Compression on Banshee

[859davidt]

Anyone know the compression spec for a Banshee? It has spark, new plugs, but won't start. It has 90ibs in the left cylinder. I have not checked the right yet.

Originally posted by 859davidt
Anyone know the compression spec for a Banshee? It has spark, new plugs, but won't start. It has 90ibs in the left cylinder. I have not checked the right yet.

90psi is tired. A healthy JUST rebuilt banshee will be in the ball park of around 125-130psi per cylinder. 110psi is where it starts to get a little tired but still strong.

Once you hit 100 you should rebuild it. Like anything, you can still ride it like that, but mid-range will be pretty much gone.

[beakerlsc]

mine had 190psi in both cylinders last time i checked it

Originally posted by beakerlsc
mine had 190psi in both cylinders last time i checked it

You're probably running like 19cc domes then in your cool head. Stock is no where near 190.

[beakerlsc]

yeah i have no clue what domes are in it

[rdstoner]

how many times should i kick my motor to get a compression reading?

Originally posted by rdstoner
how many times should i kick my motor to get a compression reading?

Just hold the throttle wide open, and keep kicking it over really fast until the gauge stops moving. It takes a decent amount of kicks but not an exact amount.

Just real fast until the needle in the gauge stops moving.

[greenskin77]

190 i just rebulit my top with new pistons and rings hones the jugs runs like a champ.
i have 406 vitto 4mm 5 mm stroke bored 80 over. now i have a cool head but dunno the dome size but was told it was next to last for race gas becase i dont want race fuel ..
but even now i only have 120 commpression even before rebulid thats all i had
what can i go up to before race gas like 150 commpresion or so ? i have timing plate set to plus 5 rite now ...

Originally posted by greenskin77
190 i just rebulit my top with new pistons and rings hones the jugs runs like a champ.
i have 406 vitto 4mm 5 mm stroke bored 80 over. now i have a cool head but dunno the dome size but was told it was next to last for race gas becase i dont want race fuel ..
but even now i only have 120 commpression even before rebulid thats all i had
what can i go up to before race gas like 150 commpresion or so ? i have timing plate set to plus 5 rite now ...

21cc domes are the smallest you can go on pump. Some people get away with 20, but most I know with 20 had to run race gas.

I believe 21's will put you around 145-150 if im correct. I don't know how it will react with advanced timing though..

[greenskin77]

ok i was just wondering about it i mean i like to get more well i would think it shoud have more maybe my commpression tester is bad
and the timing never chaged the commpresion i just put it on like 3 months ago .. wish i did it sooner it made a real low end differnce.

With stock compression domes on a fresh rebuild you should have about 125-130. My compression tester sucks and was really cheap, and it reads 100 whenever I do mine. And my cylinders were bored by passion racing with brand new wisecos. So My tester is about 25-30 psi lower reading.
So yours is probably fine.

Timing won't change compression, it simply just advances the timing. Makes it fire a little sooner for a better fuel burn.

[greenskin77]

well i went ut and bought a new good commpresion tester it has the o rings and all for a good seal.
and still yet both cyclinders on the shee i have 120 perfect both sides. i even have thn gaskets on the jugs were i am soppse to use thick ones that come with the storker kit i should even have more now in commpresion.. i just wonder if my cool head has the bigesst dome there is in it and the guy i bought off of lied about it to sell it ..i mean 120 come on now thats a stock shee i am 80 over stroked and long.. should i go get the domes.. if so what size before race gas 19 i think you said correct ,

[hondamancbr03]

Stroked and long rod has nothing to do with compression, it's all about the squish and CC's......19cc doems are the border between race and pump. My first Banshee ran 19cc domes in a cool head and i was getting 165. Keep in mind that with a two stroke, yo uhave to kick like a mother to get a close to accurate reading on compression.

[greenskin77]

hmm, i always thought the longer stork more compression i learned something new just now .. yea i had to kick a few times even with the 250r i had to kick a lot.. 165 you had. hmm well i bet my domes are way big but i am going out there now and try this again and kick it untill my foot gets blisters lol.

[hondamancbr03]

Deck height and CC's make up the compression, port timing can add to this as well but for the most part you should look at deck height and CC's to start with.....As for the Dome size, you need to take into consideration your piston size. If you have larger pistons they will take in more volume during a cycle, so with larger pistons 19cc domes would require you to run race gas when a stock piston and stock deck height banshee could run race gas with 19cc domes.
There are some really interesting articles on two stroke compression that you should read if you're into learning about the two strokes......If interested let me know and I'll post one for you.

[greenskin77]

yea post that site if you dont mind i will read up on it .
but you lost me when you said both a stock and a bored out shee with 19cc domes would both run the same commpresion and use race gas if i understood you rite.
well i went out and kicked and kicked and kicked and it did get 140 out of the shee but i read on here i can go up to 190 before race gas is this correct if so i ll probly change my domes some said they are stamped on the dome the cc .. i will check it out
oh i checked the othe shee wich is stock and it has even 120 all around .. so the gauge is correct

[hondamancbr03]

Look at it this way...If you have 19cc domes and two different size pistons, one piston (larger one) will bring in more volume due to size and compress that volume in the 19cc area, when a small piston while obviously compress a smaller amount in the same area. with 19cc domes being right on the edge of having to run race gas, i would run at least 50/50 with a .80 bore.

Your compression is too low for the engine you described...

Who built your engine? What base gaskets did they use? I assume you have a spacer plate under your barrels for the 4mm crank. Is your head 0-ringed or stock style gasket?

[greenskin77]

ok i understand the piston size and commpresion deal..
i didnt bulid the bootem end not sure who did i bought it this way ..
its a o ring cool head
gaskets under the jugs are just standered banshee gaskets. wich i have recntly read that i need the stroker gaskets so the jugs will stand up futher and give more mid to topp end and line up the ports..( this would make commpresion even lower i would think )
barrels ? you lost me there the jugs ?
ohh and i no for sure its a 4 mm i oreder the pistons and the number on topp said everthing i neede to know and it is stamped on the connectin rods to .

[hondamancbr03]

Yes barrel/jugs......

Do you have any two stroke shops in your area? When you start talking about lifting your jugs, you will be adjusting the port timing and how the power comes on. How does the bike feel the way it is? Does it bog on the bottom or pull hard from bottom to top?

As for your other post about plugs......The right plug is very important. Plugs have heat range numbers that you need to learn so you put the right plug in for your gas and riding style.

[greenskin77]

yes the plug heat range i do no about .. but i thought i ask anyhow..
well really no 2 stroke shops here they all work on 4 stroke and they try to work on 2 the same way so really i do not trust them . i will get advice somtimes just like on here and few times they streed me wrong .
well the kit recommends the big gasket for the jug wich i probly will be getting here soon.
the way it runs is amazing i cant see no dead spot in it at all if i had to pick it woul dbe the low end it studders littil more than i like it to before it hits the band
the reason i say this is my stock she studders to like all shees do but it so littil you barly notcied it .
here somthing i meant to say and keep forgetting .. i have otrs removed and idel screw in the side of carbs well use to be half way in it idel fine now the idel screws is all the way in pretty much just to idel and the air screws still work .. maybe this has something to do with the thin gasket or not ...

[hondamancbr03]

The studder could be a jetting issue....Do you know what your jet size is? You are running close the same engine i have in my play bike....What is the elevation that you ride?

If you plan on keeping your bike and working on it yourself i would suggest learning about port timing and jetting...Lifting your jugs will affect the bottom end power and cause the bike to have a dead spot....4mil long rod motors are great torque engines but you can take that away by giving it too much port timing.

I'm going to dig up a couple web sites to send to you....Nothing better than knowing how to work on your own machine better than the local shops.

[greenskin77]

ok thanks i will read up on it.. lititl reseacrh never hurts i am always doing my own work... i had 3 shees before this one and i rebulit my first one when the cranks seals went out so i did it all from bottem to topp and it still runs today thats been 5 years ago.
anyhow i no dummy with wrenches i work on it all. you might have me worng my bike now i had about 5 years now and never had a porblem with it except for rings once n a while and it get ran hard all summer 2 times a week. but thwe commpression this got me ... so i always want the peak profamnce cant have to much power lol..
this shee is only one i havent tore into the bottem yet hopefully wont have to ..
yea send those sites i will check em out ..
oh my carbs are stock wich i no is killing it
jet i no main is 330 and pilot is i cant rember rit eoff hand ill have to check it out.

[hondamancbr03]

Sounds like you know how to work on bikes......Just do a little research on deck height and CC's and you'll figure out what you want and what you should have.

Here's a website that is well known and a good source for imformation on compression and engine port work.
Do not lift your jugs until you know for sure that's the answer to your compression problem.


http://www.macdizzy.com/

[greenskin77]

hey thanks for the help thats a good site i saved it..
but i just now took my cool head off the shee and guess what i found the stamping on the domes and they are 22cc thats why compression is low i ll probly order the 19cc now..
but i noticed my new pistons i just put in not 2 rides ago the one had pits in the topp it didnt effect the compression but the pits i dont like probly means piec of ring already broke off.. i might leave it in i not sure yet.
but i am not going to space my jugs i looked at the piston hieght and it dosent come up out of the jug that much just a hair i not sure what 2mm looks like but i say that is what is coming up out of the jug at tdc. so i ll porbly lave the jugs there maybe... depending on what the 19 cc makes the moter do ...
never ends does it lol....

[hondamancbr03]

Can you take a picture of the top of the piston with the pits? Do you have feeler gauges? I would be curious to see how mch your piston really comes out and measure the depth of the cuts in your head......The pits can also be from pre-detonation, if you can show a picture it would help.

Figure out your deck height and the depth of the cut in your current domes before buying a new set of domes.

[greenskin77]

sure i need you addy i dont no how to post them on site yet..
and i am still looking for my feelers

[hondamancbr03]

Sent you a PM

[greenskin77]

ok sent i dont belive it is pre detontion i mean even the dome has pits but i could be wrong i never had pre det. before so i couldent tell u what it looked like.
well i did have a piston like melt like rubed real had with sand paper around the edgde until it was gone and rite dead in the center.. i belive it was to lean that was way back tho....

[greenskin77]

hey there i was thinkg and did some research .. and before i bumped up my compression tp 190.
what i have read was more commpression takes away the life of the crank some say yes some say no ..
my theroy i say it would be harder on it .... but how much harder are we talking i mean if it last 5 years now at 140 commpression if i go to 190 it last 4 years i would do it but if it only last 1 year at 190 then no it wouldnt be worth goign to 190..
i dunno i am just thinkg out loud here...

[hondamancbr03]

Keep in mind that 190 will require race gas, and not alllow your engine to rev as high....More of a bottom end engine with higher compression. But it will add HP.

As with any motor on the planet, more HP means more heat, which means less life....How much less? Can't answer that, i can say that i ran 165 for 4 years before needing to rebuild. I'm happy with that.