88' BF15a low oil pressure problem

[1fishaholic]

I recently acquired a 15hp Honda that I don't know the history of, other than its been stored for about 3 years. After replacing the plugs, CDI unit, fuel filter,oils, and cleaning the carb I found I have a low oil pressure issue. The motor starts on the 1st pull and idles great. On the maiden voyage, after running for about 15 minutes at 3/4 throttle the oil light goes out and the engine makes some ugly sounds. I shut it down and let it rest for a few, then start up and head back for home...sounds and runs normal. It makes it almost all the way back the dock before the light goes out and the awful sound comes back. When I got home I change the oil and it was black after only about 30 minutes of run time. After changing the oil I idled the motor another 20 minutes and it was black again. From searching on this board, I think I have a clogged oil filter. Anyone have any ideas? If I have to clean the oil screen, am I looking at pulling the whole powerhead or can I get to it from below the motor? Is this something the average guy can do and what parts do I need to order (gaskets, O rings, etc?)? Thanks for any info in advance!

 

[hondon]

Re: 88' BF15a low oil pressure problem

It's interesting that that oil becomes that contaminated in that short amount of time.What oil are you currenty using and are you aware of what the previous owner threw in there?Usually a low oil pressure situation after warm up indcates failed main bearings.Ugly noises often leave ugly results.Check the end play on your crank.You should have little or no noticeable.These are tough little engines but after a 3 year layup, who knows what kind of sludge built up in that oil pan.Before pulling the powerhead,drain the oil into a clean container and look carefully for any metal flake.

 

[1fishaholic]

Re: 88' BF15a low oil pressure problem

I'm currently using Pennzoil Maine 10W-30 and have no idea what the previous owner used. Last time I drained the oil, I drained it into a clear glass bottle. I could'nt detect any metal shaving right away, but the next day I notice some very fine(dust) metal shavings had settled at the bottem of the bottle.

I removed the pull start and gave the flywheel a yank straight up and there is a little bit of play, maybe 1/32-1/16". I know end play is measured in 100ths or 1000ths, so there might be a problem there. I bought an oil pressure tester guage today and plan on checking the pressure at 1100 RPM's...should read 8.5psi per the manuel. Would a bad main bearing affect my oil pressure reading at all? Any other suggestions? Thanks!

 

[1fishaholic]

Re: 88' BF15a low oil pressure problem

I took a couple of measurements tonight. First, the amount of play in the crankshaft is approx .006"...I could not find what the tolerances are for the crankshaft in my Clymers manuel. Second, the oil pressure looks good, anywhere from 25psi at high idle to 9-10 psi at low(~1000RPM)idle after it got good and warm. I plan on checking the oil pressure while out on the water at all throttle positions to see if it looses pressure at higher RPMs.

I also changed the oil again and it was pretty contaminated after 30 min of run time. There are small chunks of carbon or hardened oil in the bottem of the drain pan that are eaisly broken up if rubbed between my fingers. There are also still some visable metal shavings. Any other suggestions? Thanks again!

 

[pvanv]

Re: 88' BF15a low oil pressure problem

I'm not a Honda specialist, but I can offer these thoughts:

The crankshaft endplay seems a bit big, though not necessarily horrible. It's typical to expect 1 or 2 thousandths on a fresh rebuild. Yes, bearing wear will definitely affect oil pressure, especially as the oil gets warm and thins. the oil can then flow out of the bearings easier, lowering pressure.

It's possible that the motor was abused in its previous life. May have been run really low on oil, and/or severely overheated. Previous owner may even have used the wrong oil, which burned up at crankcase temperatures -- I have even seen salad oil used. Really. Sounds like you have a ton of junk in the sump (burned oil sludge, etc.) that plugs the pickup strainer once it gets warm enough to soften and get drawn to the strainer. This would also turn the oil black as it mixes in with the fresh oil. See if you can determine if the paint on the outside of the block is discolored. That will be a sure indicator of severe overheat. I have seen a few small ob's that got so hot that the paint discolored, yet worked fine after cooling down. Of course the plastic and rubber bits needed to be changed after getting that hot.

If you do indeed have a ton of junk in the sump, you will want to get the stuff out. Lazy way is to keep changing the oil every time it turns dirty -- possibly every half hour of running. Could easily be 10 or more changes. Eventually the gunk should be pretty much flushed out with the drain oil, and the oil should stay clean for a normal oil change interval. Faster and more thorough way is to get the powerhead off and take it apart and scoop the junk out. If you do take the powerhead apart, you will be able to inspect the bearings, which may be "opening Pandora's box", but it's probably better to find out than guess.

In any event, when the "ugly" sounds start happening, you are probably experiencing low oil pressure, and beating the bearings up pretty badly, possibly the beginnings of a "rod knock", which may be the source of the metal fragments in the oil. Definitely not good, and I would shut it down immediately if that starts happening. Are the bearings still serviceable at this point? Only way to be sure is to inspect them.