Metro XFI Score!

[MetroMPG]

Bob: that's actually the first difference I've seen mentioned about the ECU.

[Gasoline Fumes]

Lobe height is 39.63mm. That's an XFI cam in good condition! The normal cam lobe height is almost 1mm taller.

As a bonus, I got a Daikin clutch with almost no visible wear. It still has writing on the disc.

I'm using the Swift 3.52 gearbox over the 3.79 XFI box.

[Gasoline Fumes]

I stumbled across this browsing through my 1993 Metro service manual.

Notice the offset ring gap.

I'll get an actual pic when I pull the pistons out.

[Gasoline Fumes]

XFI piston:


XFI piston ring:


It might be hard to tell from the pic, but the staggered gap is also angled. I haven't checked if the gap is within spec yet. If it is, I might reuse them with new oil rings. Is that a bad idea?

And another craigslist score, engine stand for $10!

[Old Tele man]

...unlike in art, a patina like that is definitely NOT something you want.

...some soaking in MacKay's Engine Cleaner will remove that gunk, but it'll also make all "wear" clearances/tolerances get bigger.

...lastly, the "top" compression ring might be a problem, because it rides right up against the "wear ring" in the cylinder -- installing a new ring with its new, unworn, 'square' ring edge will be "crunching" up against "the rounded" wear ring in the cylinder...and could result in a broken ring. MORAL: the top ring and cylinder bore cleanup are critical to longivity.

[MetroMPG]

Nice photos, thanks. Interesting detail on the gap in the ring. I take it the 2-ring pistons don't have the same style ring?

[Gasoline Fumes]

Originally Posted by Old Tele man

...unlike in art, a patina like that is definitely NOT something you want.

...some soaking in MacKay's Engine Cleaner will remove that gunk, but it'll also make all "wear" clearances/tolerances get bigger.

...lastly, the "top" compression ring might be a problem, because it rides right up against the "wear ring" in the cylinder -- installing a new ring with its new, unworn, 'square' ring edge will be "crunching" up against "the rounded" wear ring in the cylinder...and could result in a broken ring. MORAL: the top ring and cylinder bore cleanup are critical to longivity.

Everything will be very clean when it goes back together.

I'm going to hone the cylinders, is that good enough? I don't see much wear in the cylinders anyway.

[Gasoline Fumes]

Originally Posted by MetroMPG

Nice photos, thanks. Interesting detail on the gap in the ring. I take it the 2-ring pistons don't have the same style ring?

My replacement rings (NPR brand) have normal flat gaps. I'll dig up some non-XFI pistons and see what the rings look like. But I'm pretty sure they're not like the XFI rings.

[MetroMPG]

Thanks. If you're willing, I'd like to know more of the specs between the two pistons/rings. To determine if a simple "ring delete" is a valid modification to a non-XFi engine.

I realize it would be a lot of work for a tiny gain, even if it could be safely done (safely in terms of the wear/mechanical implications to the motor). Just noodling.

[Gasoline Fumes]

The XFi piston places its single compression ring in a slightly different location than the top ring on the normal piston. I don't know if that's significant or not. The XFi and standard top rings are the same size, but only the XFi has the special "gapless"design. I don't see why you couldn't give the standard pistons the XFi treatment. Maybe the extra/open ring groove will collect goo and keep the other rings cleaner.


Another view of the special gap. Same ring, just flipped for the second pic.