For as long as I can remember, my involvement with Harley-Davidson motorcycles has included dealing with the dreaded “wet sump.” (Well, OK, you might not dread it, but I have learned to.) This whole “sumping” thing is a rat’s nest of misconceptions and muddled understanding in the first place and H-D doesn’t make it any better. Technically, wet sumping is simply a malfunction in a “dry sump” oiling system. Dry sump, in turn, means the oil isn’t contained within the engine it lubricates. Rather it resides in separate container. We tend to refer to these containers as oil tanks (or “oil bags”), but Buell XBs carry the engine oil in the swingarm and late-model dressers have it in a “sump” of yet another meaning, in this case (literally) an alloy casting under the crankcases. For the record, the sump under the engine is something to be relished (or envied, if your hog doesn’t have it) because it eliminates yet another facet of this “sumping”‘ business. Namely, the chronic issue of oil, supposedly contained in a tank that is higher than the engine, seeping via gravity, through the oil pump, into the crankcases.

Sportsters can suffer from “sit sump” issues as well as any Big Twin, although not particularly noted for it. The feed line, which where any device used to prevent excess oil getting into the engine cases, is the dirty one on the bottom left side in this pic. Since the pump sits very low (almost under) the cases and newer X-engined cases have a sort of minisump built into the crankcases… it’s primarily the Ironheads that might benefit from an in-line anti-sump valve.

Put another way, true wet sumping is an indicator of lubrication faults or other problems because it happens while the engine is running. On the other hand, “sit sumping,” as I call it these days, is an indicator that Harley-Davidson has done some shabby design work when it comes to allowing oil that is supposed to remain where it’s put to migrate to places it has no business being! In fairness, gravity always wins, so oil in a tank will eternally want to head for the lower regions of a power plant. It’s as true of a Honda SOHC 750 Four, and/or any British Twin, as it is a Harley.

Speaking of British, full disclosure: I own two Brit bikes—a 1974 Triumph Trident and a 1973 Norton 850 Commando. I speak of this because of certain contrasts to my FXR, as related to sit sumping. Both Brits will do it worse and more quickly than the Harley. Without resorting to a tedious technical dissertation, not knowing what to do before startup of a long-sitting Trident can cause serious damage. That’s to do with the oil filter location sharing a cavity with the oil pump, so not having oil in the filter cavity makes the pump cavitate and—oops! The Commando is better, in that even if most of the oil migrates down to the cases, as long as there’s oil in the pump, about the worst that could happen is a blown seal and a brutal kick-starting regimen. Plus… both will run like crap after starting, until the oiling sorts itself out.

This photo and its informative points is courtesy of Truett & Osborn. Good information all around, though the points I’d really like to point out… are the bits about the feed line and the vent line… and their notation about venting to air or air cleaner. Venting to air on a sit-sumped sled… is code for a big oily puddle on the ground. Venting to air cleaner is just keeping the mess on the motorcycle, not under it… or necessarily in it. Aye… there’s the rub! Please note also—the fitting for the feed line is on top of the pump which bolts to the case about midway up the side. In other words, there’s nowhere to go but down… for excess oil.

Dry-sump Harleys can’t really be hurt by sit sumping, but there are design differences that make the issue a bigger PITA than any Brit bike. Let’s begin with crankcases… as in, Harley cases don’t have any room for extra oil compared to a Brit, but worse than that… no drain plug! I understand why H-D chose the no-plug way to go, but every time I go to ride my sit-sumped Norton I can remove the case drain plug and drain the excess oil. The Trident has a sump plate, which on mine is aftermarket, and features… yup, a drain plug. So here again you can dump the excess oil in the cases. Makes it easy to start. Can’t do that with a Harley… a pity for many a dude with a kick-only Sportster… let alone a Big Twin. Forcing flywheels to slog through oil-filled cases ain’t easy on an electric start bike either, come right down to it! But it gets worse. The Brits vent the system back into the oil tank… downright logical and a lot less messy than the Harley venting… which on a sumped bike usually results in a Frisbee-sized puddle on the ground or a soggy air cleaner resembling the Exxon Valdez.

Another T&O photo for which I’m thankful… shows the feed line attachment on an S&S oil pump… which is on the bottom of the pump. No big deal in itself, but a factor nonetheless when it comes to adding an anti-sump valve in terms of where and how to re-route the feed line from tank to pump.

I don’t ride either of the British machines often. Therefore, part of the pre-ride check includes this drain plug dance. The FXR gets ridden more often… but it too is semi-retired nowadays and can sit for weeks or even months between rides. Since there’s no way to get surplus lubricant out of the bottom end, the pre-ride is devoid of any simple task that reduces sit-sumping hassles. Instead, there’s just a silent prayer that the battery is up to the task and a dump pan placed under the vent line. Invariably, it winds up being stressful, irritating and messy. Since the Buell and the other five motorcycles sharing the garage are completely devoid of this bull… it begs the point. Why put up with it?

If it ain’t broke…

So, first I need to ask… “What would you do?” Most folks apparently choose to live with the hassle. After all, technically, it cannot cause any harm… just agro. Some have gone through the oil pump’s ball and spring check valve, trying to get it to do its job. This is pretty hit and miss in my view and only helps about half the time… even then only temporarily. It has to do with the basic nature of the ball and spring (and its “seat” in the pump body) about which, more… in a moment.

But… the part that is responsible for the issue in the first place remains the same in all these pumps. The damn ball (reference #11 in this drawing) and not really the spring as is sometimes suspected. There are tools and techniques to create a better seat for the ball in the pump body, but desired results are not even close to guaranteed. Messing with spring tension, on the other hand, is almost certain to cause more problems than it solves.

Some opt to drain the fluids out of motorcycles that are to being left unused during the off-season. Workable, but that sure adds a lot more to the re-commissioning ritual when riding season comes around and, here again, there are concerns about oil pump cavitation and whether or not oil is getting pumped to critical parts in a timely manner once the engine is finally started.

A few just add a damn drain plug! This ain’t exactly cheap, because realistically it involves aftermarket crankcases, since tapping and plugging factory cases is not a viable alternative. Besides, having a way to get oil out of crankcases doesn’t exactly prevent oil getting in there in the first place, does it?

Bold techie types willing to tread these treacherous waters might resort to something more along these lines. Electric solenoid valves for marine applications, as shown, make sense. They don’t pump oil, they merely allow flow of same and the default setting is off. You turn on the key (or an auxiliary switch, if preferred), you get oil feed. As long as one trusts electricity and wiring connections, it becomes a simple matter.

So, for all intents and purposes, the ideal solution is to do what Harley (and Buell) finally did. Turn the high-mounted oil tank into a low-mounted sump pan. Custom bike builders have been known to make chin spoilers that hold oil. Folks who don’t mind cutting a critical cross-brace out of an FXR frame (horrors!) can then swap trannys for the bagger version and its built-in sump. Lastly (and my personal favorite) would be to use something similar to the sheet metal sump pan that came stock on the South Carolina-built Indian Powerplus Chiefs… if you can find (or fabricate) one. Really not easy as it sounds… nor affordable, nor practical for most.

Lastly, there’s the controversial (but cheap) notion of simply stopping the drainage from oil tank to engine in the first place. Two ways to go about that, should it come to pass, would be to add a one-way, so-called “anti-sump” valve or an inline manual shut-off. These “solutions” are both very scary and not recommended for the faint of heart or the absent minded, for massively obvious reasons. If the anti-sump valve should fail or FUBAR without notice, or you forget to turn on the flow of a manual inline valve… even once and for even a moment or two… you have lunched your engine! Mostly, conventional wisdom says do not do this because it’s not a question of “if” you’ll forget to turn on the tap, but “when.” True or not, the prospect of having an add-on automatic gadget go inop or forgetting to operate it manually in the first place in order to avoid a nuisance (that isn’t a serious problem) gives pause. Quite simply, if you do nothing you can’t hurt anything, yet if you do this you might destroy everything! Hmmm?

Knowing this about the factory arrangement should breed suspicions about how well
adding another of the same basic design, like this tidy and compact version you see here, could work. The Brit bike types try them constantly and one session on the internet will reveal that the same hit-or-miss functionality afflicts them as it does the Harleys… for the same reason… a ball and spring.

Debate, both pro and con, over this Band-Aid “fix” fills many a page on British bike internet blogs. The cons… to a large degree are because of the manual valve’s human error quotient… as mentioned. Which leaves the anti-sump variety, which functions (for better or worse) on a ball and spring arrangement, patterned after a factory part, first offered by the British motorcycle maker Velocette… in the 1920s. At first blush, it also seems like the same idea as the ball and spring that is standard in Harley oil pumps, ostensibly for the same purpose. Well, as just discussed, we’ve seen how the effectiveness of a ball and spring varies wildly at sump control—it just ain’t that good! There’s an interesting video on YouTube called “Wet Sump Valve Comparison” that pretty much says (and shows) it all… where this spring-loaded ball notion is concerned. Worth a look… if no other reason than to see how slowly oil moves from one of these in-line sump valves towards the pump. (I can’t honestly say whether the ball and spring check valve in Harley factory pumps behaves the same. But I doubt it! The reason is, H-D pumps do not have the ball and spring in line with oil flow through a hose… rather they are tangential to a port in the pump. Let’s add the fact that Harleys have a fraction of the oil pressure that British bikes produce but more volume and a ball bearing inside the hose has to restrict flow, right? Not a good recipe for success with an anti-sump valve—sorry!

So much for the logical approach to an insane addition to my FXR. I emphasize, for me, the simplest solution is almost always the one to go with. A plain, simple manual valve like this one, which I will turn on first, before the fuel petcock and the ignition key… then turn off when the bike is left to sit for more time than it should. This seems easier and better than a continuance of the considerable PITA I’ve endured for over 25 years. I anticipate that the FXR and I will both be a good deal better off.

That leaves a lever-operated manual in-line valve. Should take care of my agro and issue, if it’s attended to properly… an additional “task” I look forward to.

Adding leverage

Over a half century of riding and over half of that on this FXR has been good training for never taking anything for granted. I mean, there’s always a pre-ride check… tires, oil, lights, gas, horn, etc. Even the starting drill, though routine (gas on, two twists of the throttle, key on, kill switch off… hit the starter button)… isn’t ever rote! Thinking about it as you do it is always a good thing. So, I’m thinking about installing an in-line valve. Not recommending that anyone else does it… but I’m pretty damn sure I’m gonna. Because I’m sick of frying batteries, fragging starters, erratic oil levels, sluggish running (initially) and mostly… mostly… the damn stress and oil mess! All it will take to make it effective is adding one more simple task to the starting drill, every time, which is to make sure the oil is turned on. Same as turning the gas on.

Paranoid techie types might go a similar route, with a rather critical difference. This amounts to a manual valve, a relay and an “alarm” of some sort factory horn (or buzzer, like in the pic) using the lever on the valve as a switch, and wired to sound off if/when the key is turned on and the valve has not been opened. Clever, again, if you trust electricity and wiring more than your memory.

If need be, I’ll rig a reminder or two, in order to make an ingrained habit of it. A pre-flight checklist like a private pilot would use might come in handy too. In fact, the simplest, best idea (thanks Paul!) for a bike that lives in a secure (locked garage) type environment… attach the ignition key to the lever on the feed valve. Detach to ride and reattach when done to ensure the valve gets shut off again. Try to forget that! But one way or another—I’m done!

C’mon… anyone want to talk me out of it? Or talk me into a better plan? Call me nuts… but call me.


  1. Well I have that sumping issue with a new S&S 124 LC engine. I don’t get puking oil but a very few drops out of crank seal, running a open primary, an really pi$$$$ me off. Had that same idea as you about a manual valve inline. Maybe take that idea an put perhaps a spring loaded ball check valve inline??? Do you think that mite help??? Let me know please!!! Thanks

  2. Has any one rigged an in-line lever valve adjacent to a keyed ignition switch so that the key will not go into the switch unless the oil lever is in the full open position. If so, I would like to see a photo or two with a material list. I have a FXR with the problem

  3. The simplest solution if you suspect it’s wet sumped is before turning on the fuel, pull the spark plugs, ground the plug wires (or pull the coil power wire if that’s easier), hold the throttle open, and crank the bike several times.. This will get enough of the oil out of the crankcase to allow easier starting without burning the starter motor up, because you’re not fighting the compression of the engine. I do this on any engine that’s been sitting for an extended period just to give the oiling system a head start when the vehicle is first fired up.

    If you’re going to do the manual shut off, rather than attaching the key to the valve, I think a better plan would be pulling the fuse for the starter or ignition circuit and zip tying it to the valve handle. Accomplishes the same goal, while not compromising the security of having the key in a safe place.


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