Top End Help

[caleb205]

here's my setup, I think: 2001 banshee, cylinders just back from the machine shop w/ fresh boring .030 over with wiseco pistons and stock head. banshee was given to me in pieces by my cousin. i do not know a lot of the specifics so it's been tough trying to put everything back together. i know this bike came from a gentleman who raced banshee's as a living. he quit racing and sold off everything he had. my cousin ended up with the guy's two personal banshees and all the parts he had left over (they were friends and he had a total of 5 banshees, 3 for racing, 1 for him and 1 for his young son) when i got the bike my cousin was trying to build a monster bike out of it and was installing a monster big bore kit. i wanna say he was making it a 540 but not positive on that. the cylinders were trinity 69.5 mm that he was putting on with matching pistons. i took all that off and went back to the stock setup bored .030 over. got everything put back together and now the pistons top out before it turns over. pistons just hit the head and stop. i'm guessing that it has a bigger crankshaft with a longer stroke that's causing this. my question is what is the best option from here? would putting a spacer under the cylinder fix this, or am i going to have to tear everything back apart and switch out the crankshaft? thanks for the help in advance.

 

caleb

[J-Madd]

Do you still have the big bore pistons and cylinders? I'd just run those.

[Wildcard2]

I know its alot of work but it will save you money in the long run to tear it down find out what the crank is for sure and go up from there. Is it a long rod or short rod? Is it trued and welded?Were the cylanders bored? What are the measurements on them? all of these things are important to the top end and set up. then you will know what pistons to run. what porting you need and domes and head. if you just keep changing out one part at a time your going to brake a lot of parts before you get the set up right. would rather do the time then fork out all the money at a guessing game. let us know what the crank is. these guys will help you all the way so no stress. good luck !!!!!!!!!!!!!!!

[blowit]

First thing to do is get the head off and measure the stroke by measuring the difference from the positive travel of the piston above the cylinder deck and how low it goes. This will tell you "stroke". Then measure the difference of the outer top edge of the piston to the top deck of the cylinder at TDC. This will help me determine what crank you have. Very possible we can get it going with some different pistons.

 

You do NOT need to tear the engine down just to determine what crank you have...

 

 

 

 

Brandon

Edited July 10, 2008 by blowit

[caleb205]

that's what i was hoping was possible. i'll start doing that tomorrow morning after i get home from work. if this helps i know that with the head off the piston tops out with the top piston ring traveling just right above the cylinder wall. when this happens it goes up just enough for the top ring to travel above the wall and pop open and then it's kind of tough to compress the ring to get it to go back down. i'll check the stroke for sure tomorrow morning though. i no longer have the big bore cylinders or pistons. i'm trying to get this bike back together that way i can start teaching my young daughter to ride. i know a banshee is kind of extreme but it was free and i was a banshee nut back in my teens when i had two of them and i don't really want anything to do with a monster big bore kit. pretty sure it would scare my daughter crapless. thanks for the help though and i'll try to get some measurements tomorrow.

[blowit]

that's what i was hoping was possible. i'll start doing that tomorrow morning after i get home from work. if this helps i know that with the head off the piston tops out with the top piston ring traveling just right above the cylinder wall. when this happens it goes up just enough for the top ring to travel above the wall and pop open and then it's kind of tough to compress the ring to get it to go back down. i'll check the stroke for sure tomorrow morning though. i no longer have the big bore cylinders or pistons. i'm trying to get this bike back together that way i can start teaching my young daughter to ride. i know a banshee is kind of extreme but it was free and i was a banshee nut back in my teens when i had two of them and i don't really want anything to do with a monster big bore kit. pretty sure it would scare my daughter crapless. thanks for the help though and i'll try to get some measurements tomorrow.

 

 

If you want, you can give me a call in the shop tomorrow and I can go over what you have.

 

Brandon

Mull Engineering

316-992-6984

[caleb205]

i checked real quick this morning when i got home and the piston stroke from bottom to top is roughly 2 1/8 IN. i check both manuals i had and couldn't quickly find a spec for the stroke length, though i'm almost positive it's in there somewhere.

 

Brandon:

i'm on third shift this week and work 12 hour days so after i get some sleep i'll try and give you a call if you'd still like me to.

 

thanks,

caleb

[dajogejr]

54mm is stock stroke length.

You can buy a 6 inch digital caliper, stick the end in the spark plug hole and 0 TDC and BDC....get the measurement that way.

[caleb205]

i'll do that this weekend. if i find that it's a longer stroke crankshaft what would be the easiest solution? i know they make pistons for stroker crankshafts that fit stock cylinder heighth. would this be the easiest fix? and thanks to all that have put in their two cents. it's been a definite help.

[caleb205]

retrieved some numbers off the crank and connecting rods to see if it may help in finding an answer. only numbers on the crank are 29L and 2. i believe this may be a stock crank. connecting rod numbers are C.K. 158. i'm lost here. the only reasonable explanation to me would have to a longer stroke. i'm not a total idiot when it comes to motors but i'm not a professional either and i just don't see any other explanation. i went and triple checked everything just to make sure i was explaining it to detail and the piston is definitely topping out on the head before it completes its 'stroke' once it tops out, the kickstarter just stops and won't go any further. once i remove the head it'll complete its stroke another 1/8 of an inch (which is where the top piston ring travels above the cylinder wall). i took the cylinders off to check for numbers on the crank and connecting rods and everything looks good (no burring, nothings bent or warped, no freeplay at all....looks great) i'm just throwing this out there to see and please feel free to let me know if i'm making sense here. if the piston is traveling roughly 1/8" higher than it should, wouldn't this make the stroke somewhere around 3-4mm longer than stock at 54mm? it's been a little while since i was in school but if i'm converting it right that should put it in between 57-58mm. i'm just guesstimating things here. i don't have any digital calipers at my house to get exact measurements, but i'm just trying to see if i'm heading in the right direction.

[blowit]

I don't care if you use a stick to measure as long as you do it accurately. Without confirmation at this point, I am thinking you may have a stock stroke long rod crank. NO, just because your piston is way high does not mean it is stroked. As I mentioned, you can get all your data with the cylinders on. You now need to put one cylinder back on and see where the floor of the transfer ports are relative to the timing edge of the pistons.

 

 

Brandon

[caleb205]

i understood all that. i'll do that first thing in the morning when i get off work. i'll snap some pictures of BDC and TDC and post them to visualize things and hopefully make things easier. thanks again to all.

[caleb205]

here are the pics to hopefully make diagnosis easier.

 

Bottom of Stroke

 

Bottom of Stroke, Exhaust Side

 

Top of Stroke, Top Piston Ring just above Cylinder Wall

[Wildcardracing]

Looks like you're running a long rod crank with standard pistons. just looking at the pics, but like blowit said.....we would need some measurements from the timing edge of the piston to the deck at TDC to be sure. If it measures @5mm then 795 series wiseco's will fix the problem. If it measures @7mm then you have a 4mm stroker with long rods and you'll need 795's and rechambered head or 795's and a spacer plate.

[caleb205]

alright did some measuring and found that it is a stock crank with long rods (5mm). thanks to those who helped me through this. i really do appreciate it.

 

on to the next question though: looked up the 795 series wiseco pistons and can't find the right size i would need. their website says they come in sizes 64, 64.5, 65, 65.5...etc. the pistons i currently have are 64.75mm. so what piston would i want in this case? and please don't tell me i'll have to have cylinders rebored to another piston.

 

thanks in advance,

caleb