787 oil pump appears to be losing prime

[Squirrel]

I reinstalled my rebuilt 787 into the boat on Feb 7th. The day before prior to install I replaced all the oil lines, primed the pump with the drill until I had oil drip into the manifold, new oil filter and everything went perfect. I put the feed line and the filter on the motor, so I could just hook it up to the supply line without losing any oil that fed the pump. So motor in and lines all purged and I had to stop for the day. A few days later I had an hour so I hooked up the cable to the oil pump and finished connecting ground cables, positive cable and the connectors into the voltage reg etc... So last night, I was going to put the carbs back on, and I noticed the one 3/32 line to the mag cylinder is empty, yet the other one is still full. I have a little oil residue on the bottom of the hull, but I had that before from when I installed the engine and spilled some. So I can't tell if that line leaked, or if it somehow lost prime. I plan to spin it over and hold open the pump to fill the line and then see if I can find a leak at the pump or the manifold. I searched the forums, but couldn't find any reports of this. Thoughts...?

 

[mikidymac]

You need to get it running as cranking the engine over with the starter will not spin it fast enough to get the oil into the lines.

There are small brass check valves on the oil inlet on the rotary cover that could be stuck causing the one oil line to drain oil into the intake manifold.

Either way you should be premixing the first tank of fuel on a new engine so I would just do that and keep an eye on that oil line and see if it self purges/primes during the first run.

 

[rgardner928]

You need to get it running as cranking the engine over with the starter will not spin it fast enough to get the oil into the lines.

There are small brass check valves on the oil inlet on the rotary cover that could be stuck causing the one oil line to drain oil into the intake manifold.

Either way you should be premixing the first tank of fuel on a new engine so I would just do that and keep an eye on that oil line and see if it self purges/primes during the first run.

Premix? That is SO WRONG! you do not need to premix your fuel if your oil pump works. People who premix are too dumb to figure out why...and fix it so that resort to premix.

 

[AKnarrowback]

The premix suggestion was made in regards to a new motor installation. Always premix your fuel for ar least the first tank on a fresh engine. I throw some oil in my gas on any two stroke work where any oil line, pump, cable work has been done on the chance of something failing or being overlooked. I do this to give me ride time to bounce things around and make sure all is solid while giving me the backup to keep my motor alive if my post inspections show a problem.

It has been established that the oil pump is working but a line after the pump is not full after sitting for a time. EXCELLENT observation and catch, premix in this case would prevent potential damage on start up.

As stated, looking into the brass check valves in the rotary valve cover would be a good place to look as well as inspecting for oil line leaks.

If it was my machine I would run the machine enough to fill the empty line then shut things down, hose off the oil pump, connections and lines at the intake with brake clean until any potential residue is removed and things are dry. When all is clean just lay some fesh paper towels under the pump area and walk away for a day or two, come back later and look for fresh drips. If the outside check is dry then pull the carbs, take the RV cover off the engine only enough to lay it flat with all oil lines in place, clean and dry then leave the cover over another clean towel for a day and check for fresh oil at the brass valves.