7888 miles on it but I don’t know if they were hard miles or what?
Click to expand...
Or if it's accurate either, since it's easy to change speedos on these bikes. The crankshaft cleaning he mentioned is more in-depth and even with that few actual miles on that engine, if it hadn't had any decent maintenance it could have some gunk built up in the oil passages in the big end/crankpin and some built up in the "sludge trap" machined into the crank flywheels. These cranks are very durable as I'm sure you realize, and as long as the ball and roller/needle bearings get enough oil flow they can withstand significant horsepower increases reliably.

Crankshaft Cleaning

I've been following all of the build threads on this site and seeing the damage that foreign debris in the oil can cause I started to get paranoid about properly cleaning the crankshaft of my 71 CB450. In Teebo's most recent thread 12ozPBR mentions cleaning the flywheel area near the main...
www.vintagehondatwins.com www.vintagehondatwins.com
 
Emlupi said:
Any modifications other than those listed below are not permitted. Output shaft seal retainer mandatory.

b. May use aftermarket replacement pistons, teflon ‘buttons’ and valves of OEM size and materials. Valve guides of any material permitted. Changes to OEM valve configuration (i.e. multi-angle valve grinding) prohibited.


These are the engine mods allowed in the rulebook. As you can see, very limited. Are people doing more than this?…….well, who really knows. I’m not looking to build a sleeper or a cheater. Like I said earlier, just want to put it together correctly and have a solid, reliable engine.
I will have to contact the director and ask about oil mods. By the letter of the rules, it’s not on the list so is not permitted.
Click to expand...
Interesting, page 36 of both the early and late FSM shows a 3 angle valve seat grind. Now if they mean actual valve face grinding that's another thing verging into exotic machine work.
Funny, they're worried about the output shaft seal but not the clutch rod seal which is a known problem
 
ancientdad said:
Or if it's accurate either, since it's easy to change speedos on these bikes. The crankshaft cleaning he mentioned is more in-depth and even with that few actual miles on that engine, if it hadn't had any decent maintenance it could have some gunk built up in the oil passages in the big end/crankpin and some built up in the "sludge trap" machined into the crank flywheels. These cranks are very durable as I'm sure you realize, and as long as the ball and roller/needle bearings get enough oil flow they can withstand significant horsepower increases reliably.

Crankshaft Cleaning

I've been following all of the build threads on this site and seeing the damage that foreign debris in the oil can cause I started to get paranoid about properly cleaning the crankshaft of my 71 CB450. In Teebo's most recent thread 12ozPBR mentions cleaning the flywheel area near the main...
www.vintagehondatwins.com www.vintagehondatwins.com
Click to expand...
Man, reading that crank cleaning thread is like going down a rabbit hole! There’s no chance that I’m going to be attempting to press apart my crank, I don’t have the equipment necessary and don’t know anyone that does. I will certainly run some type of soft cable into the holes and flush it out but I don’t know that I will be able to do much more than that.
 
Even if you can flush and visually see it coming through to the big ends, you'll know the splash will make it to the cyl walls, rings, small end bushings. If not, then it won't and another crank or press work would be needed.
The splash must happen, it's the sole source of lube for those areas.
 
ancientdad said:
Or drill the plug in the crankpin and replace it with one like Jay described. I forget the name of it (Lee plug?)
Click to expand...
I would say the smaller radial drillings from that central (and larger?) pin hole could still be plugged, but to clear them would require the rod to be removed.
Hopefully it will flush (stood on end gravity should help). Maybe a real big ultrasonic bath might help. Teebo used a small pump and thin tubing to the crank pin hole pretty successfully.
Someone should invent a high pressure pulsating solvent jet (like a dental Waterpic) for this kind of deep cleaning and clearing.
 
ballbearian said:
Someone should invent a high pressure pulsating solvent jet (like a dental Waterpic) for this kind of deep cleaning and clearing.
Click to expand...
Excellent idea for the Maytag partsomatic 1.0! 1/4” NPT to 3/8 adapter on a grease gun needle nozzle to the variable speed pump on the solvent supply. Should do it.
 
Emlupi said:
Man, reading that crank cleaning thread is like going down a rabbit hole! There’s no chance that I’m going to be attempting to press apart my crank, I don’t have the equipment necessary and don’t know anyone that does. I will certainly run some type of soft cable into the holes and flush it out but I don’t know that I will be able to do much more than that.
Click to expand...
RobMan did a long soak version on his that came out good. I think it was kerosene or diesel he just soaked the crank and rotated a lot.

As for the front end, a CB450 I think has the same stem length (or really close) and takes the same bearing sizes, which would make it an easy swap.

Drum front would lower your front end a bit, disc would actually raise it a hair, unless you drop the triple down 20mm.

Throw in some progressives or just a cheap preload and heavy oil and you could tighten that up quite a bit.
 
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When I get to that stage I will revisit the post. For now I’m still getting a handle on what I’m dealing with. No telling what is lurking 👀 underneath that cylinder head.
I can say one thing for certain, I have never had to deal with so many seized up and stripped JIS screws in my life. I’m becoming quite adept with the screw extractor.
 
Just out of curiosity, on the vendor page I don’t see Common Motor listed as a source for parts, etc. Is there something I should know about them or is it just a coincidence? They seem to have quite a bit of stuff for Honda Twins and lots of resource material as well.
 
EzPete said:
RobMan did a long soak version on his that came out good. I think it was kerosene or diesel he just soaked the crank and rotated a lot.
Click to expand...
I don't have a parts washer so I let it soak in kerosene in a plastic tote that I could close up in my shed for about 2 weeks periodically scrapping out the grooves beside the bearing races and per another members suggestion running an old throttle cable with a slightly flayed end in an out of the oil passages. I also used a cheap Harbor Freight battery operated transfer pump to flush out the passages until I was satisfied i was getting good flow of fluid through the passages. I am sure it is not totally clean but in much better shape than it was. Here is a link to my posts if you want to scan them.

1972 CB450 K5 Hot Mess

Thanks for looking and I saw these as well on ebay earlier today and I am wondering when they will start making knock offs of these if supply is getting short. Thank you for checking to see if you have an extra but you may want to hold on to it.
www.vintagehondatwins.com www.vintagehondatwins.com
 
Emlupi said:
Just out of curiosity, on the vendor page I don’t see Common Motor listed as a source for parts, etc. Is there something I should know about them or is it just a coincidence? They seem to have quite a bit of stuff for Honda Twins and lots of resource material as well.
Click to expand...
They aren't there because their parts prices are higher, often significantly higher, for the same components (usually the exact same parts) than pretty much any other supplier we recommend. We have a link-exchange deal with our 3 sponsoring vendors, we give them space and exposure here on the forum and in return, they put a link to VHT on their site and offer occasional discounts to our members. Since CMC doesn't like our opinion of many of their videos, and since we can find virtually everything they sell for cheaper prices elsewhere, I'm sure the lack of interest is mutual.
 
IMG_6004.jpeg
I can see that OEM gaskets are unavailable and there are many “kits” around . I generally like to stick with factory rubber bits and gaskets but this set was included in a bin full of spares that came with the bike. I have no experience with this manufacturer, so don’t know if these are usable or not to bother. What is the consensus on gaskets and who has them?
 
I haven't used that company's kits myself but it looks like the ones that David Silver Spares sells and they have a good rep for selling good quality IMO.
 
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