Author Topic: CB750F weak points  (Read 4660 times)

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Offline Crshndbrn

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CB750F weak points
« on: August 16, 2012, 03:45:31 PM »
1976 CB750F that I'm going through from one end to the other.  I'm wondering if anybody can tell me what the weak points of the bike are so that I can make corrections along the restoration process.  Thanks!!

-Crshndbrn

Offline phil71

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Re: CB750F weak points
« Reply #1 on: August 16, 2012, 04:20:15 PM »
the fact that no one has responded yet means that there really are none.  Great bike!

Offline lostmykeys

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Re: CB750F weak points
« Reply #2 on: August 16, 2012, 05:32:09 PM »
 Most of the time the weak point is the rider.

Offline BeSeeingYou

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Re: CB750F weak points
« Reply #3 on: August 16, 2012, 08:34:22 PM »
Same weak points that plague any 36 year old CB750 K or F.  Can't think of anything that is specific to that model.  From a mechanical and electrical standpoint the CB750's are all similar enough with some changes/ upgrades/modifications over the years.
« Last Edit: August 16, 2012, 08:42:07 PM by srust58 »

Offline Dimitri13

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Re: CB750F weak points
« Reply #4 on: August 16, 2012, 08:38:28 PM »
Frame above the engine preventing top end removal with the engine in the frame.

Offline BeSeeingYou

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Re: CB750F weak points
« Reply #5 on: August 16, 2012, 08:43:04 PM »
Frame above the engine preventing top end removal with the engine in the frame.

yeah, you 550 guys just love to bring that one up. ;D

Offline scottly

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Re: CB750F weak points
« Reply #6 on: August 16, 2012, 09:11:02 PM »
Frame above the engine preventing top end removal with the engine in the frame.

yeah, you 550 guys just love to bring that one up. ;D
So do us guys with Seeley 750 frames. ::) ;)
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Offline HondaMan

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Re: CB750F weak points
« Reply #7 on: August 16, 2012, 09:31:21 PM »
If you have the 86A or 07A carbs (not the PD carbs), check the mainjet: if it has #105 mainjets, then check the exhaust valve guides, at least. Often these heads have worn out the guides (both sides) from the too-lean mixtures of the post-1975 engines (EPA stuff of the 1970s...).

The steering head bearings need to be changed to tapered roller type, if they are not now.

The swingarm pivot system is among the worst in the SOHC4 family. The center-of-the-arm grease zerk does not grease the bushings at all, so they are usually seized and damaged, or have been replaced (worst yet) with Honda's powdered-iron bearings, which eat the collar in about 5k miles or less. I rebuild LOTS of those arms from this damage, and change them to a superior, lifetime system in the process.

The rear shocks, if OEM, are long ago damp-less. They were nitrogen-filled when new, which escaped after about 2 years. The oil then went rancid in another year or so, eating the damper seals, so new rear shocks will really help it out.

If you have the size 530 chain and sprockets, so much the better: these became 630 size on the F1, which robbed the bike of some HP and shortened sprocket life quite a bit. The F1 can be easily swapped back to the more-available, less-expensive 530 size, too.

The post-1975 bikes tend to heat-shrink the head puck seals (under the rocker towers) pretty early, making oil leaks that show up on the front of the engine fins. These can be replaced by removing the cam and rocker towers, don't necessarily have to disassemble the whole engine.

The "F" bikes are all quite heavy on their right side, if the stock 4-1 pipe is still intact. This gives the bike a little bit of an uneven feel when tossing it from side-to-side. Lighter pipe(s) will help.

Don't be tempted to use 10w40 oils: use 20w50 or at least 15w50 weight in these engines. The logos and Owner's Manual(s) had a Jinglish mistranslation from 1974 onward that got this wrong. The pre-1974 manuals had it right.

Finally: the post-1975 bikes have a different 1st and 2nd gear set, which is taller than the early bikes. This gives it a "close ratio" tranny feeling. The 2nd gear set tends to wear its engagement dogs rapidly, especially with 10w40 oils and lazy shifting. Also, the top plate of the clutch has slanted cork blocks to induce slip momentarily when dropping the clutch hard, to protect these tall gears: this plate wears out quickly and makes the rest of the clutch slip.

If you have my book, it outlines how to fix most of this stuff.  ;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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Offline killersoundz

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Re: CB750F weak points
« Reply #8 on: August 16, 2012, 10:05:31 PM »
Hondaman you just made me want to stick to pre 1975 cb750's lol
My project thread:

http://forums.sohc4.net/index.php?topic=107447.0

My CB750K4 Starting up for the first time after a seized motor and rebuild!


Offline Don R

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Re: CB750F weak points
« Reply #9 on: August 16, 2012, 10:21:34 PM »
My F1 has the smaller chain, was it a running change? I thought they stayed 530 until the F2. gotta get my turn with the book I share with my brother lol.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750F weak points
« Reply #10 on: August 16, 2012, 10:25:02 PM »
I've always liked mine. Even after I blew it up in '76.  ;)  One of these days I may take the head apart (it's in the basement) and check the guides but I think they are fine with 30,000+ HARD miles. Agreed on the shocks and swing arm bushings. Also the steering head bearings but that's ALL 750's. Clutch rattle also which had a "field fix" then got upgraded in '77. I'm still running the original tranny but I sent it to Fast by Gast for magnafluxing and undercutting. All was good. Most other stuff is the same with all/most 750's and not unique to 75/76 750F's.

Some other easy upgrades could be electronic ignition, halogen headlight, after market coils with new wires, new plug caps, etc.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Crshndbrn

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Re: CB750F weak points
« Reply #11 on: August 17, 2012, 06:41:54 AM »
If you have my book, it outlines how to fix most of this stuff.  ;)

Just got here a few days ago, didn't know you have a book, but I'll keep an eye out for it.

Offline Old Scrambler

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Re: CB750F weak points
« Reply #12 on: August 17, 2012, 08:35:18 AM »
Mark's book is for sale on this site.........the gas-tanks are known for rusting out on bikes that have been sitting.....and the side-covers get brittle with age.  You have found the BEST place to get info for your bike.....take advantage of it 8) 8) 8) 8) 8)
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CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
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Offline Crshndbrn

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Re: CB750F weak points
« Reply #13 on: August 17, 2012, 09:32:05 AM »
Luckily I found one with a gorgeous tank, inside and out.  Just has 15-20 years of rust and dirt

bollingball

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Re: CB750F weak points
« Reply #14 on: August 17, 2012, 09:47:05 AM »
the fact that no one has responded yet means that there really are none.  Great bike!

Less than an hour come on. I love my bike too. If man makes it it can be improved ;) Dang it I thought mine was perfect. ;D After all it is a 78 they had 9 years to make it that way so it is as close as you can get ;D ;D
Ken


Offline TwoTired

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Re: CB750F weak points
« Reply #15 on: August 17, 2012, 10:44:06 AM »
I've been on this forum for many years.  And, likely reading it way too much of it.  Here is a summation of complaints and faults that I've gleaned from forum discussions.

The electrical system is awful with connectors that will not last 30 years. (Unless the bike is stored in a climate controlled environment with low humidity and no airborne contaminants.)

The alternator is weak, there is no cure, and does not allow added accessories or other upgraded electrical components without depleting the battery.

The battery is far too big and requires a new, modern battery  (More on this later).

The headlight is too dim.

The entire ignition system is no good.

The seat is too tall for anyone shorter than 6Ft.

The tires are too small for such a larger bike.
The rims are too narrow to accept modern wide tires.
The fenders, chain guard, shocks, and chain are all in the way of installing modern wide tires.
The spokes don't allow the use of modern tubeless tires without adding the enormous weight of an inner tube.

The bike is slow, and clearly not up to modern standards.

The displacement is too small and needs a larger displacement  (836 minimum, larger=better). The stock cam is anemic and a cause for major power loss.

The frame is poorly designed, too flexible, and won't allow doing the required engine upgrades without removing the engine from the frame.

The air filter is awful, ugly and must be discarded for something, ...anything... else.

The bike is too heavy, and can't be "flicked".

The terrible carburetors won't automatically adapt to any induction or exhaust "improvements" customizers require to make to this bike.

The front fender is a poor joke, just adds weight and does nothing to improve the already dismal handling.

The head bearings must be upgraded to roller type, before the bike can be safely operated.

The center stand has no purpose other than to add weight.

ALL the original exhaust systems are far too heavy and must be discarded.  If you must have one at all, keep it short and loud.

The chain oiler is too messy and must be shut off or defeated.
The engine cases are prone to cracking, and/or hole-ing due to poor chain selection (or maintenance), and lack of an adequate chain guard or case protector in the eventual occurrence of a chain failure.

The handle bars too high to ride effectively with your chest on the tank.

The brakes are awful and hardly stop the bike.  The basic design can't be made safe.  Modern brakes must be adapted.

The paint fades in the sunlight.  Clear coats chip and peel.

Instrument dials deteriorate and look ugly.

All the extraneous chrome is thin and prone to rusting.  (Flat black hides this effectively.)

The seat is too tall and fat and does not accommodate a small battery in the desired high CG location.

The turn signal buzzer is a bane to all mankind.

The fuel tap filter never worked right, is exceedingly difficult or impossible to maintain, and a $1 patched in inline fuel filter improves the bike's value by $100, at least.

That's all I can recall right now.  I'm sure I missed a great deal more.
However, to counter all these identified weak points...  The engine does have a good crankshaft, though.  If you use the right oil, and an oil cooler from a forum member, of course.
Oh, and wheel axles.  I don't recall anyone calling them "weak points".  But, I could have missed that, I suppose.

Once you get all these "weak points" fixed, you'll have a great bike, though!

Cheers,   ;D ;D
« Last Edit: August 17, 2012, 01:20:02 PM by TwoTired »
Lloyd... (SOHC4 #11 Original Mail List)
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Offline flybox1

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Re: CB750F weak points
« Reply #16 on: August 17, 2012, 01:09:21 PM »
hahahaha TT
Doing your best to confuse the newbies... ::) ;D
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Offline Crshndbrn

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Re: CB750F weak points
« Reply #17 on: August 17, 2012, 01:25:24 PM »
hahahaha TT
Doing your best to confuse the newbies... ::) ;D

If that's the goal, you'll have to try much harder.

Offline TwoTired

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Re: CB750F weak points
« Reply #18 on: August 17, 2012, 01:29:44 PM »
hahahaha TT
Doing your best to confuse the newbies... ::) ;D

Best?  Ha!
Just giving them the benefit of years of reading here, without the drudgery of reading all those prior posts!   ;D ;D

I guess I should have added that the tank, wheels, seats, bars, bar controls, instruments, side covers, turn signals, headlight, exhaust, air filter, shocks, have all been described as "ugly", at least once each, with plenty of agreement.

Perhaps that's what makes this forum such a valuable "resource".     ;D ;D

Cheers,
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 Jerry Rxman Griffin aka MuthaF'er

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Re: CB750F weak points
« Reply #19 on: August 17, 2012, 04:29:46 PM »
I didn't get the impression that he wants to "re-engineer" a 36 year old bike, just take care of the few 1975 issues.

After TT got done with ALL 70's era Hondas using today's standard he may as well just buy a new bike then look for today's shortcomings.

As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Killer Canary

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Re: CB750F weak points
« Reply #20 on: August 17, 2012, 04:46:19 PM »
Don't forget the difficulties in changing from summer air to winter air in the tires.
If it's worth doing at all it's worth over-doing.
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Offline ChuckG750f1

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Re: CB750F weak points
« Reply #21 on: August 17, 2012, 04:48:14 PM »
Geeez, I read the OP and was all set to mention dim headlight...and I still love my bike!!!  BTW, my '76 has a 530 chain ;) -Chuck
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Offline ofreen

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Re: CB750F weak points
« Reply #22 on: August 17, 2012, 05:25:09 PM »
After 37 years and 139,000 miles on my '75F, I figure the weak points should be showing up any time now.  I am just waiting patiently.
Greg
'75 CB750F

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Offline Crshndbrn

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Re: CB750F weak points
« Reply #23 on: August 17, 2012, 05:35:48 PM »
Haha!   Now that's the kind of replies I like to hear.  I'm picking away at it slowly, but I'm very picky about how things are done and I don't follow what most would consider any sort of normal order of importance.  I just do my thing and thought if there was a weak point such as a flat metal main fuse somewhere, I'd make corrections along the way.

Offline ofreen

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Re: CB750F weak points
« Reply #24 on: August 17, 2012, 06:39:38 PM »
Most of the weak points you uncover on an individual bike will be mostly attributable to time and a lack of maintenance/neglect.  Otherwise the F0/F1 are capable of very long, reliable service.  The '76 F is pretty much identical to my '75.  The main difference is that the '75s were hand assembled by Soichiro himself.  When the '76 came along, he delegated the task to others.  But they are still great bikes. 
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon