1976 Honda CB 750 Motorcycle--I am in the process of purchasing this motorcycle.?

Question

It needs a new headgasket. Is this a project a handy person can take on or do I need to leave it to the professionals....

Answer 1

Hi Ba,,,

That 750 MIGHT actually have a leak.

But,,Very rare few ever leak badly.

Almost ALL those things' head gasket leaked from about 2 yrs old.

It wasn't a "pouring out" leak,,
not even a "seepage" level of leak.

It was like,,Sweat.
It accumulates in that area over time,,is difficult to thoroughly clean.
And looks TERRIBLE after a while.
It stays wet-looking,,,and has the appearance of a significant leak.

Honda Leaks are sorta peculiar in most instances.

MOST engines leak because they lose the gasket-sealing integrity between Gasket & Engine Surface.

Honda,,,they originally assembled the engines with a
"Adhesive Impregnated Gasket"

The Gaskets went onto New,"Purely Clean" and Fresh Machined Surfaces,,,,,and were INSTALLED DRY.

Parts got Torqued Down,,,,engine started and run up to Operating temps,,,then SHIPPED.

No Retorquing of the parts necessary.

Way it worked was,,,,The Adhesive was HEAT ACTIVATED.
It COOKED,,to heat-set and literally BAKE the gasket to the surface.
It also Hardened WITHIN the saturated Gasket's thickness.
The hardened gasket core is what eliminated the Re-Torque requirements after assembly.

It was very much the same principle as Resin Impregnated Cloth,,,Phenolic,Micarta,,
"Fiberglass Cloth/Resin",
or modern day Carbon Fiber Composites,,etc

Scraping Honda Gaskets from surfaces during Rebuilds/Repairs is a LEGENDARY HASSLE.
It sticks Incredibly tight to metal surfaces.

Anyway---the SWEAT Phenomenon was caused by oil sorta wicking thru CENTER of the gasket's thickness.

What causes that is the Paper Fiber gasket Glues itself extremely Tight to metal surfaces.
As engine heats up/cools off during operation /shut -down Thermal Expansion cycles,,,,,

That Gasket acts like an Accordian,,in a sense.
Both outer surfaces Pull against Each Other,,,till it finally causes ruptures thru CENTER of gasket.

Silly example,,,and exagerated.....
but imagine a Cotton Pad glued between your fingers.
It's originally tight and dense,,,and ya can squeeze as hard as posible and NOT compress it it any further.

But if you spread your fingers apart,,,the CORE of that cotton pad has no resistance to Tension,,like it does to compression.
So ya begin to "split" it,,down it's middle.
It becomes increasingly porous,spongy,"fluffy".

On a gasket,,,,it's a Microscopic Effect,
But,,it's enough porosity to allow gradual migration of oil actually THROUGH the gasket,,,versus the more Typical & Common Leak path of Across OUTSIDE of gasket.

Normal Type Leaks usually get Worse,somewhat rapidly.

"Honda Leak" is a LOT more stable.
They develop a degree of permeability and get worse VERY slowly,,,,some dont ever worsen at all.

But over the life of the engine it continually LOOKS worse,,cuz it accumulates and bakes-on,,,and is Very Difficult to Totally Clean.

........................................
Point is,,,,,,,
If it is actually LEAKING,,,or even Seeping,,
Then Of Course that demands attention.

But if it's just typical ol' "Black Crack" between the Fins at the Cyl Block and Cyl Head joint,,,,,
It probly ain't worth messing with.
And Tecnically,,it ain't worth fooling with---nothing is lost by that gasket 'sweating".

It's a LOT of work to replace it yourself,,and Expensive to have the work done.

Even bikes the age of a '76 are USUALLY "manageble" in terms of keeping it Clean so it looks OK.
The oil stains dont build-up very fast.

I CANNOT tell you to use EZ Off Oven Cleaner,,,
because it EATS the HECK Outa Aluminum,,Real Fast.

But IF You happen to decide to resort to that in order to get it cleaned back to Bare,Clean Aluminum......

Do it while engine is warmed up a LITTLE above air temp.
NOT HOT,,,cuz it accelerates the chemical action way too fast.

The Coating is aways Splotchy----if the chems go Too fast it'll begin eating Aluminum while it's eating the oil/carbon stains.

Warm Only,,,
Control the application,,limiting it Strictly to the nasty area,,,,and Dont let it get on any polished parts,,like engine side covers.

It can stay On about 3~5 minutes,,,then get rinsed Thoroughly with water.
Some people have to let the Rinse water Dry,,then repeat the application,,2~3 times till it's clean.
And Immediately spray >>HOSE it with WD 40 when done.

Once it's Clean,,,Then you can see how bad/fast it's actually leaking.

Might surprise you,,,and NOT be bad enough to worry about.

Routine Cleaning thereafter with actual Suitable cleaning agents will prevent having to use harsh,dangerous stuff.

...................................
You MIGHT really,actually NEED a gasket.
Some do.
If so,,,Oh well,ya Gotta do it.

But it's a sort of "normal characteristic"(Nasty Habit) of those engines to sweat oil at the head gasket junction.

It's not RIGHT,,,but that's what they tend to do,,,and usually nothing really serious.

After you get the bike,,see what's it's really doing before just arbitrarily replacing the gasket..
Might save you some time and money.

Or,,You can ride it this summer/fall,,,
and deal with the leak in Off-Season when riding weather gets bad.

Good luck with it

Answer 2

It depends on how "handy" you are. Have you worked on motorcycle engines before? If not you may be well advised to have someone that has help you out. There is no question that you can do it yourself here, but not everyone can pull it off as easily. You may need a few special tools, too. I would suggest getting a detailed manual for this bike before attempting to do it, though. Then you can read up on the procedures, and make a more intelligent choice. I used to have one of those back in 1980. I loved that bike, it would do, and go almost anywhere, and I did. I never had to work on the engine that deeply, though. It will involve undoing the OHV assembly, and there is the tricky part.

Good luck.

Stevo.

Answer 3

this is certainly a manageable project for someone with a complete set of hand tools. I am going to assume that you have never broken down a motor before, or else you would not have asked the question.

If this bike will be your daily driver, you may want someone else to do the work. If you are a typical garage wrencher who has mostly weekends to carry out the work then it could take a couple of weeks to get everthing squared away. Between reading the manual, buying/making "special tools", and the occasional trip to the hardware store you will be spending some time.

The first time I ever broken down a Harley top end it took me almost two weeks to get it running again. Now I could change a head gasket in a little under 2 hours.

And please don't forget, there is a lot of stuff to pull off before you can even get to the motor work.

Please read a shop manual thoroughly before you begin.

Answer 4

The engine has to be removed from the frame.
That's a project in itself.
Before even opening your tool box, purchase a shop manual and read - read - read. To see if you want to get involved.
Even if you don't do the work yourself, a shop manual will be very useful when doing minor repairs and tune ups.
Purchase a shop manual before they go out of print!
http://www.motocom.com/motorcycles/

Answer 5

most anyone that has broken down and rebuilt a motor can do this for you, there are many motorcycle owners that don't trust anyone but thereselves to do repairs. But if you take it to a reputable shop, you do get a warranty on the work.
The 76 Honda is a real classic, I don't blame you for buying it.

Answer 6

you can do it yourself if you take your time and follow the manual exactly, but take the head to a bike shop to get the valves ground and ask them to check the cam bearings. I had one of those and the ones with the performance cam ( cant remember the model #) had a lot of trouble. also use 4 cycle motorcycle oil not auto oil. all the oil companys recommend that any flat tappet engine use either diesel rated -4 cycle motorcycle or synthetic oil since they had to remove theZDDP from their auto oil they released this information due to engine failures in older cars but it also applys to motorcycles

Answer 7

Back in the day those old 750 4's were quite the bike. Now if you buy 1 you better buy every one you can find for parts, there obsolete...

Answer 8

unless you have a perfectly restored 750(a real show winner). you're going to spend more than the bike is worth,having a pro do it.
if you haven't work on a cycle before, i wouldn't recommend it. just getting the timing chain back in the proper position could be a pain.and if not done right you could do more damage to the internals

Answer 9

Just buy it they are great bikes and anyone with any mechanical aptitude can do the Head Gasket and rebuild the carbs while you are at it.