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Additionally the bottom end of a 2 stroke has an oil fluid film present on the surface. 4 strokes work a little differently.
To add, polished internals aren’t always the way to go. A highly polished surface will make the oil bead off, not form a coat/film. Very misconstrued science.
The only thing I ever polish is the exhaust port and that is mostly for looks. 😉
A (slightly) rough surface is better as it encourages a turbulent boundary layer that's less likely to separate in an adverse pressure gradient (it's why a golf ball has dimples). Delaying boundary layer separation can dramatically increase flow around curves, in expanding passages, etc.
But for the specific geometry of our applications, it's probably a negligible difference inside the cases, and slightly better in parts of the intake porting. I'd bet not a whole lot better, but reason enough to skip all that work of polishing which can only make it worse.
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No way in Hell could you feel a 1hp gain using ceramic bearings. I doubt there's a measurable increase at all. Although from what Ive read some guys can notice differen motor mounts .
Polishing also diminishes heat transfer from a smaller surface area.
I’ve never tried it, but I think ceramic coating the crankcase in a smoker might be a good move. Slow down heat transfer, have a consistent surface finish and stop some of the oil in the intake charge from soaking into the case material. Has anyone tried it?
FYI, Pivot Works (under the All Balls Group) has become the "Premium" brand of bearings, utilizing 3 different Japanese brands. They're very high quality these days, for those looking for an aftermarket price with OEM quality.
The golf dimples seem to be very hit or miss. The golf ball is traveling through the air, the air is traveling through the port in an engine.
Some guys swear by it and some guys wish they had spent the money on other things.
I have flowed one automotive head that had one port dimpled, flow was the same within the margin of error to the non dimpled port. Squirted some dykem into the port to semi simulate fuel and couldn’t tell a difference from the pattern in the chamber. We got better dykem patterns from changing the seat angles and depths.
Just my experience
Edited for spelling
The concept works for both internal and external flow. But to be clear, I wasn't suggesting anyone put golf ball dimples inside their engine, just using that as a well known example of how the concept works.
It comes down to the balance of pressure drag vs viscous drag. A laminar flow will have less viscous drag than a turbulent flow. So from that perspective alone, polishing is superior.
But for geometries that have relatively sharp bends or for passages that expand along the flow direction (crating an inverse pressure gradient), you can easily get boundary layer separation. In those cases, the pressure drag created by separated flow is dramatically larger than the viscous drag. A turbulent boundary layer is less likely to separate than a laminar one, so in those geometries, a rough surface is superior (since it encourages a turbulent boundary layer). This is typical for geometries within an engine.
In the grand scheme of things, though, it's likely not going to make a significant difference for our application. My main point was that, except for in very specific cases, leaving the surface rough is the better option. Taking the time and effort to polish it almost always make it worse.
I mostly agree, in the simulations I have ran it shows an improvement with the dimples. I don’t have the computing horsepower to simulate it in a bidirectional flow with with the dynamic pressure fluctuations seen in a running engine. I just haven’t seen any real life results on the dyno or on track with fuel numbers that back up the simulations.
I’m not trying to start an arguement or sidetrack the thread. I just don’t want a post in 2 weeks that someone took a dremel to their engine and now it doesn’t run correctly, but this is vital. If we are talking ceramic bearings, there are a lot of easier ways to improve efficiency.
What bike are you referring to? If your kid is going to Loretta’s on a PW 50 it will probably make a difference but anything big bike or four stroke your not gonna feel it. I micro polish my transmissions but that’s mostly to make it shift smooth under wo throttle.
Have you tried doing it? To a 2 stroke....
Make no other changes. Polish up the crank area (like shown in the photo I posted) and the rod and crank halfs. Put it back together and ride it.
I did this exact thing in 1990.
I was taught this back in 1987 by a guy that built motors that won outdoor national motos and SX mains. He built Mago's motors when they were kids. People would come up to him at various races and say "what the heck did you do to those motors? Those things bark". This is what he did.
So, what you're saying is that 37 years ago, an engine builder polished the internals of the engine with no other changes, then spectators at the track, on a different day, in likely different conditions, determined that those changes were better by sound and their feelings (not even feelings from riding the bike) alone?
That's a bit hard for me to take as evidence, especially when what was done goes against well established fundamentals of fluid mechanics... Have you back to back tested the same engine before and after on the same dyno in the same conditions?
Try it. Forget the software models. Forget the theoretical arguments.
I did it. It makes a big difference. As much or more of a delta as a good
Pipe. A really good one.
I m not kidding.
90% of performance on a motocross bike is the rider, if polishing internal parts gives them more confidence, performance may improve!
I'll stick with polishing the exhaust port to delay carbon build-up and make it easier to de-carbon come rebuild time.
I come here in peace.
Try it. Or don’t if you have been told and convinced you have to have tumble, ruff intakes and smoother exhaust ports. If you are a believer of that religion.. don’t do it. It’s wrong as you know. Not for you. Note: I was told the exact same thing btw. I don’t blame you for one second. Maybe…I’m just a crazy old man. I m now 60 years old. Which f*C*ED with me a bit btw.
I m not here to waste you young pups time or mine. I m not here to debate. I m come to share…and learn too. I ask questions. Listen, comment on experiences I can speak to first hand etc. I look to learn from others experiences too (key word – experience. Not theory). Doing a bunch of experiments/ trial and error alone sucks. It takes a lot of time.
I’ve been riding since I was 8 years old. I ve been in the technical field in Silicon Valley since I was 24 years old. I have one of those engine-amagoerring degrees from San Jose State in the middle of Silicon Valley (not to mention working on an MBA – I pulled the plug on that after a few semesters because it was useless for me). I have worked in some serious tech companies. This thread started talking about bearings.. I worked for the company that supplied NSK bearing (Honda’s bearing supplier) the equipment to test their products for flaws as they came off the production line. Timpken bearings used the same products too. I have no need or interest in "convincing" you or anyone else of anything. I could care less what the design software you use says (however I may know folks on the team that wrote that software- and are selling it to you). I come here for fun. I seek no money… I seek no arguments. I do however want to add to the mosaic of information. I do seek to dispel theory’s and ideologies that from experience I have found to be false. There is a lot of misinformation in the world. What matters to me is practical experience. Fuck the degree and what the software models say. Does it work in the real world? That’s the test. Build prototypes. Try it. See if it works. Rince and repeat. No software program will replace real world prototypes. Heck - why do you thing mfg’er have racing programs?
I will tell you this. If you try it...you will learn something. You will find theory and the real world... are not the same thing. I too heard all the stuff you have written above about ruff surfaces, boundary layers, dimples etc. All that stuff about tumble in the intake track…. Ruff surface finishes on intake to atomize fuel…etc. Ok to smooth out the exhaust but not the intake. That would be very bad. Various models show xyz etc. Wonderful theory. Makes a lazy guy at the computer’s tummy nice and warm. And if you find something that goes counter to theory… do you share it … or keep it to yourself? Procircuit has made some positive 250 CC engine strides as of late (more holeshots). Has Mitch come out and told you what that is? Ask him… see what he has to say. Fact is if you find something that works - especially if it goes against current theory - you don't talk about it.
I did what I shared with you. The difference was … noticeable in a very good way. Power came on sooner, smoother, pulled harder. and farther. Easier to ride. Theory is.. just that. Theory. It doesn’t mean shit.
Good eye, I think it should improve the air & fuel mix too. I started a thread in March about case porting . Once I split the cases I didn’t see any material to grind away to improve flow . Only to polish it up to speed up the air into the cases b4 it hits the high compression DBP decked cylinder . My carb has a different taper bore mod. I polished the day lights out of it. If you see these gears in real life . You would get them micro polished, kinda rough castings. If you spin the gears there’s a lot of stiction there. Gears r stronger then too with the polishing & less heat. New England gear is the most reasonable at 260.00. I matched the exhaust flange to the cylinder with a dremel & smoothed out the rough casting & polished it. There was a lip that hung inside the exhaust port . Now the 2 pieces r both matched and smooth. It’s that extra tiny bit you might need to get a inch on a rider. I could go on forever about how I modded the whole pv system. All these parts r rough castings , why not blue print them into a better part.
"The difference was … noticeable in a very good way. Power came on sooner, smoother, pulled harder and farther"
Is this ^^^^ your perception from your butt dyno? As an Engineer you should understand the difference between perception and measurable data. Butt dynos do not produce repeatable measurable data. If it was data from a real dyno, please share the results.
Pit Row
Oh... wonderful topic.. Dynos. If it's all about dyno's then you don't need to race. LOL
There is this guy that worked for HRC. Back in 1980-83 ish. Built a lot of their works pipes... linkages etc. His name is Paul Turner. Another guy named Jim Reger (who did the reger engineering stuff for mini bikes - same guy) that taught us how to back port (on the intake side) a piston. Which we did. Paul Turner told us it made no difference on the dyno. So it was a waste of time. If you rode the bike with a back ported piston vs one without you would clearly realize that back ported piston one had a lot more low end power. Pulled much sooner out of turns. Fuck the dyno. LOL.
I have a real-world story about design software packages too... and the assumptions they can make…..
I was in my senor year in an engineering program at San Jose State. I walked into the room where the professors had their offices one morning. I was looking to talk to a professor who taught manufacturing process control statistics. He was well known in certain industries for his skills in this area….as I would soon find out.
I knocked on his door and when he answered I told him I had a question about a particular problem on the last exam.
He said – “ Sure, happy to go over it. However, I am expecting an important phone call. Come in but if I get that call, I need to ask you to step out of the office. You can wait out side and we can talk when I m done.”
Right as my butt was about to hit the seat the phone rang and he motioned for me to leave the room. Which I did.
I was in the waiting area for 15 – 20 mins when he opened his office door and waved me back in. I sat down. He looked at me and said “That was a friend of mine that works at Boeing. Seems the software program they use over estimated the number of (fatigue) cycles their rivets can handle. They had an accident last night. ” So you want to rely on what the sw package says? Knock yourself out. I want real world info.
The lesson – SW FEA programs are based on models. Models are full of assumptions. And assumptions .. can be wrong.
The result: Well you can read what’s below as to what happened to that plane. And the Flight Attendant.
On April 28, 1988, a seemingly routine, 35-minute flight from Hilo to Honolulu turns into terror when an 18-foot-long section of the upper fuselage suddenly tears off Aloha Airlines Flight 243. The explosive decompression and roof loss sweep flight attendant Clarabelle “C.B.” Lansing off the Boeing 737, send freezing winds of hurricane force through the cabin, and leave passengers in the first five rows of the plane completely exposed to the sky.
Miraculously, Captain Robert Schornstheimer landed the plane in Maui with no further deaths.
The bizarre incident happened about 20 minutes into the flight from Hilo International Airport to Honolulu, at 24,000 feet with 95 passengers and crew members on board. The 300-m.p.h. wind was so noisy that the pilots had difficulty communicating in the cockpit, and flight attendants couldn’t get into the cockpit to see if they were even alive. Passengers under the missing roof had no access to oxygen tubing and became incapacitated by hypoxia.
Btw that plane did and emergency landing on the island of Maui. Paul Turner lives there today…and he makes a gave tequilana (drink) from blue agave plants grown on his land. You can visit and have a drink. Ask him about back porting pistons and dynos. )
https://www.mauinews.com/news/local-news/2022/08/agave-farm-finally-see…
@PTshox You say you didn't come here to argue, then proceed to make multiple posts insinuating that real engineering (theory and simulation) can't be relied on...
In my experience (20 years of mechanical engineering consulting across many industries), it's typically the older "engineers" that hold back a project. They don't understand modern techniques, they reject technology, and crawl along using a guess and check process that's massively inefficient and often guides them down the wrong track.
I have many stories of simulations being "wrong" and many stories of them being accurate and extremely valuable for development. Note that the simulations are not actually wrong, the engineer just set them up incorrectly or used the wrong and/or too many assumptions. Similarly, well-established theory is not wrong. If the theory does not match the results, that theory was just applied incorrectly or misunderstood. Well applied theory paired with properly set up simulations using correct assumptions simply can't be beat. It leads to incredibly well designed products, that yes, are physically tested (and measured) to preform better than what was before them.
If you reject the theory, you reject the simulations, you reject the tools to measure change; you're not moving things forward efficiently. At best you're just guessing; you're not even "guess and checking", since you reject the dyno that could actually show a difference.
You've polished the engine internals, despite theory saying the opposite is better, rejected the dyno as a way to measure the difference to see if it actually worked, and relied on your "feel" on the track, which is subject to all sorts of bias, variables, etc.
That's the attitude prevalent in this industry, unfortunately, and also the one that's holding us back. It's the reason I started my company in the first place; to bring some real engineering to motocross (specifically hard chassis parts), and not be just another machine shop making flashy anodized parts that don't do anything or are actually worse than stock. We have loads of people changing torque specs on their engine mounts 5% for "better feel", or running steel bolts in certain areas because titanium is "too rigid", or switching to "floating" axles, all of which is completely wrong and ineffective.
Now it's possible, though extremely unlikely, that you've stumbled upon something we're missing. That we have incorrectly applied the theory to this particular situation and polishing actually is better. But you're going to have to provide some sort of proof other than "feel" or spectators on the side of the track 40 years ago saying a bike "rips"!
______________________________________
Anyways, apologies for continuing the thread derailment. Here's some more relevant info:
Polishing - don't bother, it won't help. Exception is the exhaust area to minimize carbon buildup. (Somewhat) Rough Surface - more ideal from a flow perspective, but likely won't make much of a difference anyway. Dimples - don't bother, any help will be minimal and you risk screwing something up if it's done wrong. Just port it and leave the surface finish that comes with that process alone.
Bearings: stick to OEM or equivalent high-quality manufacturer. Ceramic will be better, but only a small amount. Your money is better spent getting more gate drops. Additionally, ceramic is WAY harder than steel. Unless you're getting full ceramic bearing (not just just ceramic balls), the races will wear faster and the overall performance will degrade over time. Whizzy parts need a whizzy maintenance and replacement schedule as well.
Well said! It’s not just the motorcycle industry with the “feel” problems.
LOL.... wisdom comes with age.
I hope you read the fine print on the software licenses you use for the various software packages. And I hope you have a lot of liability insurance and have the right corporate structure. And a very, very good attorney. When the plane crashes it's too late to put that stuff in place.
Btw you haven't tried it... have you. So you speak about something... from zero experience.
We go from bearings inside of dirt bike motors to software licenses and aerospace engineering… I love Vital.
They guy with the computer is telling me it doesn't work... and he's never tried it. Just relying on theory.
That's insane to me.
So does stubbornness . . .
Try it... or don't. But don't tell me it doesn't work when you haven't tried it. Keyboard warriors.
I just came to discuss bearings bro
Post a reply to: Engine Builders or Moto Dads who do the work their own, what bearings do you use?!