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Author Topic:   piston failure
street31
Dirt Roller

Total posts: 12
posted October 30, 2005 04:31 PM  
has anyone experienced pulling the pin out of hyper pistons. this is the 2nd time i have done this 6900 rpm max .100 dome 383 with darts 18 nites on new pistons, are these weak or rpm limited? my buddy runs a super late and did the same thing with a J.E piston only his was at 8500 thanks Rick

fast_crew
Dirt Forum Racer

Total posts: 100
posted October 30, 2005 05:41 PM  
Hypers are known for that. aka Hyper-explosive. Suprised to see that on a J-E, (depending on bore/stroke combo). For your combo a Set of J-E SRP pistons would work very well. Trie to stay a way from Hypers or TRW forgings(Very Heavy)

Josh K.

zeroracing
Dirt Forum Champ
Total posts: 1894
posted October 31, 2005 05:58 AM  
You over reved the bottom end. If you go to the toolbox there is a piston speed calculator.
Alot of piston motor failures come from passing a "Critical speed" for the piston, The speed overal is dictated by rpm and stroke. The speed your actual piston can safely run is dictated by the material used, and the design of the piston, weight of the piston influences it also(which is part of the material/design).
Once you pass your critical speed then your asking to what I would call "pull the pin". Which is overwork the piston and yank the pin out the bottom. For a decent forged piston(name brand) should be turned a max of 5000 feet per min, this is kinda a rule of thumb to try to be safe.
For your combo your piston speed at 6900 is 4295 feet per min. But (no offense meant) the cheap material used in your pistons, leave them with a lower speed than a regular forged one. You might be able to call the manufactor and get a speed that they were designed to operate under, but I they might inflate thier numbers some.

Your friend had JE pistons, but were they flat top, also were they custom super light or something, or regular domes that are still pretty light like most people use.
Your friend had a speed of 5291 feet per min, so he passed the 5000 line by quite a bit. So I would not be suprised by it.

I agree for your combo something along the lines of srp or the mahle flat top line seems like it is nice(I think they have about a 450-500 price area setup). I prefer flat tops, becaues of lighter but that is me.

An example is a short stroke motor like 3.260 has a piston speed of 4599 at 8500, and hits the 5000 mark at about 9240.

Get some better pistons and good luck, and keep it under 5000 for your 383.

jason


street31
Dirt Roller

Total posts: 12
posted November 01, 2005 07:27 PM  
piston speed means what? and who sets these numbers? and what should my rpm be? rick

zeroracing
Dirt Forum Champ
Total posts: 1894
posted November 01, 2005 08:17 PM  
Piston speed, is how fast the average speed of your wrist pin is going.
These numbers are set by the manufacters, and by experience of alot of late model engine builders. You might be able to call the maker of the pistons, and they might tell you the actual speed that you should stay under. I am not sure of the actual equation that would be used, but It would have to involve the wrist pin material, the modulus of the piston, the design area of the section around the pin, below the pin, the weight of the piston itself. There are probably about 100 factors that involve coming up with the speed that you should stay under.
But for most good pistons 5000ft/s is a good rule, and for a heavy or hyper... piston the speed should be kept lower.

To think about it, the piston is going back and forth, and all the force of crank pushing from the bottom, and the force of the combustion pushing down on it from the top. The going back and forth, and forth, so as you can imagine as the speed increases the pull push on the pin area gets worse and worse. Until yank it out pretty much.

[This message has been edited by zeroracing (edited November 01, 2005).]

street31
Dirt Roller

Total posts: 12
posted November 07, 2005 04:05 PM  
I am confused if the piston is exploded back down the hole the pin is being pushed against the top of the piston pin bore and as it goes just past bottom dead center it is once again pushed up into the pin bore, so explain how it pulls the pin away from the piston , also can you tell me what lets say a piston speed of 4500 is in RPM ? just curious to find out,I hope it doesnt translate to something like 5300 rpm because that will not make any power at that range unless it is a 434.

street31
Dirt Roller

Total posts: 12
posted November 07, 2005 04:18 PM  
I went to the chart and did some number comparison and my stroke 3.75 with good pistons would be 7900 so you are saying it is safe to turn a 383 that RPM? how many 383 engines turn that rpm for 18 weeks and stay together? 38 years ago when i started racing i would turn stock engines 6500 all season long without failure with cast pistons and rods How was that?

Normal Sullivan
Dirt Full Roller

Total posts: 45
posted November 07, 2005 10:20 PM  
Need more info. What brand of pistons were you running? JE's? The only time that the piston pin should have a great deal of negative-load would be at TDC on the exhaust stroke. I'd be looking at crank twist, or ill-fitted piston pins, a rod with oiling problems, something like that. Same cylinder both times? Even a cheap cast piston should not fall apart at 7000 rpm.

[This message has been edited by Normal Sullivan (edited November 07, 2005).]

street31
Dirt Roller

Total posts: 12
posted November 09, 2005 04:41 AM  
I tend to agree with the fact that a cheap cast shouldnt fall apart at 7,000 these were speedpro hypers with 18 nite since new and my buddys was JE dome 355 but his were in a super late with oliver rods, crower crank and at 8500 wow! he had the best of everything and the guys he races with turn 88-91 all season long with out failure .

sc1 racing
Dirt Freak

Total posts: 426
posted November 09, 2005 09:55 AM  
who did the block work? sounds like a bad line bore.

oceanridge motorsports
Dirt Full Roller

Total posts: 29
posted November 09, 2005 03:37 PM  
How did the top of the piston look ? valve train interferance ? detonation ? maybe something from on top of the piston caused the forces that cracked it , and it just came apart at the wrist pin because that was the weak spot ? To much timing , bad fuel ? You and your buddy buy your fuel from the same place ? Do you use the same timing light ? Did you clay your motor ? What cc are those heads ?

[This message has been edited by oceanridge motorsports (edited November 09, 2005).]

fast_crew
Dirt Forum Racer

Total posts: 100
posted November 10, 2005 04:55 PM  
The biggest problem with hyper's is the high silicone content, which softens the material, and creates a grainy, porus casting. Which makes them weak overall. The pin area being the weakest. With a hyper any type of detenation for a period of time will blow the piston up in pieces right down over the pin. If there was a problem in the machine work it would not have made it that long.

Josh K.

street31
Dirt Roller

Total posts: 12
posted November 10, 2005 07:38 PM  
my buddy broke his piston last season , and i only run 34 degrees timing and 110 race fuel.there was no contact with the head, 64cc dart only .100 popup 557 cam lift @50 1.5 rockers,.125 on intake .140 on exhaust never over 6900 rpm and mostly 6400 for 18 nites with no problems, never any overheat,200degrees oil changed every other week, good champ pan good fresh valves and springs. ??????? maybe just a bad set of hypers? a few years back ran 355 with badger cast 150 domes 58cc head 7400 never broke anything on all cast parts and 100 octane av gas.???

Whitelightning
Dirt Freak

Total posts: 431
posted November 15, 2005 01:54 PM  
Thats just classic problems with the speed pro hypers. My uncles motor lasted 7 races and mine lasted 3 seasons. Same pistons same final results and when it goes it took the block with it on both of them. I would save my money and just go with a forged piston. My rules say no forged pistons in pure stock but I run them anyway, because I am not gonna tear another engine up with a hyper piston

oceanridge motorsports
Dirt Full Roller

Total posts: 29
posted November 16, 2005 09:59 PM  
hey whitelighting , you guys gonna be at swainsboro for turkey day ? How did your 602 do in the super streets ?

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Whitelightning
Dirt Freak

Total posts: 431
posted November 17, 2005 07:22 AM  
Well we finished in the top 10 in the 10,000 dollar shoot out. We were the only coil spring car to even make the show. I feel like we have plenty of power but could never get it to the dirt in the monte carlo. However we are unvailing our firebird with the 602 at the turkey race. I hope the leaf spring chasis will let us get of the corners and get r done. You have to remeber I took my front running pure stock car which weighted 3550 with driver and had 52 % rear and worked real good, so I tought if I put me a hog in it and moved up to super street it would fly. Superstreet has to weight 3300 With the 3310 carb. 3200 without, and the crate cars get the 100 pound weight break so that lets us run 3100 pounds. I had no problem getting the car down to 3100 but then my best rear percentage was 42 % and that just dont help none. I was gonna put aftermarket body on the monte to get it lighter and be able to add more weight on the rear and I think it would have been fine but we decided to try the leaf spring car and just move the Monte back down to pure stock which I may say won the pure stock championship this year @ Swainsboro. Oh well I guess that was a long anser to a simple question lol bit over all I like the engine alot. So unless something come up we will be there to try out the firebird which I may add has never seen a set of scales but we will see what happens . Are you gonna come down?

Raz_900
Dirt Forum Champ
Total posts: 636
posted November 17, 2005 04:20 PM  
The silicon in a hyper piston actually makes it harder and more brittle that a forged piston. A forged piston will deform under impact loads (like detonation) where a hyper piston shatters and parts of it break off (usually above the ringland for detonation or the pin pulls outta them).

Pistons are actually oval shaped to some degree. The more the piston is oval'd, the higher rpm it's meant to run. A stock cast is the most round and 'race' forged pistons are the most oval. As rpm's increase, the force on the pin pulls the piston round. Above the designed rpm, it pulls the piston oval the wrong way (wider across the pin instead of across the skirts) and starts to wear the edges of the skirt by the pin. The it pulls apart completely if you keep pushing it.

A typical stock replacement cast or hyper piston is round in the 3000 rpm range. Performance hyper pistons in the 3500-4000 range and forged pistons can be anywhere from 3000-6000 depending on the intended application (there are 'stock' forged pistons like the late 80s early 90s 302).

KB hyper pistons are a higher heat treat and have drilled oil return passages behind the oil ring. Most other hypers have a big slot behind the oil ring which severely weakens the pin area. I wouldn't spin any hyper other than a KB past 6000-6200 for any period of time. The light weight KB will take 7000 intermittent but I'd still use a forged piece for over 6800 for long periods of time. Get the lightest piston possible too, over 6000 those big heavy TRW slugs are going to start tearing things apart. A LW KB is 25%/150 grams lighter, give or take) than a TRW forged.

oceanridge motorsports
Dirt Full Roller

Total posts: 29
posted November 20, 2005 10:18 PM  
Can't get down for it , we will run sumter instead (1.5 hour ride vs. 3 hour ride ). We jumped up to pro stock there and have had some real decent runs .Our car really likes that 11 inch racing rubber ! How about the new years show ? They gonna run it ? We would like to come down for it ,closing on my new house last week of december , but I might be able to sneek off if I have my chores done ! Glad to hear that 602 got in the show , and put on a show .

outlawstock17
Dirt Forum Champ
Total posts: 1369
posted November 21, 2005 06:49 AM  
i've been turning speedpro hypereutectics well over 7000 for years.

no piston failures...

[This message has been edited by outlawstock17 (edited November 21, 2005).]

johder
Dirt Maniac

Total posts: 109
posted November 21, 2005 04:57 PM  
the biggest problem with hypers is the ring gap. FOLLOW the reccomended gap that comes with the pistons and you WILL be fine. Hypers run closer piston/cylinderwall clearances than forged or cast do. The ring ends but together and break the top off the piston, then it probably smashes eveyrthing else in its way the 600 revelotions it makes before you realize something happened and you shut it down

stockcar5
Dirt Forum Champ
Total posts: 580
posted November 21, 2005 08:20 PM  
not all hypers need special ring gaps...only KBs do. speed pros take normal ring gaps (.022 top .024 second give or take a little)

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