Piston Rings

[mfemenel]

I have a '78 (GE) engine out of the bus I decided to sell to fix some oil leaks/seals etc. I thought while I had it out I'd rering the pistons and learn. I haven't had that experience yet.

Looking online there are different sets with 1.75mm x 2mm x 4mm or 1.5 top and also 2.0 top ring options.
Question 1, how do I determine what the right size is?

Second question, the top ring on my pistons has 2 rings. From what i can see online that's not stock.
Question 2. WTH is that? Rebuild in it's past with different pistons than stock?

Anyway, it's all a good learning experience but I could use some advice/input before I order new rings.

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'79 Westy FI/AC/Auto
'78 Tin Top FI/Manual
'70 Ghia

[Nitramrebrab72]

VW Bus Type 4 2.0 liter have a piston with 7.3 to 1 compression with 1.75mm top groove ,2mm middle groove and 4mm bottom groove with oiler holes to receive VWOriginal Type Rings as follows top 1.73mm ,middle 1.98mm and bottom a single 3.98mm .

Porsche914/912E USA Type 4 2.0 liter have a 7.6 to 1 piston with a top groove of 1.5mm, middle 1.75 mm and 4mm bottom groove to receive a single 3.98mm oil ring.

4mm is the oil scrapper, original ones made for both VW and Porsche are identical a one piece oil scrapper with coiled spring. Mahle made both one piece for VWOriginal Type and will have 'Original Equipment Quality' on their box, they also propose the cheaper aftermarket x2 ring plus spreader. It will say 'Aftermarket' on this box.
The 3 piece oiler is a non VW design it is a MAHLE cheaper in house design and sold as aftermarket type outside the VW parts network.

Porsche top and middle rings are specific to porsche engines they are thinner and produce less friction and have a performance cut to them.
As do the porsche pistons , they have less cylinder surface contact area (less friction)they are lighter and appear reinforced they are also better balanced out of the box than the bus pistons.

Both KS and Mahle make/made Factory Original spec rings, and Mahle make/made both Factory and Aftermarket types. The after market having a three part piston oil ring , Porsche and VW original equipment quality oil ring is a on piece double scapper part with an internal coil spring.

[Nitramrebrab72]

It is just a groove to regulate the ring, the ring is one piece if not you would see it overlapping at the gap .

[mfemenel]

[Wildthings]

If you have a local automotive machine shop take your pistons and cylinder down, flop them on his counter, and let him inspect and measure the P&Cs and supply the rings.

There was some recent discussion of some brands of rings being slightly thicker to make up for wear.

[Nitramrebrab72]

The grooves will need scrapping, use a thick pair of leather work gloves and a broken in half piston ring to do it with the piston in a soft gently gripped vice.

[SGKent]

since this is your first rodeo, my suggestion is to go find a local machine shop that can inspect and clean things for you appropriately. You won't regret it.
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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin