Friday, May 29, 2020

Rinse sump while changing Royal Enfield oil?

Hand holds small bottle of clean oil in front of motorcycle.
My wife prepares to pour clean oil into my Royal Enfield Bullet.
Getting oil on my hands (and on the garage floor) is part of owning an old-fashioned Royal Enfield Bullet motorcycle. Mine is an iron barrel Bullet, the original British design of 70 years ago, but built in India in 1999.

Modern Royal Enfields are nothing like this, I assume, as they have a single drain for motor and gearbox oil, and a spin-on oil filter cartridge.

Not so my old Bullet. Never mind the gearbox, which has its own drain plug. My motor has a drain plug for its oil tank, a drain plug for the motor's sump, and an oil soaked filter to be inserted, dripping, into its home.

Changing the oil is still a simple process but, since nearly every instance is messy enough to be memorable, I've described changing the oil before.

In the previous episode I described how only 1.75 quarts of dirty oil emerged when I drained the oil tank, the separate sump and the oil filter.

The book says that the motor holds about 2.4 quarts of oil. So either I was more than half a quart low on oil, or that much oil remains inside the motor even when drain plugs are opened.

Last time I guessed that since I only got 1.75 quarts out, I should replace only 1.75 quarts. But I found afterwards that the motor tended to show well under the halfway full mark on the dipstick after a run.

So, this time, I decided I would replace the 1.75 quarts of dirty oil I (again) recovered with slightly more than two quarts of fresh oil.

But first, I wanted to conduct an experiment.

Once, years ago, while changing the oil I accidentally added fresh oil to the oil tank before plugging up the drain holes! I watched in horror as oil shot out of the bottom of the tank onto the garage floor. But I also watched in interest and surprise, as the stream of escaping oil was at first black — not clean.

In my carelessness, had I helpfully flushed out residual dirty oil in the tank? I wanted to find out.

So, this time, I videotaped the drain holes as my wife poured a bit of clean oil into the tank. Watch the video. The stream of oil emerging from the drain hole looks pretty clean, but a photo of the recovered rinse oil shows a distinctive dirty tinge. And much less oil came out then went in!

Hand hold small glass bottle now filled with recovered oil.
Recaptured rinsing oil shows a distinctive dirty tinge. And there's less than went in.
Perhaps, by rocking the motorcycle from side-to-side, as I now do, I had managed to drain out more dirty oil than I used to. This is supported by the fact that less oil drained out than the sample my wife poured in; presumably this "loss" equals the amount of oil that remains in the tank but can be brought out by rocking the motorcycle.

In any case, I conclude that "rinsing" the tank is a help, but rocking the motorcycle slightly from side to side also encourages more dirty oil to evacuate.


  1. Nice application of the Scientific Methodology!
    1) Make an observation
    2) ask a question.
    3) Form a hypothesis, or testable explanation.
    4) Make a prediction based on the hypothesis.
    5) Test the prediction.
    6) Iterate: use the results to make new hypotheses or predictions.

    My oil always seems a bit cruddy to me even immediately after an oil/filter change. There has to be a lot of hide-out going on. Change early & change often is the trick I guess. "Dilution is the solution to pollution!"

    By the by - Have you ever seen a modern "spin-on" oil filter adapted to these olde beasts? At least you'd be able to pre-fill it and avoid the dreaded "dry pump up".

    Thanks for the video. You're a lucky man - not many guys have wives willing to assist on motorcycle maintenance tasks! ;=) - CW -

  2. David, do you change the oil whilst (as the old Brit manuals would have said it) the oil is hot? I think we did that so the crud in the tank would still be in suspension and would rush merrily out into our drain pans. We hoped. How would one know if his/her oil was still dirty after an oil/filter change? Hmmm...

    1. I described my effort to change the motor oil hot here. Never again. Got burned, dropped the plug into the catch pan, reached in with a glove on... Maybe it makes a difference, but it isn't worth the pain to me.

  3. We always used to change the oil fresh from a ride. It was a thing guys who cared about their bikes did. Just a month or so ago, Roadracing News magazine ran an article about oil changing hot, warm and cold, and found very little difference. This was like heresy. I've burned myself doing it too. Hard habit to break...

    1. Well said Maynard - these "Old Spanish Customs" die hard. It always just SEEMS like it'd be better - right up to the point that objective proof says otherwise. The best reason to change oil hot is that you are getting paid by the job and really need the money! -CW-

  4. Almost 2 decades ago i was at a small dealership in Pune. The owner told me that it was their standard practice after draining oil oil was to refill the bike with Kerosine (sp) and then run it for a short while. Not ride but just run. The concept was to flush the engine. It makes good sense to me but have to confess it would make me nervous. On the other hand I have seen them run for quite a while with no oil.

    1. Anonymous6/02/2020

      Never heard of actually running the engine with kero, but I've routinely flushed out sumps/oil tanks on old bikes that have been sitting for years. Even done it on bikes that had the top ends removed that sat open with positive results.

    2. Hi Kevin - what's the scoop on making the bushing bottom end survive long term? The best info I've seen so far is keep the revs between 3000 to 5000, & don't lug it. I run 15W-50 and change oil/filter every 1500-2000 miles.

    3. Hey, if you want to watch how the pros do a Bullet oil change and rinse in the land of its birth, just as Kevin's described, at least for a UCE model, check this out:

      Shocking, right? Still, you just KNOW it loves it.

    4. In the video the mechanic in India drains the oil, starts the motor with the drain plugs out and runs it for 30 seconds, blasting out the remaining oil. Then in goes 1.5 liters of diesel fuel and again the motor is run, but not revved. The diesel is drained, fresh diesel added and this time the kicker is used to rotate the motor, with the spark plug out to prevent starting. They get a lot of dirty liquid and some shiny scarf out. But it looks brutal.


Follow royalenfields on Twitter