Cut pistons or not

[Spidy]

Ok guys, this is prolly a simple question and may have been asked before. Since my cylinders are ported and polished, does one need to cut the piston windows to match the cylinder porting? Reason I am asking this is... I'm assuming when a piston is made it is also balanced. The guy I had doing my building tells me the pistons need to be cut. Would this not wack the piston out of balance causing abnormal wear and tear on the piston and cylinders?

[Spidy]

Have blown up my Banshee 3 different times. Mind you it wasn't the same right hand cylinder all 3 times. The first time it happened I had just bought the bike. Figured, ok shit happens. Had it rebuilt and ran it for 2days and blew it up (right hand side again). Took it back to the builder, he gave me the run a round about my fuel mix being to lean. We argued about it cuz my buddy was running his kow on my fuel so I know that's not what happen or the kow would have been dead too!!

 

2nd build using my cylinders again ran for about 25 minutes and blew up the right side piston. Also trashed the crank this time.

 

3rd build was the HotRod 4111 crank (5m long rod 4m stroked) 2 new cylinders ported and polished. All this time were using Wiseco pistons. I'm sure they were stock in the first 2 builds. On this 3rd build using the HotRod crank we had to use the 795 Wiseco pistons do to the long rod setup. Ran fine a couple weeks, we even went out and drag'd it one Sunday, just beat on it keeping up with the bigger boys and there big carbs. (Mine are stock carbs lol). Went to ride with some friends the next Sunday... 15mins and blew a hole in the right side piston.

 

4th build is waiting for me to buy another set of 795's or some HotRod Stroker pistons designed to work with the HotRod crank. Before I put it back together I would like to hear some of your thought on what caused this issue. The only pieces that stayed the same in my story was the carbs and intake boots. I cant see any cracks in the boots but I bought new ones to install when I put the bike back together this time. I'm assuming an air leak somewhere..??? Will do a leak down test on it when I put it together. Thanks for any input!

Edited November 9, 2010 by Spidy

[tripledsracing]

sounds like your carbs aint big enough or fubbed up!..i would say air leak maybe but blown up 3 times id say fuel issue if its burning holes in the pistons...you are doin air leak test after you do the rebuilds?..

[Larry's Shee]

More info needed. New seals on new crank? Did the pistons melt down or did they shatter. Were new pistons in fresh bore? Leak down test? Was head on blow up side in good condition? What did the plugs look like? Lean oil mix would most likely smear piston on cyl. Also list other mods ,carbs , jetting.

Edited November 9, 2010 by Larry's Shee

[Rodneya]

Ok guys, this is prolly a simple question and may have been asked before. Since my cylinders are ported and polished, does one need to cut the piston windows to match the cylinder porting? Reason I am asking this is... I'm assuming when a piston is made it is also balanced. The guy I had doing my building tells me the pistons need to be cut. Would this not wack the piston out of balance causing abnormal wear and tear on the piston and cylinders?

 

Getting a bit off topic here.

If you cut your pistons, don't expect them to last too long. If it is not a drag only bike, I would not advise it.

 

And for the other guy who keeps destroying pistons, you need to read the Banshee jetting FAQ and fugure out what lean means.

[Spidy]

 

Here is a pic of the right side piston. The left side looks brand new still. Does it look to you guys that cylinder ran lean? I'll get back in here later and list all my mods that have been done.

Edited November 17, 2010 by Spidy

[J-Madd]

 

Here is a pic of the right side piston. The left side looks brand new still. Does it look to you guys that cylinder ran lean? I'll get back in here later and list all my mods that have been done.

 

 

Hell yeah that was lean. Air leak or stopped up carb. Most likely air leak, though.

 

As far as cutting the pistons; I really don't see the point. The top of the piston opens and closes the ports; I don't really know what the windows are there for anyway. I've theorized that they are there to get more lubrication on the wrist pin, but I don't know for sure. I know that lots of big motors don't run any windows - but maybe the longer stroke gives more time for the incoming fuel/oil to lub the pin??? Just a guess, though.

[bansheesandrider]

Hell yeah that was lean. Air leak or stopped up carb. Most likely air leak, though.

 

As far as cutting the pistons; I really don't see the point. The top of the piston opens and closes the ports; I don't really know what the windows are there for anyway. I've theorized that they are there to get more lubrication on the wrist pin, but I don't know for sure. I know that lots of big motors don't run any windows - but maybe the longer stroke gives more time for the incoming fuel/oil to lub the pin??? Just a guess, though.

Really? How about the windows are there to let the intake charge into the CRANKCASE, as all 2 strokes do. The top of the piston only opens and closes the exhaust, transfer, and if it has them, some boost ports. Unless you had a slipper style piston, the bottom if the piston would never get high enough to open the intake ports. As far as balance is concerned, most Banshees are out of balance anyway, because the forged Wisecos do not weigh the same as stock cast pistons. As long as both pistons weigh the same it is not going to really matter. If you go to The Two Stroke Shop's website there is a post about how out of balance a stock Banshee is. I used to run hand lightened Wiseco pistons with the windows matched to my intake ports. Then my builder closed up shop, so I started running the standard ProLite pistons and I did not notice any real difference in my mild build.

[J-Madd]

I'm just sayin my 16 Cheetah and 16 Twister don't have windows in them; and most builders say they're not needed (on those motors.) Maybe the longer stroke lets the charge in under the piston (instead of through windows.) I thought even on a lesser stroke the piston went high enough to let it in under, but havent had one of those apart in a while. If it doesn't then of course the windows are to let the air/fuel into the crankcase.

[sheefreak]

I would not be cutting my pistons. If there is a gain, it would be in tenths of horsepower.

 

And you most definately have a lean condition on the right side. Need to do a leakdown on every build you do. Would have saved lots of money here.

[alcoholbanshee]

I would not be cutting my pistons. If there is a gain, it would be in tenths of horsepower.

 

And you most definately have a lean condition on the right side. Need to do a leakdown on every build you do. Would have saved lots of money here.

 

 

I have no piston windows on my 10mil Twister........................seems to run good to me.....LOL

[J-Madd]

Piston Window Info

Ya'll got me thinkin about the piston windows, so I tried to do some research. Not a lot of info to be found, but the link above gives a couple of opinions on them.

[AKheathen]

lol, it's simply the type of induction they made them as from the factory. there is piston port induction, crankcase induction (pretty much all 2-stroke sleds) and forced induction. if the port is low enough that the piston is out of the way long enough, then you really don't need windows. it's a very common known mod to trim the pistons on a crank induction setup for more flow. it is, however a plain and simple trade-off of performance vs. piston life. when you trim, the piston is allowed more rock, which increases wear, which increases rock. so, basically, it starts to wear sooner, and wear rate increases as it wears..........now, windowed pistons, on the other hand, solves this problem...for the most part. a windowed piston allows for a much longer piston to be used, without the added weight, or intrusion. the trade off, is structural integrity. it's like building a load-bearing wall in your house. you trim it, and you have more walking room. or, you take a section out of the middle, and can walk right through, but it holds less load. porting the windows is like using 20"-24" on center studs, instead of 16" it may work and hold just fine for a while (i've seen it) or it can mean the difference of an earthquake bringing down the house or not, not to mention every time someone slams a well-built door, it shakes pretty good....i digress, lol......basically, a ported piston can let go and explode without warning, especially if it's not done by a pro. that being said, there are builders that know well how to do it in the most reliable manner, like where to take material off each brand and modle piston, that gives the best gain and takes the least integrity out......now, forced induction......simply the best option for 2-stroke power, minus the oil burning. been done for years, but, it was usually complicated since you need a supercharger to even run, which lacked top-end, so there was a setup which used a compressor that opened up to allow the turbo(s) to charge at higher rpm's....

[Spidy]

Alright I bought the bike and it was basically stock. It had a dirt digger clutch in it, TR-6 pipe set (Toomey), spacer plates on the intakes. That was all I could see had been done.

 

Things I have had done....

 

Bored 1mm over so its a 65mm (due to damage done on the first blow up)

 

Cylinders have been ported and polished (did this on the 3rd build)

 

HotRod 5mm Longer Rod, +4mm stroker crank HotRod part #4111 ( this on the 3rd build to cuz it trashed the stock crank)

 

795 series pistons Wiseco

 

Head work: the domes custom machined for the 2mm clearance instead of using the spacer plate... because adding the spacer plate between your cases and cylinders raises your port height. (true or not idk...???)

 

Stock carbs ( Mikuni) Pilot jet is 27.5 Main jet 390 Center notch on the needle (Cleaned Many Many Times!)

 

Uni pod filters

 

 

As you have read in my first post above, I have consistently blown up the right side... The left side burns excellent, never any trouble with it. Same set up in the carb as in the right. I don't understand how it can burn correct one day and blow up the next time I ride showing Lean. I run 92 gas and Klotz Super TechniPlate mixed just a hair fatter than 32:1 Blows my mind.

 

Anyway just waiting for pistons to show up. Got new intake boots to put on. Couldn't for sure see if cracks went all the way threw or not. the right side looked worse than the left. I could understand a leak there if looked like it was cracked threw. Better safe than sorry I guess, besides it's one of the things I haven't replaced yet. The pocket book can't do carbs yet so that has to wait for now.

[bansheesrtoys]

i have almost the same set-up but i'm running 310 mains, at 32:1 , i heard more oil is not good,because the oil doesn't fully burn off the piston and keeps building up and not allowing the gas to cool down the top off the piston like it should.i have 19cc domes but i run a spacer plate, next year i want to port and have domes cut. 100race gas,v3 reeds, reed spacer,toomey2;1 with k&n filter, stock carbs,intake.with t5's, my plugs look perfect, and my banshee runs great.