Project MR6

Each twin-cam, four-valve 1MZ V6 head is secured to the block with eight 12-point head bolts arranged around the cylinders, plus an extra Allen bolt in the vicinity of the exhaust-to-intake cam gear-drive mechanism.

Several of the head bolts are located under the cams, so we removed all four cams prior to removing the heads from the block-which then also required removing the upper timing belt system. As the head bolts are extracted from a 1MZ, the undercut central area of the bolts between the heads and threads become obvious; such bolts are designed to stretch for even head clamp-down and are restricted by Toyota to once-only usage.

We had contacted Automotive Racing Products and knew we'd be using super-duty ARP studs to clamp the heads to the block with increased force. We set aside one of each critical fastener (head, mains, flywheel) for shipment to ARP, where it would analyze them and replace each with high-strength fasteners.

Even though Toyota did not rate the 1MZ-FE as a G-series, twin-cam, sport-type performance engine in any U.S. applications (e.g., 1MZ-GE), the engine has an extremely robust design with all the potential for "G" performance. This includes a high-performance, shim-over-bucket, valve-actuating system similar to the valvetrain on the performance-oriented, sport-type 3S-GTE powerplant used in the stock MR2 Turbo, resulting in a high-rpm valvetrain that is extremely stable at higher engine speeds.

With the heads off the engine, we got our first look at the composition head gaskets and closed-deck interface between the aluminum block and heads. The combustion chambers looked healthy and clean. The cylinder bores had little or no wear-ridge above the ring contact area, and after using a chain wrench and breaker bar with huge cheater bars to loosen the crank pulley/damper, proceeded to remove all components from the timing end of the powerplant.

Rotating the V6 upside-down on the engine stand, we unbolted the oil pump pickup, the upper oil pan and a structural aluminum casting. This put the massive six-bolt main caps in plain view, and provided easy access to the rod bolts for piston removal.

Up to this time we hadn't seen a single damaged or overly worn component, but as we successively unbolted the connecting rods from the crank and pushed the pistons upward through its bores, this happy state of affairs was not to continue.

The second-from-rear rod on the starboard side of the engine revealed a distorted rod cap and bearing shells with moderate heat damage and metal loss. The source of the tapping noise from deep within the 1MZ was now clear.

Fortunately, the rod and bearing damage had clearly been recent, and the bearings had done their job, absorbing the fallout of the rod/cap distortion before the crank itself was badly scored.

The rods and bearings from other bores appeared to be OK, and it appeared as if polishing would render the crankshaft fit and ready for return to action.

The stock pistons are flat-top castings designed for the small-cc Pentroof combustion chambers, with reliefs cut on one side for intake valves. We already had a set of super-duty Wiseco forgings with identical compression and wrist/pin location awaiting installation.

At this point, we removed the eight crossbolts securing the main caps through the sides of the block, unbolted the 16 12-point bolts from the four main caps, and removed the crankshaft from the block. The 1MZ crankshaft is a solid forging with offset crank pins on opposing cylinders for even-fire operation.

The main bearings and journal surfaces appeared healthy, and the plan was to polish the crank and reinstall with fresh stock Toyota main and rod bearings. With the block open, we decided installing piston-oil squirters in the block shouldn't be a problem.