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Post by 190mech on Mar 1, 2012 20:23:49 GMT -5
103 tech;; Ive been looking at those tiny transfer channels on my 103 jug and got to examining Brents old P90 jug and scared pistons and noticed a Big difference in the skirt/channel design;  Here is the 'shallow cut' skirt in jug and case;  Heres the 'deep cut';  Much better!But some added cutting to get a smooth'airfoil shape' makes it even better;  Here is my 103 jug with its 'shallow cut' piston;(note,look at the transfer channel in the case)  No sharp,non 'airfoil' edges should be anywhere as is here;  Here is the recut and 'airfoiled' piston;  Dont know if this will add tons of power,but it'll surely flow better!! |
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Post by oldgeek on Feb 10, 2014 19:55:42 GMT -5
I picked up a new 50cc cylinder kit to replace the stock YAMAHA one on the VINO. The porting on the new cylinder is very similar to the stock cylinder. However, the new piston does not have any ports in the skirt. Did they forget to put them in? I would think that since the cylinders are so similar, that the pistons would also match up.  |
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Post by oldgeek on Feb 10, 2014 20:50:52 GMT -5
The supplier describes it as a high quality kit from Taiwan. I paid a little more for it than the average 50cc kit.
I also just noticed the exhaust flange is at a slightly different angle compared to the stock cylinder.
Possibly I could just cut my own holes in the piston, but it may be more work than I think.
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Post by 2TDave on Feb 10, 2014 21:10:57 GMT -5
The exhaust mount angle was different on my Stage6 cylinder as well. I had to mod the stock exhaust bracket and then the C16 bracket to work. The second time around was much nicer.
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Post by usmcdoc on Feb 10, 2014 22:32:52 GMT -5
I recently made a post about this not to long ago...when I had noted that many were buying replacement piston kits for their cylinders...installing them and having a worse running engine than the worn out one they were fixing. I messaged a few and asked for pics of the new and old piston and saw the piston ports were different...which would explain why the engine would not run right. Piston ports are like cams in a 4 stroke in that the cam MUST be aligned properly for correct port timing..just as the piston and cylinder ports of a 2 stroke must be properly matched for correct port timing. I did lots of research and even contacted manufacturers of cylinder kits. While the English spelling and grammar were difficult to understand..it did explain a lot. I never posted more on the subject in the original post..cause few replied to the original post with input regarding how it affects engine performance..nor did many seem to care. Here is a link to the thread..read it and take a CLOSE look at the 4 different replacement pistons available for rebuilds. You will see huge differences in porting..that just like a 4 stroke cam...would dictate engine performance...and whether it would even run at all. Link-->> 49ccscoot.proboards.com/thread/7886/commonly-mismatched-partsIf that piston came as a complete cylinder kit..we could assume it was designed for the cylinder it came with. However with absolutely no piston skirt porting as your pic shows..it looks more like a Dirt Bike...Chainsaw or Outboard Motor piston style. Which is confusing. The piston you have is a 2 stroke piston I am sure because it has 2 ring grooves..vice 3 ring grooves that a 4 stroke engine does. Do you have a link to the kit you bought? A brand name..or any info on the kit? That would give folks something to look at and help you figure out if it would work for you. You will note that in 3 of the pics..the porting is of different size and in a different location..while the 4th pic the porting is not 2 holes in the piston..but a notch cut into the bottom. The 3 pics are replacement pistons alone...while the 4th pic is a complete kit I bought. Although the 4th kit piston porting is odd..it does match the cylinder it came with. Now imagine using one of the first 3 pistons shown in the pics..using the cylinder from the kit in the 4th pic..that only has a notch in the very bottom of it. See how they would mismatch badly and port timing would be way off? In the case of your piston..a pic of the top and bottom of the cylinder would be helpful..because while some Dirt Bike..Chainsaw and Boat Motor pistons do not have holes in the piston skirt..the cylinder itself has more ports than our Minarelli/Jog clone engines. If that is the case then the kit should work for you. But I have yet to see ANY Minarelli/Jog kits that had pistons with no ports at all. Other designs of Scooter and Moped engines do however. So maybe they sent you a kit for a Puch..Tomos or some other older model of engine?? Hard to tell with no pic of both the piston and a few views of the cylinder..  So if ya could..get some pics and post a link to where you bought the top end kit..  Glenn |
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Post by oldgeek on Feb 11, 2014 6:50:02 GMT -5
Glenn, I do remember reading some of the thread you started on that subject. I forget things so quickly! I will take another look at it. I took a look at various 50cc kits online last night, and noticed that many of the kits seem to have no piston ports. Here is a link to the kit I picked up. RacingPlanetI do understand it all depends on the design of the kit as to whether or not the piston has ports in it. What I find strange is the cylinder in this kit is so similar to the stock cylinder, I expected the piston to be identical also. I will try to get some side by side pictures of them posted later today. |
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Post by 190mech on Feb 11, 2014 7:00:56 GMT -5
A case reed engine does not really "need" piston ports as a cylinder reed setup..I doubt if much could be seen on a dyno chart comparison.The port angles and layout makes a big difference though which some cheap stuff has little of either!
Yeah,cylinder exhaust flanges vary greatly,it makes pipe building a real chore if you are building one without a cylinder in hand!!
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Post by 2TDave on Feb 11, 2014 7:11:56 GMT -5
Interesting stuff. I'd forgotten about 4ts having the oil ring. Why would a manufacturer port a piston if there wasn't a use for it? In the future would I be better off to have a new cylinders exhaust mount milled rather than cutting and drilling pipe brackets?
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Post by oldgeek on Feb 11, 2014 7:21:39 GMT -5
A case reed engine does not really "need" piston ports as a cylinder reed setup..I doubt if much could be seen on a dyno chart comparison.The port angles and layout makes a big difference though which some cheap stuff has little of either! Yeah,cylinder exhaust flanges vary greatly,it makes pipe building a real chore if you are building one without a cylinder in hand!! Thanks for the info! Seems to be a lot of secrets in the 2 stroke world  As for the exhaust flange dilemma would it be ok to cut the flange off of a tuned pipe, re angle it, and weld it back on or would that kill the pipe? |
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Post by usmcdoc on Feb 11, 2014 9:17:25 GMT -5
A case reed engine does not really "need" piston ports as a cylinder reed setup..I doubt if much could be seen on a dyno chart comparison.The port angles and layout makes a big difference though which some cheap stuff has little of either! Yeah,cylinder exhaust flanges vary greatly,it makes pipe building a real chore if you are building one without a cylinder in hand!! 190mech Thank you Sir! Input from you..Brent..2 strokd and others is invaluable as you are the guys that are known for building some real screaming monsters.. The broken English replies I got from a few manufactures explained that wrist pin to crown height was important to assure proper cylinder port timing and that not all pistons are a standard 25mm 'pin to crown' height..some they make are 25.5 and up to 26.2 which increase compression and changes port timing. In regards to the placement of the piston ports..some of what was said was unclear..garbled and confusing. Such as that how high or low on the piston the porting is..determines how much primary (crankcase) pressure is needed to make the engine run at its peak. That is why some of their kits run best with a stroker crank for more swept volume.. and some need a 'stuffer crank' as the 'stuffer crank' raises primary compression by decreasing the crank case volume. But here is what gets me..if they know piston to crown height and piston port position/size matters..why don't they state in their Ads.."May need base shims to achieve proper port tuning and squish band due to piston height. Also due to piston porting a Stroker or Stuffer Crank is recommended" I don't recall whether higher up piston porting or lower to the bottom porting was what they suggested the stuffer crank for or stroker crank..  I saved the emails in my Yahoo archives..but apparently it..or I lost them. Also just like you..I have seen some cheap kits where the cylinder port layouts and angles looked like they had been hand 'chopped' in there with a Dremel tool and the ports were at a different height and size than the ports on the other side.. @ 2TDave..I wondered the same.. Why would a company port a piston if there was no need for it. My old Hoca kit had long ports near the piston bottom.. I rebuilt it with an Ebay 'cheapie' piston with small ports up near the middle. Revving was low and sluggish..almost like a 'way too rich' 2T engine does. Power was was down and even Jet changes did nothing.. @ oldgeek..try to post some links to the kits you saw that had no piston ports..it would be interesting to see. Only ones I have seen like that were high end Athena and Polini kits. But at near $400.00 I won't be buying any of those unless I win the Lottery..lol.. Glenn |
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Post by 190mech on Feb 11, 2014 20:27:44 GMT -5
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Post by usmcdoc on Feb 12, 2014 8:33:01 GMT -5
Interesting 190mech! Piston porting on the YZ 80 does seem odd as my Suzuki RM250 does not have it. Speaking of which..I wish Wiseco made Minarelli BBK pistons like the forged one my RM250 has. Not only is the Wiseco forged piston durable..but whatever they make the rings out of is good metal. I used to have to re-ring the engine after every racing season..but not since the Wiseco piston kit. Here is a pic of a Hoca BBK I bought..and at BDC the piston ports align with the cylinder ports. The second set of pics is a DR kit with just a notch for the piston port..located at the very bottom of the piston. That piston port aligns with the cylinder port before BDC..in fact the only other port open at that time is the exhaust port..which is 1/2 way open and the transfer ports are closed completely. Why the different design..is confusing..making me think there must be a reason for the different designs.. See my next post as well..   |
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Post by usmcdoc on Feb 12, 2014 8:35:31 GMT -5
Now pics of the Dr Kit...notice the difference between the Hoca and the DR..   |
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Post by 190mech on Feb 12, 2014 9:31:51 GMT -5
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Post by 2strokd on Feb 12, 2014 9:54:16 GMT -5
If its a slow piston and cylinder, cut it till its fast!  |
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So if ya could..get some pics and post a link to where you bought the top end kit.. 
I saved the emails in my Yahoo archives..but apparently it..or I lost them.
