KA24DET Build Up - Proper Valve Timing

Cam installation stories have been done over and over again in high-performance automobile publications. Many times, however, proper valve timing is never really stressed. Quality cam manufacturers always include a cam card with their cams. More often than not, this goes into the trash with the shipping package. It's been a pretty long road, but our Project 750hp KA24DET has finally gotten to the point to receive the head. We haven't touched the head since it got back from Port Flow. In this installment, again with Naoto of NPD, we'll go through the assembly of the head, installation of the cams, and degreeing of the cam timing to finally finish up our long-block assembly.

If there's one thing that we have learned so far in building this motor, it's the knowledge of realizing test fitment is critical when using newly developed parts. The camshafts that Naoto chose to run are a BC 272 degree with 10.19mm of lift. This is a huge difference compared to the stock bumpsticks at 256 degree and 8.73mm of lift. The increased lift enlarges the physical size of the lobe. While installing the cam into the head, we found that the bucket reliefs interfere with the rotation of the cam at the top of the lobe.

Using a die grinder, we remove just enough material out of the head to clear all the cam lobes. BC also designed the cam to work in a front-wheel-drive application. Since our engine does not utilize the factory distributor, we had to have the notch machined out. Once all the material is removed, we do another quick check to find that there is no longer any interference.

Naoto then moves onto installing the valves. As we went over in the previous issue (Aug. '08), we opted for Supertech 37.1mm nitride intake valves and 32mm inconel exhaust valves to help our head really breathe. Running a bigger cam requires that at high rpm, the valves are susceptible to floating or bouncing. To counter act this, we opted for a set of Supertech dual valvesprings. The raised seat pressure should prevent the valves from losing contact at our target of 7,200 rpm. Since the valves have already been lapped, we were set for installation.

With the valve in place, Naoto installs the lower spring seat, the valve stem seal, and spring. Depending on the motor, there might be an order to follow between the lower seat and the valve stem seal. (Honda B-series for example.) On the KA24 it can go either way. The seal should be tapped into place. Take care to not apply too much force because it may damage the seal. The spring assembly is then compressed with a valvespring compressor and the retainers and keepers are inserted. Slowly backing off the compressor, the keepers should hold the assembly in place. The same process is repeated for each valve.

Naoto then installs the buckets and shims. We had WPC treat each one of our buckets and plan to have them do our cams and cam journals after we finish with our preliminary testing. Supertech sent us its inner shim buckets. This is an improvement in weight over the factory shim over bucket design. With our initial delivery, Supertech sent us a couple of different sized shims for us to try out. By installing our cam and using a feeler gauge, we figure how much valve lash we have and calculate the proper shim to order.

Naoto wanted to use a target valve lash of 0.20mm ( 0.02) intake and 0.25mm (0.02) exhaust. With the target shim thicknesses in hand, we had Supertech send over the shims as close as we could get them. To get tolerances even tighter, Naoto uses an oil stone and hand grinds down the shim. The oil stone only cuts a couple micron at a time so a greater amount of control can be exercised. This comes at the cost of how much time has to be spent grinding. The whole assembly is then installed and each valve is again measured for the correct lash. This also gives us a chance to make sure there are no issues with the rotation of the cam. The cams are then removed to prepare for the installation of the head.