JE 85mm pistons.

[davidppp]

Hello all.

I have in my hands some newish JE's .

They are similar to 2.2S pistons in theory.

I would be most grateful if some kind soul might help me check their dimensions.

The skirts it the measuring point are all close to 3.3425 inches..ie 84.8995mm.

So nominal clearances are 0.1005mm..not too bad tho' bigger than mahles of course..

The diameter at the top ring land above the top ring is 3.3395 inches, or 84.8233mm.

This seems a bit big to me..now I do know they swell lots in use, being a 2-series alloy and all..

So, does anyone have any specs for them to hand, or know from experince what they are made to..?

Thanks
David

[Walt Fricke]

David

Aren't the 2.2 (and 2.4) pistons 84mm? Yours don't seem similar, in theory or in practice.

Maybe you have a set designed for a 2.3 (66x85 = 2247, but generally called a 2.3)? I could measure my Cosworth 85s (made for a 2.3) to see, if that would help.

Nowadays J&E is calling for 0.0015" clearance.

Looks like it is time for custom bored cylinders, anyway.

Walt Fricke

[davidppp]

Thanks, Walt.

I suspect the 1 1/2 thou clearance refers to Nickies, right?

JE still recommend about 3-4 thou on their 2618 alloy..but less with 4032 of course..running in castiron ..I'll be using Birals bored..

Kind regards
David

[304065]

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.

[davidppp]

Thanks, John.

What I was really trying to be sure about was the designed taper built into pistons when new: the differenece between the measuring point diameter and the undercrown diameter..

Kind regards
David

[304065]

David,

I will have an answer for you in the next week or so. . . I have my new 81mm JEs ready and all my metrology gear retrieved. . . v-block, height gage, test indicator, surface plate and a gage pin that I'll use to calibrate the height gage (it's the same gage pin I use for measuring rocker shafts). What are you using for the measuring point, about 1/2" (12.7mm) up from the bottom of the skirt? And then the top ring land?

The old FWM has a photo of a man using a Mahr Millimess in a comparator stand, no way that's accurate! Have to mount it in a v-block to hold it correctly. I have an identical Millimess and it's good to 0.001mm but holding the piston as in the factory photo would never offer repeatable accuracy. . . we can only be so lucky if they did the same thing in the Panzer engines . ..

[davidppp]

Hello, John.

Yes about half an inch from the bottom of skirt..and yes top land above top ring..both axes..

My technique may leave much to be desired ..I do what I was taught and over the years have found gives me best reproducibility.

I set the mic to size, lock it and slip it over the piece.

Then reduce by 0.5 thou and repeat until no-go..

All the while trying not to warm it with my hands..

I'd like to learn better!

Kind regards
David

[304065]

David,

No problem using a micrometer as a snap gage but I would exercise caution insofar as the carbide tips of the micrometer's anvils can easily gouge a soft aluminum piston. Inexpensive micrometer stands are available that clamp to the mic which frees up both hands to position the part AND has the added benefit of not conducting body heat into the micrometer, which as you correctly note can cause the measurements to trend smaller as you check and recheck.

One technique that I use when measuring is to make multiple passes through a set of parts to note the extent to which thermal expansion of the gaging setup is affecting the readings. This is also a nice check on the repeatability of my technique which can always be improved. It's analogous to taking five tire pressures at the racetrack so you can see the extent to which the pressure has fallen in the time it takes to measure all the way round. . .

[neilca]

All pistons are made with a taper. Always measure at the bottom of the skirt.

Hope that helps,
neilca

[kenikh]

Henry made me a set of 85mm JEs built to match bored Biral cylinders. He wrote down all of the specs for me, so I will post them when I get home.

[davidppp]

Thanks, Kenik, and John.

Great help.

I'm much more familiar with the 4032 material mahle etc use..

Kind regards
David.

[304065]

[304065]

Setup was to hold the piston in a 90 degree V-block with the indicator in a height gage. The V-block was moved along the surface plate (my granite countertop which I took the time to calibrate so I don't have to haul the 35 pound surface plate out all the time!) and the measurements taken at the indicator's lowest reading point, which is the diameter.

[kenikh]

As promised...