Some folks have asked questions about how to "flush" or clean up a dirty or abused engine that they have just purchased.   Specifically, they want to know how to do it without hurting their seals, or clutch or gaskets or cut-in-place aluminum cam bearings, etc. etc.

First, you don't want to use any kind of automotive engine flush product in your motorcycle engine.

They were all intended for high durability cast iron block automotive products and they do include stuff that can cause potential damage to a soft aluminum mounted gearcase/engine bearings, cut in place bare-aluminum cam bearings, oil soaked clutch plates type engines like ours.  Auto engine flushes are a BAD RISK in a motorcycle engine.

Some have tried Seafoam added to the oil -- still risky because can possibly thin out the oil viscosity below motorcycle load bearing limits, especially up in the cut-in-place cam bearings.  Some have taken this risk and had success.  Your mileage may vary .....  your choice, your chances.

What works great with 100% safety (this is recent personal testimony off a badly gunked up Yamaha XV535 engine) is to go buy several gallons of cheap high detergent high dispersal property DIESEL RATED oil and put it in, let it ride until it gets dirty (happens pretty quick) and change it - dirty it - change it - dirty it - and do this cycle of quick changes until the oil window clears up and the sludgy gunky mess disappears from the oil window and valve adjustment areas.

How does this work?  Diesel oil is intended to suspend soot residues from normal diesel combustion for lots of miles.  It carries a detergent and soot suspension package that goes far beyond what is in normal car or bike oils.

Motorcycle deposits are soft and friendly compared to the diesel junk that this oil is designed to keep at bay.  Two gallons of diesel oil will clean up a dirty engine safely and fairly quickly (2 months to squeaky clean) with your only effort being pulling the oil plug every couple of weeks.

How expensive is this treatment?  $15-20 max cost.

Or it can be "free" if you do it this way.  Go to Wal-Mart to the gallon oil jug area and pull out a gallon jug of Rotella T 15w40 diesel oil.  Set it to the side with the back label facing you.   Go pull a jug of Super Tech (wal-mart brand) Universal Motor Oil 15w40 (diesel rated oil) and put it label out next to the gallon of Rotella T 15w40.  Compare the rating labels.  Decide if $2.50 is really that much money to you as the Rotella T has a sterling reputation behind it.

If you pick the Rotella T 15w40 jug, then your gunk stripping is free.  Rotella T 15w40 is the favorite motorcycle oil of the entire Japanese motorcycling world, high performance bikes to V twins.  The package of anti-wear additives in this oil for cam chains and valve tappets/cams is only exceeded by Mobil 1 V-Twin and Amisol products and those oils cost $9.95 a quart.  Your Rotella T 15w40 cost you less than $10 a gallon.

Just change your oil as soon as it gets dirty.  Most of us do that anyway.

Now, back to that total junker VX535 engine that had clumps of congealed sludge sitting in the drain pain and an oil window that was totally black and it had masses of black foamy crap that were clustered all around the valve adjustment screws on the rocker arms (it had a little up-down movement path through the congealed crap in head).

That one got two gallons of the cheap Wal-Mart Rotella T wanna be (Universal Motor Oil) put through it on an accelerated basis.  The oil got sludgy filthy in a couple of days and it pulled discrete clumps of crap out of the engine the first two daily changes.  After that it was just dirty thick inside a week.  

By the middle of the second gallon I could use the oil window again to see if I had the right amount of oil in there.  Very effective engine clean up at ZERO risk to the engine.

At this point you can switch back to whatever flavor of oil you prefer for your "steady state" oil and let it keep your engine clean according to its own additive package chemistry.

NOTE:

Please do not reply to this thread --- our moderators are very quick to trash-can any form of oil war on this board and this thread is about "how to flush a very dirty engine safely" -- not about your favorite brand of oil.