Where Do I Measure 2.0 94mm Mahle Pistons? Options

[DBF]

I want to check my pistons before I just buy new ones. There is no scoring, and the ring lands measure well within spec, but I cannot find information on where to measure the piston diameter. If it's like other Mahle pistons, I know you have to measure "X" distance from the skirt. Is that true for the stock 94mm Mahle pistons? If so, anyone know how far from the skirt?

Thanks!

[Dave_Darling]

The Factory manual specifies measuring at the bottom edge of the piston skirt. It lists a table with a couple of oversizes on the 1.7, only standard size on the 1.8, and the 2.0 table seems to have been published incomplete without the size data in it!

The 1.7 piston sizes have three tolerance groups within each size.

1.7: 90mm cylinder nominal
Standard:
Blue tolerance, Cylinder 89.990 - 89.999; piston 89.95mm
Pink tolerance, Cylinder 90.000 - 90.009; piston 89.96mm
Green tolerance, Cylinder 90.010 - 90.019; piston 89.97mm

First oversize:
Blue, cyl 90.490 - 90.499; piston 90.45mm
Pink, cyl 90.500 - 90.509; piston 90.46mm
Green, cyl 90.510 - 90.520; piston 90.47mm

Second oversize:
Blue, cyl 90.990 - 90.999; piston 90.95mm
Pink, cyl 91.000 - 91.009; piston 90.96mm
Green, cyl 90.010 - 91.020; piston 90.97mm


The 1.8 table only shows the standard size, with only two tolerance groups shown.

1.8 liter engine, 93mm nominal:
Standard size:
Blue, cyl 92.992 - 93.008; piston 92.97mm
Pink, cyl 93.002 - 93.108; piston 92.98mm


The 2.0 table has entries for two oversize groups, but all of the entries are blank. It notes that the nominal cylinder size is 94mm, but we already knew that.



There may be more information in the Little Spec Book, but I don't have access to my copy at the moment.

--DD

[DBF]

Thanks. That helps. I am surprised Porsche/VW used the same blue-pink-green color sequence for the oversized pistons/cylinders. Different colors on the various over-sizes would make it easier to know what you are expecting (or hoping) to find when measuring piston and cylinder to see if they can be reused.

[Dave_Darling]

Frankly, the 1.7 motor is the VW 411 motor. (Ignoring the engine tin and exhaust, and assuming the vertical oil filler.) So it's not that surprising they use the same color codes.

--DD

[bob164]

I checked my little Spec Book, nothing on 2.0 or 1.8s either.

[DBF]

This is turning into an interesting engine project. The valve guides, especially the exhaust of course, were very worn which prompted me to go further pulling the engine apart. The pistons are in amazingly good condition, but the cylinders are very worn. I can make out two marks at the top of the piston stroke in the cylinders like the engine was run with two different deck heights. The rod bearings were scored a bit, but the crankshaft bearings looked good. The cam lobes were well worn, but the pushrods and lifters show little wear. The crankshaft and case are also well within spec. I can tell the case was split once before and I'm thinking someone did an economy rebuild back when these cars were inexpensive cars and used some just barely within spec used parts to save a few bucks.

[Superhawk996]

I'm thinking someone did an economy rebuild back when these cars were inexpensive cars and used some just barely within spec used parts to save a few bucks.

Almost a certainty with these cars. Found low compression ratio bus pistons in the engine that came with my car. Nothing like rebuilding an engine to make less power than stock. (IMG:style_emoticons/default/av-943.gif) 50 years of DAPO’s before you got it.