Honda 9.9A - Oil Sucked in Through Breather Tube

For the past few years the engine, which currently has 351 hour on it has been pulling oil through the breather tube into the carburetor under load at speeds above 1,300 RPMs; large amounts of white smoke exhausting. Other than that it starts fine and seems to run AOK; no misses and the spark plugs are clean. This past weekend I did a compression test with the results below:

Top: 162 dry 200 wet
Bottom: 135 dry 145 wet

Seems to be a big difference with bottom being weaker.

My best guess is that there is some damage associated with the bottom cylinder, maybe a broken ring that is building up presser in the engine crankcase that forces the oil through the breather tube at high RPMs. This may have been caused by my running the engine for several minutes with the water valve closed several years ago.

Can you tell me if the compression test is consistent with my assumption? If no is there some other troubleshooting that you can recommend?

Thanks in advance
Rick

Just my opinion, for what it's worth.

The top cylinder increase during the wet test jumps out at me and indicates that the rings on that cylinder are leaking pretty badly. Your readings are practically "textbook" for ring leakage on that cylinder and would account for some of the excessive "blow-by" that is over pressurizing the crankcase.

Obviously, the bottom has an even more severe problem as well but the smaller pressure increase during the "wet" test MIGHT not be indicating the leakage is all at the rings.

Keep in mind that these cylinders are horizontal and to do a reliable wet test, you must first make sure the oil added to the cylinder is allowed to spread and cover the piston crown. If you tilt the outboard all the way up so that the cylinders are more vertical then use a squirting type oil can to add the oil, then you have a much better chance of accomplishing this.

But, maybe more important than the wet vs. dry test is that you have such a large difference between the two cylinders. It is about a 12% discrepancy between the two and some, not all, engine builders say 10% is too much.

The next logical step in your effort to diagnose "what's wrong" with cylinder #2 would be to do a cylinder "leakdown" test. If you have not yet checked the valve adjustment for being too tight, then now would be a good time to do that before continuing with any pressure testing.

jgmo
Wow your reply is very insightful! Looks like I need to do the wet compression test again to ensure that the oil did spread as you suggested. Please be aware that this is a modified Honda 9.9 saildrive 280 where the boat is in the water and I am unable to move the engine.
Many Thanks!
Rick

Before you get into a major repair, I would recommend a decarbonation with SeaFoam or Yamaha Ring Free.

Most likely the engine does not have a low pitch prop on it and it has not been running at high rpms....probably just putt putt putt to get you in and out of the slip. It also has probably not really gotten up to temperature if it only runs for a short time. Not good for the engine.

Mike

Sometimes a small tank with a concentrated dose of Sea Foam then run the "crap" out of it will help. It will smoke like crazy. The instructions are pretty good on the can. Make sure, as always, that the oil level is 1/4 inch below the full mark.

Once you do that, take compression again. You will most likely have to change you oil and spark plugs after all this.

You might just get lucky.

I want to re-inforce Mike's suggestion with the SeaFoam. Two lady friends who were running a 6 hp Suzuki on their sailboat were lamenting the fact they would need to remove the engine, take it to a dealer for major repairs because it was missing, "making oil", and generally running like crap when they could get it started. I told them about the Sea Foam treatment and explained how to do it. They took it through two treatment cycles. Called me back and couldn't thank me enough. Apparently the old susie is running better than ever after blowing out a ton of black junk.

Again, as Mike said, their problem was that they were using the motor to just put put around and never opened it up. They are now SeaFoam fans and promise to open up the engine whenever they feel safe doing so.

Mike & CHawk
Thanks for providing this information! My engine certainly fits the description of "old susie" since I only use it 40 minutes per sailing trip; 20 to go down the river and into the bay & 20 to get back.

Question: A friend had suggested using Chevron Techron to decarbonize. Is this equivalent to Seafoam?

Many Thanks
Rick

Here is an update:

Ran engine @ 2,400 RPM for 20 minutes while spraying 1/2 can of Sea Foam into the carburetor; put 2 oz. of Sea Foam in oil prior. Reran compression tests after while hot with the following results.

Top: 145 Dry 190 Wet
Bottom: 115 Dry 145 Wet

There is a 26% difference between the top bottom dry results. The difference between the dry/wet within each cylinder seems somewhat consistent.
Rick

Well, while it is entirely possible the rings are leaking because they are stuck in the piston "lands" (grooves) due to carbon, they ARE leaking significantly.

If she is badly carboned up, I certainly see no reason not to keep trying the Sea-Foam for a bit to see if conditions improve. I have also used a product called "Berryman's Chemtool" to spray in the carb to accomplish this in the past. It might be less expensive than Sea Foam.

If the decarbonizing doesn't yield any positive results, then the old girl is probably just worn down and will, someday soon, let you down going up that river.

That #2 cylinder is on the verge (if not there already) of not making enough compression to reliably vaporize the fuel. This in turn is putting more strain on the upper cylinder to keep her turning and burning.

Sorry, but that's what the tea leaves say to me.

The good news is, other than getting the engine out of the boat, these are relatively easy and inexpensive to overhaul if there isn't too much cylinder wear. And, the parts are still available.

jgmo
I am hoping to limp through the season and have made arrangements with the local Honda Marine dealer to service it. I really appreciate your feedback and suggestions. Have a great summer.
Best
Rick

Best of luck to you.