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Posted by: LT80
Strokers have been tried. I have one sitting in the drawer. BR>This weekend we raced against against a VERY reputable LT80 motor builders stroker. The speed down the straights was the same. My 82cc motor (+.05 over)was in front of it.The stroker was under a more expierienced and older rider. My rider has been to 2 TT's and is 8 years old. So I'm not convinced that it's worth it.
FYI::For 2mm, there is no case work in volved, it clears.
Try it! Nothing ventured nothing gained. BR>Why would you have to make your own rod (rod length don't make the stroke different)? The position on the crank halves is whats changed.
Posted by: LT80
I don't know how much the other machine was stroked. He said he noiticed a difference with it.
How are you going to raise the cylinder up that much? Make a plate?
Posted by: LT80
Oh yea! I've lightened the flywheels. It surely helps. BR>The reed cage thing:: This surely can be improved on, but no easy way.I've heard of modding a KX60 cage for the LT.
Posted by: LT80
Your correct on the size of carb to cage thing. I used to think that the 20mm was too big. Then I build this Eton and the guy sends me a 28mm (and the cage to go with it). So I go to the Mossbarger site and they say the 90cc's can indeed handle 28mm.
So for us, it's getting a cage that will not restrict like the stock one.
Good thinking
Posted by: LT80
All night long I've been thinking about this rod length thing.
I understand why you want to build your own rod for the knife-edge trial, but The length of the rod +/- I don't understand.
Are you thinking longer or shorter? Either way that don't effect stroke. What am I missing?
What's 1mm equall in thousandths? (I think I know this but I want to confirm)
Posted by: LT80
OK, finally got time to answer BR>Flat piston: I'll take your word for it on this one. I've thought of lathing a piston flat, but I feel it would be to thin. I haven't looked into another piston that has the same pin size and location.
Head and spark plug: You will not have any trouble here.The LT80 head modded has plenty of room for the spark plug.Understand now that we allready are running a B8HIX plug instead ot the BP style. The P means protruded and is for stock, low rpm machines. It's protruded design is made to keep the plug clean.That's why their for stock/lawn mowers/etc.
I'll PM Dstroyer on how to make a head. You are correct, the squish band is very important.Some ppl think the squish band means the clearance between the piston and head, it's not. A wide squish band is better.
Compression will not change because it makes compression from the exhaust port up, and this isn't going to change because of the stroker.
Bubba's explaination of Xmm up and Xmm down is why I thought 2mm was sufficient. I feel that the only porting difference will be in lowering the transfer openings and the bottom of the exhaust port to allow the stroker to do it's thing. I point the transfers, not nessesarilly raise them. I've learned that the farther you raise the transfers(past a certain point) it makes the machine slower.A simple way to look at this is: transfers open when the piston is 1/2 way down the exhaust port.
What Dstroyer is refering to is the "exhaust scavenge" To bring in more fresh fuel mix is the objective.
As far as re-sleeving, no. I haven't seen a reason to. I have the tools needed to do my work with it in place.
Asfas,, I agree w/bubba. Your smarter than you think on all this
Posted by: Bubba297
Jack, 1mm is equal to .03937, or roughly .040 as most like to round off.
Posted by: Bubba297
OK, set back and think about this. When you stroke a crank, you are actually just moving the rod big end outward on the crank web just half of what the total stroke will be. If you are going to stroke the bike 6mm, then the piston actually goes down farther 3mm and up farther 3mm. So you would only need a spacer and gasket 3mm total. When stroking a Banshee 4mm, you can get the spacer for the base, or you can get a head gasket spacer for the top of the jug. The later of the 2 is more desireable for most people as it keeps the port timing to more acceptable levels. With the head spacer I have matched the port bottoms to the piston at the bottom of the stroke and done what was needed to get port timing correct. With the case of a 2mm stroke for the LT, I wouldnt see any problem with using a spacer plate for the base, as you would only need .040 to get everything lined up. That would probably work better because you get more crankcase volume too. If you go a lot of stroke be sure the piston ring end gaps dont get into port openings and cause a problem.
asfasasu3, dont confuse a long rod motor with a stroker. You can use a long rod with a stock stroke. The piston pin is relocated to keep the piston height correct. When going long rod, in most cases, it is helpful in 2 ways. The rod angle is improved and the side loading of the piston is actually reduced becasue the pin is farther up in the piston. That frees up power. The second big thing is that your dwell of the piston (how long it stays at the top of the comression stroke) is increased by a fraction of a second and promotes better combustion and power. Hope this helps,Bubba
Posted by: Bubba297
Quote
Originally posted by: asfasasu3
asfasasu3, dont confuse a long rod motor with a stroker. You can use a long rod with a stock stroke. The piston pin is relocated to keep the piston height correct. When going long rod, in most cases, it is helpful in 2 ways. The rod angle is improved and the side loading of the piston is actually reduced becasue the pin is farther up in the piston. That frees up power. The second big thing is that your dwell of the piston (how long it stays at the top of the comression stroke) is increased by a fraction of a second and promotes better combustion and power. Hope this helps,Bubba
Bubba, I understand the longer rod desire. I've been around long rod and stroker motors in drag cars for years. The rod length does effect dwell. But in most cases not enough to tell even on a dyno. The biggest reason for running longer rods in those motors is to reduce the angle of the rod and reduce side friction that it creates on the piston. (and it also adds alot to the strength of the rod) Kinda like the knife edging. It helps in motors when the rods have to "cut" through the oil in the pan. (although alot of top builders don't like to use rods like that, they would rather use crank scrapers) The dwell is most effected by the stroke, not the rod length. I'm sure rod length can come into play some, but from what I've seen from professional engine builders is, its not enough to really factor in. (maybe in NASCAR where every 100th counts) I've had to study camshaft design in school, and if I remeber right. The larger the base circle the longer the dwell at bot tdc and bdc. The reaction of the piston will slow down as the stroke increases, meaning, as it reaches the top, the slower the piston will move. This also happens at the bottom, in which in the case of this 2 stroke, will hold the ports open alot longer. Looks like just changeing the stoke would result in about the same thing as raising the ports and making them wider. (wider coming from holding the open longer)
I thought you said you were an idiot??????img src="i/expressions/face-icon-small-wink.gif" border="0"> I re-read your last post and realized you were talking about side load from the stroke increase instead of rod length increase. Sorry about that. I think for those that look for every last ounce of power those things all do matter. For me....... well maybe not worth the time or effort although I do like pittling(?) with things.Bubba
Posted by: SANDMAN430
seems like a lot of money on something they out grow so fast we us the 80 for bathroom runs now. but we have found a new form of racing adults on the mini's
Posted by: SANDMAN430
oh that makes a lot of difference, i thought you would be into it a 1000 bucks
Posted by: madracing
2mm stroke. around 500.00. case work crank work and stroker plate
Posted by: DStroyer
Has anyone in here ever tried a stroker crank for an lt80? Im going to give it a whirl here soon. My sons 80 finally pooped out here with the last round of porting in the cylinder. I thought, this time around, Im going to make this thing sing. Ill split the cases and see what length we can go. Ill have to make my own rod with knife edges. So, I was wondering, has anyone givin this a go yet, and if there is anything I should keep in mind?
Gary
Posted by: DStroyer
Thanks for the replies,
I own a CNC machine shop, so the work is not a problem. The only cost I will be the gaskets to put it back together. I realize the kids will outgrow the quad, but my son will be on it all next year. I wouldnt be doing this if he wasnt.
Gary
Posted by: DStroyer
Lt80,
There are 2 reasons for the possible new rod. First being, Im not sure how much stroke I can increase it until I get into the cases. 2mm is not worth the effort. It will probably be 6 mm minimum. With that size stroker kit, I will need to add to the length of the rod also, since the cases wont allow enough clearance. 2nd reason, I want to add the knife design to the rod. This has been proven on tons of adult quads to be more effecient, so I want to try it out on this mini. The stock rod doesnt allow for that feature without drastically weakening the rod.
If you were racing someone with a 2mm stroker kit in the 80, there probably shouldnt have been that much difference in speed. JMO.
I just picked up the new cylinder, it should be here by the weekend. I will get rolling on this project once it gets here. I have a couple of ideas with the porting I would like to try.
Gary
Posted by: DStroyer
Yes, Ill make a plate and add it under the cylinder. While Im in there with the cases split, Im going to take a really close look at how the reed cage sits and its flow into the cylinder.
Jack, have you tried lightening any flywheels yet? I just finished a friends Lt80 flywheel the other day. That Lt pulled harder off the line than it ever has before. Huge difference. Im not going to list the weights here, because of all the work I have done to it. He has a very mild motor, but now it revs very quickly. He entered his first harescramble race and stomped the competition. I was expecting to see a loss in power somewhere, but it didnt seem to have any down sides.
Gary
Posted by: DStroyer
We are thinking along the same lines. If the cases are apart, the mods are easily done. Personally, from using the 20mm keihin carb for awhile now, I think the carb is too big for the reed cage, even ported. When I make the changes, I will try to incorporate a more effecient cage into the mix. I may even go back down in carb size to get a higher velocity instead of volume.
Gary
Posted by: DStroyer
Hey guys,
Sorry it took me so long to respond, work has been hectic.
Jack, you are correct on the rod length thing. I went back to the research about this and you are right, you dont need to lengthen the rod. It would cancel itself out if done. Good catch!! This is why I posted it in here, to get feedback on this. As for how it works on a 2 smoke. My opinion, , the more volume of fuel and air pulled into the cylinder with vacuum, means more power. The stroked crank will do just that. I may have to play with the transfer and intake port height a little, but personally, from what I have seen, it is not going to affect the cylinder compression. For a 6mm stroke, you would add a 6mm plate under the cylinder, less a base gasket height. The head will not have to be changed since the piston is still coming to the top of the cylinder as if it was stock. Although, to bump the compression up to where I think it should be, I will drastically change the head design. You are correct about altering the spark plug length due to altering the combustion chamber. I will most likely run a shorter plug, since the plug will be drastically closer than stock. Im even looking into fabing my own piston, based on what Ive read about the flow of F/A flows over the surface area of the weisco piston with the rounded dome. It does not seem to be efficient. The flatter the piston, the more effiecient it will be. Take the CR125 piston for instance. They run about 160 psi cylinder pressure stock. So, I think getting a better squish band is a priority to get more ponies. I would just copy the weisco piston, accept add a flat surface on top.
Jack, do you agree about the piston theory? Also, have you resleeved any cylinders yet?
Gary
Posted by: DStroyer
Thanks Bubba,
I apprciate all the info. Its going to take a few tear downs when this is done to get it right.
Gary
Posted by: asfasasu3
Things to keep in mind hu? Well for starters, I would suppose that you would have to have the crank welded up and then turned back down. Unless you have the equipment to do this, take it to someone with a very good reputation for this. By the way, this will cost alot of money!! Next you will have to watch the piston positions as it moves up and down in the cyclinder. In 2 strokes, this is where the timing comes into play. I have no idea how to figure all that out to make it run as good or better than stock but I;m sure theres people out there that can help you. Also remeber that you'll have to get a custom piston made. (another iteam that can be very costly) Make sure you check piston to deck clearance. You don't want to have that custom made piston hit the head a gernade before it evens starts. I geuss if your making a new rod, then you could use the stock piston. Just watch the timing of everything.
Posted by: asfasasu3
Ok, I know as well as most on here do that I'm an idiot. So here it goes anyway.
How does the stroker crank work in a 2 cycle? It would appear to me that making the crank swing 6mm or what ever, father down and farther up would change things very drasticly. Would it not bring the piston down and uncover the ports alot more (6mm to be exact) and also for alot longer of a time. In whinch it would loose a tremendous amount of compression and waste unburt fuel? Then theres the up stroke. I realize your talking about spacing the jug up, but would that not make the ports open thing even worse? Would you raise the jug 6mm? If you did, would you not still have to mill a tremendous amount off the head or sleeve? (to get the compression back up) In which case, I know you could reshape the head, but you would also have to do something about the spark plug wouldn't you. I mean changing the combustion chamber that much would really mess up the burn from the plug, would it not? Plus the plug length would also come into effect wouldn't it? Then theres the rod ratio. I know how knife edging works, but wouldn't the added friction on the piston to sleeve wall, from the piston being pushed sideways from the longer stroke, be alot more than that of the rod swinging through the gas/oil mixture. (then again maybe it would offset each other)
DStroyer, I am very glad there are guys like you (and Jack) willing to go the extra mile and spend the time it would take to try and figure these things out. I hope you can get this thing together and give us a ride report some time soon.
KEEP UP THE GOOD WORK!!
Posted by: asfasasu3
asfasasu3, dont confuse a long rod motor with a stroker. You can use a long rod with a stock stroke. The piston pin is relocated to keep the piston height correct. When going long rod, in most cases, it is helpful in 2 ways. The rod angle is improved and the side loading of the piston is actually reduced becasue the pin is farther up in the piston. That frees up power. The second big thing is that your dwell of the piston (how long it stays at the top of the comression stroke) is increased by a fraction of a second and promotes better combustion and power. Hope this helps,Bubba
Bubba, I understand the longer rod desire. I've been around long rod and stroker motors in drag cars for years. The rod length does effect dwell. But in most cases not enough to tell even on a dyno. The biggest reason for running longer rods in those motors is to reduce the angle of the rod and reduce side friction that it creates on the piston. (and it also adds alot to the strength of the rod) Kinda like the knife edging. It helps in motors when the rods have to "cut" through the oil in the pan. (although alot of top builders don't like to use rods like that, they would rather use crank scrapers) The dwell is most effected by the stroke, not the rod length. I'm sure rod length can come into play some, but from what I've seen from professional engine builders is, its not enough to really factor in. (maybe in NASCAR where every 100th counts) I've had to study camshaft design in school, and if I remeber right. The larger the base circle the longer the dwell at bot tdc and bdc. The reaction of the piston will slow down as the stroke increases, meaning, as it reaches the top, the slower the piston will move. This also happens at the bottom, in which in the case of this 2 stroke, will hold the ports open alot longer. Looks like just changeing the stoke would result in about the same thing as raising the ports and making them wider. (wider coming from holding the open longer)
Posted by: asfasasu3
Bill, I don't claim to know alot about this either, but I am a draftsman by trade. And if you really think about it. The crank turns in a circle. So the centerline of the bore is lined up with the center line of the crank. No matter at what angle the "V" is, it will be directly above the crank. The reasons for making it a "v" is to shorten the overall length of the motor.
Posted by: asfasasu3
I"m with ya Bubba!!! And I really appreciate (had to look that one up) what these guys are doing. My hats off to them and all like them. I have kinda made our LT a hobbie in progress. I read everthing I can about these things and have tried alot of them. I'm a gear head at heart, but I don't have the funds, time or equipment to tackle some of this stuff. (although thers not much I wouldn't try) Dstroyer asked LT80 if he had resleeved any of these lately. I have done this just last month to our LT. I was waiting on parts and decided to give it a whirl so I could clean up the ports better. Is it any wonder why I ask so many questions on here? I'm always trying to put our stuff back together!!! LOL!!! Like I mentioned before, I hade to study camshaft design in mechinal drafting classes I've taken in the past. (for those wondering, crankshafts fall into this group) And this is something that really sparked my interest.
Posted by: elraptor02
it shouldnt be that expensive it you have materials and a cnc shop
Posted by: STUARTFAMILYRACING
I know I'm way over my head in this thread but I've got a question? asfasasu, would the geometry of the V-8 engine design have anything to do with the "rod design/piston sidewall friction" question? I didn't know if a piston positioned directly over the crank would have different characteristics than that of one in a V block.
Bill
Posted by: STUARTFAMILYRACING
I see what your saying. The only force that would affect it would be gravity.(The weight of the piston laying against the cylinder wall) That would really be nitpicking - wouldn't it.
DStroyer, I want to know all about this little monster when you get it going.
Thanks
Bill
