HD Evo Engine Flush


Jul 15, 2009
New Mexico USA
Is there a commercially available product that would be safe to use for flushing the oil system on a roller bearing crank, OHV engine?

I'm thinking about something that could be added to HDEO like maybe Rotella, run at an idle until warm, and drained. Not something that would be part of a regular OCI, not something to run in service, just something to clear out oil passages and get crud out of an engine that has been sitting for a very long time on an unknown oil.
Thanks much.

Back story -- after running a couple of engines on reasonably good quality oil (GM 4.8 on Chevron 5w-30 for over 100K miles and an HD Evo that was run on who knows what for a long time then one OCI on Citgo V-Twin formula followed by one OCI on Lucas 20w-50 V-Twin formula not my bike not my choice) I switched them over to Mobil 1.

On both engines the oil came out at every OCI about like you'd expect until the M1. The first time I drained the M1 the crud that came out was just unbelievable.

Not a real big deal on the 4.8, if anything it ran better.

But this is not something good for a Harley motor, especially an Evo unless all of the crud comes out. The way the oil passages are drilled, the way the oil delivery is prioritized, the way the relief valve works, and with the oil filter on the return side of the pump (between the pump and the oil tank,) it can be really bad news if small amounts of accumulated crud gets loose but is not flushed through. It just doesn't take much at all to plug the passage that feeds the crankpin. Seen it more than once.

So yes, the idea here is to assume that if we don't know anything at all about previous maintenance and the bike is older and has been sitting a long time, we want the insides cleaned up, just not suddenly all at once unless there is some reasonable belief that the crud can be pushed through and won't block a passage or skid some rollers.

I didn't know there was such a thing as that Mystik JT-8 until you posted it here, it really does look like an excellent choice.
I don't really believe there is anything that will clean out an entire engine, in a 20 minute flush procedure that's safe to use. First, how would enough gunk get into a engine to the point it needs to be flushed?. Using a good oil brand like, enter your brand here, will clean up as much as it is ever going to clean. The key is to use/run the engine to get it hot and circulating for miles, not just idling in the driveway. The filter will do it's job as long as there's oil going thru it. Alot of brands swear their oil will keep your engine clean. The only problem is, you'd have to disassemble the engine to see if it does or not. If your engine runs, load it up with clean oil and ride it.,,
Keep running Mobil 1 V-Twin 20W50 synthetic oil with a clean filter and rest easy. Maybe want to shorten the OCIs initially? That is all I ran in my 2008 Road King Classic 96c.i. and never lost a wink of sleep.
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Just do shorter OCI's on whatever oil you choose. There's no mystery here. Look at my sig. My Evo has all kinds of oil run in it over the years.
The brand and type of oil is way over thought. Besides, you most likely will not put enough miles on your Evo for it to matter anyways.
Nothing but oil in the motor. No ''cleaners". Do you really want to dilute the oils film protection of a running engines bearing surfaces? Even for a minute?
As said a good synth. oil and a run it and see how fast the color changes. If it's that dirty it will darken quickly, do another oil/filter change.
Follow-up: After running M1 V-Twin in one of the Evos I mentioned that had been run on automotive oil and left to sit for a long time, the lifters collapsed at highway speed. The previous owner had cleaned the tappet screen, no problem there.
Pulled the cam cover, tappet guide blocks, oil pressure gauge, and pressure relief valve out, sprayed PB Blaster into the passages followed by compressed air. The crud that came out was not like anything I have ever seen.

Put it back together, new oil filter, fresh M1 and the bike runs great.

I probably will go to the Mystik JT-8 at some point, it looks like a good oil at a good price.
If the M1 V-twin is releasing deposits, I would definitely keep using that. This is perhaps the only story I've read that indicates this product could have Group V.