Yes I agree.... BUT the scavenger pump feeds the pressure circ pump. So if it's not being fed right it's pressure will be affected. The scavenger pump has to have a low NPSH curve. At what point does that part of the oil pump package get hurt thus effecting the pressure pump. Is it pulling a negative atmosphere and causing in whole or inpart the scavenging issue? Is it a seal, piston oilers, A balance issue between the two pumps? A over all engine ventilation issue? Tracking oil pressures can give a a look in the window. The data point I would like to know is the gpm. Serial pumping has some unique issues.

Off to Fayettville Ar. And some fantastic two lane riding. Have a great day folks.....

 

Enjoy the ride.

IMO, the reason we don't see low oil pressure is because the scavenge side can keep just enough oil flowing to the pan to keep the hi-pressure side fed BUT still leave too much oil in the bottom of the crankcase. Which would explain why so few low oil idiot lights are reported as going on for sumping engines. The sump side is not "sumping" oil from the crankcase at a high enough rate to stay ahead of the high pressure side. At first it was thought that loose oil jet screws were letting oil flow into the crankcase at a rate that overwhelmed the scavenge side of the pump. But too many sumping engines are being reporting as having oil jets properly torqued. I always thought it was wishful thinking on the engineers part looking to have the cause be manufacturing instead of a design/engineering flaw.

I'm now convinced (nothing but circumstantial evidence) that this is an oil flow design issue that is not properly in balance. Design of oil channels or oil pump or both that is resulting in improper balance between the low and hi pressure sides of the oil system leaving the majority of the oil in the crankcase (where its causing damage) instead of leaving the majority of the oil in the pan where it belongs.

I believe they know the answer already but need to figure out the least costly remedy for engines on the market or manufacturing line today (right now its just replacing burned up engines or replacing oil pumps for sumping engines that haven't yet destroyed themselves) AND the least costly re-design change for M8 engines going forward.

Hard to understand how this couldn't have been easily tested in the lab before launch. Put a stock M8 bike on a dyno. Run a full tank of gas to empty at full throttle just below redline. Measure the oil in the pan and crankcase after shutdown. Do the exact same test with each of the stage kit upgrades. Do the same test for both the 107 and 114/117 M8 engines. Its really not that complicated or that costly to determine if the M8 oil flow design works in the real world!!

 

If you are in fact correct about this, why isn't it happening to every M8?

 

Could be one of 2 possibilities.

1) variation in manufacturing of oil flow channels or machining between parts. Some are good and some are bad??

2) variation in riding style. Guys that never run above 3500 rpms might never experience sumping ....that is until they do run above 3500 rpms for extended periods of time. This is the "pregnant" possibility. Just a matter of time and circumstances. Of course time is only relevant to HD for 2 yrs but time is relevant to the bike owner until they sell the bike.

 

Whats the "pressure circ pump" AFAIK the scavenge/return pump only feeds the oil tank.

 

I would add in a hidden design issue that causes the problem to occur when the above 2 conditions are right. I wouldn't say that it has to be above 3500 rpms.. If may simply be some riding style that wasn't duplicated during testing.

 

Definitely possible, but I personally believe if you give me an M8 bike that has the POTENTIAL for sumping and I'll make it happen. Its a pretty simple exercise from my point of view. Lots of throttle changes at higher rpms such as riding hard in the twisties OR a long distance run 50+ miles at higher speeds or at least higher rpms (3500+).

The stage 3/4 bikes are typically built by guys that run harder in the twisties which I think made the sumping display itself sooner than with a stock M8 bike.

 

There simply should be NO sumping. Most proper race engines have dry sumps systems similar to HD.
Since they don't seem to have scavenging problems like HD you'd think the MOCO engineers would at least take a peek at all the dry sump systems out here to get a clue as to properly design an effective system.
They have been in this mess before but never to this extent. So much from learning from prior experiences.
I guess I'm not clear as to why HD didn't design the system to over-scavenge rather than under-scavenge. It's very easy to slow/restrict scavenging if necessary rather than trying to increase scavenging without redesign.
Bobs

 

I have been following the M8, the sumping issue, and the oil migration from trans to primary issue since the introduction of the M8. I've followed all the threads about the issues, on here and the other forum...

I have to admit I am shocked it hasn't been sorted out yet..... I was sure it would be fixed by the introduction of the '18 models..... stupid me...

I so wanted to update my '12 Limited to an '18 Limited with a stage 4, I just wanted a little more umph in my touring bike....

The money I was planning to spend on updating my '12 Limited is looking more and more like it may go to FuelMoto instead of the MoCo.... I really dig that Outlaw 126....

Yes, while the M8 issues truly suck....In the big picture, there are much worse problems I'm glad I don't have to deal with.....

 

Or don't suck enough??