Through the years, the builders we've talked to seem to have one thing in common, which is all the time and effort they spend on the ways they go about getting "that little edge". They tell us about special piston and ring designs, the porting and cams they've developed and again, how successful they've become in getting "that little edge".
We think that's great, and they are far more knowledgeable than us on those subjects. But they hardly, if ever mention what they do in terms of making sure those pistons and rings they use are working at 100% efficiency.
When we talk to customers, we sometimes ask a few questions, this response is common:
"You do know that rings need to be flat and round to work right?" "Yup, sure do!"
"And those ring lands need to be flat and parallel to work right also?" "Absolutely."
"On your last build, do you know if those rings were actually round and flat?" "Well, they were supposed to be."
"And the lands were flat and parallel as well?" "I assume so."
"Did you check?" "Ah, no. That's the manufacturers job, that's why I pay them the big bucks."
Any engine is simply an air compressor. It pumps air and the better
the parts work, the more air it makes. It's that simple.
We all know how pistons and rings work, the pistons go up and down, driving the crankshaft and the rings create a gas seal to keep the gasses in the combustion chamber where they belong. And for the most part, they work well, but could they work better?
Piston seizure - let's look at how it happens:
To most, piston seizure is most commonly caused by heat, detonation, piston growth (due to heat), uneven growth, not enough piston clearance and sometimes too much/little piston clearance. Although all of these are factors, let's dig a little deeper, let's look at the actual process as it happens.
When a piston seizes, what's happening? It's simply "welding" itself to the bore. So in order to weld anything, you need two things: One, heat, and two, "filler rod". In this case the heat is combustion gasses and the "filler rod" is simply the surface of the piston.
So looking at the above, the common thread is heat, that's correct. But most think the heat is absorbed by the piston, allowing it to grow in size. But is this entirely correct? Can a piston grow sufficiently to allow hard contact with the bore? Yes in a very few cases, but typically no.
Let's look at why. During some work with Katech Racing some years ago, we learned that (in autos), 70% of the heat a piston sees is dissipated by the piston rings, they are therefore, it's cooling system. In fact, we were surprised to learn just how cold and wet a day in the life of pistons really are. Far cooler and wetter than you might imagine.
So yes, in some cases pistons combustion heat can cause excessive growth, in boosted engines for example, but bear in mind that the melting point of pistons is in the range of 1200 deg/F.
Ring seal - what we do to make it better:
For everything to work right, the rings need to be flat and round. We test every ring we use on a surface plate first and do a light top/bottom lap to check that they are absolutely flat and have no dish. Since most dirt bike rings are actually rolled steel rings, we look for two problems:
One, they commonly have "dished" flats. We look for contact on the OD of one side and on the ID of the other side.
Since this cannot be fixed, they're dicarded. How often does this happen? About 10-20% of the time. Once they check flat, we do a further surface lap until we have 100% contact across the width on both sides.
Two, since it's nearly impossible to roll a perfect circle at the ring ends, they tend to straighten out at the ends. We've all seen this looking at used rings, heavy contact at the ends but little or no contact say, 3/8" from the end. To verify roundness, we use a fixture to lap the ring faces and look for a consistent pattern. When we're done, we then look at the ring face under a microscope, if the "contact patch" is uniform, the ring is now ready to use.
The below image shows the "before and after"
Our solution - MicroBlue® coated pistons and rings:
Now that we have flat and round rings, we need improve their sealing properties. Many people assume most blow-by goes past the face of the rings. Although this can happen, the fact is most of the leakage occurs as gas enters the ring top, then travels behind the ring and underneath it and into the crankcase.
It's important to understand that MicroBlue® has an atomic interaction with all lubricants. What does this mean? It means that the coating is a powerful lubricant magnet that greatly increases the oil film thickness on all coated parts. In the case of rings and ring lands, we now a greater amount of oil in the ring lands that is far more efficient maintaining ring seal.
Think of the bottom of the ring and the ring land as two pieces of glass with oil between them. You can't pull them apart, right? Therefore, if you cannot lift the ring off the bottom land, it simply cannot leak, period.
As far as the ring face goes one, our face lap insures uniform contact and the coated ring face insures the ring floats on the oil film of the coated bore. Ready for more good news? Since you have to "touch to wear" if there's no ring face/cylinder contact, how can there be ring wear? That's right, it's gone.
And remembering that the piston rings/lands are it's "cooling system" and oil does a better job of conducting heat than air, the entire piston assembly now runs much cooler. How much you ask? Simply measure your EGT's before and after (a 100-300 deg./F. is common). Yes, you'll be very surprised.
NEXT READ: PISTONS & RINGS: PART 2