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piston skitrt clearance

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Kind of a random question, but does anyone know what the skirt clearance is for stock j35a4 pistons to cylinder walls???

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my guess would be .002"

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I don't know, but on the LS motors it matters on the material of the piston, factory piston on a LS are a Cast hypertutectic so they are at .002-.003 the 4032 pistons are .003-.004 and the 2618 are .005-.006 and when you go to a boosted application It adds .003 more clearance depending on boost

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7 hours ago, ltpyro said:

Kind of a random question, but does anyone know what the skirt clearance is for stock j35a4 pistons to cylinder walls???

Please post your build details as you go.

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So from the PDF above the clearance is approx. .0011 of an inch.

 

8 hours ago, Kraut_n_Rice said:

Please post your build details as you go.

Hopefully I'll be building up the motor after this coming season.  I'm still figuring out what I need to do to get to the end result I want.  This question came up because I read some posts on here that referred to "cylinder wobble" or cylinder vibration".  I've never heard of these terms but thought maybe they were the same as piston slap and then the snowball lead to wondering what the clearance was.

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Posted (edited)

What are you trying to accomplish with a rebuild? More power? Reliability? Turbo? If it's the first two another salvage yard engine would be easier and cheaper. If it's because you want to turbo it I'd recommend  forged pistons and good rods. As Alper said, cast pistons require less piston to wall clearance, forged pistons require more, John@Outfront is probably in the ballpark with .002".  I'm not much help with what Honda wants. 

But since you are asking, to do it right...…...

Starting with a clean bare block you will need to either measure all of the cylinders for taper and roundness yourself, or have an engine machine shop do it for you to determine if the block needs to bored and/or honed. Once you determine what it will take to get the cylinders straight/ round and what type of piston you want to use you can look at your piston manufacturers chart to find the piston that will be required for the diameter of hole you will have (stock bore, .010, .015, .020 over etc). Once you have the pistons in your possession, the machine shop will bore if necessary or final hone the cylinders to fit the particular pistons you have. You can then have the new pistons and rings weighed and compared to the old to determine if it needs to balanced, they almost always need to be balanced after replacing pistons. 

Another option if you just want to "freshen it up" is to use a ball hone to deglaze and reapply the cross hatch to the cylinders, then install your new stock bore pistons and rings. This will remove material and make them bigger but it's usually not an issue if done by someone who knows what they are doing. Watching YouTube isn't going to cut it, sorry. A machine shop hone is an even better option. Different types of rings require different cylinder finishes. Unfortunately there isn't a one size fits all approach. 

Internal engine assembly is definitely something that should be left to a professional if that's not your forte. And yes please post your build details. 

 

Edited by fortyfour

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Posted (edited)
33 minutes ago, fortyfour said:

What are you trying to accomplish with a rebuild? More power? Reliability? Turbo? If it's the first two another salvage yard engine would be easier and cheaper. If it's because you want to turbo it I'd recommend  forged pistons and good rods. As Alper said, cast pistons require less piston to wall clearance, forged pistons require more, John@Outfront is probably in the ballpark with .002".  I'm not much help with what Honda wants. 

But since you are asking, to do it right...…...

Starting with a clean bare block you will need to either measure all of the cylinders for taper and roundness yourself, or have an engine machine shop do it for you to determine if the block needs to bored and/or honed. Once you determine what it will take to get the cylinders straight/ round and what type of piston you want to use you can look at your piston manufacturers chart to find the piston that will be required for the diameter of hole you will have (stock bore, .010, .015, .020 over etc). Once you have the pistons in your possession, the machine shop will bore if necessary or final hone the cylinders to fit the particular pistons you have. You can then have the new pistons and rings weighed and compared to the old to determine if it needs to balanced, they almost always need to be balanced after replacing pistons. 

Another option if you just want to "freshen it up" is to use a ball hone to deglaze and reapply the cross hatch to the cylinders, then install your new stock bore pistons and rings. This will remove material and make them bigger but it's usually not an issue if done by someone who knows what they are doing. Watching YouTube isn't going to cut it, sorry. A machine shop hone is an even better option. Different types of rings require different cylinder finishes. Unfortunately there isn't a one size fits all approach. 

Internal engine assembly is definitely something that should be left to a professional if that's not your forte. And yes please post your build details. 

 

Well said. You need a machine shop with a dial bore guage to measure and set clearances. In a performance engine with new pistons you should also set the ring end gap. For a dune car it will be higher since the motor is run so hard.

 

https://www.glamisdunes.com/invision/index.php?/forums/topic/348722-knock-knock-shes-broke-35-nissan-vq35de-engine-rebuild/&do=findComment&comment=5074648

https://www.glamisdunes.com/invision/index.php?/forums/topic/348722-knock-knock-shes-broke-35-nissan-vq35de-engine-rebuild/&do=findComment&comment=5075574

https://www.glamisdunes.com/invision/index.php?/forums/topic/348722-knock-knock-shes-broke-35-nissan-vq35de-engine-rebuild/&do=findComment&comment=5074650

https://www.glamisdunes.com/invision/index.php?/forums/topic/348722-knock-knock-shes-broke-35-nissan-vq35de-engine-rebuild/&do=findComment&comment=5074811

 

Edited by onanysunday

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Posted (edited)
7 hours ago, ltpyro said:

So from the PDF above the clearance is approx. .0011 of an inch.

 

Hopefully I'll be building up the motor after this coming season.  I'm still figuring out what I need to do to get to the end result I want.  This question came up because I read some posts on here that referred to "cylinder wobble" or cylinder vibration".  I've never heard of these terms but thought maybe they were the same as piston slap and then the snowball lead to wondering what the clearance was.

The wobble is because the deck is not closed. The cylinders can vibrate independently of the block 

Have to have a closed deck block in higher boost applications.

Edited by Legit Duner

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3 hours ago, fortyfour said:

What are you trying to accomplish with a rebuild? More power? Reliability? Turbo? If it's the first two another salvage yard engine would be easier and cheaper. If it's because you want to turbo it I'd recommend  forged pistons and good rods. As Alper said, cast pistons require less piston to wall clearance, forged pistons require more, John@Outfront is probably in the ballpark with .002".  I'm not much help with what Honda wants. 

But since you are asking, to do it right...…...

Starting with a clean bare block you will need to either measure all of the cylinders for taper and roundness yourself, or have an engine machine shop do it for you to determine if the block needs to bored and/or honed. Once you determine what it will take to get the cylinders straight/ round and what type of piston you want to use you can look at your piston manufacturers chart to find the piston that will be required for the diameter of hole you will have (stock bore, .010, .015, .020 over etc). Once you have the pistons in your possession, the machine shop will bore if necessary or final hone the cylinders to fit the particular pistons you have. You can then have the new pistons and rings weighed and compared to the old to determine if it needs to balanced, they almost always need to be balanced after replacing pistons. 

Another option if you just want to "freshen it up" is to use a ball hone to deglaze and reapply the cross hatch to the cylinders, then install your new stock bore pistons and rings. This will remove material and make them bigger but it's usually not an issue if done by someone who knows what they are doing. Watching YouTube isn't going to cut it, sorry. A machine shop hone is an even better option. Different types of rings require different cylinder finishes. Unfortunately there isn't a one size fits all approach. 

Internal engine assembly is definitely something that should be left to a professional if that's not your forte. And yes please post your build details. 

 

Well just for the record, I am not trying to bore the cylinders myself.  I would use a shop for anything that precise.  When I get a little closer to figuring out what I want/can do for a build I'll start a thread going on it.   But, just for a quick look into my madness...…..  

I do want a turbo v6 car.  I have a honda 3.5.  I would like to make it a twin turbo for no other reason than I think it looks better and If i'm going to spend the money to improve the car I do performance as well as looks.   I also don't like the idea of motors being a throw away component just because they are somewhat inexpensive these days, or at least these motors are somewhat.

I'm not 100% sure that is the best motor to get me what I want after reading some posts on here.  Sure everyone agrees that the honda takes boost well, up to a point.   That point seems to be about 7-8psi on stock parts.  After that I hear about "cylinder wobble".  No one has ever really explained what that is to me (I also never asked on these forums).  So I was, out of curiosity trying to work out if cylinder wobble was the same thing as piston slap, just with a different term with different people.  So I was looking into what the stock piston for these motors looked like.  So far I can make out that it is a short piston with very little skirt.  This make me think that yes the issue with high boost on this motor is piston slapping the cylinder wall.  I'm still unconvinced that the cylinder wall is "vibrating" or "wobbling" as this implies to me that the cylinder is moving in some way, and if it is that would be way worse than piston slap and the cylinder could move up or down, which should not be the case.

Please correct me if I'm wrong on the cylinder wobble vs piston slap.  I'm not that old... but my knowledge comes from my father who is old, lol.  

I know there is a lot of knowledge on these forums, but I'm not the type of person to just except an "it doesn't work" or "that's how it is" answer.  I like to know why and then see if that can be changed.  So apologies ahead of time if I don't accept and answer right away with out asking questions or doubting, I Don't mean anything by it and am definitely not trying to insult anyone. 

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58 minutes ago, Legit Duner said:

The wobble is because the deck is not closed. The cylinders can vibrate independently of each other.  

Have to have a closed deck block in higher boost applications.

Could you explain this in more detail?  How are the cylinders vibrating? because like I said above that makes me think they are moving and therefore can move out of place.

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A closed deck means the actual cylinder are supported by the block at the top.  Honda blocks only support the cylinder at the base.  Support at the top doesn't allow the cyclinder to move at the top.  Piston slap is the  when the piston is allowed to excessively rock in the cylinder on the wrist pin.  

Stock Honda block 

image.png.702bfc9fba3ea90baf15a9dae8c7d009.png

 

Honda block with aftermarket sleeves.

image.png.a988bbe72d667e3e8dd84f261fa0998a.png

LS block.

image.png.647862213da211ddee61ae41d51ba82f.png

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49 minutes ago, ltpyro said:

Could you explain this in more detail?  How are the cylinders vibrating? because like I said above that makes me think they are moving and therefore can move out of place.

It's caused by resonance. Top of cylinders have no support.

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36 minutes ago, Kraut_n_Rice said:

A closed deck means the actual cylinder are supported by the block at the top.  Honda blocks only support the cylinder at the base.  Support at the top doesn't allow the cyclinder to move at the top.  Piston slap is the  when the piston is allowed to excessively rock in the cylinder on the wrist pin.  

Stock Honda block 

image.png.702bfc9fba3ea90baf15a9dae8c7d009.png

 

Honda block with aftermarket sleeves.

image.png.a988bbe72d667e3e8dd84f261fa0998a.png

LS block.

image.png.647862213da211ddee61ae41d51ba82f.png

 

5 minutes ago, Legit Duner said:

It's caused by resonance. Top of cylinders have no support.

Ok, that is a good explanation, now I can understand the difference.  Would you believe that a google search didn't come up with that? 

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Posted (edited)

look at kraut_n_rice pic of the v6 honda.  look how the cylinder are attached to each other.  the outer cylinders are attached at one point.  the center cylinder attached at two points 3 an 9 o'clock. now apply massive pressure and tell me what shape the center cylinder would look like.  it would move more in the 12 and 6 o'clock directions. less then at the 3 and 9.  this is the cylinder flexing. over 1000's of cycles this can actually scrub the head gasket and cause failure.  look at the LS block. each cylinder is attached to the block at 4 places. far superior for boost.  imagine if you could support all the way around the bore?

Edited by John@Outfront Mtrsprts

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Posted (edited)

Surprised no one has linked this yet.

 

Edited by Kraut_n_Rice

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4 minutes ago, Kraut_n_Rice said:

Surprised no one has linked this yet.

 

who is that handsome man?  good video.

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49 minutes ago, Kraut_n_Rice said:

Surprised no one has linked this yet.

 

I've actually watched this video a while back when I was looking up what an open deck motor was.  Unfortunately I didn't get what cylinder wobble was from it.  I did understand why you can't put a small attachment point at the top of the cylinder.

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So what's a reasonable expectation from a j35a4 with stock rods and pistons vs high quality forged rods and pistons?  I would love to make 500hp, 50/50 mixed fuel would be ok with me, don't want to run e85 though.  Been saving up for the build after this season.  Going to be a big job as its going to include a transmission swap, just not sure which one yet.

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Boost and a stock A4 need race gas.  50/50 isn't going to get you reliable 500HP, doubt race will either.  Will it make it a couple times?  Sure.  Will it last until Veterans day?  Doubt it.

If I'm going to build a motor, it will have a tune for pump, and one for race.  Race will be "No Fu*ks Given" mode.

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11 minutes ago, ltpyro said:

So what's a reasonable expectation from a j35a4 with stock rods and pistons vs high quality forged rods and pistons?  I would love to make 500hp, 50/50 mixed fuel would be ok with me, don't want to run e85 though.  Been saving up for the build after this season.  Going to be a big job as its going to include a transmission swap, just not sure which one yet.

Do yourself a favor and if available run the E85.  Ethanol is magic in a boosted motor due to its cooling effect.  And although you will burn more at a stoich of 9.8 to 1 it will be far cheaper than race gas. And easier to find at the pump. (I assume you are in Cali).  Fuel system with ptfe lines and steel fittings is easy. No paper filter. Glass 10 micron and stainless 100 micron.

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Posted (edited)
12 minutes ago, Kraut_n_Rice said:

Boost and a stock A4 need race gas.  50/50 isn't going to get you reliable 500HP, doubt race will either.  Will it make it a couple times?  Sure.  Will it last until Veterans day?  Doubt it.

If I'm going to build a motor, it will have a tune for pump, and one for race.  Race will be "No Fu*ks Given" mode.

Is this because the compression is too high?  I'm assuming pulling more timing from the motor or doubling the gasket isn't enough to drop it?
 

Is 400hp or 450hp more reasonable?

Edited by ltpyro

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2 minutes ago, ltpyro said:

Is this because the compression is too high?  I'm assuming pulling more timing from the motor or doubling the gasket isn't enough to drop it?

There are many factors affecting boost,  compression, and what you can get away with. Here is my effective compression ratio with boost figured in. The higher the compression the more likely hood of preignition. That is why you need better quality fuel.  I don't think you could ever double up on the head gasket and even if a thicker one is available it might drop it 1/10 of a point. Example 10 to 1 down to 9.9 to 1.  Not enough to do anything.  The motor needs a certain amount of timing to work properly and you can only pull so much out. Larger injectors are needed as well and the duty cycle must be correct for each injector. An intercooler is also a big factor on intake air temps. My motor years ago with no intercooler and only 7psi had IATs over 200 degrees. Now at 12 psi and a larger properly sized intercooler it is 30 degrees above ambient.   Also a dune car with paddles puts a lot more load on an engine vs lets say a street car. I know my car on a steep hill AND on the dyno will pull extra boost because the load is so hard. If you want a boosted motor to last you must have the proper fuel for the setup.  My Nissan is a very unique setup and I am not a Honda guru. But the principles are the same. With that said you can get some good advice here and I would recommend doing some searches on this forum for past discussions.

 
Quote

 

Boost and Altitude Correction to Compression

You are running 12 PSI of boost at an altitude of 1000 feet. Your motor's static compression is 8.8 :1. At this boost level and altitude your effective compression ratio is 15.78 :1, and without altitude correction your compression ratio would be 15.98 :1

 

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34 minutes ago, Kraut_n_Rice said:

Boost and a stock A4 need race gas.  50/50 isn't going to get you reliable 500HP, doubt race will either.  Will it make it a couple times?  Sure.  Will it last until Veterans day?  Doubt it.

If I'm going to build a motor, it will have a tune for pump, and one for race.  Race will be "No Fu*ks Given" mode.

How much power can the Honda bottom end handle? Just for reference I know my car now on a Mustang dyno made 350 rwhp (485 crank with the 2d at the time). Dynojet of course would read way higher on the HP number. Anyway I think I was at about 320 rwhp on E85 and 10psi boost when this happened. Of course I beat on that stock motor for 10 years and amazing it lasted that long.

20170117_171429_resized.jpg.0b621f4b1dcaf992ad831018eb111061.jpg

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J motors are making up to a claimed 6-700whp on stock bottom ends. (Street racers)

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