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CB350 to cafe' from scratch by a (not so much) teen

Alon

Well-known Member
Joined
Jul 26, 2024
Total Posts
61
Total likes
30
Location
Israel
Hey everyone! I'm bringing this build over from Do The Ton.
cb350 to cafe' from scratch by a teen
TL;DR I bought this basket case bike when I was 18 (now almost 28) and it's been something that I tried to do but understood eventually that if I don't concentrate and keep this moving week to week then it's probably gonna be done when I retire 😅 (credit to my dad).
It's a 1973 CB350K4 that I bought from someone that took it apart and started doing cafe style mods like the seat hoop and then just gave up. I found a pic from a build thread he started to show the state of the bike as he got it.

IMG_1779.PNG

I'm now at a state where:
- All aluminum covers are polished.
- Motor is rebuilt with larger pistons (65.5 instead of the original 64) and everything else stock.
- I have a PAMCO electronic ignition (ordered when he was still in business) and Rick's reg/rec.
- All parts are powder coated.
- Connected lower triple tree and swing arm to the frame.

IMG_2595 2.jpeg

I hope you guys like it and I'm open to any advice and comments! Feel free if you want to comment on something from the build thread in do the ton (LINK).
 
The easiest way to install the engine is lay the engine on it's right side(clutch) and set the frame over the engine. Install the bolts and then set upright to add nut and tighten.
 
Welcome Alon. My advice is to do any fixing of the footbar brackets now before you have to lay on your back to tap or weld them.
 
ballbearian said:
Welcome Alon. My advice is to do any fixing of the footbar brackets now before you have to lay on your back to tap or weld them.
Click to expand...
Thanks ballbearian!
Just to make sure, you're talking about this part? If so, I do have a tiny crack that I'll need to weld. Bummer cause it's already been powder coated.


IMG_2585 Large.jpeg

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Alon said:
Thanks ballbearian!
Just to make sure, you're talking about this part? If so, I do have a tiny crack that I'll need to weld. Bummer cause it's already been powder coated.
Click to expand...
The female threaded holes in the frame (welded in nuts) are a pain to deal with later. Also, the exact length bolts are important for strength and to prevent stripping those threads.
That cracked footbar may not be a big problem. a larger washer and longer bolt could do it for now and it's easy to remove and fix later.
 
I got the wheels trued, got the tires on and then the wheels balanced.
These are the original sized rims from DID (front 18x1.60" and rear 18x1.85")
Buchanan's stainless steel spokes
Front tire: 3.00x18 DURO HF317 VINTAGE STREET RIB (RB2) F
Rear tire: 3.50x18 DURO HF314 VINTAGE UNIVERSAL (K81) F/R

IMG_2854.jpegIMG_2855.jpegIMG_2856.jpegIMG_2857.jpegIMG_2858.jpeg
 
I’m trying to bolt back the engine into the frame and I can’t get the two bottom holes to line up with the frame. Any suggestions?

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I see what you mean about the hole alignment, but I'm not sure if you realize there is a spacer missing here. I'm also curious about the diameter of the allen bolts you're using in the motor mounts, it they were a tight fit then it might have taken up some of your "wiggle room" to shift things around a bit and get all the bolts in place. And if you have already tightened any of the motor mounts bolts, you should loosen all of them to allow some shifting to get the others in place along with this spacer (#4 below) in the aforementioned gap lower left front of the engine.

honda-cb350k3-super-sport-1971-usa-frame_bighu0028f4026_e863.gif


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I have the spacer and haven’t tightened the bolts.
I ordered the kit from AlloyBoltz:
alloyboltz.com

HONDA CB350 CL350 SL350 TWIN POLISHED STAINLESS STEEL MOTOR MOUNT BOLT KIT | Alloy Boltz

Here is a great way to dress up your Honda 1968-1973 CB350, CL350 & SL350 and get rid of those rusted, oxidized Motor Mount bolts with this beautiful polished 100% stainless steel 31 piece Allen bolt kit for the Honda engine. A similar kit from a polish shop will cost you over $150.00 Installing...
alloyboltz.com alloyboltz.com
The 2 rear mounting bolts and 2 bottom front are all M10 bolts (I think, measured now with a ruler).
 
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Ditto on the above and you should also block the frame a bit to lift it off the work bench. Either that or remove the oil drain bolt as I think this is what is keeping the engine from dropping low enough to align the holes.
 
I think the Part Catalogue, from our library, has diameter and lengths of bolts. Totally loosen all the top mount bolts, for sure.

Scrape away powder at contact points for an electrical ground that is necessary.
 
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Seems like I got the right bolts, also in Partzilla it mentions M10 bolts:
1734211327775.png
 
I would think you can get stainless metric bolts relatively easy?
In US, being mostly Imperial (inches) metric stainless tend to be a premium price (thanks to all the 'import racers' watching 'Fast' series of movies).
I just get a selection and shorten them as needed,
50mm long is a 'standard', 65mm is next 'standard length.
I was going to mention thread damage but got beaten to it :ROFLMAO:
Oh, glad you finally made it here.
 
Yeah I’m getting a new one today. It went on smoothly but just wouldn’t separate from the nut.
 
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I'm stuck...
I took out the bolts at the top and took out the oil drain bolt.
I tried putting the rear bolts first and then the front ones but the front just won't line up.
I also tried the other way around, and the weird thing is that without any bolts at all, I can't even get just the front bottom left to align (the one with the spacer).
The other problem is that there's no way the spacer's gonna fit, it's missing like an extra 4-5 mm (0.17 in). I didn't have the spacer so I got one from eBay: https://www.ebay.com/itm/196685628996
The spacer measures 12.5 mm (0.49 inches).
Another thing is that you can see in the last photo I circled where one of the bottom case bolts is touching the frame on the left side. This is when the engine is sitting as far right as I can push it.
Thanks for all your help up till now!


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Some more pics, these are just with the two bolts in the back (not tightened, without the nuts).


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Aside from the possibility that the frame is slightly tweaked in places for whatever reasons unknown, I see two things right away: the head of the allen bolt in the crankcase is too tall to be used in the engine above the lower left front motor mount position, it shouldn't be hitting the frame there and a typical metric crankcase bolt wouldn't. The other thing that stands out is the left front motor mount boss on the crankcase has been broken and welded in the past (likely from someone leaving out the spacer and tightening the bolt until it broke the mount off the crankcase), so the hole location might be slightly different than it was originally.
 
The broken fins and what looks like repairs to both front motor mounts leads me to believe that the frame is indeed tweaked as AD mentions.
 
I got the engine like this and got it fixed by an aluminum welder, because most of the base of the holes was there I wouldn’t think the crankcase would be the problem.


IMG_3545.JPG
IMG_3544.JPG
 
Was the motor in the frame when you bought it or was the motor purchased separately. If the engine was purchased separate from the frame, then the frame may be ok and it's the motor mount holes that are off.
 
boddy said:
Was the motor in the frame when you bought it or was the motor purchased separately. If the engine was purchased separate from the frame, then the frame may be ok and it's the motor mount holes that are off.
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No it's the original motor and frame, I did buy it already out of the frame but it's the original motor according to the documentation.
 
boddy said:
Can you see any damage to the frame in the front motor mount area. I suspect the frame was hit from the side.
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Not really, the motor mounts, look like they came like that from the factory, no visible damage.
 
I got the right side bolt in now by pulling the motor strongly downwards and hitting the bolt in with a rubber mallet.
So the front bottom left with the spacer is causing the issue.
As @ancientdad said, the engine case bolt above the mount is an issue. So I cleaned the original bolt and will try replacing it, though it doesn't seem that different. The head is a little shorter than the new Allen head bolt.
 
Could be that the weld on the right motor mount is too thick not allowing enough clearance for the spacer on the left.
 
Alon said:
I got the right side bolt in now by pulling the motor strongly downwards and hitting the bolt in with a rubber mallet.
So the front bottom left with the spacer is causing the issue.
As @ancientdad said, the engine case bolt above the mount is an issue. So I cleaned the original bolt and will try replacing it, though it doesn't seem that different. The head is a little shorter than the new Allen head bolt.
Click to expand...
I replaced the allen head bolt with the original hex and now it’s not touching. I have both rear bolts in and bottom right side in. Just the spacer side left.

IMG_2910.jpegIMG_2909.jpeg
 
ancientdad said:
. . . The other thing that stands out is the left front motor mount boss on the crankcase has been broken and welded in the past (likely from someone leaving out the spacer and tightening the bolt until it broke the mount off the crankcase), so the hole location might be slightly different than it was originally.
Click to expand...

boddy said:
Can you see any damage to the frame in the front motor mount area. I suspect the frame was hit from the side.
Click to expand...
While it is possible that a PO tried to assemble the engine to the frame without the spacer in place, and thereby broke the engine, I suspect that the damage was caused by someone in the past attaching an aftermarket engine guard to the bike as an accessory. A low side crash tweaks the frame and breaks out that chunk where the spacer goes. The damage that is apparent to the eye is confined to the engine guard and the missing chunk of of the crankcase, but the frame was tweaked at the same time. It just doesn't readily show the damage till you try to put the engine back in. I have read of this happening several times. Do some googling and you will likely find it. I remember that the editor of Mcy. Classics Magazine ran into this once while trying to work on a CB350, and wrote about it in the magazine.

{Edit} Look here for a picture of the guard I am talking about.
 
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Alon said:
I’m trying to bolt back the engine into the frame and I can’t get the two bottom holes to line up with the frame.View attachment 40436
Click to expand...

Alon, before you wrestle that engine into the frame, take another look at your kickstarter shaft. It should be round on the end, with crisply defined serrations. From your picture, I think yours is trash and should be replaced if you ever want to use the kicker. I'm not sure where that flat surface on your kick shaft came from, perhaps a bodge by a previous owner because the serrations were worn away? What does the mating lever look like?

To replace the shaft, I believe the engine needs to come back out of the frame and then the cases must be split. That is why you should check this issue first.

For your frame issue, you might measure the width of the engine, add the thickness of the spacer, then gently spread the frame to that dimension by somehow using a small hydraulic jack. Note that ballbearian measured 143 mm width on two of his frames.
 
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ballbearian said:
I've still got that monstrosity. It might be special circus equipment for the acrobatic midget team to hang off of.

I'm getting 143mm between frame mounts on two different frames.
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I’m getting about 140.7 mm
Is this the measurement you made? @ballbearian

IMG_2933.jpegIMG_2930.jpeg
 
I tried spreading just the mounts, not the frame tubes. I got it to move a little and I could probably get the spacer in with a little more work.
But the main thing is that the bracket doesn’t line up with the engine.
IMG_2937.jpeg
 
If the frame was bent in a crash, and that is still just a guess, it got bent in two or more directions at one time. Your best bet might be to see if there is a shop in your area that can straighten the frame to spec. with a proper jig. In the end, you don't want to have any part of the engine or frame severely stressed to bolt it together.
 
I live in Israel, so we don’t really have shops that actually bring to spec. Mostly it’s just scrap it and buy new.
I thought of taking it to a shop and maybe get them to move the bracket, grind it off and weld it back aligned.
Another thought would be to try and expand the hole in the bracket and fill it with welds on the opposite side. In other words move the hole a little.
I feel like these are really bad ideas (especially the second one 😅).
 
You need to make sure that the drive sprocket stays in proper alignment with the rear wheel, and that the rear wheel stays in proper alignment with the front wheel.

Maybe inquire at an autobody shop to see if they can mount the frame to a jig and then pull/push that bent side back to line up.
 
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Alon said:
I live in Israel, so we don’t really have shops that actually bring to spec. Mostly it’s just scrap it and buy new.
I thought of taking it to a shop and maybe get them to move the bracket, grind it off and weld it back aligned.
Another thought would be to try and expand the hole in the bracket and fill it with welds on the opposite side. In other words move the hole a little.
I feel like these are really bad ideas (especially the second one 😅).
Click to expand...
I know it wouldn't help very much, but the aluminum in the repaired crankcase lug could be opened up a little bit so that last bolt could be fitted. Yes, there's a reason the hole is not aligned right, and maybe it tells us something happened to the bike that you're not aware of, but once the engine is secured and you put the rear wheel and drive chain on so you can check the alignment of the sprockets, that will help tell you if things are close (along with rear wheel alignment in the swingarm, by checking the distance from the center of the swingarm bolt to the center of the axle on each side). Then when you put the front end on the frame you can check the alignment of both wheels and have someone watch the bike as it rolls toward them to see if the wheels align that way as well. That will let you know if the frame is a problem or not.
 
I think boddy is on the right track. Some heat on there would help a lot to be able to straighten things without cracking. Do you know anybody with an oxyacetylene torch?
 
But it also needs to be bent like this:
Is it even possible?

IMG_2937.jpeg
 
See how the the most forward part of the tab is pinched tighter to the frame? That’s altering the geometry in that direction.

It may be best to align all the other bolts. Tighten them down, install the rear wheel and if everything is centered, have a new mounting tab welded on. It’s probably going to be an easier route than trying to straighten one that’s been folded before. It’s kind of like origami- once you fold the paper all up, it never goes flat again.
 
EzPete said:
See how the the most forward part of the tab is pinched tighter to the frame? That’s altering the geometry in that direction.

It may be best to align all the other bolts. Tighten them down, install the rear wheel and if everything is centered, have a new mounting tab welded on. It’s probably going to be an easier route than trying to straighten one that’s been folded before. It’s kind of like origami- once you fold the paper all up, it never goes flat again.
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When you say install the rear wheel, does that include the drive chain? And what should I check to make sure it’s centered?
 
Alon said:
When you say install the rear wheel, does that include the drive chain? And what should I check to make sure it’s centered?
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If you're using the original wheels and axle with spacers in the correct positions, checking the drive chain alignment will tell you if the rear wheel is centered correctly. And as I mentioned previously, by checking the distance from the center of the swingarm bolt to the center of the axle on each side you can verify the rear wheel alignment in the swingarm,
 
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