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Jugs and Slugs: Confessions of a JE Piston owner

Well, with all the chin music on the forum as of late with regard to the relative merits of JE pistons, no display of photographs of my new set of 81mm JE pistons would be complete without the required anticipatory arguments:

1) Yes, I know some people don't like JE's. I have read every thread on this forum about it, and spoken with the thought leaders of the Engine Rebuilding Community. Steve Weiner in particular is "on the record" and I deeply respect his opinion based on long experience. I have spoken with Grady about the matter at length. At the end, I had to make a decision based on the below criteria and elected to go with the JEs.

2) Mahle doesn't make an 81mm piston unless you want a 906. So if you want to overbore Biral cylinders for a teeny-weeny displacement bump and to true up the bores, you have to spend $,$$$ for a set of 906 Mahles and then mill the tops of the pistons off to lower the compression down from 10,3 to a more reasonable 9,3 or so. Dem's expensive shavings you betcha!

3) My supplier for the pistons, Dr. Charles Navarro of LN Engineering "Nickies" fame, has hundreds of sets in use and his own constellation of data points to draw from. His experiences with JE have been positive, as long as you are very specific with what you want and don't go too crazy with the design.

4) I am aware that there are new Mahle Nikasil in 80 or 84 available. Unfortunatlely, the fin pattern is different which violates the Concours rule. This is not a race engine, it is the prime mover of a time machine that will have a hard redline at 7,000 and spend most of its life on the street between 3,500 and 6,000.

5) Bla bla bla show us ze pistons already!









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Old 09-22-2007, 04:44 AM
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Old 09-22-2007, 04:47 AM
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Old 09-22-2007, 04:48 AM
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A few comments.

1) Note the skirt is coated with dry film lubricant, this will reduce scuffing at startup.

2) "M" forging.

3) Anti-detonation grooves above the top ring. The reasoning is this moves the top ring down and is intended to dissapate the shock wave associated with detonation before it can seize the top ring in its groove. Given the reputation of 2,0 liter heads for detonation, I thought this was worth a try. As the old Cole Porter song goes, "Experiment. . . and you'll see."

3a) Ring package is 1.2 top ring, 1.5 second ring, 3mm oil ring. Compare this to the original 2,0 liter spec of 1.5, 2.0 and 4mm for the oil ring. Locks are JE wire lock, not those spiralocks that sliced somebody's hand open.

4) Note the sharp edges on the valve reliefs. These will be knocked down with abrasive cloth prior to installation. They aren't exactly knife edges but I don't want any hot spots from the thin metal, this can cause preignition.

5) Valve reliefs are sized for "S" valves which are larger than the 39/35 nailheads in my engine. However, the hope is these will unshroud the valve for better breathing. I ran the calculation to determine the change in dome volume if you made the reliefs clear the valves by only 1mm and it didn't make a material difference in dome volume, so we went with the larger reliefs.

6) Note reconditioned cylinders by Milennium Technologies. Fins were lightly bead blasted (Concours) and the cylinders match-honed to a clearance of 0.003" +.0005 -0.000. I'll have some of my usual graphs when I have time.

7) You cannot see the cross-hatch in the photos but it's there, and it's beautiful. Many cylinders look like somebody used a piece of 80 grit, this is a very fine hatch to faciliate ring rotation that is invisible to the camera.

Any and all comments, suggestions are welcome!
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Last edited by 304065; 09-22-2007 at 05:03 AM..
Old 09-22-2007, 05:00 AM
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pics

John, they look Very nice. Also I am working on an engine that should have some orig. hardware for you.

Mike Bruns JBRacing.com
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Old 09-22-2007, 05:10 AM
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Nice stuff
We use these






Old 09-22-2007, 06:48 AM
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Old 09-22-2007, 07:43 AM
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"7) You cannot see the cross-hatch in the photos but it's there, and it's beautiful. Many cylinders look like somebody used a piece of 80 grit, this is a very fine hatch to faciliate ring rotation that is invisible to the camera.
"


John,
Beautiful pieces.

But cross hatching for ring rotation or to facilitate piston ring break-in with the cylinder surface? I haven't heard about the former. the latter is the historical reasoning.

Sherwood
Old 09-22-2007, 07:53 AM
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Thanks Gents. Olivier, beautiful stuff. Those look like 906 pistons, what is the CR?

Sherwood, cross-hatch has to do with break-in and the angle is also attributed to oil retention on the cylinder wall and the rate of ring rotation AND friction. Most of the ring manufacturers mention this in their catalogs and claim that the correct hatch is around 20-25 degrees.

Here is a good paper on the subject from MIT. http://dspace.mit.edu/bitstream/1721.1/32371/1/61516071.pdf
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Old 09-22-2007, 10:20 AM
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JE Pistons

Nice looking pistons but I do understand some of the concerns about JE and I have been confused by some of the material selection.

I believe, but have no first hand experience that the 81mm JE is quite a bit heavier than the Mahle 'S' Piston but have no idea of how it compares with 'E' and 'T' pistons but I would be very interested to know.

I guess for fairly stock street motors the weight wouldn't be critical but for a high revving competition engine I must say that I would worry.

I have also been concerned about the selection of 2618 alloy for all 911 applications.

I can accept that for very high performance Turbo and Nitrous engines that this material has better metallurgy and a higher temperature capability than the higher Silicon alternatives but for street use this shouldn't really be much of an issue.

I would like to be able to buy a piston in 4032 material which has more silicon for a street motor.

I have two reasons for this preference.

The first is that the expansion of 4032 is lower than 2618 and if the pistons are being used with rebored Biral cylinders I believe that this is an issue as clearances will need to be relatively high. If they are used with Nickasil cylinders I would accept it is much less of an issue. I also believe that LN will manufacture 2618 cylinders to help overcome this issue with race motors.

My other concern with 2618 is in the area of ring groove wear. I believe that the presence of a reasonable amount of Silicon improves the wear characteristics in the groove area. I think that this may be reasonably important for a street engine that may clock up moderate to high mileages.

This may be more of an issue with a 2.0 litre motor due to the relatively low wrist pin position and I have certainly seen quite a few Mahle S pistons with badly worn ring grooves.

It is interesting that JE Sport Compact pistons are made from 4032 and they are fitted to Turbo motors such as Subarus and EVO's.

Confusing really.

Last edited by chris_seven; 09-22-2007 at 01:01 PM..
Old 09-22-2007, 12:58 PM
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John,

As usual, things are looking very nice! Did JE do the low friction coating for you, or did you send them out on your end? Could you explain a bit more about that... Thank you, in advance.
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Old 09-22-2007, 03:48 PM
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Chris, all excellent points. We talked over the issues of the relative expansion rates of 2618 vs. 4032 during the decision process. Charles is on record on the forum preferring the expansion rate of 2618 to 4032 as it's more closely matched to the aluminum (aluminium? ) he uses for the Nickies cylinders.

Mass is 374 grams. 901/02 Mahle "S"= 364 +/- 3g. Up to '68, the 901/05 weight was the same as the "S." From 1968 on, Type 2000 (901/01, 05, 06) pressure-cast pistons are 371 +/- 3g. So they weigh the same as the later cast pistons. So you could say it's a 10g difference, I haven't weighed the pins yet.

In my case we used a clearance of 0.003 +0.0005 -0.0000" and coated the skirts. The goal is to maintain a tight clearance for reduced noise at startup and have some protection against scuffing.

Here's a calculated clearance chart until I have the actual specs.



Jon, the coating was applied by LN Engineering, who sourced the pistons through a vendor in Reno, NV.
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Old 09-22-2007, 03:52 PM
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John,

Very interesting weights and the JE is lighter than I had been told but still quite heavy by modern standards but I am sure that they a fine for street engines.

I am in the process of trying to specify a relatively high end 2.0 ltre Twin Plug Motor and I am struggling to find pistons with a lower than stock weightto complement the Ti rods we plan to use.

The pistons that Oliver has shown look interesting and some more detail would be useful.

Thanks for the data
Old 09-23-2007, 02:48 AM
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Pistons look nice, just make sure you take off those sharp edges on those valve pockets.
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Old 09-23-2007, 04:20 AM
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John and I decided that for his particular engine, that the pistons did not need the lighten combo. I would imagine with under-crown profiling, that the pistons would be quite a bit lighter.

A good example of the weight savings is as follows- I happened to make a set of flat top 98mm JE Pistons and a set of 105mm JE Pistons. They both used the same thickness ring lands, wrist pins diameter, pin height, etc. The 105s had the lighten combo (including under crown profiling, etc) and the 98s did not. The 105s came out to the same weight as the 98s.

I've had some experience with the 2618 forging and cast iron cylinders (with bores having been nikasil'ed and have pretty much figured out what piston to cylinder clearance is sufficient for the street, as we don't have the luxury of having 4032 forgings to use in cast iron or biral 911 cylinders. I always coat the skirts in an application with JEs and cast iron or biral cylinders.
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Old 09-23-2007, 06:55 AM
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The coating on the skirts is actually applied by JE. I now use Calico Coatings for about 50% of my pistons and have JE do the rest. It saves quite a bit of time having JE do it in house. Most customers don't want to wait the extra 1.5 weeks to have Calico do it.
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Old 09-23-2007, 06:57 AM
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What is the additional cost associated with coating, and is this a longevity issue?
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Old 09-23-2007, 07:16 AM
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Charles...Has anyone tried Teflon buttons on the skirts of the pistons?
We used to do this on race motors to keep the pistons vertical in the bore and reduce friction.
I know our motors got torn down more often, but I have had several engines on the track circuit that lasted more than 3 years in the Sportsman class (3 to 4 races a night, twice a week) and the engines put out good power.
The question of sustained Teflon endurance would be the point I suppose.
BTW....the rings would look great at each tear down, because the piston cannot "rock" on the pin.
A side benefit is the quietness of the engine at start up.
Bob
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Old 09-23-2007, 07:20 AM
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I've never used teflon buttons, ever. I have friends that run aluminum buttons in their blown alcohol dragster (3000 hp x 10,900rpm redline):

http://www.rosspistons.com/accessories_detail.php?cat=24&item=85

Depending on a few variables, piston coatings usually run about $50/piston, when you include thermal barrier and skirt coatings. That same $50 gets you coated ring lands too if Calico does them.

I've had many race engines that I've had a chance to inspect our cylinders and pistons from and the coatings are very durable. In street engines, I have seen skirt coatings last 100,000 mi (some of the first Nickies and JE's I ever did before LN was LN have passed that mark and are still runnning on the same Goetze rings in big type 4's).
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Old 09-23-2007, 09:50 AM
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Charles:
I understand the button retainer in the pin hole idea.
It can be aluminum or Teflon....does the same job.
The buttons I am referring to are placed in the skirt at 90 deg to the pin.
The idea is to not allow the side of the skirt to touch the bore.
We used either 3 buttons (about 3/8" diam) in a triangular pattern, or 4 in a box pattern fairly low on the skirt and just above the exposure point when the piston is at it's lowest.
Because of the lack of rocking of the piston, the rings do not barrel as normal rings do.
The Teflon buttons were a force fit into the bore (Teflon is a little spongy) and when the piston and buttons were oiled slightly, there was very little friction.
Also...we sometimes used standard pistons with over-sized rings in an over-sized bore...the buttons taking up the play.
Bob
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