Author Topic: Rebuilding my confused Honda.  (Read 1207 times)

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Offline constant_gardener

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Rebuilding my confused Honda.
« on: June 01, 2017, 09:18:57 PM »
Hi everyone,

I'm new to this forum, and I had this bike for awhile now. Most of us thought it was a K7 when the previous owner was advertising it for sale. It was manufactured in 1977, and I'm pretty sure it's a F2 model.

It has the following frame number:   CB750F1101112 , and engine number: CB750E2612248

Bike has never run right since the day I got it, so a couple of mates and I tore the engine apart, and we're trying our best to get her back running right.

From what I read, the F2 used a domed shaped piston, what I pulled out of this bike looks like a K piston as it's flat, and in a box of parts I have, I think there's a set of F1 pistons (a different shaped dome piston).

I'll upload more pics of the rebuild.







Offline TwoTired

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Re: Rebuilding my confused Honda.
« Reply #1 on: June 02, 2017, 08:13:09 AM »
Sure looks like a K model to me.  F models have a black motor, a 4 into 1 exhaust, a rear disc, and dual front disc, and a seat cowl out the back.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline flybox1

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Re: Rebuilding my confused Honda.
« Reply #2 on: June 02, 2017, 09:07:08 AM »
Based on your vin, thats a K1 frame.  The engine color is confusing.  VIN says its an F2, but....
Just the F2/F3s had black engines.  All F's had a rear disc brake, not a drum.
Does the engine look like its been blasted/painted? 
It is not uncommon to find transplant engines.  My K8 came with a K1 engine, now it has an F3  ;D
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline flybox1

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Re: Rebuilding my confused Honda.
« Reply #3 on: June 02, 2017, 09:09:22 AM »
Might be an engine from transition period between clear F1 engines and black F2s....i dunno  :-\
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Bankerdanny

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Re: Rebuilding my confused Honda.
« Reply #4 on: June 02, 2017, 09:48:48 AM »
But doesn't the F in the VIN indicate an F model or do all 750's have that? The VIN info at the 750 info page doesn't list the prefixes, just the #'s.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline 754

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Re: Rebuilding my confused Honda.
« Reply #5 on: June 02, 2017, 09:57:36 AM »
Looks like a lot of 73 or later parts, with tank and fork ears and sidecovers painted to resemble earlier stuff. Fork headlite ears are 73 or later.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline BomberMann650

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Re: Rebuilding my confused Honda.
« Reply #6 on: June 02, 2017, 10:01:33 AM »
I thought the f/k delinieation was made from the first three numbers after the letter.

Cause every 550 had an E in the motor serial

Offline 754

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Re: Rebuilding my confused Honda.
« Reply #7 on: June 02, 2017, 10:43:00 AM »
If it is a f frame, the sidestand should be further back.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline flybox1

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Re: Rebuilding my confused Honda.
« Reply #8 on: June 02, 2017, 10:50:33 AM »
Fits within the K1 frame vin range


Model   Model Year   Production Dates   Frame #                 Engine #
CB750 F0   1975   Jan 1975 – Feb 1975   1000002 to 1015054        2500004 to 25115085
CB750 F1   1976   Mar 1975 – Nov 1976   2000003 to 2022317        2525094 to 2563530
CB750 F2   1977   Nov 1976 – May 1977   2100011   E2600004-
CB750 F3   1978   May 1977 – May 1978   2200001   E3100001


K
Model Number   Model Year   Production Dates   Engine#        Frame#
CB750   1969/70   1969 – 1970                   E1000001        1000001-
CB750 K1   1971   Aug 1970 – Nov 1971                    E1053399        1044806-
CB750 K2   1972   Nov 1971 – Sep 1972                    E2000001         2000001-
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline 754

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Re: Rebuilding my confused Honda.
« Reply #9 on: June 02, 2017, 11:01:59 AM »
Is that a gas guage on the tank, does not look stock from the side.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline martin99

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Re: Rebuilding my confused Honda.
« Reply #10 on: June 02, 2017, 02:33:45 PM »
There is absolutely nothing 'F' about that bike that I can see. Sure is a nice looking bike though. FO and F1 were bare engines, F2/3 were black. Could well be a transplant but not from an F2/3 unless someone went to the trouble of stripping the engine of its black paint.

I'm pretty sure, though I've not done it myself, that a 'F' motor can be fitted to a 'K' fairly easily but requires an offset final drive front sprocket. Might be worth looking to see if this is the case to help solve the conundrum.
Build threads:
77 750F2 Refresh Project http://forums.sohc4.net/index.php?topic=144075.0
TRIBSA http://forums.sohc4.net/index.php/topic,160296.0.html

1977 CB750 F2
1958 Norton Model 99
2011 Triumph Street Triple 675

Offline constant_gardener

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Re: Rebuilding my confused Honda.
« Reply #11 on: June 05, 2017, 07:31:06 PM »
Hi everyone, yes, they have sand blasted/soda blasted the engine. There is a gas tank gauge, I managed to find a guy who makes them in a place in Taiwan.

What I suspect happened was that the bike lived it's life as an F2 until one of the previous owners thought "Hey, wouldnt it be cool to have a K model?" so he bought a K frame, changed the VIN number on the frame and mounted the engine in it, and bought all the bits and bobs to make it look like a K model.

I just took a look at the pistons and it seems they are K model pistons, I was told that the heads on the F2 are different, so I'll measure the valves, the F2 has 31 and 34mm valves.

Offline 700504

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Re: Rebuilding my confused Honda.
« Reply #12 on: June 06, 2017, 02:21:06 PM »
Does the final drive have a single bolt and a big washer, or does it have tabbed lock washer and/or lock ring and an oiler bolt?
1978 cb750k
1977 cb750f2
1974 cb750k
1973 cb750k
1981 cb650 (rip)
1969 ct90

Offline drumstyx

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Re: Rebuilding my confused Honda.
« Reply #13 on: June 06, 2017, 03:30:00 PM »
Doesn't the K tank mount on a wider or narrower frame than the F tank?