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Discussion Starter · #1 ·
Hey guys I got around to tearing down my pocket bike motor for ***** and Gig's which is actually proving to be helpful. Turns out the motor was running pretty hot, the gaskets were all shot, and I want to upgrade my piston. However I need some help on info- my piston seems to be a stock cast piston with a 'w' or 'm'. The top is burn to all hell, and even after sanding it, id like to just get another one with more boost ports? but which ones are good and bad? you guys know better than I. Also any links are appreciated. I broke the bottom ring taking it out but the top one is fine, im going to hold off on getting a ring set in case I find another piston and say it only has one ring (though I prefer two). Tell me what you think?
 

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Discussion Starter · #2 ·
Which pistons would you guys recommend? Whats your opinion on boost ports (2-4) Links are gladly excepted, im looking on amazon and there seems to be only like one piston.
 

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You want to look on Ebay. Search up big bore kit pocket bike,etc. There are two differnt size of pistons, 40mm and 44mm. They also have different wrist pins. A 10mm wrist pin with a 40mm piston and a 12mm wrist pin with a 44mm piston. Also if you do get a differnt size pistion for example you upgrade to a 44 then you also need knew cylinder head. I would say 2 transfer ports plus the two stock ones. You will make more power with a 4 port than you will with a 5 and you get better piston ring life. Parts indvidually are so expensive. For example a FFC or full circle crank is around 60 on ebay when a complete BBK with piston, FCC, New head with better compression, new spark plug, Full gasket set is around $100(canadian dollars). So I would recommend getting a 4 port BBK with new piston,head,gaskets,etc.

5 port (red one)

I could not find a complete 4 port with the little small bolts for holding head on. Here is an ideal one. COMPLETE SET. It is a 5 port. What you could do is maybe just look for a 4 or 3 port and then just swap the cylinder head but again it would probably be cheaper to buy a new full BBK. And if you don't ride it until it overheats and dont abuse it super bad it should be fine. BTW this is from china so maybe 20-30 days to get here. You could find a US shipper but you will pay more. Btw I lokked for just 1 FFC and I found them as high as $70(canadian) dollars. And for 20 bucks more you get a full set.

http://www.ebay.ca/itm/44mm-Big-Bor...kes-/331241199374?hash=item4d1f83970e&vxp=mtr
 

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Discussion Starter · #4 · (Edited)
Thanks for the insight Poketbik! I hope some other members come alive and can pipe in too haha. Im really trying to stay away from BBK's, not because im cheap, but because i dont want any more rotating mass. Im trying to find the best piston (windowed or not and which design?) along with a cyl head which has more ports (or dremel myself) than this one with the stock 2 offset ones) My theory being, small displ. + high rpms (along with more gas, hotter accurate spark, and more air = me happy. and if that doesnt do it im looking at the gearing. Currently 6 - 55. Also, ive seen the fiberglass reeds. anyone offer carbon fiber?

Another thought is (i have a dremel) how big and where have you guys cut the ports on these? not only intake, i can do the exhaust also if anyones found noticable pressure problems after all the intake work. (which i would almost doubt too since theres less matter after the combustion takes place)
 

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Never forget that rotating mass adds torque! As long as the balance is kept in check you can still get tons of rpms, stroker kits are what cost rpms because of the added distance the piston must move per revolution. Formula 1 engines are all bore and no stroke which is a main reason they can turn over so dang fast!
 

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Well if you know how to use a dremel you can really do anything to these bikes.
 

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Discussion Starter · #7 · (Edited)
Thanks for joining in NaSa! Ive read a bit of your posts about related stuff, and always nice talking to a fellow tech ;P I just got done reading one post where you guys were all talking about the zh-1 barrel being more torque oriented and i feel like the torque is acceptably strong but its hard because i have no other pockets to compare it with. It does get up quick, and i did replace the clutch/housing, however it still retains the stock flywheel/internals so stock rotating mass is there. Personally i think its more impressive to keep the stock displacement how it is and make max power out of it-nothing against bbks.. idk, they just almost seem like too easy and common of a way to get power, just not the powerband i want. I entertain the tuning aspect of all this. Do you guys happen to know the stock compression with this ZH-1 head (40.2cc)? Ive seen my bike referred to as an SQ bike the front does have SQ stamped with a long number following. Also when taking the bottom ring out it broke, but the top one is fine. I know mechanically it would work, but does anyone ever run them with one ring or is there just too much pressure loss? Worst comes to worst i just get a new set of rings haha. But i wouldnt mind trying one ring. The crosshatching in my head looks pretty good for what its been through so i think it should seal up fine..the rings appear to be shaped the same. My main concern right now is on compression. I need to get it and my spark perfect.. but i cant do that untill i figure out my air flow /ports or dremel work (i need a friggin' flow bench for this thing i swear..) and that leads me to---> ive seen too many kids online complaining after they 'port' (dremel to hell) their bike heads that they lost power one way or another, and only a few have i actually seen that look correct and like they would add some much needed air. Supposedly theres a guy on this forum who was cutting some ports out for people? I would be completely fine with doing it myself, i just ponder on how deep to cut them, how high up the wall i go, nd anything im missing. Sorry this is all So much at once ill try to be less scatterbrained :p Appreciate all your guys feedback, this is my first pocket bike. Heres some updated pics from todays work so far. Pics in order- jb welded my muffler back onto the exhaust, i know its not pretty its still drying-ill eat my shoe if it comes undone. Then painted the metal starter cover since im repainting the rest of it, got the rotors nice and cleaned off / lightly scratched with 200 grit, the frame sitting all empty and what not waiting to get painted, and finally the rims which are coming out fluorescent green.
 

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Thanks for joining in NaSa! Ive read a bit of your posts about related stuff, and always nice talking to a fellow tech ;P I just got done reading one post where you guys were all talking about the zh-1 barrel being more torque oriented and i feel like the torque is acceptably strong but its hard because i have no other pockets to compare it with. It does get up quick, and i did replace the clutch/housing, however it still retains the stock flywheel/internals so stock rotating mass is there. Personally i think its more impressive to keep the stock displacement how it is and make max power out of it-nothing against bbks.. idk, they just almost seem like too easy and common of a way to get power, just not the powerband i want. I entertain the tuning aspect of all this. Do you guys happen to know the stock compression with this ZH-1 head (40.2cc)? Ive seen my bike referred to as an SQ bike the front does have SQ stamped with a long number following. Also when taking the bottom ring out it broke, but the top one is fine. I know mechanically it would work, but does anyone ever run them with one ring or is there just too much pressure loss? Worst comes to worst i just get a new set of rings haha. But i wouldnt mind trying one ring. The crosshatching in my head looks pretty good for what its been through so i think it should seal up fine..the rings appear to be shaped the same. My main concern right now is on compression. I need to get it and my spark perfect.. but i cant do that untill i figure out my air flow /ports or dremel work (i need a friggin' flow bench for this thing i swear..) and that leads me to---> ive seen too many kids online complaining after they 'port' (dremel to hell) their bike heads that they lost power one way or another, and only a few have i actually seen that look correct and like they would add some much needed air. Supposedly theres a guy on this forum who was cutting some ports out for people? I would be completely fine with doing it myself, i just ponder on how deep to cut them, how high up the wall i go, nd anything im missing. Sorry this is all So much at once ill try to be less scatterbrained :p Appreciate all your guys feedback, this is my first pocket bike. Heres some updated pics from todays work so far. Pics in order- jb welded my muffler back onto the exhaust, i know its not pretty its still drying-ill eat my shoe if it comes undone. Then painted the metal starter cover since im repainting the rest of it, got the rotors nice and cleaned off / lightly scratched with 200 grit, the frame sitting all empty and what not waiting to get painted, and finally the rims which are coming out fluorescent green.
No problem dude! at the bottom of all my posts is a link to "Setting your Squish" I would start with that, the how-to with the pictures will teach you how to measure and set your squish, this can be done using a thinner base gasket or no base gasket at all but some RTV gasket maker instead.

The desired squish number is .5mm or .020" in inches.
 

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A port is basically just being able to stuff more air and fuel on the down stroke. Here is a pic from an old thread about doing a simple small port. It should be the same height as the normal transfer ports and maybe 203mm deep???? Just make sure you dont go deep enough to come out the side of your head. If you do it properly and take yout time it should work out fine. I would proably recommend doing to small ones. I have heard adding more than that will give you less power or maybe even one bigger one.
 

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Just don't forget to set the squish first because you always want the bottom of the (Intake and Exhaust) ports level with the top of the piston at BDC (Bottom Dead Center) for maximum flow!

ps.

Those pictures are of adding a 5th port, also known as a boost port, one of the main reasons for a boost port is the "swirl" effect it adds / aides in mixing the fuel and air at the last possible time for better combustion.

Nick.
 

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Discussion Starter · #11 · (Edited)
Hey guys, thank you both first off because now its going to happen. You got exacly what im looking for! But NaSa isnt his pics of a 4 port? Or am i missimg something? 3 Intake port(s). To one Exhaust port? Good looking out on that reminder of the piston being at bdc. Im working with the dremel right now on the plenum. Hopefully this will help hold more air (between the carb and reeds) for a snappier throttle while cruising or at mid throttle, ill be so happy with that responce midrange in the transition to high end flow with the extra port! The plenum is not pretty, YET.. just getting the meat and potatoes at the moment and being ever so gently and sketched out that im gonnd poke right through the thin cheap metal casting haha. What do you guys think about finishes? mirror or semi fine finish . Ive heard arguements against both, but personally like semi fine finishes.. on 4 stroke motors that is.. these two strokes move air so quick that a mirror finish might be better? Got more of the painting done, its starting to come together.... :D
 

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I see intake and exhaust port or ports on the left and right and a boost port added on the bottom. You usually want to keep transfer ports in even numbers. 1 in 1 out or 2 in and 2 out. A boost port is usually a single added port.

In a way you are right. A boost port can be counted as an auxiliary intake port.
 

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Try doing the cheap triple stage reed mod or get carbon fibre reeds for lees high end flutter.
 

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Discussion Starter · #14 ·
I would love some carbon fiber reeds, ill have to see what i can do to get my hands on some. I dont know about the reed mod youre referring to Pocketbik but ill look into it! I did play with the reed setup a little. Before i get into that-- last night i was at a stand still with that cheap harbor freight dremel we had laying around and once the electrical problems started and bits broke i was ****ed! My room mate noticed and said were going to run to home depot in the AM - fast forward to this morning and he said go and get the biggest most inclusive dremel package they have, and its yours. I was dumbstuck. Extatic! The thing makes life stupid simple. I just didnt have the $2xx to drop on it. So i redid the porting on the plenum, i cleaned almost all of the casting flaws (doing so increases strength) anywhere i spotted one, and carefully shaped the reed cage a Tiny bit. It didnt effect the sealing of the reeds on the opposite side, but will help direct airflow incoming on the top end. I need to take some 220 then 2000 grit to the plenum still to get it how i want it. i feel if i remove any more metal from it ill be risking the structural strength of it (moreso than already). I also strategically ground the exhaust pipe a little but cant do much without risking grinding on the weld and thats a no go. Thoughts? It still has one piston ring and im going to look at possibly trying it and seeing if the motor likes it or if it needs more sealing. Less friction is always a plus :)
 

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That looks good. I wouldn't smooth the exhaust manifold, case, head, really any of the internals inside the engine or else the fuel sticks to it. I was told by a probably one of the most knowledgeable members on PBP to leave it rough. He said he goes over it with 100 grit sandpaper. Pocket bike parts Florida has Carbon fiber reeds for $10 and if you place an order of $100 you get free shipping. Here is a link to the triple stage reed mod I was talking about. It's called cheap reed mod for cag.

http://www.pocketbikeplanet.com/showthread.php?t=39770

I had the same problem with bits getting used fast so I went on ebay and and got 136x bits for ONLY $15. That's Canadian dollars so it would be cheaper for U.S. Plus I got some proper grinding set for actually grinding metal, called tungsten carbide cutter burr set (10 pieces) for only $15. Only bad parts is I just got to wait a few weeks to get them.
 

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Well the exhaust port can because you don't have to worry about the fuel sticking because there is none.
 

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A 5 port would have 3 upper ports and the side ports for 5. With 3 upper ports there is little cyld wall for the piston to ride on and it wears out a lot faster, it wears grooves up and down the top of the piston. Best is a wide 3rd port. I like a minimum of .600" wide to .750" on a third port. For some of what I call my Hot Rod engines I get a 2 upper port kit w/ cyld w/ copper head gasket, piston, rings, gaskets & an alum allow head. See them for $40 on eBay all the time. I cut out the rail in between the 2 upper ports to make one wide 3rd port. The new 4pc winged billet B/B kits all have 3 upper ports. Better to take that head and put it on 2 upper port cyld, stock or make one big upper port. PS: on a new engine you don't have full power till the rings seat and bearings where in, maybe 4 tank full of gas.
 

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Discussion Starter · #20 · (Edited)
EPR thanks for chiming in! Also read info from a few of your threads. So I think im misunderstanding a couple things and it kind of threw me off, so lets get a few things straight? The exhaust port which the pipe/muffler combo bolts upto is the ONLY exhaust port on the head were referring to (ZH-1). The two stock ports to the right and left of the head are Intake, stock from the factory (assuming it has no boost or other ports besides the exhaust). The boost port is also considered an intake port, and should only be open from BDC to (wherever the top of the stock ones also end) and NOT anymore past it, which could cause valuable pressure to escape the cylinder at the wrong time, right? EPR, can you clarify what you mean by upper ports and lower ports? After I read your post I was sure were talking about 2 completely different heads haha. I am thinking upper ports are the same as boost ports (like the pics Pocketbik attached a couple posts back) If they are different, what are the differences? Here's what I think of all this. 5 intake ports is too much (for my application as it sits) and in general doesn't seem worth the wear unless its a race bike that gets rebuilt often. Seeing as I don't know the stock CFM of this motor, compared to what it was when I got it from my friend (beat up but running descent), compared to now (having done dremel work) also comparing it to how efficient everything else is working together (carb/exhaust/compression/fuel mixture/spark plug temp/cyl rings/octane/uncontrollables), im going to play this one safe and wait on adding a boost port or alternate intake port. When I do though, it will probably be one wider one like EPR is saying- and not two smaller or skinnier ones. I really wish I could find my way to a flow bench with a couple ZH1 heads running different set ups, compare CFM at different rpm ranges and maybe even the swirl effect so we all have some kind of base knowledge to go off of. Has anybody done this type of flow testing with these heads already?? I couldnt seem to find anything about the flow (IN DEPTH) on these but it makes sense. They're inexpensive, cast, lesser quality than a nice one that I can easily get. But thats no fun.... :)

Also-

EPR, are the copper head gaskets worth upgrading to? Why do you use them on your hot rod engines? Whats your opinion on people running no gaskets and only sealant like what NaSa was saying a few posts ago? (easy compression bump)

Pocketbik, I think there was a small misunderstanding in how I said I ground some areas of my engine away. I am only removing (by dremel sanding bit) casting flaws where two halves come together or uneven edges, making them flush and nothing more. This increases the pieces strength. But what you said also makes a Very good point- and I totally forgot to factor in the 2-stroke oil! How thick the oil molecules are and how sticky it makes the mix. The person you're referring to is correct, we dont want the hydrocarbon/oil/air mixture to stick and accumulate against the walls (mirror finish) or in any particular spot other than the combustion chamber - we want it to kind-of float over the surface and tiny uneven edges. So thank you for mentioning that :)

NaSa, about the exhaust- I didn't make the Exhaust Port on the head any different, I was talking about the exhaust pipe flange/weld and how I put my finger in and felt the edge of the flange where it meets the weld. There was maybe a 1-2mm space around the entire circumference where I took my dremel sanding bit and kept going round and round the inside till it was meeting the weld. Stopped there because of the heat , weight, vibration and overall stress on it. I dont feel like getting the bike together, then having to buy and wait for Another new exhaust pipe to come in all cause I was a little careless with the dremel :p

I apologize again for talking your ears off! Please correct me if im mistaken
 
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