Air leak on right side of engine, near spark plug hole?

akpasta · Post by **akpasta** » Fri Mar 27, 2015 3:11 pm

G-Man wrote:The skull lines the entire combustion chamber in the head. The valve seats are in it and the spark plugs are threaded in the cast steel, hence the term skull.

G

So eventually the whole skull will deteriorate and fall into the combustion chamber? Does employing a copper washer at the plug do anything?? What a bummer design flaw. Basically renders all superhawks potential time bombs no?

G-Man · Post by **G-Man** » Fri Mar 27, 2015 3:42 pm

I think that some show the problem and most don't. The skull sits on top of the cylinder sleeve and is supported by it. Where the head has been opened out like the one in my picture there is less support and more chance of problems.

It might be an idea to try a thick machined steel washer under the plug and see if that would provide better support. It would have to bed down onto the aluminium to make it worthwhile.

G

akpasta · Post by **akpasta** » Fri Mar 27, 2015 3:47 pm

G-Man wrote:I think that some show the problem and most don't. The skull sits on top of the cylinder sleeve and is supported by it. Where the head has been opened out like the one in my picture there is less support and more chance of problems.

It might be an idea to try a thick machined steel washer under the plug and see if that would provide better support. It would have to bed down onto the aluminium to make it worthwhile.

G

Arg. Check out this Honda service bulletin I discovered searching around online:

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

G-Man · Post by **G-Man** » Fri Mar 27, 2015 4:25 pm

Interesting that Honda were trying to dodge their responsibilities....

Skimming the top of the barrels might help.

G

akpasta · Post by **akpasta** » Sat Mar 28, 2015 3:06 pm

So is the engine shot? Is there anything I can do other than dropping the engine and replacing the cylinder/head? I've never done that on a 4-stroke I'm not very confident in my abilities or my garage space to be honest. Davo suggested punching and staking the area around the plug hole to seal it off. Anyone tried that? Anything that possibly salvages the engine without removing it would be ideal. If it's only a "matter of time" sadly it might be better if I fix it on the short term and sell it "as-is." What a bummer.

akpasta · Post by **akpasta** » Sat Mar 28, 2015 3:23 pm

... I think I'm screwed. My problem seems to be number three on the severity list:

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.

mike in idaho · Post by **mike in idaho** » Sat Mar 28, 2015 3:57 pm

One option is to get some 1/4 inch thick aluminum washers made with an outside diameter big enough to cover the leaky joint and install then with some long reach(D8E) spark plugs.