Building a K24/K20A2 "Frankenstein" Hybrid Engine

Decide on your K24 donor before buying anything. A CR-V K24 is the cheapest and most plentiful choice and makes sense if you plan to replace the rods and pistons anyway. A TSX block carries higher-compression pistons, stronger rods, and factory oil squirters, but costs more and is harder to find; a CR-V block instead has bosses that can be tapped for squirters later. From the K20A2 you will reuse the head, cam caps, VTC actuator, timing chain with tensioner and slide rails, oil pump, oil pan, windage tray, oil cooler, knock sensor, and their fasteners. Gather both complete engines and set up a clean, well-lit space with room to work before starting.

The crankshaft pulley bolt is torqued extremely high; on this build even a 380 lb impact would not move it. Fit a crank-holding tool (a Moroso/Honda unit runs about $75 from Summit Racing and needs a single breaker bar, while a roughly $25 Amazon tool requires two breaker bars, and a breaker bar can also be rented from AutoZone for about $25). Never substitute a torque wrench for a breaker bar, as the drive will shear off. A set of impact sockets from 10mm to 19mm is worth having for the whole job. Loosen the crank pulley bolt on each engine before removing anything else.

Remove the crank pulley, then the water pump; an 8mm socket handles the water-jacket crossover fitting. Take off the VTC actuator (a single 10mm bolt) and pull the timing chain cover. Its 10mm bolts hide all over the front plate, including two thicker bolts at the lower outside corners, so recount before prying, and do not confuse them with the three bolts along the bottom of the oil pan. Break the cover free from its grey sealant at the upper inside corner. Loosen the cam caps in the factory sequence and lift them off as one assembly, with long zip ties keeping the caps together and in order. Remove the head bolts in sequence and lift the head straight off. Inspect the piston crowns and valves for contact marks if the engine may have been over-revved.

Take off the clutch and flywheel using a 10mm 12-point socket for the pressure-plate bolts and a 17mm 12-point socket with an impact for the flywheel bolts. Remove the oil cooler with a 32mm socket, a 10mm on the inner fastener, and a 19mm for the plug on top. Support the block on a sturdy cradle, turn it over onto rags, then unbolt and pry off the oil pan, followed by the oil pump with its chain and tensioner, and the windage tray; a metric hex-bit socket set speeds the rail bolts. Bag and label every part you will carry over. On this engine a spun No. 2 rod bearing turned up, which is why only the head and accessories from the K20A2 are reused.

Repeat the teardown on the K24, discarding its head, VTC actuator, and rusty top-end hardware. Put a locking pin in the K24 chain tensioner before removing it. Flip the block onto a soft wood surface to protect the deck, then pull the oil pan; two studs sit where pan bolts belong, so back them out with a double-nut or vice grips, since you will use the K20A2 pan hardware anyway. Check the pan and bearings closely: metal filings or chunks signal a damaged or abused engine.

The K24 will not accept the K20A2 oil cooler as it sits. Remove the oil filter, then back the protruding threaded pipe out of the K24 with vice grips so the block ends up with threads that match the K20A2. Open up the oil-cooler passage: a machine shop is the safe route, though a careful hand can do it with a Dremel. Only after machining, remove the hex block plug above the oil filter opening and blow every trace of metal debris out of the block. Do not install the oil cooler at this stage.

A CR-V K24 block has bosses for piston oil squirters that must be drilled, tapped, and fitted, with the squirters carried over from the K20A2; a TSX block already has them in place. This step was skipped on the featured build, but it is worth doing (using a high-powered vacuum to catch filings while drilling the pilot hole) if you are also upgrading the rods and pistons.

Clean all sealing surfaces thoroughly. Refit the oil pump with its chain and tensioner and the windage tray onto the block. Scrape the old Hondabond off the K20A2 oil pan, lay a fresh bead, fit the pan, and torque its bolts to spec. A clean, well-sealed joint here is what keeps the finished engine from leaking.

Set a new Cometic head gasket on the block; the specialty gasket from the Club RSX store came in cheaper than the OEM part even with shipping. Lower the head into place and run the head bolts down in the factory tightening sequence. This is the most critical step of the build, and getting it wrong risks warping or leaking. Install the cam caps in their torque sequence, but leave the front-center bolts slightly loose so the timing chain can still be routed.

Fit the timing chain, both slide rails, and the tensioner. Because the hybrid combination changes how everything indexes, the timing marks will not line up on their own; set the crankshaft to TDC and align the marks by hand, checking carefully, since a timing error here caused trouble on the original build. Draw the left slide rail across to load the tensioner, finish torquing the cam caps, then pull the locking pin out of the tensioner.

Reinstall the timing chain cover and VTC actuator and torque them to spec. Mount the K20A2 oil cooler onto the machined K24 block; it should fit exactly as it came off. Bolt on the K20A2 water pump with a fresh bead of Hondabond, connect the hose between the oil cooler and water pump, and reinstall the crank pulley.

Remove the original K24 knock sensor and install the K20A2 knock sensor in its place. Mount the intake manifold with a Hondata gasket, coating both faces with Hondabond, and install the starter. For engine management, run a K-Pro Type S ECU on the stock Type S harness. Keep the redline near 7500 RPM unless the bottom end is built, because the longer-stroke K24 moves the pistons faster than the Type S does at 8600 RPM, and CR-V rods are weaker than TSX rods.