OK...I may get corrected by Eric, Rich, Bill, Terry, or any of the guys who have forgotten more than I have ever known about engine dynamics, but I want to give you my take on the break-in thing...
When we rebuild a motor, the cylinder will have intentional hatch lines on it. These small lines, or swirls around the piston jug will help oil to be distributed along the path of the piston by the oil ring.
The more perfect the circle of the cylinder is, the better the breakin will be, due to the fact that the piston surface and the rings match up.
The more out-of-round the cylinder is, the harder it is for the rings to seal things up well. This can result in a loss of compression, and in a 4 cycle motor, abnormal consumption of oil.
If the cylinder is slighltly out of round (egg shaped) then there will be high spots and low spots. The high spots are in contact with a small bit of the ring surface. These high spots will actually wear down, as will the rubbing surface of the ring. The rubbing and taking away of metal in these areas will finally subside when there is more surface area of the cylinder in complete contact with the rings surface.
This is reffered to as the rings "seating".
On mass production bikes, it is very easy for the machine work to be slightly sub-standard. I suspect that being the case on the Honda's that were having seating problems.
An aftermarket machining will more often be of much better quality. The circle of the piston bore will be more true and round. Which will allow for a better break in seating of the rings, without a noticible loss of compression, and very little wear between cylinder wall and ring face.
The rate of the wearing of the high spots is contingent on what sort of product is supporting lubrication in that area.
Oil lubes protect metal from wear by forming a thin layer of oil between the mating surfaces. This wedge of oil keep the metals away from one another and will not allow the small hills and valleys of the metal surface to break through the wedge and get to the metal on the other side. This is reffered to as "full fluid film" or "hydrodynamic" lubrication.
Problem with oil is, it takes a certain volocity and pressure at the microscopic level to keep the oil forming a layer between the metals.
When there is not enough force to keep the oil wedge in place, there are additives in oils that take over, so to speak, when the fluid film fails.
The additive package of the oil provides materials that take over the job of lubrication that the oil can't perform. This is reffered to as "barrier" or "boundery" lubrication.
Comman components of additive packages in oils are Zinc-d and molybdenum, although there are a host of others. These items will coat the metals surfaces with electrically charged polar molecules that form a protective barrier on the surfaces of the metals. They will allow some of the metal to be sheared away when there is contact, but the simple act of the intial shearing lets the chemicals that now reside on the metals oxide layer change the way the shearing takes place. Instead of high heat that gets created with unprotected wear, the intial wear changes the construction of the oxide layer and lets the wear sort of smooth itself in, in laymans terms. I could go on and on about what happens molecularly at this stage, and some of it is yet to be fully understood by the lubrication engineering community. But the simple facts are that the breakin is completely reliant on the barrier package of oils, and the trueness of the machine work itself.
If the metal is being protected by nothing, then the wear of the mis-matched parts will create great heat at the micro level. This changes the metals make-up and allows for even more wear, since the remaining surfaces are brittle and rough from the last pass of wear.
This can continue until the surfaces are eating at each other until failure.
If there is a barrier additive in place when the wear occurs, then the shearing of the metal in high spots still takes place, but the chemical reaction that the additive provides keeps the metal from micro-heating and keeps the metalurgy consistant, until more surface area is in contact, OR volocity and pressure build, allowing the oil to finally form that wedge between the surfaces and do the job it was intended to do.
Start-up and shut-down are the most critical times during a break in...or anytime for that matter. When we start the engine, there is no oil being pumped, or being moved. And it may only be a stroke or two that is not being protected before start. But that momentary unprotected time takes off loads of metal in mis-matched (or brand new) jugs. This is the time that the barrier additives of the motor oil is so very important.
Break-in fluids and materials are simply barrier additives in concentrated form. The very best know product for barrier protection at break-in is molybdenum, or "moly". Moly can cause problems when high concentrations of it are introduced to the clutch plates of a bikes wet clutch, so it is not advised to use moly break-in products.
But you should use a break-in fluid of some sort. Whether it be a specific sort of fluid, or simply a good motor oil. Something needs to be used. Not only are you seating the metals of the jug ands rings, but there are bearings and races that are also in need of a wear in, albeit nothing compared to what the cylinder and rings see.
But in the case of the cam lobes, lifters, and the journals, even the slightest bit of unprotected wear can result in less than optimum engine performance.
Granted, once the engine is up and running, there is oil being introduced to the parts. But that intial start and the shut-down can be terrible for eating away metals if your oil doesn't provide a good barrier package.
When we slother on a rebuild fluid, we have treated the metals surfaces so they can handle times like start-up that there is no oil and additives being sloshed around. Most break-in treats will also still be present on the metals surfaces for some time. Even if you drain the oil right away, the treatment on the metals still remains for some time.
I could go on and on, including the synthetic and dry-run issues, but I'll save that for another rant.
And, nick...
I find the story about the straw full of Borax very interesting. I can see where it would be looked at as an old school way to get the wearin going fast...which in my mind is a bad thing. BUT, there are issues that may be taking place with that method that the old school guys never even considered. They simpy knew it worked and used the method.
I am going to investigate this procedure a bit more, as I've never heard of it. There could actually be something happening chemically with borax that may have been a good thing.
Don't do the borax thing though. :) Plenty of products that are far better suited for the task.
WAIT...I think I just posted what I did in the last post here...ony with more boloney and hot air! LOL... oh well...
