Topic: Did this frame and bike exit the factory together? CB750

[ken65]

hi all, i have a dilemma, I'am interested in a bike , the frame #CB750-2231612  which according to all the tables i could find indicate its a K3, the engine #CB750E-2431435 and according to tables is in the K6 range,  by the way its a US bike,  now firstly are the tables from this site and others considered dead accurate or are they ball park figures , the seller assures me they were married at the factory, and secondly has anybody got any conflicting proof or numbers being so far apart, for example, you bought the bike brand spanking new of the showroom floor and the numbers didn't add up similar to this, thanks in advance for helping me solve this puzzle,,  regards ken

[lucky]

Frame numbers and engine numbers never match.

[ken65]

yes i realize that numbers arent the same,or rarely match if ever, so your saying  it's possable it came from the factory with these numbers,  thanks

[RSchaefer]

When I started this process 4 years ago I always thought everything from Honda was pretty accurate and there were no significant variations, Japan culture and all.  Over time I began to realize many things happened at the factories over time and significant variations like this did occur.  All that said the difference between the engine # and the frame are usually pretty close like say within 50 numbers of one another.  I am rebuilding a '75 CB750F and my frame and motor are 43 numbers apart.

I would recommend asking Mark Paris or on the forum his handle is Hondaman, I think you can search and find his contact info.  He has been very helpful to me and all the rest of us and was taking copious notes in the K0 thur K6 timeframe and could give you a better idea about what might have happened.  I've heard things like they were making so many CB's in that time frame that they may have gone back and reworked some reject frames for instance and put them on say K6 motors, making the bike more a K6.  There are many many other things on the bike that would point to exactly what year it is.  I'm not sure on the K bikes but I think it actually says on the frame sticker the month and year, in addition to the number.  What is the month and year of manufacturer?

It also could be that the motor was replaced at some point after K3, maybe by Honda or maybe a PO.

[DanJ]

My K-3 numbers are 2000 apart but the first 2 numbers are still 22

[ken65]

thanks for the replies, i havent seen the bike yet so i cant say what month and year are on the tag but its being sold as an 73, what makes it harder aswell is the seller has k1 parts on it aswell, the motor does have the 3 pillars though on the engine, i will try and track down hondaman, ken

[RSchaefer]

I don't think Mark will mind me posting his email address here (mgparis@concentric.net)

[ken65]

thanks mate, have sent him an email. ken

[MoMo]

K3 frame and K6 motor according to my resources.  Unless the seller bought the bike new he does not know.  I once bought a bike from a seller who swore the 750 k3 was originally black. Larry

[Stev-o]

  I once bought a bike from a seller who swore the 750 k3 was originally black

Never believe the PO.....

[Geeto67]

Let me ask you, does it matter?

So what if it has had an engine swap in its past, most of them have.

[seanbarney41]

+1, k3 is no more especially valuable than a k6

[Dream750]

No reason to pester HondaMan, otherwise he will never finish his new book titled: SOHC 4 Performance Handbook 
 
Your K3 frame number: CB750-2231612 is correct for 1973. The K3 was only sold in the USA making this a straight forward frame & engine Identification. As published by American Honda, K3 engine numbers begin at: CB750E-2200001 and any K3 engine with a 22XXXXX serial number is considered “series” matching as in the example DanJ posted in reply #4.

The K6 engine CB750E-2431435 is not factory original as a “series” matching engine. The K6 engine will work in a K3 frame. However, the K3 oil tank must be replaced with a K6 oil tank for proper operation due to the K6 oil system and crankcase design change.

[ken65]

 thanks dream750,      i can take it to the bank that the timeline tables are accurate,   thats what i wanted to here,

quote  from geeto67     -                      Let me ask you, does it matter?

So what if it has had an engine swap in its past, most of them have.     really, i never realised , why's that?

[RSchaefer]

Well just to make sure we don't confuse.  I would not say that "most of them have" relative to an engine change!!  Its a 35+ year old vehicle so folks may have blown an engine, modified an engine, etc. necessitating a replacement motor, but most of the folks I know in the VJMC for instance are operating the original frame/motor combo from the factory, which from my point of view is more typical, not a different motor!

[ken65]

thanks for the reply RSchaefer,    i think 1 thing needs to be pointed out here. In australia, these bikes are much more expensive than in the US, this particular bike has a price on it of 10 grand, ,  an original K0 in mint condition  here usually has an asking price around $20000 plus , plus the same for a top full resto K0, as for K2's, 3 , 4 etc, you dont get much change from 8 to 10 grand for one needing little work,      from 5000 to 7000 or so many of these bikes are almost a project., needing 1000's spent on them , parts are stupid expensive here and ive been buying all my stuff from the US,  As an example i recieved a quote from the dealer here of $31  for a float bowl gasket,$71 for a float set, (valve, seat, washer)  , these bikes here are an investment of sorts and these little things can make a difference when it time to sell,   regards  ken

[lucky]

Are you going to go over every aspect of the bike like this?

[Geeto67]

  really, i never realised , why's that?

These bikes are old, and they were new at a time when people didn't care about collectibility or preservation. People used to treat this stuff like tinker toys made out of toilet paper. It's was all interchangeable and disposable. It's the same way with cars too, when muscle cars were just used cars a numbers matching car was a rare sight because it meant you weren't out beating the tar out of it as god and Detroit intended. As the hobby grew that was what became valuable so people began to take care to restore and preserve those while others were still treated disposable and eventually got used up. Pontiac made 89,000 GTOs in 1967 alone - when was the last time you saw one out in the wild? Honda made 83,000 cb350s - same question (don't answer if you live in Brooklyn, the cb350 is the new motorcycle roach of NYC).


My point is this: unless you are in the 100% factory correct restoration crowd, what does it matter if the bike is correct? I can't tell you how many cb750f's I owned that had K0 engines. There are 2 in my garage now. Why? Because for a while that was the only engine you could get speed parts for. Both of them have over-bores and other valve train hop up goodies that wouldn't work on the f engine if you were building a hot rod out of a new bike in 1976. Engine swaps happen.

Final thought: in the 80s and 90s nobody cared about cb750s. They were literally $100 used 10 and 20 year old bikes. My neighbor couldn't sell a nice clean k0 in 1991 for $300. I ended up with a ton of them because for a while it was cheaper to buy another running bike than fix one that broke.

[Terry in Australia]

G'Day Ken, as has been said above by our American cousins, the engine and frame were definitely not "married" when that bike rolled off the showroom floor.

I understand your concern regarding this, the bike is what an unkind restorer would call a "Bitsa" (Bits of this, bits of that) and would not be considered as valuable as a complete original bike with the "correct" numbers.

If you're after an original CB750 with all the right parts, then keep looking mate, there are better ones out there. I've got a friend in North Carolina with a warehouse sized garage full of old CB750's, I'm considering buying a couple from him, and if you're interested, let me know. Cheers, Terry.

[Geeto67]

thanks for the reply RSchaefer,    i think 1 thing needs to be pointed out here. In australia, these bikes are much more expensive than in the US, this particular bike has a price on it of 10 grand, ,  an original K0 in mint condition  here usually has an asking price around $20000 plus , plus the same for a top full resto K0, as for K2's, 3 , 4 etc, you dont get much change from 8 to 10 grand for one needing little work,      from 5000 to 7000 or so many of these bikes are almost a project., needing 1000's spent on them , parts are stupid expensive here and ive been buying all my stuff from the US,  As an example i recieved a quote from the dealer here of $31  for a float bowl gasket,$71 for a float set, (valve, seat, washer)  , these bikes here are an investment of sorts and these little things can make a difference when it time to sell,   regards  ken

There is so much wrong with this logic I don't know where to begin.

If you are looking for a bike investment, you are looking at the wrong bike. You should be looking for a fully restored k0 (or an f3 if you got them in Australia). Uniqueness and rarity drives collectibility and the k1-k6 cb750 is the ford mustang of the motorcycle world (I'm sorry I don't know what the most populous classic car is in Australia, it just means they are not unique or rare).

Bikes are a risk when it comes to value. You spend more to minimize the risk. A the same time they aren't making any more of them so usually they don't depreciate the same way new stuff does. Honestly if what you are telling me is true about your market it is a pretty safe gamble you can get your $10k out when you want to sell later (provided the world financial markets don't have another 2008). Bikes are a losing money proposition anyway - you never get the fuel or insurance premiums back when you sell.

Again, what do you WANT the bike for? Do you want to ride it as Honda intended - fast and loose? Do you want something to polish and impress people with in parking lots and shows? Do you want a place to park your money with the expectation you can buy a house when you go to sell? You need to figure this all out before you even start looking. Just curious, why a cb750? There are other bikes out there I am sure are similarly priced that are better why this make and model?

Once you start bringing numbers in it is useless to talk any further about the value of something without seeing pics.

[disco]

Without wanting to hijack the thread...but can Dream750 or someone else please elaborate on why the K3 oil tank cannot be used with a K6 motor?? I know there is some variations with the crankcase breather system but didn't realise it was that important.

[70CB750]

Of course they can be used.  I am gonna mate K3 oil tank to F3 engine - and you are right, the only variation is breather system, basically emission stuff.

Without wanting to hijack the thread...but can Dream750 or someone else please elaborate on why the K3 oil tank cannot be used with a K6 motor?? I know there is some variations with the crankcase breather system but didn't realise it was that important.

[Geeto67]

I thought the change was for the 77-78 K bikes and the 75-78 F bikes. Those are when the oil tanks stopped having breather caps. I pulled out and looked at 76 K tank and I didn't see a difference but I also don't have the stock cap for it.

[Dream750]

Without wanting to hijack the thread...but can Dream750 or someone else please elaborate on why the K3 oil tank cannot be used with a K6 motor?? I know there is some variations with the crankcase breather system but didn't realise it was that important.

Well, it can be important.  
 
The K6 oil tank was redesigned internally allowing all excess oil to be returned to the crankcase. The earlier K0-K5 messy and unsafe vent-to-atmosphere design was eliminated. The K6 chain oiler was also eliminated. The K0-K5 chain oiler was supplied by an internal oil tank separator and external hose fitting. The K6 crankcases received an internal oil flow redesign and a new crankcase part number to reflect these changes. In stock form, the K6 engine should be used with a K6 oil tank allowing the redesigned oil system to work together as the Honda engineers intended.

This does not apply to custom made oil tank applications.
 
The K6 crankcase vents to the atmosphere via the cam cover hose.
   

[RSchaefer]

Guess that might be a good thing for Ken65 to check on this bike for sale, to see if it looks like the bike has a chain oiler?