JE clearances
 

All those I have checked are 0.0015" in JE supplied cylinders and the rings came gapped to PAG spec.

Well I know that JE's are designed to have the skirts collapse to some degree at break-in. That's one reason why our platers do not match hone to used pistons, only new ones, since the clearance is based off an uncollapsed skirt.

skirt collapse
 

Sounds interesting, precisely why and how they do that?

It's the same with any new piston- that's why each manufacturer specifies precisely where to measure their piston, since it will be different measured elsewhere. If I ever do set up a set of cylinders with used pistons, I usually coat their skirts (I use Calico Coatings) and then measure the skirts and base the bore off of the the largest piston, since they will all be different.

Once you have pistons and cylinders that have been run for a long length of time you can assertain the wear by the ridge in the cylinder. There should be NO ridge in a good cylinder. The original hone marks should still be showing. If your cylinder has no ridge you can forget about measuring it for wear, it has none that is significant. The piston does wear, but it it the ring lands that wear, not the piston diameter as the piston should never be making contact with the cylinders. A feeler guage is placed between the ring and the piston groove. If the gap is excessive you need new pistons. The rings and the ring lands are the wear surfaces on a piston, not the piston diameter or its skirt. If for some reason the skirts and diameter are worn, the ring lands are much further gone, so measure them first. ring lands are ok, then the piston is ok. No ridge in cylinder, then its ok. PS any good cylinder should have NO wear as the oil should have prevented it. Most modern cylinders do not wear enough to worry about.

Fresh rings in old cylinders need a proper seating surface. A few passes with a grape style hone will do this to any cylinder.

Collapse?
 

I am still interested in the how and why of collapse which this does not appear to address?

Would it not be just as easy to match them when all measurements are known for the used set.

You would have to match each piston to each cylinder since I can guarantee each piston is different, which is an extraordinarily tedious and time consumng process compared to taking a single new piston and setting an entire set of cylinders off of that. It's really not a question of ability, it is of cost vs. gains- you might as well use a new set of pistons if you're going to go through that much trouble. The only cases where I jump through all these hoops are if there is no source for new pistons and the originals (in spec) have to be re-used.

Hello all.

New mahles pistons are not cylindrical.they are a complex shape like an oval barrel!

hello, Terence..I see you are a UK builder...what engines do you do?

And what price can you get for pefect Bore to cylinder bore and plate please?
Or maybe they are just boring and resleeving with a thin Nikasil plated liner now..I hear this is the latest technique?

Kind regards
David

Kind regards

Kind regards
David

Quite so David, all pistons exhibit a combination of taper and camming to accommodate the range of thermal and mechanical operating conditions imposed upon them.

I would not recommend sleeving a 911 type cylinder except in extremis to save a unique motor.

Are you looking simply to rebore or overbore, can you please be very specific about existing components and finished specification.

Also which pistons and who provides them?

Where are you located.

TAM

Hello Terence.

I am currently preparing to build a pair of 2L engines:
Last time I spke to PB they were advocating sleeving wherever possible to optimise the nikasil process...

But I did not go into more detail.

I like you would prefer a solid cylinder..in fact I have found the iron cylinders better than the Birals when I mesure the ovality after use..

But I'm sure the way to go is solid cylinders like the Squeezeform ones from PB, or the Nickies, or Henry's new ones..

So far as pistons go, I'm planning to get a batch of custom ones done..for racing 2L engines.
But I doubt they will come from JE..their pistons for the 906 are heavier than the 1969-technology 2L Mahle's!

Kind regards
David

David,

In recent times PB are offering to rebore and coat with the proviso that they cannot control concentricity of the spigot. But I think this problem is more theoretical than real at the odd thou' or so.

Good old iron, so stable, but a touch weighty! Even PAG has gone forged barrel on road stuff in recent years and I certainly would not argue it.

The 98mm JEs are about 200g lighter than the cast pots in the 95s, so it may be that they did not have a suitable forging for the 2 litre. It could be worth another try as they have a more flexible approach than Mahle does these days. I talked to Cosworth about this years ago but the details are off the hard drive.

As I also like to play with motorcycles JE is a potentially useful resource.

TAM