Few years back I built a 402 with a 6.0 cast iron block, Wiseco pistons with .005 clearance or so I thought, 6.125 H-beam rods 4.00 Eagle crank. Motor made 555/525 on an engine dyno and 460/440 rear wheel. By the time I made it to 350 miles it had used 5 quarts of oil. Disassembled engine and found that the piston had excessive rock on the piston skirts. I sold every piece of the engine and washed my hands of it after I found the preceding problem. Now a customer wants to build something of the same caliber. LSX block bored to 4.155, Eagle 6.125 rods, 4.00 stroke, 4.155 Wiseco pistons. As I honed the cylinders for this motor I had mixed emotion about it. Clearance at the manufactures measuring point showed to be .004 (On the line of the piston in the picture). The LS type blocks in my shop all measure 5.625 cylinder length. As you can see in my other pictures that line is right at 5.625 when the piston will be at BDC. I have even mocked the engine up to see if the line is exposed at BDC and it is. Now at that line the piston tapers off as it moves towards the oil ring which it should. But the clearance more than doubles as it does it (.008). This is also the same place that my 402 engine showed very heavy skirt damage. I'm not saying there is anything wrong with the maching of the pistons but it does go out of tolorance at that point because of design limits. The piston company told me the major size of the piston starts at .800 below the oil ring which just so happens to be the black line and said it would be fine. Much talk after that lead to them hanging the phone up on me, oh well. I would like to hear other's opinions on there 4.00 setups. Maybe this is why GM has 6.067 rods and 1.187 ch in the LS7 and I would like to know the cylinder length on the LS7 as well. If pictures are hard to see I'm sorry.

 

From Steve - Race Engine Development....you even posted in this thread haha...

Looks like there is a problem with the piston design. You should look into Diamond pistons.

 

Yes I remeber that thread too. But why does the aftermarket keep pushing this junk on people and then eveyone acts in denial about it and there is no problem. If I'm not mistake isn't Wiseco wining the on line poll that someone has going right now.

 

LOL, i believe you're right. Diamond might be a little more expensive in some instances, but you get what you pay for. If the tapper'd down portion of the piston is getting exposed and rocking too much, of course thats going to cause some serious damage, and trap oil too. I can see now why you burned a quart every 100 miles...

 

I have just taken Probe pistons out of my 383, the rock on those was HUGE. You could see at the top of the bore where the tell tale marks showed the rock. I am swapping the block as we speak and i have put Mahle in the LS3 block i am building. The skirts on the Mahles is much longer ( Did not measure ) , I too had ridiculous oil consumption, its the only reason i am undertaking the conversion. But everytime i filled the fuel tank i had to top the oil!! The Mahles have no where near the rock, just by pushing the pistons in the block you can tell this.

 

It's all in who designs the piston and what they are going into as far as power and cylinder length. Wiseco and Diamond both have pretty low taper designs that have pretty high break points that are made to work in these OEM LSx blocks. They do not have this problem unless they are ordered wrong usually.

Wiseco doesn't use skirt D1 (that is checked at .800 down) on almost any LS1 4.000+ stroke design unless they knew you had a Darton or C5R or LS7 etc. block with a longer cylinder or unless it's a custom that you are running more power through that you needed more taper.

I have had mulitiple threads about this as long as 7 years ago and any normal engine builder should be well aware of this potential problem. The other piston builders regularly make pistons that do not work with the short cylinders of the LSx engines but Diamond and Wiseco have taken this into consideration.

We have built nearing 700 4.000 stroke deals in OEM blocks with Wiseco pistons and you can see them all over the internet and in quite a few magazines and they don't have this issue of course. Diamond's normal LS1 skirts don't either and the threads about certain Diamond combos smoking were also due to those particular engine shops and their errors as well.

Probe has a particularly low taper design so they don't usually have this situation either but they are a very lightweight design and they will rock quite a bit if the skirts are collapsed which I have seen on a few I had to freshen. New they do not rock much at all.

I have seen quite a bit of JE stuff that rocks double what the average Wiseco/Diamond stuff does and it will use oil like crazy. These are high taper, low-on-the-piston break point pistons that need a 6 inch cylinder and still rock a lot cold anyway. I don't use stuff like that or the customer has no warranty whatsoever on that aspect.

 

Haans, I'm the one that asked Steve to start doing my sleeves at 5.800 and longer because of this. I have many apps where I use the lower break point skirts on power adders etc. and I wanted that extra length. Trying to hone a 6.000 long C5r cylinder is a ***** to do right. 5.75-5.850 is much easier and you can do some much longer strokes.

We haven't had issues like MAC has with his engine on ours that have over 4.000 strokes in them like 4.100 / 4.125 / 4.185 / 4.200 / 4.250 so there's more going on here than meets the eye. There's also a lot of extra prep that goes into a stroker and other things like cylinder wall finish and geometry and rings used that will cause these issues.

I will say that I do not use certain pistons in certain applications on my stuff because I have fixed so many of these deals from other engine shops including some with Diamond and Wiseco but they were all easy to figure out as to why they are smoking and most were not because of the pistons. I am fixing two more right now and the guys that have them can report back to this thread.

 

Very interesting stuff. What are some of the reasons for more piston taper on power adder motors? Is that to relieve some of the pressures that build up inbetween ringlands?

 

Basically with way more power you have way more heat going through the top of the piston and it grows bigger in diameter more so than when a piston is handing much less power and will be more prone to sticking in the bore so the piston manufacturer will want to make the top smaller even under the oil rail on a large power adder style piston and have more clearance. The point of max skirt size cold will also be lower down from the oil rail with more taper and more away from the heat as well so again it's not as likely to stick in a bore even at the same clearance at that largest point cold. I am probably simplifying this stuff more than I should and of course the piston forging has a lot to do with how the piston changes when really hot so that is what the piston engineers/techs are for.

I do agree with MAC that the stroke VS. cylinder length thing gets screwed up a lot and that's why I had all those threads years ago already. Wiseco and Diamond though usually get that part right as they have been specializing in this marklet and are well aware of this issue. I can't say that about some of the other pistons I have seen and I have had the exact same situation that MAC is describing in a BIG way with some other piston companies stuff. I have even seen some custom Diamonds and Wisecos made wrong as well due to the people involved and miscommunications but their normal stuff and custom stuff if you order with this in mind comes out right. That's how we have as much business as we do because I am hyper aware of this and some other situations.

I think the Probe problems might be related to the skirts being collapsed due to who knows what but those pistons have very little taper and don't rock a lot at all when they are new. If you have tight pin clearance or extreme power through them they are so light it seems they can suffer the skirts collapsing somewhat and then they will rock much more. Big NOS engines will do this over time and they also need much more skirt strength and thicker pins to keep the pistons and skirts happy.

 

Now you all have me wondering if my combo is messed up I am in the process of assembling a 4.030 iron block with a 4.00 eagle crank, bme 6.100aluminum rods, and a set of weisco pistons the pistons are a new part # K464F3... Am i going to have a problem??? If so im going to stop now....

 

Thanks for the great explanation. Right now I just got done taking the heads off my 427 motor, I also checked the piston rock at TDC, and it was measuring 25thou total rock, is that about normal?

 

This piston in the picture and stated above is a shelf stock Wiseco I don't have exact part number in front of me we bought it less than 2 months ago. So it seems as if Wiseco is not taken this problem seriously enough to fix on later model pistons and they say there is no problem. I have read many previous post about this years ago but the problem seems to still be around. That is why I'm bring it back from the dead and to keep newcomers aware.

 

Really what your emphasising MAC is that a qualified builder should be doing this for people. It isnt as simple as just buying a few parts off the shelf that say ls1 and stuffing them into a block. There are a lot of things that go into a depenadable build and the amateur builder can't possibly get them all correct if they dont know about them in the first place. And its a good point brought to attention by you.

 

I doubt it but I have not heard of that part number?

 

Yes that is right on the nose for that skirt at room temp with no rings when we are checking deck.

 

Mac what piston is that one you have right now as far as part number?

You realize that all pistons rock "more" at BDC but the question is how much?

The pistons I was saying that I would not run will rock an easy .150 thou or more cold at BDC and about .040 at TDC with the same .005 running clearance where they say to measure.

The Wiseco and Diamond pistons do rock more at BDC but not enough more to cause problems.

Even many aftermarket stock stroke pistons rock more at the bottom then at the top due to the skirt design etc.

 

K446F155 is the number for the kit and 6446F155 is on the top of the piston. Yes I understand they rock more at BDC because 95% of the applications out there some of the skirt does come out of most blocks somewhat causing the rock. When I get a chance I will see how much rock it has a BDC. I have only measured clearance at that point which gave me the uneasy feeling.

 

Like i said they are a new part # they are suppose to be a -3cc valve pocket for an l92 head, not sure how they achieve this yet. Ill post a pic when they get here next week..BTW. thanks for the info....

 

Well I understand your thoughts as again I know several pistons that did do crazy stuff back in the beginning and these may be different from the ones we always use. Do these new pistons have the 1/16, 1/16, 3.0mm ring grooves?

 

You're welcome and I will ask Brian Nutter about them for both of you guys. They should be alright at the current time but I will ask about them anyway.