Oil at spark plugs
Oil at spark plugsI was taking the spark plugs to look at the color. There was some oil around sealing washer on both sides so the oil is from the exterior. That is my question, where can this oil be coming from?
I've posted this reply in a couple of other threads over the last several years, but I'll post it here too.
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. This info is 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"
Vince, great info! My engine has ALWAYS done that, I recall seeing oil around the plugs from "way back when", in the '70's when I was riding it regularly. It still does it to a mild degree, and I assumed it was seeping down from the cam bearing cover and ignition housing. It's great to finally have a mystery solved!
1965 CB77 305 Super Hawk
1989 NT650 Hawk GT 1981 Yamaha XJ550 Seca Being a cynical Brit, I detect a little evasion of responsibilities in Honda's message. To admit a real design flaw would have been very expensive. Interestingly, early Dream motors, don't have the iron skull and don't have the leak....
My friend owned a Volkswagen Golf which leaked gas from the carburetor and made his wife ill. After fitting three replacement carburetors they finally gave up and said "they all do that sir" claiming they had done 'everything'. He sued them and got his money back for the car. They met their match ...... G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F Sara
No I think the skull was a short(ish) lived experiment. Early Honda CB400Fs used to leak around the head joint but that was just due to poor sealing. They put longer studs in later models but I cannot quite see how that would fix the problem.....:-) Luckily, I have a later one but it still weeps a little. G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
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