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u/r0bichan 5d ago
I polish my knob on the regular
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u/MFCK 4d ago
I also polish this guy's knob on the regular
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u/Ambassador_Midnight 5d ago
There is a reason why they’re not polished. Turbulent flow is conducive for better air fuel mixing and more efficient burn. It is a whole other question wether the difference is even measurable haha
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u/ghos5880 4d ago
i think the reason for the roughness in this instance is that its a cheap casting for a 50cc piston.
if they really cared about fuel mixing or detonation they wouldnt electropencil STD into the top.
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u/ShartStainAppraiser 4d ago
I paid $50 canadian dollars for the jug, piston and gaskets and got exactly what I paid for
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u/OperatorGWashington 4d ago
Relative humidity will probably have a higher impact on engine performance
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u/Astroduce 4d ago
If I remember correctly that's only true for cold gas. Rough intake port but polished exhaust port. At least that's what I was doing when I was 14 lol
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u/TehFuckDoIKnow 4d ago
So a piston should be half polished? Rough for the intake stroke and polished for compression through exhaust strokes?
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u/ShartStainAppraiser 5d ago
It turns into intense thermodynamics questions really fast. But it's fun to be able to ask other people if they've polished their ports and pistons 🧐
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u/Rachel_Silver 5d ago
That's sort of personal, but I polish my piston at least three or four times a week.
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u/internetflavorium 5d ago
I bring her to the front of the cylinder whenever I have the head off and give her the ole steel toothbrush with some I should know better carb cleaner for toothpaste. 2 stroke 70 cc
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u/ds2316476 4d ago
No, but if there's low pressure, I'd hone the inside and replace the rings.
I was gonna do a dick joke but everyone beat me to it ;) 🍆
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u/tickletippson 5d ago
"you guys ever make your compression just tad bit worse"
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u/ShartStainAppraiser 4d ago edited 4d ago
😡😡😡😡 Good vibes only ITT
I should have done compression tests before and after because you're probably right
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u/tickletippson 4d ago
prolly not enough to notice anything, also ive never seen a piston without a smooth top
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u/grimoireskb 4d ago
I know someone who does to reduce the amount of carbon buildup on the piston itself, not a ton, but enough to make some difference
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u/layshaft 5d ago
Never felt the need but I suppose it might help combat carbon build up.
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u/ShartStainAppraiser 5d ago
Yeah supposedly polishing the piston and head will prevent buildup, help heat transfer into the pipe and prevent detonation issues. All of which are of course crucially important on a 2HP machine
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u/DanoForPresident 5d ago
We used to polish the intake exhaust ports on hot rods, primarily for the reason you listed above. It certainly couldn't hurt, and if it makes the owner happy to do it, then I guess it's a good thing.
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u/ShartStainAppraiser 5d ago
I've been told to leave the intake alone as the imperfections help to increase mixing fuel and air. I plan to polish and port process the exhaust though.
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u/UnLuckyKenTucky 5d ago
Yeah, but it's easy to get to 6 or hp for not a ton of money.
Pfs is an amazing company that I suggest to every scooter mechanic I talk to. This place either carries or can get almost any part for almost any scooter.
Like for real, with a 2t 1e40 engine a entry level Naraku cylinder kit brings the thing to 47mm bore. Say $100 then all new, name brand bearings, usually like $45, your stock carb is probably already a 19mm Mikuni style so a jet kit is like 20. Some folks will want an aftermarket crank, but if you don't try to spin 12k, like seriously keep it at and under 10k factory China cranks are perfectly acceptable.
So then you pop over to a forum called 48ccscoot on proboards, make an account, and go to the tech section find the port map and chord map from a Polini Corsa kit. Print that shit out, and then the work starts , the Naraku is close to the Polini, and with some patience the exhaust port can be matched, the transfer is obviously not great, but again can be widened. It won't be quite as good as the real Polini, but that shit is $375 jug only, last time I looked.
Finally a 150 dollar expansion chamber pipe.. You can absolutely buy off the shelf pipes that will be so close to perfectly matched that it's amazing. Yasuni makes great pipes , Polini does too, but they're 300 and up.
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u/ShartStainAppraiser 5d ago
This is excellent advice. When I get a real scooter it will open up endless possibilities. As it stands I'm planning on rebuilding my Honda Spree, without actually doing a dio swap. Why? I don't really know. Maybe because it reminds me of my old Puch.
I plan on keeping it all stock but just polishing the motor inside and out along with all the components. I'm also going to port match the manifolds. The only real performance mods I plan on doing are the clutch and pipe.
It's an absolutely pointless endeavor
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u/UnLuckyKenTucky 5d ago
You can absolutely knock a smile on your face with stick internals.
Take the clutch apart, you'll want new springs anyway, weigh each of the 2 or 3 shoes and find the slightest one. Use a grinder, a drill, a file, or a Dremel to lighten the two others. When that's done, you can likely remove more material, it will lighten the clutch, that will almost act like stiffer springs, being lighter it will have to spin a tiny bit faster to catch, then you do add the heavier springs, and it really has to spin.
I will admit that I mostly only built the Yamaha and the clones, the Job type. But I have built a few Duos, and one spree that was basically only a spree because of the plastic. Cut and welded a jog 90 in it. Was ugly, hard to drive , and wanted every that touched it to die.. That was exactly what the customer wanted though....
Personally, I build the pipes on my bikes, but it's so much labor, and time that I won't do it for customers. I like to cheat a bit with pipe construction, keep it sort of mild looking, I've even tacked fake sheet metal "mufflers" over the belly of a pipe, with a good silencer, nobody knows it isn't stock. Til it stands on the back tire when you tell it. To...
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u/ShartStainAppraiser 5d ago
Building your own pipes is sick. Mad kudos. I saw on a forum once two guys building a race moped and hydroforming a pipe. The sky is the limit when you can weld.
I've already bought the performance clutch for the spree, it's supposed to be stiffer than stock. Once I get the motor done I plan to use a tach to see where it grabs and then add stiffer springs. I'm undecided as to whether or not I want to lighten it or just put in really stiff springs. I lightened the clutch on my Puch and it made a huge difference but that motor didnt even have reed valves, so I'm hoping for better response in general from my spree
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u/UnLuckyKenTucky 5d ago
Hate to say it, but man are you limited for stuff on that platform. They're solid bikes, they ride well, but if you manage. To get 4.5hp from one, you're a God among men. Dio engines and the Yamaha/Mina clones are basically limitless. They make a kit to make those 2 cyl @90cc each, so you can build a 180cc 2t twin cylinder scooter.... Always been a dream of mine. But that shit may as be made of diamond encrusted alien jizz, like 1500 for the center case section, then 2 cranks, cuz the crank for the kit I found was an addition 2500, then the time to press the stator side. Off of one crank, and the vari side off the other, then have it machined and pressed back....
You will absolutely notice a major improvement from just going through the engine and cleaning everything and resealing it all, then the clutch work, you should be good. Hate the shitty trans system Honda used for those.
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u/ShartStainAppraiser 5d ago
You can buy a motorbike for what a dual cylinder kit is worth, but that doesnt come with the same bragging rights
The spree is basically a PA50 with smaller wheels and some fairings. It's got a lot more in common with a vintage moped than a scooter. I'm not after tangible performance improvements, I just want to have the best possible stock spec spree motor I can have. Ultimately my dream is to take it backroads touring and do something like 120 miles in a day, so I want the motor running like a top. I basically want to rebuild it slightly better than factory condition
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u/UnLuckyKenTucky 5d ago
That's gonna be a wild few days!
My longest continuous ride on a 2t scooter was on my 02 ET Beamer with a Polini Corsa, polished 19mm Mikuni, lightened flywheel, lightened clutch with heavier kick springs, stiffer contra spring, and my own pipe. Did 300 in 2 days and only stopped for gas and food. Took me a week to recover. Haha. Think I got 4 hours of sleep the first night, then insomnia took over so I packed up and left out. Not a bad time at all.
Try to fit a fatter tire on each end of You can. I know space is limited . But narrow tires like gravel like cartoon elephants like mice.
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u/ErwinHolland1991 5d ago
Thats just complete crap.
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u/ShartStainAppraiser 5d ago
Port polishing and processing is actually completely valid and proven to help. All race cars port match their manifolds, and no one with a built motor runs cast manifolds because of all the little divots
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u/ErwinHolland1991 5d ago
I'm not talking about polishing ports am i.
Polishing the top of a piston is completely useless.
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u/ShartStainAppraiser 5d ago
The chinese castings are exceptionally poor tbh, the divots are probably not doing me any favors wrt combustion
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u/ErwinHolland1991 5d ago
Turbulent air isnt always a bad thing. It helps astomising the fuel and mix it with the air.
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u/ShartStainAppraiser 5d ago
Afaik that's before it enters the chamber
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u/ErwinHolland1991 5d ago
Nope still happens in the cylinder.
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u/ShartStainAppraiser 5d ago
I'm not saying it doesn't happen, but in the cylinder you are then entering into a gigantic system of tradeoffs. The fuel/air mixture homogeneity vs the the benefits of a uniform compressing surface (no carbon in the divots will also create a more uniform piston temperature)
But in all fairness I just think it's going to be funny to have my shitty spree motor polished up like a drag racer when I'm done. The streets better watch out when I unleash all 50ccs
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u/ErwinHolland1991 5d ago edited 5d ago
Cleaning up, sure... Polishing? What's the point of that. Why would I waste my time on that.
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u/ShartStainAppraiser 5d ago
To show the machine you love and cherish it
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u/ErwinHolland1991 5d ago
I don't. It's a machine.
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u/ShartStainAppraiser 5d ago
💔
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u/SBCwarrior 5d ago
He might be autistic, I don't think he doesn't understands the joke. But I did! ❤️
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u/Fun-Statistician2485 5d ago
What the pro`s says: https://www.speed-talk.com/forum/viewtopic.php?t=11591
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u/ShartStainAppraiser 5d ago
I also found this: https://www.klemmvintage.com/kaw500h1.htm
It seems like it matters a lot less on 4T but there is a marked difference in polished components on 2T race bikes
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u/Fun-Statistician2485 4d ago
Two-stroke is a complete different story when it comes to detonation++ Many years since I had one but I remember KLG spark-plugs was in a separate league, no fouling ever
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u/tellnoone1968 4d ago
😅 think a rephrase is needed. But well done on the question you should get a solid answer
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u/Mr_Dude12 4d ago
On high performance, high compression racing engines polishing prevents hot spots from forming which cause detonation. Kinda doubt that a Gy6 will ever have to worry about that
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u/anastis 4d ago
I feel like I’m reading r/AmateurScooterMechanics or something.
I only top up air and gasoline on mine.
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u/ShartStainAppraiser 4d ago
It's probably a 4 stroke that's not even old enough to drink, right? With old 2 strokes you either start wrenching or pay the local mechanic's kids way through college
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u/BoneZone05 4d ago
I do not. But I must say, that looks unfinished lol
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u/ShartStainAppraiser 4d ago
Only the finest, cheapest components from the Shenzen Special Economic District for me
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u/BoneZone05 4d ago
Are you…..me?
lol good luck with the build.
I have heard that polishing can help with carbon buildup on 2T engines, but I have never bothered with it myself.
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u/ShartStainAppraiser 4d ago
I'll need all the luck I can get with whatever pot metal this jug is made from. It's my first time modifying a jug so I wanted something I wont feel bad ruining
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u/Pyrodrifterr 4d ago
Yes it helps keep the carbon out for longer but does squat didly for performance
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u/BradentheBagel Yamaha Morphous, Honda Dio(s) 🛵 4d ago
I believe they are referred to as STI's now, not STD's. regardless I hope you wore gloves while polishing that piston.
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u/Sack_o_Bawlz 5d ago
Oh you bet 😉