# Why are oe bored aftermarket pistons bad?



## kevin splits (Aug 23, 2010)

So I ordered JE low comp pistons in oe bore, with IE rods along time ago(3-4 months). Just to now see NGP does not recommend a oe bored aftermarket JE piston to be exact... For that they recommend Weisco.. NGP recommends a .5 overbore. I chose against it because I don't feel like dropping 1k to have the cylinders bored and deal with those potential problems. They were installed in the motor yesterday, and ya who ever said you can run low comp internals on a n/a motor, I say to you :sly: Pretty rough but once warmed up idle isn't so bad. I didn't do the install, wasn't even there, 

So Pete, Josh, Issam, why is oe bore not recommend, and did I make a mistake taking that route?


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## kevin splits (Aug 23, 2010)

Also for the idle. Should I maybe switch to a hotter plug? Then when the turbo is on, switch back or go to a step colder? 

Only reason I did internals first was because of that whole Eurojet valve cover thing, that may have caused piston ring wear from the oil starvation... The shop that did it said that cam lobe is VERY scratched up, but it should be ok.


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## whitefang (May 4, 2012)

From what i understand, all engines create wear. evn on low mileage. thats why we brake in our engines after rebuilds. putting new pistons in an old bore can be done with a hone and rings, but the best results i would assume is when boring over ensuring a "true" axis for a fresh start. aside from this, I cant really answer your question. 
I was wondering, do you find that with the lower compression on your NA engine makes it sound a little bit like a diesel?


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## kevin splits (Aug 23, 2010)

whitefang said:


> From what i understand, all engines create wear. evn on low mileage. thats why we brake in our engines after rebuilds. putting new pistons in an old bore can be done with a hone and rings, but the best results i would assume is when boring over ensuring a "true" axis for a fresh start. aside from this, I cant really answer your question.
> I was wondering, do you find that with the lower compression on your NA engine makes it sound a little bit like a diesel?


 They honed it. I'm gonna hit 80k miles on the oem block tomorrow morning. I just notice vibration. I'll get an exhaust video. It'll be on my phone so we'll see how well I can capture sound. Idle rpm seems lower, but I just worked a 14 hour day so it may just be my exhausted mind.


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## kevin splits (Aug 23, 2010)




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## tay272 (Aug 22, 2007)

Does kinda sound like a diesel VW but not quite. Could just be because its idling a little lower then usual. Cant answer your question about the pistons tho, I have no idea there.


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## kevin splits (Aug 23, 2010)

tay272 said:


> Does kinda sound like a diesel VW but not quite. Could just be because its idling a little lower then usual. Cant answer your question about the pistons tho, I have no idea there.


 I think it finally adapted to whatever was goin on. Consistant 700-750idle rpm now. 

Ya it caught me off gaurd when I saw that on there sight. I was checking to see what the oe bore pistons were going for now, and saw that under the .5mm overbore pistons. 

Im still curious as to why they recommend Weisco over JE for oe spec?


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## CoNGLoMeRaTeGTi (Apr 4, 2007)

The short answer is: 

Because VW did a poor job of boring the blocks properly.


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## thygreyt (Jun 7, 2009)

CoNGLoMeRaTeGTi said:


> The short answer is:
> 
> Because VW did a poor job of boring the blocks properly.


 can we just drop it at a shop and have it balnced and honed? making sure that its 82.5mm all round... 

or does one NEEDS to over bore it?


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## kevin splits (Aug 23, 2010)

thygreyt said:


> can we just drop it at a shop and have it balnced and honed? making sure that its 82.5mm all round...
> 
> or does one NEEDS to over bore it?


 Seems fine now, just violent shakes on cold start.. I know they had to hone 3 of the 5 cylinders to match 2 of the cylinders, and then filed rings to get it perfect. I think the vibration is the rings breaking in. They used amsoil break in oil, I have no idea what weight tho. They say my cam is pretty f'd up from that baffle falling out of the valve cover. The rocker may be fractured too, they didn't have a scope to see if it was a scratch or crack. 

This shop builds very fast Supras, and whatever really.


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## kevin splits (Aug 23, 2010)

When we pull it apart again for ARP stud set, I'll snap some shots. They had the car all week, did great job. I would not have been able to do this myself, actually no one can do it at home unless you want to try your hand at a perfect hone job. 

So Fred, ya these will work, and my compression is fine as well as timing, so I guess only side effect is the vibration. Everything else seemed to be mental.


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## nothing-leaves-stock (Mar 1, 2005)

all forged pistons make knocking or wierd noises till the engine is warmed up....shake and misfire? no...noises yes. 

i use drop in pistons all the time.... weiscos are nice pistons tho. they may not make a drop in size. i've used both JE, ross and wiesco. all noisy on cold starts


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## kevin splits (Aug 23, 2010)

nothing-leaves-stock said:


> all forged pistons make knocking or wierd noises till the engine is warmed up....shake and misfire? no...noises yes.
> 
> i use drop in pistons all the time.... weiscos are nice pistons tho. they may not make a drop in size. i've used both JE, ross and wiesco. all noisy on cold starts


 I didn't know if NGP had a bad experience with drop-ins or what. I'm not familiar with their 2 turbo Rabbits other than I know they've changed hands a few times. 

Have almost 200 miles on them so far driving it like a old person. Seems to be working itself out as they break in. But ya the motor is fine once warmed up. Good to know, thanks.


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## vDub624 (Oct 8, 2010)

i just bought drop in low comp pistons too. and was wondering what your actual bore size of your block was. I've measured my pistons 10 times and they seem to be 5 thousands under stock. i know that is probably the most amount of clearance you want on forged pistons but i am afraid that my block may be a tad worn and then ill have to spend 800 on brand new over bore pistons.(actually got these low compression pistons USED from nap for a good deal) if its anything over 5 thousands clearance i will not out them in as I'm pretty sure they will make soooooooo much noise and end up piston slapping too much, i only wanna take my engine apart once.


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## kevin splits (Aug 23, 2010)

vDub624 said:


> i just bought drop in low comp pistons too. and was wondering what your actual bore size of your block was. I've measured my pistons 10 times and they seem to be 5 thousands under stock. i know that is probably the most amount of clearance you want on forged pistons but i am afraid that my block may be a tad worn and then ill have to spend 800 on brand new over bore pistons.(actually got these low compression pistons USED from nap for a good deal) if its anything over 5 thousands clearance i will not out them in as I'm pretty sure they will make soooooooo much noise and end up piston slapping too much, i only wanna take my engine apart once.


 It should come down to the rings honestly. I wasn't there. They had my car for around a week. The stock piston rings were in pretty bad shape. They had to hone the cylinders and file rings, so I'm gonna go ahead and say my bore was within the limits. 

I don't have any piston slapping, I know what that sounds like  Just vibration on cold start and like Josh said knocking, which I didn't notice, but since he said that I sort of hear it now. My motor mounts are shot tho so I'm gonna blame the vibration on that. The motor was taken out and put back in on the dead oem mounts. I think the trans mount is popped.


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## kevin splits (Aug 23, 2010)

Also whats the brand of that turbo you have fs? I may take it if its real.


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## Rod Ratio (Jun 6, 2012)

nothing-leaves-stock said:


> all forged pistons make knocking or wierd noises till the engine is warmed up....shake and misfire? no...noises yes.
> 
> i use drop in pistons all the time.... weiscos are nice pistons tho. they may not make a drop in size. i've used both JE, ross and wiesco. all noisy on cold starts


 Dead wrong Josh. Sorry bud. 

Wiseco and Mahle tend to use 4032 alloy which expands at the same rate as factory pistons, and requires a factory cylinder to wall clearance; which results in a factory like, smooth running engine, that doesn't wear excessively, consume oil, or make any more noise at startup than a stock engine.

JE, and the Mahle's and Wiseco's designed for EXTREME (read 700 whp+) use the slightly stronger, but more thermally unstable 2618 alloy. Id never run 2618 alloy in anything but a race engine, that gets rebuilt frequently.

That said; if you are assembling engines with 4032 alloy pistons, and still getting piston slap while cold, you're assembling it to the wrong tolerances, and DOING IT WRONG...

All aftermarket pistons are not created equal, and obviously some engine builders need to stay up on the current specifications of the products they use..


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## kevin splits (Aug 23, 2010)

*+NEIL*+DIAMOND*+ said:


> Dead wrong Josh. Sorry bud.
> 
> Wiseco and Mahle tend to use 4032 alloy which expands at the same rate as factory pistons, and requires a factory cylinder to wall clearance; which results in a factory like, smooth running engine, that doesn't wear excessively, consume oil, or make any more noise at startup than a stock engine.
> 
> ...


 So that's why NGP recommends the Wiseco over JE for the oe bore? 

And your saying in theory my harder JE pistons are going to cause frequent engine rebuilds?


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## Rod Ratio (Jun 6, 2012)

kevin FaKiN spLits said:


> So that's why NGP recommends the Wiseco over JE for the oe bore?
> 
> And your saying in theory my harder JE pistons are going to cause frequent engine rebuilds?


 Yep. The boys at NGP know what they are doing. Id spend extra on a custom set of 4032 alloy pistons if it were my engine.

FWIW I had a one off set of mahle pistons made for a 1.8t, and it was about $400 extra for the set. Wiseco would definitely be cheaper than Mahle tho; if they will make em.

Im mentioning custom pistons because I just looked on IE's site, and they only have je's listed for 2.5's.

And yes the 2618 pistons literally wear your bores out over time; due to the looser tolerances. 

4032 is a far better choice all around. Factory longevity, no increased oil consumption, no slap, better compression, etc.


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## AJmustDIE (Dec 22, 2010)

I was reading down this thread down facepalming until I seen somebody had actually brought up the differences in 4032 and 2618 alloys.


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## thygreyt (Jun 7, 2009)

INA always recommends Mahle to me. i now understand why. 

i dont get why other companies **cough** sell the "other" alloys


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## AJmustDIE (Dec 22, 2010)

Racecars, bro.


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## kevin splits (Aug 23, 2010)

thygreyt said:


> INA always recommends Mahle to me. i now understand why.
> 
> i dont get why other companies **cough** sell the "other" alloys


 Hey. Live and learn I guess. Luckily 2.5 blocks are next to nothing in value. After talking to Neil Diamond I'm bummed I didn't go with high comp pistons and slap a 35r on it  Insta-spool


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## Dronks (Jun 7, 2011)

AJmustDIE said:


> I was reading down this thread down facepalming until I seen somebody had actually brought up the differences in 4032 and 2618 alloys.


 Same here. 

OP: Those 2618 pistons could run fine for maybe 40K miles but the walls will need a bore and hone when it gets to sloppy. Depending on your miles per year, it might be cost-effective just to leave them in.


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## JohnnyDrama (Feb 15, 2012)

I wouldn't recommend JE or Wiseco pistons due to the amount of noise they make. I've seen them cause issues with the ability to tune with them. CP or Mahle :thumbup:


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## kevin splits (Aug 23, 2010)

Dronks said:


> Same here.
> 
> OP: Those 2618 pistons could run fine for maybe 40K miles but the walls will need a bore and hone when it gets to sloppy. Depending on your miles per year, it might be cost-effective just to leave them in.


 I love how Neil said something and now everyone is attacking the material the piston is made out of! Lol starting to get the fealing everything after that post is just " ya what he said posts" the motor will be fine. The car isn't a daily anymore. I may be going a different route with what's in the bay so ya I'm sure I have more than 40k till its done


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## [email protected] (Jan 2, 2009)

That's just plain wrong. JE's and most of the VW Wiseco's are made out of the exact same material as CP's... The only time they make excessive slapping is when some hack machine shop sets the piston to wall clearances wrong- or somebody hones the hell out of a stock block, doesn't measure anything, and slaps them in... Those two circumstances- unfortunately- are much more common then they should be. 

That leads me to the main reason why we don't recommend drop ins, unless there is really strong reason to do that... When you buy a set of pistons from a very good manufacturer they are reasonably exactly sized- usually a set of JE's are within .0002", a set of wiseco's about double that tolerances... Then your machine shop measures the pistons, and sets the piston to wall clearance to what is needed for your application. A careful machine shop will even match the piston variances to the variances in their bore job, giving the most accurate piston to wall clearances. 

When you just slap them in on OE bores- the piston / wall clearance is a best guess- and you really have no clue unless you measure it. That piston manufacturer assumes the bore is a nominal size- takes a broad stroke at a theoretical piston to wall clearance that *should* work for everyone, and lets it roll... Is it really a surprise that sometimes it doesn't work out? I don't take gambles like that with engines unless it's absolutely necessary- like if I was given 12 hour notice to build a motor, or similar. Especially if the motor is anything but almost new. 

A JE piston motor will not have audible slap when cold unless it's built really loose. Maybe you could hear it a tiny bit if you had a stock exhaust, stock motor mounts, and stock everything else- but the motors we build you can't hear them ever... We don't have any issues with knock sensors, and they hold up even to bonneville style "stand on it full throttle forever" loading. Do it right, do it once, and don't blame the parts for your slapping **** together. :thumbup: 

Kevin- the ECU probably needed slightly more ignition timing / throttle % to bring the idle up with the lower compression. It should be fine


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## kevin splits (Aug 23, 2010)

[email protected] said:


> That's just plain wrong. JE's and most of the VW Wiseco's are made out of the exact same material as CP's... The only time they make excessive slapping is when some hack machine shop sets the piston to wall clearances wrong- or somebody hones the hell out of a stock block, doesn't measure anything, and slaps them in... Those two circumstances- unfortunately- are much more common then they should be.
> 
> That leads me to the main reason why we don't recommend drop ins, unless there is really strong reason to do that... When you buy a set of pistons from a very good manufacturer they are reasonably exactly sized- usually a set of JE's are within .0002", a set of wiseco's about double that tolerances... Then your machine shop measures the pistons, and sets the piston to wall clearance to what is needed for your application. A careful machine shop will even match the piston variances to the variances in their bore job, giving the most accurate piston to wall clearances.
> 
> ...


 Whelp... I feel better know. The shop that did it promises me its as robust as they could get it. Ya I think the ecu was like wtf? Then after awhile the rpm are up to what they were before. Vibration is just the stock mounts. Gotta order those soon


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## AJmustDIE (Dec 22, 2010)

Was not attacking JE, they have a mighty fine, STRONG product. But it's thermal expansion properties warrant it's use as drop in, and as you said, this is almost always a mere guess away from a problem thousands of miles down the road.


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## [email protected] (Jan 2, 2009)

Ya, that is an issue with pretty much any piston though. The Mahle's can be built really tight- but they aren't anywhere near as strong. 

CP's, most VW Wiseco's, Arias, Ross- all of them are the same material as JE. Some of the all motor Wiseco's are 4032, but not most turbo apps.


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## kevin splits (Aug 23, 2010)

AJmustDIE said:


> Was not attacking JE, they have a mighty fine, STRONG product. But it's thermal expansion properties warrant it's use as drop in, and as you said, this is almost always a mere guess away from a problem thousands of miles down the road.


 Ya if you use a shop that takes drop in literal. The shop I had do it builds 1400hp 2jz and bores, sleeves, blueprints race engines. What irked me is I do most things on my own. This no way in hell anyone can do at home, so looked to them. It took them a week of measuring honing and matching everything and half a day after that to install and get it back together. So I was gonna be uncomfortable at the slightest thing I don't feel as normal. I don't have slapping, I know what that sounds like I don't know where that came into the conversation? Had a bit of knocking but it seems to sound around when it was stock at this point. Seem to have a new exhaust tone.


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## kevin splits (Aug 23, 2010)

[email protected] said:


> Ya, that is an issue with pretty much any piston though. The Mahle's can be built really tight- but they aren't anywhere near as strong.
> 
> CP's, most VW Wiseco's, Arias, Ross- all of them are the same material as JE. Some of the all motor Wiseco's are 4032, but not most turbo apps.


 So if I would have went with high comps could have ended up with the 4032?


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## [email protected] (Jan 2, 2009)

Nope. It would have been 2618 whatever you did.


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## kevin splits (Aug 23, 2010)

[email protected] said:


> Nope. It would have been 2618 whatever you did.


 I'll be completely honest. I went with "drop-ins" to save money. No other reason, just that one. And ya it saved me money, the install would have been almost twice the price for a over bore! As it breaks in its looking like they did a fantastic job. Have a couple hundred more miles to go before I change the oil, then as soon as I settle on a turbo I'll get that goin.


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## kevin splits (Aug 23, 2010)

[email protected] said:


> Nope. It would have been 2618 whatever you did.


 :thumbup: So I guess my question stands! Why Wiseco over JE because their tolerances are stricter?


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## Issam Abed (Feb 12, 2004)

kevin FaKiN spLits said:


> :thumbup: So I guess my question stands! Why Wiseco over JE because their tolerances are stricter?


 6 of one , half a dozen of the other. If I had to choose a 2618 piston for a custom application JE would be the first pick out of all the following: 



CP 

Wiseco 

Arias 

Ross 

 

JE has come a long way over the last 10 years in how they design there pistons and they actually do a pretty decent job , however , Mahle runs the show. They can make a 2618 alloy piston in any spec you want but you are paying for it.


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## Rod Ratio (Jun 6, 2012)

[email protected] said:


> Ya, that is an issue with pretty much any piston though. The Mahle's can be built really tight- but they aren't anywhere near as strong.
> 
> CP's, most VW Wiseco's, Arias, Ross- all of them are the same material as JE. Some of the all motor Wiseco's are 4032, but not most turbo apps.


 The 4032's are MORE than strong enough for MOST turbo applications, and you know this Pete. Unless a setup is being pushed to the hairy edge; the 2618's are of zero advantage to the user. Ill take a tighter piston to wall clearance, less oil consuumprion, and longevity over unusable 'headroom' in a street car.

You've said yourself that "4032's are plenty strong for a street 1.8t up until you eclipse the 550whp mark" pretty much verbatim from your keyboard.

Add in another cylinder, and some quick math. Judging by your own statements the 2.5 should be good for 687.5 whp; before 2618 alloy would be a better idea.

Pete,

I understand the point you made about sloppy engine assembly; as I said the same thing in a post previous to yours, but you've effectively contradicted yourself, and your own website descriptions with your statements in this thread.

Are you defending your own choice to only offer the 2.5 pistons in 2618 (which I believe to be a decision based on dollar cost averaging, since the 'saleability' of the 2.5 platform was unknown when you decided to offer parts for it)? Or have you since changed your stance due to a recent crop of 4032 failures (that I've never heard of)?


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## [email protected] (Jan 2, 2009)

That's all fine- but who's going to make you these 4032 pistons on a one off basis? Mahle won't- well they will but figure $1500 / 5 cyl set- retail, and a few months to get them done... We can do custom wiseco's, but really JE owns the hell out of the custom piston market... People don't like waiting the 2 weeks for JE's let alone the 6-10 for wiseco. I can get JE to do customs on their budget SRP forgings, which are 4032, but honestly the 2618 FSR turbo forging is far superior- it's stronger, lighter, less friction, etc. 

So really, the options for custom 4032's are limited, and this market (2.5L) is all about customs because there is no volume... Now, all those issues aside, the difference in thermal expansion between 4032 and 2618 is only about 13%... The difference between those two, and a stock piston, is about 3 times- so you're really talking about two things are very close to the same anyways on a relative scale. It's not like you can build a 4032 piston wicked tight, and hammer on it when it's cold- nope- all the same basic issues as with 2618... Needs to be warmed up. Even mahle drops 4032 for apps they know are going to make power or take a beating. FSI mahle's are not 4032, for example. 

Now, IMO the real trade off between the two is that 4032 is harder, 2618 tougher... That means 2618 ring lands wear faster over the long haul... You can have them hard anodized, but $$$$. Still, the vast majority of forged pistons made ARE 2618, and they DO work fine in street cars, except when either shops screw up, or err on the side of ridiculous caution and build them super loose. Then they rattle like hell and don't last- neither would a 4032 piston in the same circumstances. 

:thumbup:


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## Rod Ratio (Jun 6, 2012)

OK. So it *is* more about availability, as you haven't contradicted a single point I've made; including availability.

Im definitely not here for a pîssing match, as I have a ton of respect for what you've done in our market Pete:beer:

I never stated that the 4032's were ideal for an 'all out' setup; such as a drag car, quite the opposite in fact. 

For a car like Kevin's, or any other performance 2.5 street build under say 700 wheel; the 4032's would be a better pick. 

Save of course for proper tuning


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