Author Topic: 1972 CB350 Twin  (Read 1994 times)

Offline Nurse Julie

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1972 CB350 Twin
« on: June 03, 2020, 09:31:59 PM »
Advice please, the above model / year, what model would it be K what 🤔
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Offline Lynx

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Re: 1972 CB350 Twin
« Reply #1 on: June 03, 2020, 09:44:58 PM »
We only got the k4 in Britain but in 1973 officially. I had a 1971 K2 but it was a bored out 250.

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Offline florence

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Re: 1972 CB350 Twin
« Reply #2 on: June 03, 2020, 10:06:20 PM »
I have a UK 1972 which as far as I can tell is a K3 but originally it was a 250.  I don't think the 350 was available in the UK in 1972.

I bought my bike in 1985 and a year later, when the engine blew up I bought a 350 engine which was from a 1974 machine (K4).  Biggest problem I have had has been crankshafts (big end), now on 3rd one after 16000 miles.  I think I was a bit too right hand heavy in my youth and couldn't afford a bigger machine so the poor thing got thrashed.  I've always found the CV carbs to be a weakness, especially in the winter, the slides would stick.  Have since changed to Amal 932 slide carbs and it is surprising how much more responsive it is. I'm not bothered about originality.


Online Bryanj

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Re: 1972 CB350 Twin
« Reply #3 on: June 03, 2020, 10:32:27 PM »
I think 72 350 ought to be an import, all the 250 and 350 suffered from owners not cleaning out the centrifugal oil filter

Offline florence

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Re: 1972 CB350 Twin
« Reply #4 on: June 04, 2020, 08:55:20 AM »
that's right, I used to clean mine when I changed the oil, circa 1000 miles.  Sadly, all the parts I was using were second hand with unknown servicing.

The engineer I use for rebores etc said these cranks cannot economically be rebuilt.  That was a few years ago, not sure if still the case?


Offline flatfour

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Re: 1972 CB350 Twin
« Reply #5 on: June 04, 2020, 09:16:02 AM »
I owned a 1972 CB250 K4, bought new in that year. It ran well until after laying it up for a while over winter, there was quite a lot of vibration evident when it was put on the road again in the spring. As it now out of warranty (only six months in those days I seem to remember) I traded it in for a 500/4.

When the dealer stripped it for repair and resale, they found that a bearing on the crank (roller or ball?) had pitted due to rust, so fitted a new crank. All maintenance was through the dealer beforehand and the bike was only a few months old.

A friend of mine bought a CB350 (325) in metallic green in what we thought was the first year of availability, I think around 1974. He certainly did not buy it when I had the 250, as he tried the 500 before buying but decided that he wanted less bulk and weight so aimed for the CB350 as an alternative.

Online Bryanj

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Re: 1972 CB350 Twin
« Reply #6 on: June 04, 2020, 10:47:35 AM »
Cranks probably are worth doing now due to short supply, maybe Alpha bearings?

Offline AshimotoK0

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Re: 1972 CB350 Twin
« Reply #7 on: June 04, 2020, 11:03:26 AM »
that's right, I used to clean mine when I changed the oil, circa 1000 miles.  Sadly, all the parts I was using were second hand with unknown servicing.

The engineer I use for rebores etc said these cranks cannot economically be rebuilt.  That was a few years ago, not sure if still the case?

Yea a '72 350 woud most likely be a USA import K4. You can instantly spot an import as the mudguards are different .. we got deeply valanced rear and the front .. UK one has stays that go inside the mudguard blade (USA ones are like 400/4 & 500/4 ones with stays that bolt on outside) Also the UK350K4 that we got in 1973 was only available in Candy green. K4 model also had different forks with bolt clamps on the top yoke. sadly we never got the K5, B1(germany)  model with front disc brake .. also known in Japan as the G model BUT not G5...  that was a complete re-design.

I guess it wasn't economically viable years ago to rebuild cranks for CB250/350 using new parts but there are a lot of NOS spares around now if you shop around. BTW the 350 crank is different to the 250 as it has more big end rollers. Also the K4 primary drive changed to a single row gear as opposed to double offset gears in the K0-K3. My mate Graham Curtis rebuilds cranks but has not done CB250K yet but doubtless he woud have a go at one if chivvied enough. They sold a million of these bikes though in various guises so often easier to buy a decent used crank. If I am ever buying one,Ii take a new gudgeon pin with me  nd try it in the small end as lack of maintenance usually causes wear here and is a good indication of the 'general health' of one of those cranks. Graham bushes the little ends on CB72/77 cranks but with a very thin bush to maintain strength of the little end. (poo pooed by some people though)

I found in the early C72 manuals that Honda did a very slightly oversize gudgeon pins as a spare part (DS have these I think) .. I guess you reamed out the small end eye and piston.
« Last Edit: June 04, 2020, 11:06:31 AM by AshimotoK0 »
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Offline florence

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Re: 1972 CB350 Twin
« Reply #8 on: June 04, 2020, 11:26:42 AM »
I only have two cranks left now, one in the bike and one spare (250)

The 250 crank will work in the 350 but the con-rods are thinner which would make me nervous but I am told it is OK.

Ash, what was the advantage of the single primary drive gear as opposed to the offset one?  I have both kinds in my spares.  Is the offset one about making it quieter?

They are a great little bike, full of character, very easy and fun to ride.  I always wished Honda had made a bigger version, i.e. SOHC 650 twin. I only stopped regular use of mine when I got the 500/4 which is better for long journeys.

Offline SteveD CB500K0

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Re: 1972 CB350 Twin
« Reply #9 on: June 04, 2020, 11:30:38 AM »
The 350 was what everybody wanted as soon as they’d passed their test.

The “350” on the side panel meant more than the lack of L plates!

Of course, we all really wanted a 4 but well out of reach


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Offline AshimotoK0

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Re: 1972 CB350 Twin
« Reply #10 on: June 04, 2020, 11:42:53 AM »

Ash, what was the advantage of the single primary drive gear as opposed to the offset one?  I have both kinds in my spares.  Is the offset one about making it quieter?


Not sure .. I guess the earlier design sounds better engineering wise .. cost cutting perhaps. I didn't realise the K4 had that single gear primary setup until a coupe of years ago when I stripped K4 250 engine i got ina job lot of stuff.
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline florence

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Re: 1972 CB350 Twin
« Reply #11 on: June 04, 2020, 11:55:40 AM »
there are some funny changes, I have one set of crankcases, quite early, that have the CB350 size cutouts for the barrels even though it is a 250.  The later 250 crankcases have the appropriate sizing.


Offline Lynx

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Re: 1972 CB350 Twin
« Reply #12 on: July 01, 2020, 06:05:51 PM »
The 350 was what everybody wanted as soon as they’d passed their test.

The “350” on the side panel meant more than the lack of L plates!

Of course, we all really wanted a 4 but well out of reach


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Yes I bought my 350 after passing my test in 1981. Trouble is I'd only owned it about 2 weeks when I decided to rag it down the duel carriageway to see how fast it would go. It did 95mph on the clock but when I got back home it was pissing out oil. It turned out all the piston rings had broken. Even though it was only 10 years old at the time, I had a right job getting parts for it. It's probably easier now! I was told by one dealer to try the natural history museum  ;D. It had Hepolite pistons in it which weren't made anymore. When I finally got hold of some Honda pistons, I discovered it was a bored out 250 and I had to get them machined, so they didn't hit the head  ::).
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Triumph Speed Triple RS.

Previous bikes include
1976 Honda CB400F Now sold :-(
CB350K3 x2
CB250G5
CX500C
VF500F2
VF1000FE

Offline cooleronthecoast

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Re: 1972 CB350 Twin
« Reply #13 on: July 01, 2020, 06:15:36 PM »
The 350 was what everybody wanted as soon as they’d passed their test.

The “350” on the side panel meant more than the lack of L plates!

Of course, we all really wanted a 4 but well out of reach


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I had a '74 K4 350 for a while (must've been 1976) before I got a 400/4. It was an OK sort of bike.  I say that because they were never going to turn heads like the IL4s did back then, but it sounded nice and had decent performance for the time.
Now where did I put that 10mm socket?

Offline philward

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Re: 1972 CB350 Twin
« Reply #14 on: July 01, 2020, 09:38:54 PM »
I owned a 1972 CB250 K4, bought new in that year. It ran well until after laying it up for a while over winter, there was quite a lot of vibration evident when it was put on the road again in the spring. As it now out of warranty (only six months in those days I seem to remember) I traded it in for a 500/4.
[/quote
Similar story but a year earlier - My first bike was a 71 250k3 and broke the rings coming back from Brands trying to keep up with (and didn't) a 750 Honda and Trident (guys from the Manchester 171 Club) - I replaced them before it broke again and bought a 500Four
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Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

 

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