Honda FRM Liners - Wrenchin'

Mahle is about the only aftermarket alternative when it comes to FRM-compatible pistons. Mahle pistons are available in a variety of different compression ratios and bore diameters that Honda doesn't offer.

Both, early closed-deck and some late-model open-deck H-series engines feature FRM cylinder liners. Notice how there isn't a crosshatch pattern on their bores; FRM liners are as smooth as glass. Although strong, FRM-lined blocks aren't indestructible--no block is. When damaged, an FRM-lined cylinder can usually be bored up to 0.020 inch without disrupting the actual cylinder. But the process is far more complicated than a typical bore and hone, and special pistons and rings are required. The right way involves three graphite honing stones that, one by one, slowly cut away at the lining. The machinist begins with the roughest stone where larger cuts are made and makes his way to the smoothest of the three, which leaves the cylinder walls almost as smooth as glass. Unlike conventional, steel-lined cylinders, FRM-lined ones do not reveal a crosshatch pattern, which is partially what makes them look and feel so smooth. Once the cylinder liner's size is achieved, the machinist then applies silicone paste to the cylinder walls with specially made cotton pads. The pads spin inside the cylinder walls, warming up the paste until it adheres and turns the cylinder walls black. Finally, the cylinders are polished to a near mirror finish.

As with any sleeve installation, the original bore diameter is measured first.

A series of special graphite stones and compounds is used to achieve the glass-like finish that FRM liners require.Following Honda's success with the third-generation Prelude's B21A1 liners, it implemented FRM technology into C32B NSX engines. The linings didn't just reinforce the V-6 engine block, they allowed for less friction and a slightly smaller and lighter engine (dimensionally, the same as older C30A engines yet 0.2 liters larger inside) thanks to a more compact cylinder design made possible by FRM liners. Many Prelude H22A and H23A engines were built similarly.

When disaster strikes on an FRM-lined block, the only alternative is to fit the cylinders with steel liners. Of course, steel sleeves like these are far stronger than the OEM ones, but aren't necessary unless you're looking for serious power. First, the block was torn down and hot tanked of all its grime and debris. The H was then set up on a jig, and the computer was programmed to digitally measure the block. The FRM liners are then cut from the cylinders to the exact thickness of the new steel sleeves that are then pressed into place. Once pressed in, the cylinders are bored to match the new pistons and honed according to the rings we'll be using. Since the block's now fitted with steel cylinder liners, a more conventional crosshatch pattern is made, which helps with oil retention and cylinder lubrication. The block is then decked for a perfectly flat surface to ensure proper cylinder head and head gasket sealing. Any sharp edges are then smoothed out along the outside edge of the block, a process machinists call "chaffering." What little leftover funds we had were spent on align-honing the block, micro-polishing the crankshaft, and balancing the entire rotating assembly, including the clutch pressure plate and crankshaft pulley. Skip any of these steps and you could rob your engine of power, decrease bearing life or, worse, destroy a bearing altogether.

The cylinders are bored out to the same size as the new sleeves' outer diameter.

The sleeves are then pressed into place.

It's a good idea to micro-polish the crankshaft anytime a block is torn down and its bearings are removed.

Since we're installing a new Clutch Masters clutch and flywheel, we had the pressure plate, flywheel, crankshaft, and crankshaft pulley balanced. You've got two choices when considering aluminum pistons: cast or forged. Most OEM pistons are cast, which are good in terms of longevity and suitable for engines that are used daily. Cast pistons are formed by pouring melted aluminum into a mold shaped like the final product. Forged pistons, on the other hand, are made of lighter materials, which can allow an engine to rev higher, yet remain much stronger than their cast counterparts. Forged pistons are formed using a large press that pounds a single block of metal into the desired shape--a piston in this case. The tooling is expensive, which means forged pistons typically cost more. CP Pistons is one such leader in the world of forged pistons. The company can design pistons to accommodate the widest variety of applications, from stock replacements to high-performance.

Since the block was at Valley Engine, we had them finish the job with some custom head work. The H22A top end was ported, polished, and fitted with Skunk2 stainless steel valves and valve springs. We also checked clearance for the Skunk2 cams and made sure that the deck surface was flat. If you're going to go to the trouble to build an engine, you might as well do it right the first time. Whether you stick with the FRP liners or go forged, be sure to select the right pistons and rings and drop your block off at a reputable machine shop. This isn't the time to skimp.