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Old 09-21-2007, 06:05 AM   #1
bugeyes
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Angry Newly sleeved EJ257 - Bores out-of-round!!!

Just had my EJ257 sleeved, bored, honed etc for my new buildup.

As I am very anal with my engine builds I was checking the bore clearance and roundness.
To my great dissapointment the bores measure up to half a thou out of round. My first thoughts were the cases have been put togther and torqued prior to bore/hone but the builder tells me it was not done like this.

It beats the hell out of me how a new (non mass produced), sleeved block can be out of round.

Pistons are new coated CP's. Piston to bore clearance seems to be acceptable although with the pistons being perfectly round the clearance obviously differs depending where you measure it.

Anyone know what the acceptable limits are?

I must admit I am considering going an oversize already.......
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Old 09-21-2007, 11:32 AM   #2
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Did the person boring them use a plate to simulate the head torqued to the block before they bored it? (I forget the name of the plate, it was a big discussion in here a while back and caused what seemed to be out-of-round bores, but were actually round when the heads were put on)
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Old 09-21-2007, 12:54 PM   #3
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was a torque plate used, as 8complex is asking...it will make the bore without the head bolted down be out of round...with the head torqued on it will/should be round.
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Old 09-21-2007, 12:56 PM   #4
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half a thou is pretty bad, are they all in the same direction? that may indicate a problem with the chuck
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Old 09-21-2007, 02:05 PM   #5
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This happened to me years ago with a honda motor sleeved at bensons.
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Old 09-21-2007, 02:41 PM   #6
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Quote:
Originally Posted by bugeyes View Post
... although with the pistons being perfectly round the clearance obviously differs depending where you measure it....
Pistons are NOT perfectly round. They are "cammed" because they expand thermally in one direction (parallel to the wrist-pin) more than the other.

Could this be throwing off any of your measurements?
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Old 09-21-2007, 03:15 PM   #7
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Quote:
Originally Posted by SaabTuner View Post
Pistons are NOT perfectly round. They are "cammed" because they expand thermally in one direction (parallel to the wrist-pin) more than the other.

Could this be throwing off any of your measurements?
Are you meaning to tell me that pistons have an ovate profile? I find that hard to believe based on the fact that they are turned in a lathe. I suppose they could fixture them a couple thou off center. However, doing this would mean the part would have to be index chucked which could make for production nightmares.
Also even if the pistons were "cammed" they would be that way in order to be concentric to the bore after they have expanded. By your own logic the bore should br perfectly round, and the pistons are "cammed" in order to be round after non uniform expansion.

The ideal cylinder bore is perfectly round. There are no provisions to make bores eccentric while honing them that would throw off measurements as you described; and it is doubtfull there are any during piston machining either. Honda used grossly ovate pistons and bores on a prototype motorcycle, and gave it up due to production difficulties and cost.

Last edited by MartinSTi05; 09-21-2007 at 03:40 PM. Reason: adding details
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Old 09-21-2007, 03:32 PM   #8
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Bugeyes- you have to understand all the stresses your are applying to an engine because of the sleeving process.
It has taken me many many different machinists before I was able to get an exceptable job!
The sleeved blocks I offer are damn near perfect!
- No sinking sleeves
- True bores
- Mains align bored and honed (this area often gets thrown off during the sleeving process)
(shouldnt this quality be expected from a machinist?)
I would suggest getting a piston set a few thou larger in diameter, and have a machinist true up the bores.
I would be happy to help you, or email Nick@JE ndiblasi@jepistons.com.
This is costly, but the correct way to go about it at this point (the cylinders should have been able to be trued to the pistons you currently have).
Doing this procedure with the block halves torqued together correctly and the deck plate torqued to the block using the same fasteners used to attach the cylinder heads.

Martin-
Alot of pistons these days have a "cam" profile. This in fact means the skirts have an ovate profile. This is now done by a CNC (this process was done by hand many years ago).
There are hundreds of profiles that can be used based on application.
Cobb Engines uses these types of pistons.
Cam profile changes are based on wear patterns seen on the piston skirts.

- J.
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Old 09-21-2007, 03:33 PM   #9
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Quote:
Originally Posted by bboy View Post
half a thou is pretty bad, are they all in the same direction? that may indicate a problem with the chuck
I don't have a bunch of engine building experience...but I think .0005" is not bad at all.

http://www.allpar.com/mopar/redram.html

Search the page for "round". You will see the max out of round of the cylinder bore.

They allow .005" (10x more than what you are talking about). Now, that is a non-turbo engine....

We need an expert opinion here..

Patrick
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Old 09-21-2007, 03:41 PM   #10
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Partick

The factory Subaru spec is the following

Taper- Standard= .0006"
Limit= .002"
Roundness- Standard= .0004"
Limit= .002"

So the ammount Bugeyes is talking about is exceptable for a factory engine.
So it comes down to how intricate you are. If it was my engine I would have a higher expectation for a race engine.

- J.
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Old 09-21-2007, 03:45 PM   #11
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Quote:
Originally Posted by MartinSTi05 View Post
Are you meaning to tell me that pistons have an ovate profile? I find that hard to believe based on the fact that they are turned in a lathe. I suppose they could fixture them a couple thou off center. However, doing this would mean the part would have to be index chucked which could make for production nightmares.
Also even if the pistons were "cammed" they would be that way in order to be concentric to the bore after they have expanded. By your own logic the bore should br perfectly round, and the pistons are "cammed" in order to be round after non uniform expansion.

The ideal cylinder bore is perfectly round. There are no provisions to make bores eccentric while honing them that would throw off measurements as you described; and it is doubtfull there are any during piston machining either. Honda used grossly ovate pistons and bores on a prototype motorcycle, and gave it up due to production difficulties and cost.
http://staff.washington.edu/ryanlee/...7;20Design.htm

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Piston Design

Pistons are designed with features which perform specific functions during engine operation. The piston head or crown receives the majority of the initial pressure and force caused by the combustion process. The piston pin area is exposed to a significant amount of force due to rapid directional changes. It is also subjected to thermal expansion caused by the transfer of heat from the head to the body of the piston. The piston pin area is subject to more thermal expansion than other areas of the piston. This occurs from the thermal expansion properties of cast aluminum alloy and the mass in the piston pin area.

Some pistons are cast and machined at the factory into a cam ground (elliptical shape). An elliptical shape is an oval shape in which one-half is a mirror image of the other half. These piston shapes provide an advantage in conforming to the ever-changing dimensions of the cylinder bore. The piston is designed to be an elliptical shape when cold. As the engine reaches operating temperature, the piston pin bore area expands more than other thinner areas of the piston. At operating temperature, the piston shape becomes a circular shape, which matches the cylinder bore for improved sealing and combustion efficiency.
-Adrian
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Old 09-21-2007, 03:52 PM   #12
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Quote:
Originally Posted by MartinSTi05 View Post
Also even if the pistons were "cammed" they would be that way in order to be concentric to the bore after they have expanded. By your own logic the bore should br perfectly round, and the pistons are "cammed" in order to be round after non uniform expansion.
I never said the ideal bore was not round. However, when it was said that the measurements (clearance) around the piston varied with position, I thought it should be pointed out that SOME variance is NORMAL due to piston "camming".

ALSO ... it's NORMAL for cylinder bores to be slightly out-of-round when cold IFF (if, and only if) they were "hot honed". Many ultra lightweight racing engines won't even turn-over until warm coolant is run through the block and cylinder head because they are so out-of-round when cold.

It's possible, if this block was "hot-honed", that it is perfectly round when it is at operating temperature, but not round when at room temperature.

Just food for thought ...
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Old 09-21-2007, 04:02 PM   #13
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This thread reminded me of an engine from the past.
The Honda NR750, Oval pistons!
Have fun honing this one!
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Old 09-21-2007, 04:57 PM   #14
bugeyes
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The measuring of the bores was not done by checking the clearance between piston and bore. The piston size was measured as recommended by the manufacturer specification sheet. This was done with micrometer at a point approx 0.5" abouve the bottom edga between the skirts.
The bores were measured up with a internal micrometer. It was during this process of bore measuring the out-of-round was picked up.
Therefore the error in roundness was not due to any piston "ovalness".

I can see the variation is within Subaru spec but for a performance engine, frankly I would like to have seen it damn near perfect.
I'll have to think about my options with this one.

Thanks all for you replies......
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Old 09-21-2007, 05:59 PM   #15
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Quote:
Originally Posted by bugeyes View Post
I can see the variation is within Subaru spec but for a performance engine, frankly I would like to have seen it damn near perfect.
I'll have to think about my options with this one.

Thanks all for you replies......
Just don't forget what I mentioned about hot-honing. I don't know if your engine was, and most aren't. But, before you give up all hope in the thought that this is too out of round ... it's still possible that it's closer to perfectly round when warm even without hot-honing.

I mean ... you never know, right?
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Old 09-21-2007, 06:01 PM   #16
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Quote:
Originally Posted by Jeremy@Cobb View Post
Bugeyes- you have to understand all the stresses your are applying to an engine because of the sleeving process.
It has taken me many many different machinists before I was able to get an exceptable job!
The sleeved blocks I offer are damn near perfect!
I know who sleeves your blocks...the work is top notch!

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Old 09-22-2007, 03:15 PM   #17
charliew
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Default measuring bores

I've seem two machinist side by side measuring parts at a fastener manufacturing plant be .0005 different. You can hand a mike to two different individuals and until they learn to tighten the mike the same they will read .0005 different easily. Mikeing parts is a time consuming learned skill.

Charlie
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Old 09-23-2007, 06:09 AM   #18
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Quote:
Originally Posted by MartinSTi05 View Post
Are you meaning to tell me that pistons have an ovate profile? I find that hard to believe based on the fact that they are turned in a lathe. I suppose they could fixture them a couple thou off center. However, doing this would mean the part would have to be index chucked which could make for production nightmares.
Also even if the pistons were "cammed" they would be that way in order to be concentric to the bore after they have expanded. By your own logic the bore should br perfectly round, and the pistons are "cammed" in order to be round after non uniform expansion.

The ideal cylinder bore is perfectly round. There are no provisions to make bores eccentric while honing them that would throw off measurements as you described; and it is doubtfull there are any during piston machining either. Honda used grossly ovate pistons and bores on a prototype motorcycle, and gave it up due to production difficulties and cost.
no he's saying they are made round, but when they expand in the heat they will not be perfectly round.
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Old 09-23-2007, 06:50 AM   #19
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Originally Posted by prometheum View Post
no he's saying they are made round, but when they expand in the heat they will not be perfectly round.
No, what I was saying was that IF they WERE made round, they would NOT be round when they expanded, and thus NOT fit in the bore well. So, they deliberately make them "cammed", or NOT round, when they are cold so that they ARE round when warm.
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Old 09-23-2007, 07:00 AM   #20
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Quote:
Originally Posted by bugeyes View Post
Just had my EJ257 sleeved, bored, honed etc for my new buildup.

As I am very anal with my engine builds I was checking the bore clearance and roundness.
To my great dissapointment the bores measure up to half a thou out of round.
we're talking about 0.0005 of an inch or milimeters?
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Old 09-23-2007, 02:16 PM   #21
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Quote:
Originally Posted by bugeyes View Post
Just had my EJ257 sleeved, bored, honed etc for my new buildup.

As I am very anal with my engine builds I was checking the bore clearance and roundness.
To my great dissapointment the bores measure up to half a thou out of round. My first thoughts were the cases have been put togther and torqued prior to bore/hone but the builder tells me it was not done like this.

It beats the hell out of me how a new (non mass produced), sleeved block can be out of round.

Pistons are new coated CP's. Piston to bore clearance seems to be acceptable although with the pistons being perfectly round the clearance obviously differs depending where you measure it.

Anyone know what the acceptable limits are?

I must admit I am considering going an oversize already.......
If the bore/hone was done with the case halves apart, you will have more issues than out of round. Most likely you will have taper as well

Was the deck surfaced with the case apart also?

The stock STI block is good for 750WHP, why would you cause yourself the pain and cost of sleeving it?
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Old 09-23-2007, 09:11 PM   #22
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Quote:
Originally Posted by Jeremy@Cobb View Post
Partick

The factory Subaru spec is the following

Taper- Standard= .0006"
Limit= .002"
Roundness- Standard= .0004"
Limit= .002"

So the ammount Bugeyes is talking about is exceptable for a factory engine.
So it comes down to how intricate you are. If it was my engine I would have a higher expectation for a race engine.

- J.
Good stuff...thanks for the info!

That was the expert information I was looking for.

Patrick
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Old 09-23-2007, 10:15 PM   #23
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That half a thousandths will most likely be gone once you first start the motor as the rings seat too the walls.
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Old 09-24-2007, 06:36 AM   #24
Illicit1
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I have to agree ^^ halt a thou (0.01mm) is nothing to worry about. as soon as the block heats up she'll move more than that.
I've made a supercharger housing out of billet ally that was perfect on the machine but when we took it off the bores moved a couple of hundreths (about a thou) and the engineers said they could still used them.



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