New OASIS message for Engine Rattle

[Donkey]

More than scar, know plenty of jdm sti motors that went pop because a piston sticks in the bore. They run tighter clearances than they should to prevent slap. Put on a bigger turbo than stock, run it hard and boom, piston wedging in breaking all the things. US motors run hypereutechnic pistons and so just puke Ringling every so often

Yeah 3 times while I owned mine. A lawyer later and I was out from under that horrendous pos.

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[Sandoval]

More than scar, know plenty of jdm sti motors that went pop because a piston sticks in the bore. They run tighter clearances than they should to prevent slap. Put on a bigger turbo than stock, run it hard and boom, piston wedging in breaking all the things. US motors run hypereutechnic pistons and so just puke Ringling every so often

I'm all too familiar with the ej ringlands. They will not tolerate the slightest detonation. I would still take a factory forged ej207 over any USDM mill though.

 

[bdub85]

More than scar, know plenty of jdm sti motors that went pop because a piston sticks in the bore. They run tighter clearances than they should to prevent slap. Put on a bigger turbo than stock, run it hard and boom, piston wedging in breaking all the things. US motors run hypereutechnic pistons and so just puke Ringling every so often

My 07 STI cracked a ring land on the dyno. That car was making close to 600whp on race gas, so it wasn't that shocking. lol

 

[MastrHU]

Good to know. Thanks.

 

[chopsui]

This is good to know. Thanks for the info.

I am curious as to how this affects the spray-bore cylinder lining. Wouldn't it eventually wear it away? Or is the lining harder than the piston surface?

 

[montreal ponies]

This is good to know. Thanks for the info.

I am curious as to how this affects the spray-bore cylinder lining. Wouldn't it eventually wear it away? Or is the lining harder than the piston surface?

Here is a link Stanglife posted before .

Post is from a GM engineer on piston slap.




quote:
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Are you talking about piston slap during the first few minutes of warmup..??


If so...that is what it is. Nothing to fear or nothing really wrong...just the piston noise until the piston warms up to fill the clearance to the bore.

Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless..but it is the source of piston slap in most all situations.

To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.

Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.

Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.

Unfortunately, when the performance and fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.

The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.

It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.

As an example of what the piston pin offset can do, it was common back in the early 70's to turn the pistons around "backwards" in the large displacement Chrysler engines to gain power. Those engines had large piston pin offsets to create thrust load to control the piston slap. So much thrust load and friction was created that just turning the pistons around in the bores was often good for 10 HP. The engines were very quiet with the pistons in correctly and they slapped like crazy, especially when cold, with the pistons reversed so as to reverse the pin offset.

Racing engines do not have the pin offset and thus the pistons slap like mad...but no one hears them over the open headers...LOL.

The noise is an annoyance but will not hurt anything and the engine is fine.

I don't remember if that engine had full floating pins or not but they can also cause some ticking just after start. Same sort of deal...the "correct" clearances in floating pins will cause clicking after startup for 30 seconds or so. To prevent the start up noise, the floating pin clearance must be kept so tight that the pins are almost press fit again.

 

[Jubilex]

Ok so does the noise sound more like a rattle than a slap? Ever since I removed my resonators I notice more of a rattle when the engine is cold and I'm wondering if this is it. Sounds almost like something under the car like below the driver (not the engine area) is rattling. Almost like the heat shield where the resonators were wasn't put back securely and was rattling up and down some.

Is this the piston slap people are talking about? I checked everything under my car and it all seems secure...

 

[jasonstang]

Ok so does the noise sound more like a rattle than a slap? Ever since I removed my resonators I notice more of a rattle when the engine is cold and I'm wondering if this is it. Sounds almost like something under the car like below the driver (not the engine area) is rattling. Almost like the heat shield where the resonators were wasn't put back securely and was rattling up and down some.

Is this the piston slap people are talking about? I checked everything under my car and it all seems secure...

A piston slap sounds like a click or tick sound.

 

[EFI]

Its because forged pistons expand and contract more than the standard hypereutectic pistons. If a forged slug was fit tightly into a bore it would scar the shit out of the walls when heated.

I assume the Voodoo pistons are the basic 4032 forging which should be pretty damn quiet since those pistons don't expand as much as 2618 forgings.

My Mahle forged engine is dead quiet even on winter cold startups (eg. below freezing). My friend's Cobra which utilizes the same type of piston forging is also dead quiet. Another friend's STi with JE 2618 pistons is a bit noisy during warmup, but that is to be expected with those pistons.

What is not expected is a major manufacturer charging those kinds of prices with 4032 pistons just saying "deal with it" to the consumers. Especially when the noise should not be there.

 

[Sandoval]

I assume the Voodoo pistons are the basic 4032 forging which should be pretty damn quiet since those pistons don't expand as much as 2618 forgings.

My Mahle forged engine is dead quiet even on winter cold startups (eg. below freezing). My friend's Cobra which utilizes the same type of piston forging is also dead quiet. Another friend's STi with JE 2618 pistons is a bit noisy during warmup, but that is to be expected with those pistons.

What is not expected is a major manufacturer charging those kinds of prices with 4032 pistons just saying "deal with it" to the consumers. Especially when the noise should not be there.

I'm not sure what the material used is. I wonder how accurate the machining process is though? A factory wrx/STi uses an a and b piston because the bores aren't 100% accurate. I know the voodoo is a hand built motor but hand built probably means install parts out of a box.

 

[Tank]

Not just that... The four engine fails have likely increased the awareness of the sound to the owners and concern is raised.

Four this forum knows of...

 

[Trackaholic]

What is not expected is a major manufacturer charging those kinds of prices with 4032 pistons just saying "deal with it" to the consumers. Especially when the noise should not be there.

What makes you think the noise should not be there?

-T

 

[SpursFan]

Ok so does the noise sound more like a rattle than a slap? Ever since I removed my resonators I notice more of a rattle when the engine is cold and I'm wondering if this is it. Sounds almost like something under the car like below the driver (not the engine area) is rattling. Almost like the heat shield where the resonators were wasn't put back securely and was rattling up and down some.

Is this the piston slap people are talking about? I checked everything under my car and it all seems secure...

If your hearing a rattle you may have the same issue as me, and bad exhaust valve. When I first started hearing this now documented noise it seemed to grow from a rattle to vibration after putting miles on the car. Turns out the drivers side exhaust valve is making most of the noise. The piston slap stops after warming up but the exhaust always makes the noise with valves closed.

 

[Rogue]

The Boss engine was the same way and mine was bullet proof for five years of heavy track use. Voodoo is a little more noticeable, and they probably had enough owners bring them in with concerns to issue this bulletin.

I didn't notice it personally but I can vouch for the Boss 302 motor being bulletproof. I tracked the hell out of mine for a solid 3 years - that motor would run hard on the track all day long and then drive a smooth 200+ miles on the highway to go home. I personally think these flat plane crank motors will prove to be higher maintenance than the 5.0's but so far proving to be very strong for both track and street.

 

[stanglife]

I assume the Voodoo pistons are the basic 4032 forging which should be pretty damn quiet since those pistons don't expand as much as 2618 forgings.

My Mahle forged engine is dead quiet even on winter cold startups (eg. below freezing). My friend's Cobra which utilizes the same type of piston forging is also dead quiet. Another friend's STi with JE 2618 pistons is a bit noisy during warmup, but that is to be expected with those pistons.

What is not expected is a major manufacturer charging those kinds of prices with 4032 pistons just saying "deal with it" to the consumers. Especially when the noise should not be there.

If they are the same as the Boss/Mahle units, they are 4032. They are installed REALLY tight. .0035, I think was the spec. Regardless, with the skirts being so short, they rock until warm.

Regarding the hand-built aspect of these motors. I also "hand-built" my Boss motor from the bare block up. The piston/rod/ring assembly came ready to go. I bought a bore gauge and it looked like zero machining was required. I brought everything to a local race shop that I trust just to get a second opinion. It was perfect out of the box. All I did was ask the shop to measure all of the bores and pistons so that I could make sure the were matched as closely as possible (still a .00015 variance in some cases, so you don't want the smallest piston in the largest hole or vice-versa). Point being, the parts come off the shelf pretty close to perfect. In my case, the block needed to be debur'd BADLY, so I can see how so much junk ends up in the filter, if this isn't done during production.

http://93coupe.com/2012-mustang-boss-302-block-prep-for-engine-build/

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