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Author Topic: cb750A with a cb750K motor?  (Read 3257 times)

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Offline paulages

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cb750A with a cb750K motor?
« on: February 13, 2007, 01:44:37 am »
i searched, but couldn't find a relevant thread. what's compatible from the hondamatic model and the other SOHC 750's? i know people use the alloy rims, but what else? can a K motor replace the A engine? i know very little about this oddball bike, other than that the cb400m hondamatic i rode felt like a scooter. there's one on craigslist for $200, and i have any extra engine, and plenty of parts looking for a home.
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paul
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1974 CB550 (735cc)
1976 CB550 (590cc) road racer
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1972 NORTON Commando Combat
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eldar

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Re: cb750A with a cb750K motor?
« Reply #1 on: February 13, 2007, 06:22:13 am »
Pretty much all the parts are usable, other than the weird engine and tranny. You should be able to use the top half though but dont quote me on it.
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Offline jrrobertsjr

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Re: cb750A with a cb750K motor?
« Reply #2 on: February 13, 2007, 06:59:04 am »
Carbs are more restricted and CAM is milder.

The swingarm on the 750A was wider to allow for a half inch wider rear tire. The hubs had different widths on them as well to help everything line up.

It is a great project frame if you want something a bit different. Mine was a K frame and it all fit together with the 750A bits that I got.

Oh yeah. The swingarm bolt is like 6 inches longer. You will need to grab one of those from a K bike. They are cheap.
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Offline bill440cars

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Re: cb750A with a cb750K motor?
« Reply #3 on: February 13, 2007, 07:28:37 am »
Quote from: jrrobertsjr on February 13, 2007, 06:59:04 am
Carbs are more restricted and CAM is milder.

The swingarm on the 750A was wider to allow for a half inch wider rear tire. The hubs had different widths on them as well to help everything line up.

It is a great project frame if you want something a bit different. Mine was a K frame and it all fit together with the 750A bits that I got.

Oh yeah. The swingarm bolt is like 6 inches longer. You will need to grab one of those from a K bike. They are cheap.

            Well, I'm sure glad I hesitated to respond to this. I didn't know ,but I  just thought because of the different shape of the trans area of the cases, that the frame would be different to mount it up. Live and learn,huh? ??? ???

                                                          Later on, Bill :) ;)

                                                 
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Offline jrrobertsjr

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Re: cb750A with a cb750K motor?
« Reply #4 on: February 13, 2007, 08:59:05 am »


Certainly don't take my word as gospel.

I had neither the frame nor a 750A motor. Just the swingarm and rims. The carbs and Cam I am pretty sure about and it was easy to see the differences on the rear hub.

The bolt that was sent to me with the rear swingarm was way too long.

Bill knows way more about this than I do about this stuff, so check the frame for differences.

I am still on a steep learning curve.
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Offline bill440cars

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Re: cb750A with a cb750K motor?
« Reply #5 on: February 13, 2007, 09:13:48 am »


    Whoa there jr, I never said that I knew the info. I was just glad I didn't jump in and offer an opinion on this because it would be based on having only seen a 750A and not from actual first hand knowledge on the subject. If I know something, I'll gladly share, but if it's only a speculation I try to make that clear.
I don't ever want to mislead someone.

                                             Later on, Bill :) ;)
             
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Member # 1969
PRAYERS ALWAYS FOR: Bre, Jeff & Virginia, Bear, Trevor & Brianna ( Close Friend's Daughter)
"Because HE lives, I can Face Tomorrow"                  
 You CAN Teach An Old Dog New Tricks, Just Takes A Little Bit Longer & A Lot More Patience!! 
             
Main Rides: '02 Durango, '71 Swinger & Dad's '93
                  Dakota LE 4x4 '66 CB77 & '72 SL350K2
Watch What You Step Into, It Could  End Up A Mess!

Offline paulages

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Re: cb750A with a cb750K motor?
« Reply #6 on: February 13, 2007, 10:40:16 am »
in other words: a K engine will drop right in then? seems that's the answer i'm getting...
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paul
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1974 CB550 (735cc)
1976 CB550 (590cc) road racer
1973 CB750K3
1972 NORTON Commando Combat
1996 KLX650 R

Offline jrrobertsjr

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Re: cb750A with a cb750K motor?
« Reply #7 on: February 13, 2007, 11:03:24 am »

Someone out there will know for sure. Bill and I believe that it might work but we sure don't want to give you bad info.

Can any others with CB750A knowledge verify that a K motor will work in this frame?

I am going to call a friend of mine in Denver that owns a motorcycle salvage yard to see if he knows. If I can get in touch with him, I will let you know what he says.
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Offline eurban

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Re: cb750A with a cb750K motor?
« Reply #8 on: February 13, 2007, 03:00:38 pm »
Don't know for sure about swingarm differences but the alloy DID rear wheel rim for the spoked Hondamatics is identical in size to the 17" chromed steel rim that is stock on the 77/78 K bikes.  Far as I know they both use the exact same size tire as stock.  I would thus wonder if JR is correct that the swingarm is indeed wider.  It may be (I'm not real familiar with the earlier Ks) that it is wider than a pre 77K bikes while it may be the same size as the 77/78ks.  If it is wider then the reason may have to do with sprocket locations rather than wheel width . . . .
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Offline jrrobertsjr

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Re: cb750A with a cb750K motor?
« Reply #9 on: February 14, 2007, 06:10:22 am »
http://www.sohc4.us/index.php?option=com_content&task=view&id=98&Itemid=51

This article located on this site explains a great deal about the 2 bikes.

I know the comparison is with an F model but it is still good info about the tires and carbs.

Johnny
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Offline bill440cars

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Re: cb750A with a cb750K motor?
« Reply #10 on: February 14, 2007, 07:32:26 am »


      Hey Johnny,

                     Good post there on the 750A. Didn't realize that it was here and had some interesting
      info. I knew about the "Parking Brake" but not that the trans was kicked into neutral by putting
      down the side stand. 8) I don't remember if it was mentioned but, the 750A has a kick starter
      stashed under the seat and you temporarily install it if needed. Now, is that weird or what? ???

                                                          Later on, Bill :) ;)
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Member # 1969
PRAYERS ALWAYS FOR: Bre, Jeff & Virginia, Bear, Trevor & Brianna ( Close Friend's Daughter)
"Because HE lives, I can Face Tomorrow"                  
 You CAN Teach An Old Dog New Tricks, Just Takes A Little Bit Longer & A Lot More Patience!! 
             
Main Rides: '02 Durango, '71 Swinger & Dad's '93
                  Dakota LE 4x4 '66 CB77 & '72 SL350K2
Watch What You Step Into, It Could  End Up A Mess!

Offline eurban

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Re: cb750A with a cb750K motor?
« Reply #11 on: February 14, 2007, 10:24:47 am »
Good article.  As the article mentions, the spoked Hondamatic and the spoked GL1000s share the same alloy DID wheel rims (19" front and 17"rear) The 77 and 78Ks also used the 19,17 wheel size configuration with identical width rims but made of steel.  The 76F uses an 18" rear.  These alloy rims make a nice upgrade to the stock steel ones in the K bikes and they are a direct fit in the 77/78k bikes. Earlier bikes will need the rear spokes from the 77/78K bikes to make them work.  Although I am not certain, I believe the Autos used a 630 size chain like the 77/78ks and Fs.   Like I said earlier, I would think that the autos swingarm is probably the same size as the 77/78Ks . . .In general Honda seemed to use many parts (turn signals for instance, as well as wheel sizes) from the GL1000 first on the 76 auto and then introduced into the K and F series in 77.  They also introduced the acellerator pump style carbs first on the Auto and then in the 77/78ks and Fs.  Of course the Ks&Fa got a larger 28mm variety.  One final interesting thing that I haven't been able to confirm but I do remember reading somewhere is that at least some years of the Auto had a removable frame rail above the engine so that the top end/cylinders  could be worked on with the engine in the frame.  I know that some people here would give their left nut to be able to do skip the nasty business of pulling an engine for a valve freshening procedure so it would be interesting to know if the autos frame has this feature or not.  Could be worth the $200 just in itself . . . .
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