Like the title says, wondering if big bore kits like the 124/128 from fuel moto, s+s and others solve sumping/transfering. I would hate to drop the money and still have to worry about it sumping. On the other hand I have no problem dropping the coin if the kit solves it and is actually reliable. Thanks for the help to those in the know!

 

STRYCH9 sure seems to have one of the more impressive bb builds I've seen reported here, reliable, no issues IIRC and doesn't consume oil..if I was doing one I'd want to ping him for advice and try and copy what he did

 

All I can say is that my 120 FM setup has never sumped, it apparently stopped the minor fluid transfer between the primary and transmission, and consumes no oil at all between 5K services. I'm running conventional Kendall GT-1 Competition 20W-50 with boosted zinc. I will also add that I still have all of the OEM oil pump components in the engine. No seal, no upgraded pump. No problems.

In fairness, I did my build @ 9K miles, and hadn't sumped to that point with my Stage I either. I did have some slight primary transfer, which stopped after my build.

 

I have an FM 124 build with no sumping and completely reliable. It does have the S&S oil pump though and only have 4,000mi since the kit install. I'm running Mobil 1 20w50 motorcycle oil and keep the level about a quart low per FM recommendations.

 

I keep mine right on the 'full' mark.

 

Big Bore kits do nothing for sumping IMHO. We have a test bike that has been through many engine changes during testing and to date it has never sumped. This was one of the first M8's out back in 2016. Bike was purchased as a 2017 107 Oil Cooled. Picked it up the day after the M8's were released (Aug 2016) by the factory. Got many various cams and exhaust run and by the time it had 2500 miles on it it was upgrade to a SE 114 big bore kit and then back to cam and exhaust testing again. Then the engine was pulled and a 114 factory crankshaft added that had been to Darkhorse to be checked and balanced prior to being install. New engine displacement up to 120 cu in and back to cam testing and exhaust testing. All the time it has the original first release(2016) oil pump and cam plate and does not sump.

So why, we have no idea but it's one of the lucky ones. So if you have a sumper, adding a big bore to it typically doesn't solve it and for the most part it appears as the engines get larger the more of them that sump. Plenty of people have added S&S or Feuling pumps and plates hoping that would solve sumping but it hasn't and god knows where the factory is at with oil pump changes today and people still get sumping engines.

 

Go figure -- maybe running the engine oil low only helps with bikes prone to sump, or maybe it's just coincidental, or not related at all. Certainly FM and S&S see some credibility in it, but there's no good explanation of why it might help with sumping.

 

and then you have Fueling Parts recommendations...so many theories, testing, etc. but this far into it not one identifiable root cause or silver bullet solution

These breathing dipsticks remove unwanted build-up of blow by. Blow by is found in engines with excessive leakdown through the rings/cylinders which is a common issue with large displacement big bore engines. Feuling test results show a decrease in engine oil sump levels, more freely/smoother revving engine, increased MPG and decreased blow-by.

TECH TIP: Feuling highly recommends staying off the rev limiter and running conventional oil in the M8 engines to help maintain ring seal and minimize blow by.

OIL LEVEL - DO NOT OVERFILL OIL TANK
It is important to get the correct hot oil level in your bike. Feuling recommends running the oil level 90%-99% full when hot.

Note: The oil pick up port is on the right side of the engine. Letting the bike idle or warm up on the kickstand will naturally fill the engine case and skew the oil level in the tank.

 

Agreed.
What's funny about that is MoCo tells you in the owner's manual to idle it on the stand before checking. I never do; I idle it upright when I pull it into the garage after a ride. I check the oil then, always.

 

same here, after $tonecold made that recommendation a long time ago..it's proven to be most accurate