2.0 S Piston/Cyl group size question.

[Silverbullit]

The original pistons have a very sloppy top ring just out of spe. Fortunately bought a spare set a few years back. However, 4 are size 5, and 2 are size 6. I see some overlap in the specs. Where is this measure taken, and how critical is it to the rebuild. As you know these p/c are quite difficult to source. Thanks, Brian

[tom1394racing]

Brian

Measure the skirt diameter of each piston and the bore diameter (4 locations) of each cylinder. If you can pair the pistons and cylinders in a manner such that the piston to cylinder clearance for each of the (6) is less than 0.004", you will be good to go.

[Silverbullit]

Thanks, Tom. I'll do that. What I need to know is if I can install the spare p/c that are 4of group 5 and 3 of group 6. What does the 'group' reference and how do I measure it? Thanks

[edmayo]

Are you referring to the number in the triangle at the base of the cylinder? If so that is the height grouping. Although the actual height difference is very small (from memory maybe about a .001") you should keep the same heights on an engine side. What you are avoiding is putting a ever so slight deflection in the cam housing when it is bolted down.

[tom1394racing]

Here you go....

[Silverbullit]

Thanks, gentlemen. Exactly what I was asking for. Now I can measure accordingly. With 12 p&c, I'll be able to get the right combo. Thanks again.

[tom1394racing]

Here is an example of a set I recently did for a customer.

[Frank Beck]

Brian

Measure the skirt diameter of each piston and the bore diameter (4 locations) of each cylinder. If you can pair the pistons and cylinders in a manner such that the piston to cylinder clearance for each of the (6) is less than 0.004", you will be good to go.

.004" clearance? Hummm...
That's quite a bit for an 80mm street set up.

[tom1394racing]

Porsche recommends a max allowable rebuild piston to cylinder clearance of 0.15 mm (0.006") for the 2.7 engine (see below). That would scale to around 0.005 " for a 2.0 engine.

The common wisdom seems to be 0.004" max clearance.

[Silverbullit]

Continued thanks. Tom, so in the chart for your customer's set I see 4 Height Grp 5 cylinders and 2 Grp 6. According to the manual I'm using, cylinder-to-case shims can be used in different thicknesses/multiples to achieve uniform cylinder heights. Is this advisable?