With the exception of copper materials, whenever you reuse a gasket (head gasket or any other gasket), you run the risk of premature gasket failure. A new gasket conforms to the irregularities found on the sealing surfaces when compressed. Regardless of the type of gasket material used, the gasket is permanently compressed. This is called "taking a set".
How Important Are Gasket Dimensions?
Very. All of the figures associated with the deck are critical. Let's look at deck height first: Deck height is measured when the piston stops exactly at Top Dead Center in the bore. The measurement is taken from the deck surface of the block to the piston "flat" (quench area). Each and every combination (rod-piston-gasket) requires a different deck clearance.
Before you think deck clearances and compressed gasket thickness figures are inconsequential, check out the following trio of extremely common, but hypothetical combinations -- all based upon the same 4.030" bore, 355 c.i.d. small block Chevrolet:
| Engine Number | 1 |
2 |
3 |
| Piston To Deck Clearance (in.) | 0.018 |
0.010 |
0.000 |
| Head Gasket Compressed Thickness (in.) | 0.041 |
0.018 |
0.018 |
| Piston Dome Volume (c.c.) | 10.6 |
10.6 |
10.6 |
| Combustion Chamber Volume (c.c.) | 76 |
76 |
76 |
| Final Static Compression Ratio | 10.4:1 |
11.2:1 |
11.5:1 |
Given the hardware mix, there's a wide range in the final compression ratio, even though the combustion chamber volume and the piston dome volume remained constant. Equally important is the actual operating clearance of the engine. If the engine is warm, and running at high RPM, then the deck clearance will change. In operation (especially at high RPM), the connecting rods stretch, the wrist pins flex and the pistons rock. When all of these factors are added together, then the actual deck clearance changes (the figures decrease). And because of this fact, different deck clearances will be required for different combinations. As a rule of thumb, a mild drag race engine requires roughly 0.035-inch total deck clearance. This figure includes the compressed thickness of the head gasket used. Meanwhile, a heavily modified engine might mandate 0.045-inch or more total deck clearance. As you can see, the compressed thickness of the head gasket used plays an important role in the overall deck clearance figure.
| Sources | |
| Clark Copper Head Gaskets 10510 Nassau Street Blaine, MN 55449 PH# 763-786-9590 Website: clarkcopperheadgaskets.com |
Federal-Mogul Corporation World Headquarters
26555 Northwestern Highway Southfield, MI 48033 PH: 248-354-7700 Website: www.federal-mogul.com |
| Flat Out Gaskets 664 Tower Rd Mundelein, IL 60060 PH: 877-837-9200 Website: www.flatoutgroup.com |
Mr. Gasket Company 10601 Memphis Ave. #12 Cleveland, OH 44144 PH: 216-688-8300 Website: www.mr-gasket.com |
