| Author | Message | ||
     Benm2 |
I've been looking around for Buell pistons, and I haven't been able to find any lightweight "slipper" type pistons. Does anyone know of any, or know why they aren't made for the Buell engine? | ||
| Rick_A |
What's a "slipper" type piston? | ||
| Mikej |
I can't get to the Wiseco web page from here for some reason. Steve is talking about slippers a little on another thread currently. | ||
| Benm2 |
slipper pistons have no skirt on the sides of the pistons the piston rod goes through. Also, in these areas, there is a minimum of aluminum below the oil ring. they're lighter. If you've got the time, ducati has got a pdf file available for engine upgrades on "classic superbike" that shows some pretty pictures of them. | ||
| Jrh |
omegapistons.com...in "piston data"shows a photo comparison of what Bens referring to.The wiseco+JE Buell pistons i've seen are the so called "pot"style. | ||
| Pammy |
Wiseco makes the piston. The slipper piston as a VERY short skirt. I have a set of 88" inch Wiseco for sale, already coated. $283.00 for pistons, rings, wrist pins and clips. As stated before the skirts, such as they are, have been power-coated. I can e-mail a pic if anyone is interested. Or if I can figure out how to post one, I will. | ||
| Pammy |
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| Rempss |
Buell slipper style pistons here. Skirt is not coated though, I sure would. Dry-film lubricant, apply it at home - Techline. (DFL-1 on skirts) Jeff | ||
| Featheredfiend |
Slippers have been around for many decades. In the past they were considered an option for a street Harley that would not see much mileage. Reason being, the abbreviated skirt allows a greater chance of piston rocking in a long stroke motor, leading to cylinder scuffing. I avoided using them for this reason. Maybe the coating addresses this. My choice would be to reduce weight from the flywheel rather than the piston. Feathered | ||
| Budo |
I used the Hurricane pistons from Brain Nallin. They look great and 12k miles later seem to be working fine. | ||
| Benm2 |
Pammy: Thanks, but I don't have the cash for the REST of the 88" conversion. Jeff, thanks for the info, is millenium still around? Can't find a website for them, although American air cooled still seems to have one. All, why aren't the Hurricane pistons slipper-type? Are they designed for more "long term durability"? Are near-stock bore slipper pistons available from wiseco or elsewhere? | ||
| Pammy |
I've got customers that have been running them for over 30k miles. | ||
| Rick_A |
I never knew there was a name for a piston like that. I've wondered about the wear issue, too, but everyone I've talked to about it says basically what Pammy said...it's not an issue. The main reason for the Wiseco's design is that they're forged so the material is heavier...and they remove material in non critical areas in order to keep them the same weight as stock. About the only good thing about cast pistons is they have less expansion when heated and can generally be run at closer tolerances..and they're cheap! | ||
| Blake |
Rick, How much more dense is an aluminum forging versus an aluminum casting? Which alloys are you talking about? Does that apply to all forgable and castable aluminum alloys? How much less is the coefficient of thermal expansion of an aluminum alloy casting verus a forging? Is that uniform in all directions, or does it depend on the orientation of the forging's grain?  Blake | ||
| Featheredfiend |
I ran hi-comp forged pistons, though not slippers, in my bagger with good results. I took a little care in initial warm-up with the extra expansion characteristics of forged. The engine used no oil between changes and the extra piston noise reminded me of past shovelheads. Not a bad thing. A little nostalgia with a modern(for a Harley) design. If one is running a matched weight(to stock)forged slipper piston I can see no advantage other than somewhat less friction. Doubt my rear dyno could tell the difference between stock and slipper unless one was a higher compression. Feathered | ||
| Socal |
Here is the coated piston from Pammy.  | ||
| Rick_A |
It's just how 'tis. I don't know the exact stats...and don't need to know...they vary between manufacturers. A same volume of forged aluminum will always be heavier than cast in pistons. For obvious reasons a forging will always have a denser grain. Most all cast pistons have a high silicon content that further lessens the expansion. Any piston is tapered and elliptical when cold...regardless. The crown is always smaller than the skirt, due to it being the hottest point, and the skirt is always the widest point, perpendicular to the boss, because the piston boss absorbs more heat. It's hard to see in a big piston, but if you get a hold of a little 'un it's readily apparent. So a forging, having a denser grain and thicker wall...lacking the silicon content...will naturally expand more than a cast. When you buy/install the stuff the manufacturer(s) tell you what clearances to run. Knowing the exact stats seems pretty anal to me. You'd be hard pressed to find it any other way. Anyway...think of the above if you ever take off on your vehicle without warming it up! | ||
| Stormfool |
Having some experience hot-rodding aircooled engines (VWs) I can say that they do indeed have a different expansion rate. I believe it is because of the density--more material to expand. Hypereutic (silicon impregnated alloy) aluminum is the norm forged or cast because of its wear characteristic. Did I spell that right? Likewise I am curious (banal not anal) about the relation between grain and expansion characteristics of forged materials under rising heat. My instincts tell me that it would tend to expand more along its length (i.e. with the grain).At what point does the metal cease to expand? Any metallurgists out there? My idle curiousity hungers for factoids. Are teflon buttons used as well? I know this is common in automotive slipper pistons. Pammy, any reasons for using slipper pistons? Is it just to reduce reciprocating mass? | ||
| Rick_A |
Teflon buttons are just another way of securing wrist pins. They are a little more expensive and the most secure. I haven't heard of any forged pistons using silicon in their alloys. The forging process would destroy its properties. There's 3 grades of silicon imbedded pistons...and they all pertain to cast alloys... Hypoeutectic...less than 12% silicon content Eutectic...12-12.5% Hypereutectic...12.5% or more | ||
| Pammy |
Slipper pistons= less weight, less drag. Clips instead of buttons for weight as well.So you can use shorter(lighter) pins. Sorry metalurgy and quantum physics and the like are beyond me. You'll have to talk to Blake about that. | ||
| Rick_A |
There's a very simple way to look at it...the denser and thicker it is, the more molecules there are to expand...anything further than that...I don't know. | ||
| Stormfool |
Thanks for the clarification on the alloys--forging destroys the silicon? I could have sworn those forged pistons I used were made of hypereutectic. I'll take your word on it. | ||
| V2win |
I had my bike on the dyno the other day doing some fine tuning. On the last run, I had the rear piston break. It is a Wiseco, 3 13/16 flat top that comes with the Millennium cylinders. (Short skirt, slipper style) If I can get a picture of it, I will post it here. It broke the ring land off where the relief for the intake valve is. We ran the engine up to 6500 rpm. 109.? hp. and 101 torque. I am going to change to forged, regular skirted pistons and then finish tuning the beast. Happy trails, John | ||
| Hootowl |
Stormfool, Hypereutectic pistons are always cast. Eutectic means that the metal has no plastic state. The quicker the metal makes the transition from liquid to solid, the fewer casting flaws there will be. They are almost as strong as a forged piston, and they are more thermally stable. | ||
| Imonabuss |
V2win, That's a classic failure, and it means the valve pocket was too deep. Were they standard Wiseco Pro Thunder type ones, or were they relieved for more cam? If you put in any piston with the same valve pocket to ring land spacing, it'll happen again. | ||
| V2win |
These were just the normal Wiseco 10.5 to 1 pistons that come in the Millennium "Kit". That area is the weakest part of the piston because of the valve relief but I can find no good reason for the failure yet. There is no evidence of a detonation problem that I can see. That jug always made a little more noise than the front one after we installed the big cylinders. I am just going to get some good forged pistons and start over. I may have to send the jugs back to Millennium for a little hone job. I wont know until I get the pistons in hand and measure them. Sh!t happens John | ||
| Rick_A |
I've been looking at piston manufacturer sites...and what I gather is that forged can withstand high temps and detonation to a higher degree and duration...and they won't shatter like cast during a failure. It seems that for any special application...nitrous, turbo, blowers, high compression, etc, a forged is the way to go. As far as most normally aspirated street applications a quality cast piston seems to be ideal. They have better wear resistance, too. | ||
| Pammy |
Most of the time that type of damage happens when ther is a 'too lean' condition(fuel curve too lean on top end) or possibly some detonation that went unnoticed. The 'slipper' pistons would have nothing at all to do with that failure. | ||
| V2win |
deleted by V2win | ||
| V2win |
I finally got a pic of the Wiseco piston that failed while on the dyno. It is a 3 13/16 bore that came with the Millennium cylinders. I now have a set of Nallin pistons coming for the engine. I thought some might want to see it.  | ||
| Steveshakeshaft |
Hmmm, there isn't a lot of "meat" (cute engineering term!) between the inner of the top ring groove and the outer of the valve relief is there? A small defect in that area would (IMHO)definitley contribute to a premature failure. If that Wiseco piston was a standard product, they've just gone down in my estimation. Pammy, might we not see some damage along the edge of the undamaged valve relief if that was detonation damage? (Melting, Pockmarking, Loss of edge definition?) Just my 2 cents. Regards Steve http://www.ukbeg.com steve_s@ukbeg.com | ||
| Rick_A |
Detonation failures usually look more like erosion and are most often on the exhaust side. |
