Are JE pistons supposed to be noisy?

[code7rpd]

I recently completed a 3.2 short stroke with nikasil cylinders and JE 9.8/1 pistons. When the car is cold I get a dull knocking type of sound which goes away once the car is warm. I have heard JE's are noisy but don't known if this sound is consistent with how JE's sound

[cgarr]

They can be noisy if the side clearance is too great, I am using 98mm J&E 10.5/1 with a clearance of .0015 without any problems.

[code7rpd]

I never checked the clearance - I bought the cylinder and pistons from EBS Racing and assumed they were good to go.

[Henry Schmidt]

When building a Porsche engine or any high performance engine for that matter, the only assumption that should be made is that "you can't assume anything !"

Sounds like piston slap to me.
Fear not weed hopper, a little piston slap won't hurt anything.
It's just a little annoying. In fact loose means less friction, less heat and more horse power.

[ChrisBennet]

Like Henry said, never assume. Coming from EBS, I'd think that the side clearances would be matched (if they are replated cylinders). You can never assume that though.
For example, the last 2 sets of "9.8:1" JE pistons I received from EBS (for a 3.2SS I was building) CC'd out to 10.5:1.
-Chris

[code7rpd]

Thanks guys - at least I know for next time.

[A Quiet Boom]

You oughta here drag pistons on a V8 with a 4" stroke, you'd swear the rods where loose.

Henry's right, never assume anything. I've had custom pistons made by reputable manufacturers not measure out properly, same with a custom crank. It only took me one assumption to never assume again.

[fireant911]

Originally posted by Henry Schmidt
Sounds like piston slap to me.
Fear not weed hopper, a little piston slap won't hurt anything.
It's just a little annoying. In fact loose means less friction, less heat and more horse power.

I do not have a wealth of experience rebuilding engines hence my 'clarifying' question... Is piston slap not due to additional sidewall clearances? It is my understanding that during normal operation only the rings are in contact with the cylinder wall not the piston skirt. If additional sidewall clearances are present I can see the point about less friction and less heat but I am having trouble accepting the statement about more horsepower. How can this be? Would the additional clearances in fact allow more combustion gas blow-by thus decreasing the power?

[Henry Schmidt]

The piston dome determines compression ratio. The rings seal the compression in. The small amount of piston rocking (piston slap) has no effect on compression.
More hp is a function of less friction. Be it very little.
There are small areas of fiction throughout the engine that when accumulated cause horse power loss. By themselves these small losses are relatively meaningless but added together equal measurable horse power loss. Many of the piston manufacturers are coating their piston skirts in an attempt to control some of this friction.
This parasitic loss is the target of a plethora of magic oils, engine additives and "snake oils" that form a multi billion dollar industry. Mobile One, Z-Max, Slick 50 and STP, are just a few.

[hcoles]

ditto on check all parts and clearances coming in either from a machine shop or e.g. EBS - quality processes don't really exist in the classic sense in the aftermarket IMHO...there could well be exceptions but not many

[cstreit]

I'm not sure I'd lump Mobil-1 in with "snake oils" Henry... Porsche certainly doesn't. What's your beef with it?

[Henry Schmidt]

Originally posted by cstreit
I'm not sure I'd lump Mobil-1 in with "snake oils" Henry... Porsche certainly doesn't. What's your beef with it?

It looks like you're bringing your own bias to the discussion.
Judging by your post I would guess that you think Mobile One is a "magic oil."
I don't have a beef with any of them. I was just saying that there is an entire industry devoted to controlling friction in engines.


BTW: I wouldn't put too much faith in commercial partnerships. If I'm not mistaken, Porsche derives a financial benefit from using Mobile One.

[cstreit]

How biased... It's just a good easily available synthetic oil.

Using the term "snake oil" implies that Mobil-1 is an inferior product or doesn't perform as advertised (especially when comparing it against REAL snake oils like slick-50)... Do I think it's better than many other high-grade synthetics? Nope. But I can't buy Redline and some others at the local store and haven't seen an appreciable wear differences between engines that ran one vs. the other.

So I'm genuinely curious if you're implying it IS inferior to standard synthetics and why....?

[Henry Schmidt]

The bias is in how you read my post.

I didn't imply anything. I stated that there were " magic oils (certainly not a negative more likely positive ), engine additives ( relatively benign) and snake oils (certainly negative)." You are the one that assigned the negative to Mobile one.
I just said it was part of a multi-billion dollar industry. This is a clear and accurate statement. It was not my intention to imply any negative to any specific product.

But since you asked so nicely, my opinion about Mobile One and for that matter all synthetic oil is that it is very thin and has a tendency to cause early 911 engines to leak more than they already do.

I also have a problem with any oil that advertises extended use.

I am a firm believer in changing your oil. Time is an issue with oil changes as well as mileage. I hope this answers your question.

BTW: Porsche would run Monkey sweat in their engines if they got paid enough. Believe me Porsche gets paid to endorse Mobile One.

[cstreit]

I did interpret your post that way... However I get your drift now...

My favorite is the new Castrol commercials that imply your engine will be slow without it.

Perhaps LubeMaster can expound upon the lubrisoty of Monkey Sweat in case porsche does switch.

[armandodiaz]

Originally posted by ChrisBennet
Like Henry said, never assume. Coming from EBS, I'd think that the side clearances would be matched (if they are replated cylinders). You can never assume that though.
For example, the last 2 sets of "9.8:1" JE pistons I received from EBS (for a 3.2SS I was building) CC'd out to 10.5:1.
-Chris

Is it possible to measure compression ratios? How?

[Henry Schmidt]

Originally posted by ChrisBennet
................ the last 2 sets of "9.8:1" JE pistons I received from EBS (for a 3.2SS I was building) CC'd out to 10.5:1.
-Chris

That would make perfect sense. JE manufactures what they call shelf (generic) pistons and for 98 mm they have 9.5:1, 10.5:1 for both 3.0 crank (70.4) and the 3.2 crank (74.4). Your discovery fits.

The reason to sell shelf pistons is that they a cheaper and they can be purchased one at a time with little or no lead time. Custom pistons must be ordered in sets of 4 or more and require 3-6 weeks lead time.

[ChrisBennet]

Originally posted by armandodiaz
Is it possible to measure compression ratios? How?

Yes. It's a pretty standard operation when building a motor. You use fluid measurements and engine dimensions (stroke,deck height, etc) to calculate the difference in cylinder volume between when the piston is at the bottom of the stroke and the top of the stroke.
If the engine is all together there are other methods.
-Chris

[armandodiaz]

Thanks I'll have to read up on this.

[PPilot]

Monkeys don't sweat.they just get very dewey.......