Engine Cylinder Head Spacer Shim
Representative Photo, actual item may vary
Yukon Gear & Axle YSPSR-004 3.20mm Carrier Shim for C198 Differential
What Is an Engine Cylinder Head Spacer Shim?
An engine cylinder head spacer shim — also known as a head saver shim or head gasket shim — is a precision-engineered, ultra-thin metal spacer placed between the cylinder head and the engine block. These seemingly simple components play a surprisingly critical role in engine health, especially during rebuilds and resurfacing work.
When a cylinder head or engine block deck surface is machined or milled, even a small reduction in height can throw off several carefully calibrated engine parameters. Specifically, cylinder head spacer shims are designed to restore valve train geometry, valve clearance, compression ratios, and cam timing to factory specifications on engines where cylinder head and/or block surfaces have been resurfaced below factory limits.
Why Cylinder Head Spacer Shims Matter
The relationship between the cylinder head and engine block is one of the tightest tolerance fits in any engine. Even a few thousandths of an inch of material removed during resurfacing can cause a cascade of issues:
- Valve-to-piston clearance problems — A head sitting too low reduces the distance between valves and pistons, creating potentially catastrophic contact.
- Compression ratio creep — Milling raises the effective compression ratio by reducing combustion chamber volume, which can lead to detonation on pump fuel.
- Cam timing drift — On overhead-cam engines, bringing the head closer to the block alters the relative position of the cam drive, retarding or advancing timing.
- Timing chain flutter — Changes in deck height can affect timing chain tension, leading to premature wear or rattle.
A properly selected shim, typically installed on the block side with the head gasket placed on top, restores the original deck height and brings all these factors back into specification. They are available in a range of thicknesses — commonly around .020" cold-rolled steel — to accommodate the specific amount of material removed during machining.
Key Considerations When Choosing a Cylinder Head Spacer Shim
Selecting the right shim requires knowing your engine's make and model, the specific amount of material removed during resurfacing, and whether you are running a conventional head gasket (shims should always be used with conventional gaskets, not MLS multi-layer steel types). Consulting your engine's factory specifications or an experienced engine builder is the best starting point to determine the correct shim thickness for your application.
Top Brands in Engine Cylinder Head Spacer Shims
Several trusted brands in the gaskets and sealing systems space offer cylinder head spacer shims across a wide range of domestic and import applications:
- Yukon Gear & Axle — Best known for precision drivetrain components, Yukon brings its hallmark commitment to tight tolerances and application-specific engineering to the spacer and shim category, making them a dependable choice for builders who demand accuracy.
- Auveco — A long-established supplier of specialty hardware and service parts, Auveco offers a broad catalog of small but critical components, including shims and spacers suited for professional shop use.
- Ratech — Widely respected in the drivetrain rebuilding segment, Ratech's attention to precision-fit small parts translates well into engine sealing applications where correct geometry is everything.
- USA Standard Gear — With an extensive catalog spanning drivetrain and engine components, USA Standard Gear provides a strong selection of spacer shims covering a variety of domestic vehicle applications.
- ACDelco — As GM's OEM and aftermarket parts brand with a catalog spanning over 90,000 parts, ACDelco brings factory-validated engineering to cylinder head spacer shims, making it a go-to source for GM vehicle owners seeking a precise OE-quality fit.