On my 1995 ST1100 I have oil leaking out of a machined hole on the back of the right head assy. The hole is about 1/2 inch diameter and back inside about 1 inch is another hole of apps.1/4 inch. The left head has the same hole. Is this some kind of vent for the engine? If so why is oil coming out of it? The bike has 48000 miles and this anomaly just started. The left head is clean and doesn't leak. I have a Honda factory manual and there is absolutly nothing in there about this "hole" and what the purpose of it is! Any help would ne appreciated.
engine oil leak
- Thread starter dragontailjunkie
- Start date
John OoSTerhuis
Life Is Good!
I think you’re referring to the drain passages for the spark plugs. You may have a valve cover gasket leak that’s found its way into the spark plug recesses.
Please confirm.
John
Please confirm.
John
Pull the little square panels in the sides of both side fairing pieces...the ones that cover the heads. Check for oil leaks around the valve cover. The formed gasket/seal is easy to miss-install. Also possible is the valve cover mount screws may need replacement. There is a soft seal on the bolts (4 per cover) that ensures the cover is both firmly secure and can't be cracked. Squashed or deteriroated washer or worn bolt threads can result in a leaky valve cover gasket.
pull the spark plug leads and look inside the holes where the plugs sit, you'll likely find oil in one or both of them on the side where you see the oil leak.
The valve cover gasket has a couple of circular sections that seal off the plug holes, that seal is leaking somehow.
The valve cover gasket has a couple of circular sections that seal off the plug holes, that seal is leaking somehow.
Drain passages for what from the spark plugs? This problem has me baffled.Is engine oil supposed to drain to the outside?? I thought about plugging this hole but was concerned about messing with venting issues. At the back of the 1/2 hole is another hole about 1/4 diameter???
The plugs are recessed in a deep hole. The place where you see the oil leaking from is an open passageway from the spark plug hole, to allow fluids like rainwater or motor oil to drain away rather than create a pool in the spark plug recess.
the gasket that Al posted helps illustrate the point. If the circular part of the gasket in the middle isn't seated properly, oil will flow past the gasket and into the center hole, where the spark plug is located. Oil is circulating freely throughout the area inside the big diameter of the gasket, and the gasket is trying to prevent it from entering the two smaller circular holes in the middle, which encircle the spark plugs.
Hey I appreciate the help and will pick up a gasket. Thanks to you and Al
I appreciate the help and will get a gasket.The valve cover is most likely leaking. Oil gets around the spark plug enough to leak out the hole. The hole is there to let water out or oil out.
One more detail about the valve cover gasket, the way the 4 bolts clamp down on the valve cover is a bit odd compared to other bikes. When you remove the bolts you'll notice they have a metal shoulder just above the threaded portion. That shoulder bottoms out on the cylinder head and you can't tighten the bolts beyond that point. In a cutout in the valve cover where the bolt holes are located, there's a rubberized 'grommet' that sits in that hole. Since the bolt bottoms out on the shoulder, the force applied to the valve cover is transmitted through that rubber grommet, and they compress over time. Its a good idea to replace the grommets along with the valve cover gasket, because if they compress too far the gasket won't seal properly, even if its a brand new gasket.
You don't have to replace them every time you change the gasket, but they do compress over time so if you're a new owner to the bike replacing them now is probably a good idea so you know where they stand.
You don't have to replace them every time you change the gasket, but they do compress over time so if you're a new owner to the bike replacing them now is probably a good idea so you know where they stand.
You will also need some silicone sealant for around the half moons of the gasket.
Another point about replacing those bolts that hold the valve cover to the cylinder head. Since the cylinder heads are canted outward, there is a tendency to have difficulty getting the bolt in the hole and folks have crossthreaded one or more. If the bolt does not start in with finger pressure, don't force it. Over tightening will strip the soft threads in the head.
Thank you. I appreciate the update
Seen a little oil weeping from the back of my valve covers a couple weeks ago when i was changing my spark plugs. I'm not losing oil so no big deal yet. But with 77K miles and 21 years of age I bet the original gasket is old and brittle. My sparkplug holes / tubes were dry though. I may have to plan on doing this job someday. My 2011 Mazda was much worse. It had 107K miles and when I pulled the sparkplugs to change them 3 out of 4 were coated with oil.
Would be a good time to do a valve check as well, and don't forget to install new rubber grommets.
Good advice last time they were checked I had 14K miles on it and they never charged me for new valve cover gaskets so I know they reused the old ones.
That Honda oil you use is probably corroding the seals and gaskets.
Yeah that's probably it
