Piston and manifold mods with pixs

egjsc

egjsc

New Member
Hey guys, I picked up these tips on this form and just thought I would post some pics of the work I did including beveling piston skirts(for increased oil film on cylinder walls), ramped exhaust top side of piston for better exhaust evacuation, trimmed intake skirt to match intake port size, and ported the intake and exhaust maifolds to match port sizes. I was going to ramp the transfer port sides of the piston too but i spilled a tiny bit of water on my cheap dremals speed regulator so it shorted and would only run at max rpm.. I didnt feel comfortable using it at that speed so well see if a few days time may dry out and work again. If it doesnt ill prob soder a new regulator on it. Engine runs very well lots of mid and top end power. Im using a gt5 jug with bannana pipe, thunder cdi, Sha clone 15mm and matched cases with dax bottom end assmby. I have a 40tooth sproket and once i hit 30mph the engine starts to viabrate which is weird because I thought the dax balanced crank would take care of that. Its definitely smoother than it was stock but I still have atleast 1/2 throttle more I am unable to use. Im thinking a lighter wristpin and better needle bearing and lighten up my piston might help? If you guys have any tips on helpn smooth out the higher revs so i can use the other half of my throttle id be happy to give em a try.

Also I parked and locked my bike up today out side of walmart while i was grabbn some eggs, i walked out the store and a guy carring a bike caught my eye. Some guy apparently cut my thick cable lock and was trying to run off with my bike. My blood boiled I snuck up 10ft behind him and yelled"Hey mother**cker im going to **ck you up!" He whipped his head around and threw the bike down which then REALLY got me going. He was pretty over weight but he got so scared he took off running faster than any guy that size should beable to run while he was screaming "They made me do it! My friends made me!" I kept yelling and cursing at him, luckly i was able to think the situation through for a split second and decided its best to let him go because i was so reved up and i had a knife with me i always carrie when im out in town and didnt want to do anything stupid i would regret later.(fyi my knife never left my pocket) sooo.... anywho i ordered a huge u-lock and also a loud bike alarm. NEVER USE CABLE LOCKS NO MATTER HOW THICK THEY ARE!Get a u-lock! Well that was my day hope you guys had a better one! Ride safe and hope you gota kick outa my story!
 

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Not bad on the piston, intake, and exhaust... It does take some practice, but I've seen a lot worse...
A few things that'll help even more would be to get a shorty intake and open it up on the inside to match the venturi diameter of the carb, the stock intakes are only 13mm on the inside so even putting on a bigger carb won't help performance very much, but there are some shorty intakes on ebay that can be opened up, and there are some aftermarket ones that are already open enough to take full advantage of the carb.
The banana pipe is ok bet it's designed to run best at rpm's these engines just can't reach, and they also have a very small and restrictive stinger so they're also restrictive. You can wake one of these up by cutting it so the outlet is atleast 16mm or more, 1" on the outlet is about as big as you would want to go. On the other side, you can cut the flange off but leave enough metal on the flange to weld in a section of steel pipe, then use a section of silicone hose the same diameter that's about a foot long, then take it for a spin, then trim it down until it hits where it'll work best for you and weld in a section of steel pipe to replace the silicone you were using for experimenting.... It's probably easier and more practical to get an SBP pipe or snake pipe and be done with it, but if on a really tight budget, the banana pipe could be modded to work a lot better.

The piston looks good and you cut about the right amount off the bottom of the skirt for better intake duration, the ramping on the exhaust looks ok, but should taper in about 1/2" and be about 1 to 1.5mm lower than the rest of the top of the piston at the exhaust port. Once you get your dremel going again, ramping the transfers down the same amount will make a noticeable difference too. You'll get the best torque increase tho by widening the actual exhaust and intake ports. Just going 1mm wider on each side will make a noticeable difference, raising the roof of the exhaust 1 to 2mm will also make a noticeable difference but the power will come on at a higher rpm if you take off too much from the roof. For the transfers, just getting rid of that casting ridge on the roof is all that's usually needed, you don't want to raise the transfer roofs, but can ramp the piston at the transfer openings. Then knife edge the transfer openings at the bottom of the cylinder, this really helps. I go a lot further with porting the transfers but don't mess with the actual openings inside the cylinder, they're really good where they're at, and raising the roof any could really kill off the power because they could open before all the exhaust pressure is bled off... not good... But you can get a bit more power and smoothness by removing that casting ridge.
For the head, I don't know if you messed with it yet, but shaving off at least 1mm from the gasket mating surface will give you more compression and a good boost thruout the rpm range, just use a sheet of sandpaper on a glass surface and sand it down until at least 1mm is taken off, this will also help with head gasket sealing since these arent very flat right out of the box. Getting a Puch or Fred head will also help with compression, but also help keep the engine cool as the stock head doesn't do a very good job keeping a performance engine cool.

Anyway, good work so far and if you need to know anything else on how to make it fast, just ask.
As far as your engine vibrating, it could be a mounting issue as you want the engine mounted solidly to the frame with no rubber spacers of any kind in between the engine and frame. The more solid and rigid the engine is mounted to the frame the better and most if not all the vibration you're feeling will go away. These engines also tend to have a lot of vibration when new and it'll go away as the engine breaks in as well.
 
Good info thanks for the reply. I dont quite understand what youre saying abt the 1/2in thing with the piston ramping i did on the exhaust side top side of piston. Do you mean i should start the taper 1/2in in towards the center of the piston from the edge?( I feel like this would decrease combustion area thus reducing compression.) If so how wide should the tapered area be? Does the same 1/2in thing apply for the transfer sides of the piston if i were to ramp them? I was thinking the same idea for the pipe too! Great minds think alike has some truth to it i guess! I can tell the pipe is lacking punch especially down low and years I spent modifing gopeds when i was younger i learned lengthing the "header" will increase the low-end effect of the pipe. I might just get an x-port because its easyer but then again there is more money down the drain that could be towards the sbc plus i doubt the x-port will lengthen the pipe enough to put the power where i want it. I was going to chop the stocker and use that tubing to lengthen the new one, but good tip on using the rubber tubing to test it and get the power where i want before welding it. I accually did feel the tip on the bananna pipe did seem alil too small and restrictive when i blew through the pipe when i first got it. I wasnt sure if the restriction was due to the tip size or if the baffle looking part of it used some sort of chambering(kinda like the stock one) that restricted it or if it was restricted like that so it ran better(which i doubted because its from china and cheap and im almost certain they didnt do any tuning/testing on the pipe before production) Im more than likely going to go with the sbp pipe. I feel its one if not the best pipe for the money once i can afford it. I may just try to tune this one in alittle better while im waiting though. If/when i do ill post results with pics for everyones info.
I did mount the engine with a piece of bike inner tube between frame and mounts(not folded or doubled up). I do have the upgraded front mount with the thick plate and dual u-bolt design.. The engine does not move when trying to push the cylinder head side to side while holding the bike frame steady. Do you feel this would be causing the viabration im feeling when the engine is at higher rpm? To re-emphisize i feel like the engine is over revving, its not soo much of a physical viabration although there is a specific rpm it exponentially gets worse and I hold throttle a few hundred rpm below this point when cruiseing(about 30mph) but im only at half throttle when at that speed. Im going to try getting a polini wrist pin herd they have a large inner diameter so they are lighter and also a better needle bearing both and see if that helps.
 
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Also, what do you mean by knife edging? Im not clear on what this process involves. When you say to widen the intake and exhaust ports, should i widen them all the way through to the piston opening side of the ports?
 
Ok i get the idea of knife edging.. thanks. Already matched up case and cylinder trasfers too. One of the first things i learned from reading on this form to do that would make an an improvement
 
You got the right idea on the 1/2" thing, the idea is to give a very smooth transition to the port so more air can move in or out... I do most my work with the dremel but switch to a flat file to straighten things up and finish with fine sandpaper. Same applies for the transfer openings. When I say 1/2" tho, it's a rough estimate, but 3/8" to 1/2" would be a good tolerance here. For widening the ports I'm talking about the sides and not the roof or floor. Raising the exhaust roof by 1mm is beneficial tho, then ramping a piston to see how much further you can go before you lose power or until you feel that "happy medium", measure how far down you ramped, then cut that amount out of the exhaust roof and put a stock un cut piston back in. The only way to increase transfer duration tho without effecting the blowdown would be to ramp the piston so my newest engine has transfer ramps but no exhaust ramp.
I think you got the idea of knife edging so no need to explain there...
And for the engine mounting, take the inner tube sections out and just mount it nice and tight, take it for a ride and you should feel the difference... even the slightest movement on the mounting is enough to give the engine that "running start" to hit the frame and over time it can cut thru frame tubes... There's a lot of discussion on this in here as well.
For the exhaust, you're right, these X pipe headers are a waste of time and money unless you just like the way they look, they're just too short to make any real difference, but may come in handy if making a custom exhaust setup, but that's about it. If you really want a good custom pipe and money's not a problem you could get an expansion chamber from Treatland and weld it to Fred's Fire Breather header or use his Kx fire breather adapter, this is one of the best exhaust headers out there for making a custom setup. Otherwise, the SBP pipe works great. I made my first pipe out of a KTM 50 pipe that was cut up and the bends re clocked until it fit, but my new builds are getting kx 65 pipes. Even on the 50cc KTM pipe, the stinger is almost 1" diameter so there's no restriction there, and this is one of the bigger factors for top speed. Even with a straight pipe the bike can hit some impressive speeds once the restrictions are gone. As far as modifying pipes go, cutting up pocketbike headers or cutting the bends out of a stock pips end welding into your setup is an easy way to get the bends you need, same with an old set of handlebars, they're good for harvesting bends from and old Harley or other big cruisers wil usually have the 1" bars.
 
Right on, i will try removing the small piece of inner tube that i used and ill let you know what happens. Im also going to fire up the dremal and see if giving it a few days to dry out helped the issue with regulating the speed. If it works ill probably widen the intake and exhaust ports and ramp transfer sides of piston, ill post pics when i do. I have a new cylinder and piston set on the way so ill beable to play around alil more aggressive with the dremal and find out how much material i can remove until the performace becomes negitivly effected. I love the idea of the kx65 pipe and the use of small cc dirtbike pipes. Im an avid dirtbike rider as well, the design and performance of the exhaust systems on them seem far superior when compared to any motorized bike exhaust. I would toltally go down that route if my welder didnt get stolen from me. I bet it would sound pretty sweet with the silencer and im sure the power curve would be amazing once you find the best pipe/silencer combo.
 
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