blowit

I know what he is talking about. The adapter just does not have the long reach threads like the spark plug because it is made for lawn mower type plugs. They also generally do not have a schrader vavle right at the tip and that is a big no no. The proper test adapter should show a nice bump in cranking compression. Brandon

VERY big difference in having the right compression tester adapter. You should pump up 135psi or so with the correct tester. That does not always means your motor is perfect, but sounds like you lack support there so run it till it blows! Brandon

^ :thumbsup: B

If you plan to keep it, be smart about it and open the engine and have it mic'd so you know. I and some other very experienced builders could probably give you a god idea just by turning the engine over but that is still a best guess. You call. 30 bucks in gaskets and a few hours of your time. Brandon

NOPE. You will base your rebuild totally on hours and use. NOT, on compression. That is the easiest way to a new engine. You can easily break a piston skirt while still pumping new compression numbers. See it all the time. Brandon

Did not mean to ruffle your feathers there. I would agree that even I have skewed from the original question but I think it was about V twins for some reason which has little relevance to a Banshee engine, I agree. Firing "order" obviously would not be applicable to a single or twin, but cylinder "phasing" is VERY important. By simply changing the Banshee from a 180* phased engine to a 90* phased engine, we will affectively change the way the power is delivered and completely change the power curve. The diesel was just an example of a 2-stroke design engine making good torque at low rpms. they absolutely can do it but must be tuned for it. Remember the first generation Polaris ATVs? Very low rpm, stump pullers, in an ATV! A YFZ will not be pulling too many stumps. I would even be so bold as to say there really are no draw backs from a 2-stroke in terms of power. It really just comes down to efficiency and emissions. If those two items are addressed, a modern 2-stroke can come back with an attitude. Brandon

Not going to shoot holes through all of that novel above but I will throw a few things at you. 2- stroke diesel.... cylinder phasing.... Port timing..... 2-strokes are far from gruntless. Also, compare the power made per liter from a good chain saw or weed whacker. Rather impressive number without an expansion chamber. Once you add more than one cylinder, One of the most critical things that determines an engines power curve is cylinder phase. Notice how all OEMs have their own flavor for firing order as well. Those variables have a large affect on how power is made and when. inline, 40*, 50* 90* 180* V twins, common crank pin, dual crank pin, they all make power differently. Also, more than one cylinder does not mean less revs/cylinder. Everything still sees the same speed. The larger benefit of multiple cylinders is reduction of reciprocal mass thus increasing safe rpm potential. Just a few thoughts I guess Brandon

Yes, in most cases, a set of pipes will allow a Banshee to jump higher, give the rider "perceived" larger balls, increase HP by 200%, allow a Banshee to do doughnuts, acheive the 20mph needed to hit the linked table top, and more!!! Sorry, just could not resist :biggrin: You might take notice though, that he IS wearing a helmet! Must have wanted to live to tell about it. Just needs to get other dude to follow suit. Nothing cool about flat melons. I do believe he was rolling stock shocks too. Ouch. DMC, hopefully you have upgraded by now. I think the first time I tried some triple rates, I took off and "accidently took a 15ft vertical and flat landed it. F%&$^*. I think actually thinking about the soil in my shorts while in the air but the bike landed without breaking both my legs so I was a happy camper :biggrin: Sold on suspension ever since. Brandon

huh ??

No, timing between a stock crank and 4mm crank are totally different when comparing on the same cylinders. The key word here is rod angle. Porting for a 4mm addresses not only timing issues but changes in cylinder flow from the stroker crank. At least when it is done correctly... Yes, you need to lose the plate. I strongly suggest you get an engine builder to look at your engine. Brandon

In my previous post, I sounded rather snippy. I did not intend that. I was merely stating what I needed to answer the question accurately. If your engine is apart y chance, we can probably get to the bottom of this. If not, I can still probably get close if you are willing to cc test your combustion chamber. You will have to remove a plug and fill the combustion chamber with test fluid at true TDC. With that volume and I go off your stated duration, I can work it from that angle. Any thing else really is just assumptions and since I cannot agree with your stated displacement vs ratio, I would not know which might be closer to accurate. Brandon

There again, I need to know how the CR was derrived. Is this CCR or SCR? Static or corrected? Is the trapped volume actually as stated? See, if I just adjust for that dome, I could have to raise that CR by two full points! See where I am at. VERY tough to ball park some of this stuff. Here is what I need: port height of exhaust, neg piston travel from deck to timing edge, piston series, total "test" volume of head, squish clearance, elevation, squish angle. Now I can help you. Without this stuff, I am going off someone elses data and it would only be a guess from my seat. brandon

I am sure there must be a catch in how your builder is accounting for the head displacement. The displacements are most certainly not inline with the quoted ratios. I also have no way of knowing if this is SCR or CCR but I am guessing CCR by the quoted duration. Some guys just make domes differently. Is this 21cc tested volume, 21cc trapped (calculated) volume, 21cc calculated total trapped volume, etc. Things that must be accounted for in a stroker are the above deck piston travel, and the dome piston dome displacement. I am sure with a little testing, you could get to the bottom of it. Just to answer the general question here, cranking compression has "zero" to do with the compression ratio. The ratio "is" what is important when building an engine. You are absolutely on the right track by asking about ratios and I commend you for doing so. The pressure on that little gauge is a "guide" not a "bible". Try this one, go compression test your weed whacker! They generally pump up around 170psi or more yet typically have a compression ratio around 6.5:1. That is a general statement keep in mind.... Point is, your compression gauge don't mean squat for building an engine but your calculator does. You gauge is helpful only to test the "condition" of an engine and that is still only one of many tests. If I only had a dollar for every person that said their compression was like new so the motor must be fine....... Brandon

I would like to know how you calculated that? Can you post your formula? Brandon

Much of the lag can probably tuned out with proper jetting. We typically lower the OEM needle and raise the pilot jet a bit to correct many of the issues. You would have to share your engine and pipe/carb/pipe setup to get you much more than that. You really need a head mod and advanced timing to help put more oomf on the bottom. Brandon

Just missed a Mod Quad shell on egay for 65 bucks. Grrrr

Looking for a used head shell. Don't want pro design. Don't need the domes. thanks.

We are looking for an ATV salvage yard that does a large amount of business. Any leads? Mostly Banshee stuff.... Reason we want a salvage yard is we want to buy a large number of items all at the same place to minimize our time input. Thanks Brandon

Not real sure what builder you talked to but I would be very concerned if someone advertises the same porting for a stock stroke and +4mm stroke. TOTALLY different! As mentioned , port timing and window verticals must be adjusted for the 4mm. Some guys get pretty used to doing one type of build and I am just guessing the guy you talked to has not done much in the way of stroker motors. Not saying he can't do decent porting but when you start changing things up like stroke, rod length, etc, you really need to apply the math to have a clue as to what is going on. Anything else is just a guess. may need to find someone that better knows stroker porting. Brandon

As unfortunate as it may be, you will probably have to get pretty verbal and bug them quite a bit to get anything done. My "first" course of action would be to get statements from real engineers or engine builders as to what caused the failure. I certainly see their point that the steel they use will be certified as such and would be extremely rare to have a failure from material deviations. The first thing I would want is a hardness test. This will not detail the type of alloy used but at least you can test in several places and compare to the other side to see if the temper is knocked out or if it is vastly our of harness range. I would say, unless you get technical with your research as to "why", they may continue to give you the run around. Brandon

In extremely high tune engine ( like karts) where absolutely everything counts, it has shown some gains, but i really doubt you will see any substantial gains from it in a multi cylinder engine. The theory is to aim the ground strap at the intake to shield the center electrode from "spark snuff" but really could be easily over come by a better ignition system. Because of the most modern combustion head domes, much flow at the point of combustion is very symmetric which would not matter too much with plug indexing. All in all, we have not done enough testing with this to know for sure but tend to lean towards "not applicable" to banshee or similar engines. Many sled motors utilize similar designed heads so I would tend to think they would not benefit from the idea either. Brandon

A defect is certainly possible. Careful inspection of the pieces by a professional should determine if there was truely a defect in the material. One thing to look at closely is the flywheel. Out of balance conditions can cause extreme vibrations and radial forces on the crank. I really doubt the crank got hot enough to actually break. That would be DAMN hot and the bearings and other surfaces would be showing it like charred oil in the crankcase from that. I would get an engineer on the phone from them and send them pics of the situation. If it is truely a defect, they need to know about it anyway. Brandon

Yes, a 7mm will work but must be done carefully and correctly. We will not do a 10mm crank on stock cylinders any more because they just suck compared to the cub motors from lack of transfer volume/flow. ie, you can't feed it very well. They also suffer big time from port timing being way out of the bubble for optimal performance. In our opinion, the 7mm is the largest sensible crank for the stock cylinders. Brandon

Not entirely true. The engine will rev to the limit but will have no power there without mods. If you whack the throttle in neutral, you "will" find the rev limit rather quickly. brandon

You are fine. Run it.... Even with stock ports, your CCR is still in the green. With porting, your CCR will drop a bit so give it hell on 93. We have plenty of them on the sand with a similar setup without problems. Brandon