LSX piston issue's
 

Ok guys I have my 440LSX down right now over the slugs from the crankshaft coming out and almost going through one of the pistons, Well after looking over everything I noticed all 8 pistons are cracked inbetween the wrist pin and skirt. I would love to know what could cause this to happen and also what i found to be weird is all the even side pistons cracked on the bottom side of the wrist pin and all the odd side cracked on the top of the wrist pin ONLY.
Also all the pistons have alot of pistion scuffing and with every pistion is only scuffed on the side that cracked, example all the odd piston have scuff marks only on the top side and all even's have scuffs on the bottom side.

Here is a pic of the crack. Any info would be great


http://i46.photobucket.com/albums/f1...e/103_3041.jpg

did the wrist pins feel extremly tight when it was assembled?

Tight as in forse fit NO they fit perfect and still do, After i took the pic i took them apart

What crank are you running "stroke"? Possibly a balancing or high RPM sling of the piston on the big stroke.

man that sucks i followed your build of that motor on n2s its a nice build to bad that happened

Its a 4.0 stroke

Now i did have a balance issue because the crank lost 2 slugs and the car was raced about 15 passes on motor and then i sprayed it and when it pushed oil every where i thought i had a broken ring, I tore the motor down to find a piston had a small hole in it from the slug

just wondering, thought that i may have caused extra heat.

Following your post over at YB.


Robin

What is your piston to wall clearance? Are the pistons marked as a stock set would be with a "front" only, and not a top and bottom? Who forged them? I'm just curious here, and I hate to hear that. Wish I could offer some help.

What block are you running?

It looks to me that the bores aren't long enough and the skirts are coming out of the bottom of the hole and rocking in the bore. This would also explain the scuffs and cracks on your pistons since they are on the thrust side only. This is by far the biggest drawback to stroking an LS engine. I recommend putting longer sleeve in ANY LS motor if you have more than a 3.622 stroke.

its a LSX block

here is a pic of the piston out of the bore

http://i46.photobucket.com/albums/f1...e/103_3046.jpg

.004 clearence and yes they are marked front, They are diamonds

You may want to give Brian Nutter a call at Wiseco. He is very well versed in this and may be able to help you out.

LSXNOVA

my Wiseco's are being custom built as we speek,i've run Diamonds,wrist pin to thin,skirts to deep,then i ran Mahle,big shot Nos needs big wrist pins,deflection causes pistons to crack on the bottom,ur crack is further out though,seems like an allignment problem,and ur rod didnt look centered in that pic?is that the casting quality of the Lsx ? Call Wiseco,my pistons are built around a new style of rings,i think their the first set built for LS motors,....i'll ask them if there's a part # for them,i do know the pins are huge and very heavy,.....

Hey there, there are a couple issues here. I'm not a fan of forging struts that "angle out" from the pin bosses to the skirts. We won't do it unless we're running a full boxxed forging to keep the pin bosses from flexing..which is what is occuring here. Our standard parts angle in from the pin bosses to skirt. Some Diamonds are the same way.

A thicker stiffer wristpin always helps..but it depends on how much you're spraying it etc. The span between the pin bosses is crucial when you start making "big power". I don't know how much power you're making, but any open free area of wristpin that isn't supported by pin boss or rod is put into bending rather than shear...and can cause issues.

Well I wanted wiseco piston but for some reason two years ago when i built this motor I was unable to get you back on the phone to complete the order, I left atleast 10 emails called a dozzen of times even faxed TWO orders inn and never got a return call or email so I went with Diamonds, Every time i calld they told me i needed to talk to you you where to one doing the LSX stuff but anyway glad you posted here.

Now for the problem, I am running H13 Piston pins at .185 is this not good enough? as far as power level I dont realy know, with Paula in the car it weigh's close to 3900lbs and it went 128mph in the 1/8 so i would say some where near 1,000rwhp this is on a 42pill direct port should be 450hp on N20.

Many problems here and probably not the piston's fault. Like I said over at YB you normally run almost .008 on that forging and not only .004 on a big NOS engine. You got some weird stuff going on. I have used tons of those exact same pistons and never seen anything like that yet. I use both Wiseco and Diamond and just don't see stuff like this.......ever.

The fact that the heavy metal came out too is probably irrelevant maybe but their are many serious issues with this deal. I understood that you yourself built this deal and had someone else machine it? Your choice of .185 H13 tool steel pin should be fine and was a good move. Damn going back over there now it says you did have like .007 piston too wall?

What do the pistons measure at the bottoms of the skirts now?

Also Brian is a very busy guy there at Wiseco and it's hard to talk to anyone like that. I call back quite a bit myself as he's got a lot to do just like all of us but he knows his stuff.

I just measured a few pistons and the best i could tell they measured 4.175 and the bore measures 4.183

I know Brian's a busy man but i was just tired of tring to get a hold of him to order the piston's. I have always built my own stuff with letting the machine shops do the machining and setting bearing clearence ect.. but i didnt know what i need to order for this motor and we where tring to make the LSX shootout then so was left with no choise but to go else where with the build. Hell I'm a dealer for wiseco I own a race ATV shop and we sell nothing but wiseco in all our powersports.

now on these pistons I went back with diamond again and i hope this issue was something to do with the crankshaft loosing nearly 90 grams of weight but i still have my doughts but what i can say is this motor had about 100 passes on it when we replaced the crankshaft and the pistons where not like that, The only thing that changed was MORE nitrous I went from a 34 pill to a 40 then to a 42.

Hi sorry for not being as available as I'd like. I could have 3 clones here and not get all the stuff done.

I hear ya man lol I know its tuff

If i have anymore problems with piston's i will give ou a call