Cb77 oil leak

[sarals]

Hey thanks for the insight, I'm going to give that a try tonite. My leak sounds similar to yours in that it happens when the bike gets good and hot.





Cheers

Rick

Rick, you're welcome! Let us know what happens.

[leonvjames]

There is also a possibility of oil getting between the steel crowns and the aluminium head casting and then coming out round the spark plugs. My CB77 has been doing it for years. Old age probably.
Leon.

[Vince Lupo]

There is also a possibility of oil getting between the steel crowns and the aluminium head casting and then coming out round the spark plugs. My CB77 has been doing it for years. Old age probably.
Leon.

Honda had sent out a service bulletin regarding this phenomenon back in the 1960's, and it has to do with the cast iron 'skull' separating from the aluminum castings of the cylinder head, thereby causing a seepage at the joint around the spark plug holes. They said that other than it being a mess, it wasn't anything to really worry about. Mine does it too.

I posted this several years ago in another thread, but here it is again (info via Bill Silver):

"SL #65 6/1/66 HONDA MOTORCYCLE SERVICE BULLETINS
OIL SEEPAGE NEAR SPARK PLUGS IN ENGINES WITH ALUMINUM CYLINDER HEADS

American Honda receives occasional complaints of the tendency for certain models with
aluminum cylinder heads to seep a small quantity of oil near the spark plugs. In some cases,
dealers have replaced cylinder heads in an effort to eliminate this seepage. This bulletin is
intended to clarify our policy in relation to this problem, and to suggest some countermeasures
that we have found to be effective. In cases where it can be confirmed that the spark plug sealing
washers are not leaking, accumulation of a stain, or oil residue, near the spark plugs can be traced
to oil seepage from the joint between the combustion chamber "skull" and the aluminum cylinder
head casting. Since the spark plugs are threaded into the iron skull, rather than into the soft
aluminum casting, this joint must "come to the surface" near the spark plugs. Although it is no
mystery how oil reaches the outside of the engine, it is difficult to determine the source of the oil.
Apparently, oil reaches the joint from the oil-bearing chambers through internal porosity in the
aluminum casting; such porosity is extremely difficult to avoid. Once oil enters the joint, it has an
almost unimpeded leak path to the outside because the skull is not bonded to the head casting.
Our studies have shown that machines experiencing this problem can be graded into three broad
categories, based on the severity; each category should be dealt with in a different manner:

1. A stain or oily residue collects near the spark plugs over a period of several days or weeks.
Seepage of this magnitude should be considered a normal, inescapable consequence of the
cylinder head design, and no repair should be attempted. Customers complaining of such seepage
should be assured that no defect exists; suggest more frequent cleaning of the engine.

2. More severe seepage causes definite accumulation of liquid near the plugs; following a hard
run, oil droplets or streaks can be found on the air cleaner covers, etc. Although a "defect" is not
necessarily indicated by this seepage, countermeasures are often necessary to satisfy customers.
We have found that seepage can be slowed or stopped in the following manner: a) Remove spark
plugs and completely clean the region around the plug holes so that the joint between the skull
and the casting can be seen. b) Using a dull punch, punch a ring of depressions, tangent to each
other, in the aluminum immediately outside of the joint.

3. Liquid oil "bubbles" from the skull/head casting joint, puffs of vapor can be seen when the
engine is suddenly accelerated. In these cases, a definite defect is indicated, i.e., actual
separation of the skull and head casting. In most cases, however, the cylinder, rather than the
cylinder head , is the faulty part. We have found this problem to be most commonly related to
"sinkage" of the cylinder sleeve in the cylinder casting, such that the upper surface of the cylinder
sleeve is below the upper surface of the cylinder casting. When this "sinkage" occurs, the
Honda 250-305 Super Hawk Restoration & Maintenance Guide
combustion chamber skull is not forced into intimate contact with the cylinder head casting and
severe oil or vapor leakage, near the sparkplugs can occur. The recommended repair is, of
course, to locate and replace the faulty part.

Source: SL #68 4/29/66 HONDA MOTORCYCLE SERVICE BULLETINS"

[fab60]

Great find Vince! Now I hope mine is either case 1 or 2!! HAHA I've check my compression and its 175/180

[Bob750]

I may be having this issue with our Dream. Ours might be in the #3 severity class though. See my 19 second video. Kinda bumming me out.

[48lesco]

Bob - I'd try the punch procedure on that before I abandoned hope. I think you're more than qualified! Dream heads are fairly plentiful, but of course there's no guarantee you won't buy the same problem. Were the liners flush with the cylinder deck and did you use an OEM head gasket?
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[Bob750]

The liners were perfect. The gasket was provided in the set sold by Classic Honda Restoration, and was not OEM. Oil began seeping there early on but snugging the head nuts a couple lb-ft really helped that. If the sleeves haven't sunk since the rebuild, could the non-OEM gasket alone allow this sort of problem to arise after 400 or 500 miles?

Bob - I'd try the punch procedure on that before I abandoned hope. I think you're more than qualified! Dream heads are fairly plentiful, but of course there's no guarantee you won't buy the same problem. Were the liners flush with the cylinder deck and did you use an OEM head gasket?
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