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,,
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.
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.
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.
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
· 1 decade ago