Author Topic: Will a F motor fit in an A frame?  (Read 2429 times)

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Offline Mr Freeze

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Will a F motor fit in an A frame?
« on: April 18, 2014, 08:43:59 AM »
Hey guys, I have a 1978 CB750A that is currently running, but just learned that it needs a head gasket. I happen to have an opportunity to buy a 1978 CB750 F donor motor for a good price.

Does anyone have any insight to whether this swap is possible?

Offline 70CB750

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Re: Will a F motor fit in an A frame?
« Reply #1 on: April 18, 2014, 09:04:43 AM »
I know that 78F fits 73K frame - with alterations to the swingarm and left rear shock mount - yours should fit unless A frame is different.
Prokop
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Offline Old Scrambler

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Re: Will a F motor fit in an A frame?
« Reply #2 on: April 18, 2014, 09:12:11 AM »
The motor will bolt in...............but I do not know for sure if the chain size and sprockets will match..........check both pitch and width at the rear.  That's quite a change for performance................be aware...........the F2-3 heads are known to develop worn valve-guides at less than 20,000 miles.
Dennis in Wisconsin
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Offline Mr Freeze

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Re: Will a F motor fit in an A frame?
« Reply #3 on: April 18, 2014, 09:42:37 AM »
Well I think if I get my hands on the donor bike that I'm going to do a head and valve job on it before I even install it. I just talked to the guy and it's a K motor.

Offline 70CB750

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Re: Will a F motor fit in an A frame?
« Reply #4 on: April 18, 2014, 09:51:16 AM »
If its a K, you should be fine with the valve guides and I venture to say that sprockets will line up too.

Does A have disc brake in the rear?
Prokop
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I love it when parts come together.

Dorothy - my CB750
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2006 KLR650

Offline Mr Freeze

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Re: Will a F motor fit in an A frame?
« Reply #5 on: April 18, 2014, 10:56:47 AM »
No there isn't a rear disc brake on the A. Check this ad out. Guy said it was a K, the brake setup is pointing to an F.

http://philadelphia.craigslist.org/mcy/4428060169.html


Offline Old Scrambler

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Re: Will a F motor fit in an A frame?
« Reply #6 on: April 18, 2014, 01:31:12 PM »
Looks like an F0 or F1 motor (short intake rubbers) in an F2-3 chassis with a K-7-8 rear fender.  Try and get some frame and motor IDs.  You can make it work if that motor is good....................
Dennis in Wisconsin
'64 Triumph Cub & '74 Honda CB750 Bonneville Salt Flats AMA Record Holder (6)
CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
'63 CL72 Project(s)
'66 CL77 Red
'67 Triumph T100C
'73 750K3 Owned since New
'77 750F2 Cafe Project
2020 ROYAL ENFIELD Himalayan

Offline Mr Freeze

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Re: Will a F motor fit in an A frame?
« Reply #7 on: April 18, 2014, 04:05:28 PM »
Yeah I don't know if maybe it's a K motor with some parts from an F, like the boots and carbs? It's some kind of hybrid cause weren't the 1978 motors black? It's an odd duck but I'm really just looking for a good motor so it don't care much about the rest.

Anyways, I'm going to go see it Monday, check compression, and all that madness. I have a set of 74 K carbs that I'd fit to it. Everything else on my bike is ready to go and I'll probably stash away my A motor for something in the future.

Offline Grnrngr

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Re: Will a F motor fit in an A frame?
« Reply #8 on: April 19, 2014, 09:54:29 AM »
Don't forget to get all the clutch handle parts also..
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Offline hondamaticdave

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Re: Will a F motor fit in an A frame?
« Reply #9 on: August 31, 2014, 11:12:57 AM »
I'm thinking of doing this myself. I love the style of the A. Bigger tank, gl1000 style wheels. My thoughts are that this would be awesome with a strong K motor. Maybe 836 kit. Sounds like fun to me. Very much so.

Offline brandEn

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Re: Will a F motor fit in an A frame?
« Reply #10 on: August 31, 2014, 11:48:52 AM »
If the sprockets don't line up I have a cush drive from my 1978 F3 comstar wheels that might help.

Offline hondamaticdave

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Re: Will a F motor fit in an A frame?
« Reply #11 on: August 31, 2014, 02:30:27 PM »
Sweet. Well my motor is leaking oil slightly from the head gasket, near the chain tensioner. Its not a big problem really. I also don't like the high rpm at 70. For the cost of sprockets, chain, head gasket, and all that, its not to far of a stretch to just change out to a K motor and be done with it.

Offline dave the welder

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Re: Will a F motor fit in an A frame?
« Reply #12 on: August 31, 2014, 03:10:15 PM »
don't forget you have to mount an oil tank
don't buy it build it

Offline hondamaticdave

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Re: Will a F motor fit in an A frame?
« Reply #13 on: August 31, 2014, 03:15:19 PM »
Yep this is true. I'd have to figure that out. Thanks for the info.