Deck Height

[Flat6pac]

I need the measurements that coincide with the delta 5 and delta 6 for Mahle 2.0 and Mahle 2.2 cylinders

TIA
Bruce

[Steve@Rennsport]

Given the variations in each engine case and set of heads (after re-surfacing), you need to set deck height at .040 using whatever thickness base gaskets is necessary.

[tom1394racing]

Bruce

Are you looking for the cylinder height specs associated with the 5 and 6 cylinder height groups?

[Flat6pac]

Yes, I need the delta number height for each of those cylinders. Its in the small tech book but the mice were in the drawer nesting
Thanks,
Bruce

[304065]

Deck Height Issues......

[Bobboloo]

Group 5 is 82.200 - 82.225 mm (3.236 - 3.237")
Group 6 is 82.225 - 82.250 mm (3.237 - 3.238")

[Flat6pac]

Thanks for the responses, found in a book, the height of the cylinder is different from 2.0 to 2.2 by some 3 mm
Bruce

[304065]

3mm is a huge amount, the geometry of the engine didn't change that much. What "book?"

[Bobboloo]

The numbers I got were from the factory manual. My manual didn't give any additional info for 2.2 cylinders. That's not to say that cylinder height didn't change for 2.2s' just that my manuals didn't show it.

I know the cylinder heads changed for 2.2 and I believe the CE ring gasket also started with the 2.2 so maybe this would account for a change in cylinder height.

[jcge]

According to the Mahle Website

901 02 (2L) CYLINDER PN = 503WR18 NOMINAL HEIGHT = 82.25 (80mm bore)
911 01/02/03 (2.2L) & 2.3L CYLINDER PN = 503WR19 NOMINAL HEIGHT = 85.45 (84mm bore)

a difference of about 3mm...

[304065]

Hmm, you are right.

Tolerance Groups for Cylinder Heights, 2.0 Liter Engines, 1969-models

Marking A
5 82.200-82.225

6 82.225-82.250

Replacement Parts
R5 81.950-81.975
R6 81.975-82.000

Tolerance Groups for Cylinder Heights, 2.2 Liter Engines, from 1970-Models
Marking A
5 85.400-85.425
6 85.425-85.450

Replacement Parts
R5 85.150-85.175
R6 85.175-85.200

From the little white book p.38 (3M XII/71 M) 1st English Edition.

This causes me to rethink my engine geometry worksheet-- with different cylinder heights, this means the 2,2 cases have a different spigot height.

66mm stroke
130mm rod center-to center length
34mm compression height (for all 2,0-3,0 pistons)
1.0mm deck height

Half the stroke is 33 + rod length 130 + compression height 34 + 1mm deck = cylinder head mating surface is 198mm above the centerline of the crank, minus 82.200 for the cylinder height + .25mm spacer is 82.450mm, this puts the spigot base at 116.05mm

For a 2,2, same calculation except you deduct 85.400+.25mm or 85.650 for a spigot base of 112.350.

For the 2,4, half of 70.4 (35.2) + 127.8 = 163 + 34mm + 1.0mm =198mm (that part matches).

Hmm so IF you use 2,0 cylinders on a 2,2 case you end up with higher compression because the spigot base is 3.2mm closer to the centerline of the case. This has the practical effect of pushing the piston closer to the head. Let's add it up . . .

112.350 + .25mm + 82.200 = 194.8mm. If you use a 66mm crank and 130mm rods and a normal piston, you end up with a reciprocating assembly that protrudes 195mm from the centerline of the crank-- for a deck height of NEGATIVE 2.2mm.

I never read this anywhere!

[jcge]

John C - Mahle list the compression heights for the pistons as 34mm - are you sure about the 32mm in your calcs ? (not being smart...I don't know the answer)

Regards
John

[tom1394racing]

I'll bet the 3mm difference is in the thicker head gasket used on the 2 liter motors.

What do you think?

[tom1394racing]

Mystery solved.

Note the "lip" that extends from the bore of the 80 mm cylinder at the top. It centers the head gasket and sets the cylinder length for the engine geometry. The difference between the height of the gasket surface and the lip is 3 mm. The cylinder length to the gasket sealing surface is around 82.5 mm. The length to the top of the "lip" is around 85.5 mm just like all the other 911 cylinders that do not use a thick head gasket.

[304065]

Tom, I think you nailed it with your second post. I don't believe there is any change in deck height due to the 2,0 liter head gasket because the "lip" (the cylinder liner) protrudes further than the compressed height of the gasket and it is this surface that seals against the recess in the head. The gasket is sort of a backup.

But that DOES shed light on Porsche's cylinder height testing method-- when they changed the gasket surface the measurement changed but the geometry remains the same.

Now, why one would build a 2,0 on a later mag case except for race purposes. . .

Thanks! Your "library" of Porsche engine parts never fails to impress.

[304065]

Corrected compression height to 34mm and revised math.