This engine has -.019” piston to deck clearance, so we’ll mill .017” off the top of the block to yield a final deck clearance of -.002”, meaning that the pistons are .002” “in the hole”.

We deck the blocks parallel to the main bores, making absolutely sure the deck is perfectly perpendicular to the cylinder bores in every axis.

The top of the block is then carefully de-burred to remove sharp edges and any possible “tits” of aluminum that could become unwanted debris in the cylinders or water jacket. Removing all the edges also prevents cut fingers during block handling.

I’m also using a minimal chamfer at the tops of the cylinders to ease the ring’s insertion into the cylinders during assembly, but I stress that it’s “minimal” and a good ring compressor will be necessary to install the piston/ring/rod assemblies without damaging the rings. Excessive chamfers at the top of the cylinder make assembly easy, but since they under-hang the head, they represent crevice-space that unburned hydrocarbons love to hide in, contributing to combustion inefficiency.

Next up for the block is enlargening the oil gallery that connects the oil pump to the oil filter pad on the firewall side of the block. We also polish the entire length of the galley and do considerable grinding inside the oil filter pad as well…all in an effort to reduce pumping losses in the oil system. The individual oil ports inside the maim bearing saddles are also smoothed and thoroughly de-burred.

With every screw-in plug removed, the block is then scrubbed with hot soapy water several times and the cylinder bores are carefully wiped with Bounty paper towels and lots of WD40. After the block has been blown thoroughly dry, it’s bagged and rolled into the assembly room.

The rest of the engine has been in work simultaneously.

The cylinder head is a GSR piece that we got in a trade. Its original owner had “ported” on it and we declined to touch it once it arrived here a couple years ago. We traded him a GSR head, which once ported, made a much more suitable combination for his usage.

This “reject” head was to become a flow bench-only piece, but I figured that, assuming it doesn’t leak water, or oil into the ports, I could possibly make it work well enough for a street head on my 2-liter combination.

The first operation in preparing the head was to mil the deck of the head so that it’s absolutely flat and parallel to the camshaft bores of the head. We have a special fixture for doing this on our Peterson milling machine, so setting it up is quick and easy.

The valve guides in this head were in excellent condition, so the next step is to machine the valve seats and the adjacent chamber radii for the 84.5mm bore we’re using. This is accomplished on a Serdi machine and all intake and exhaust seats are referenced to a tolerance of +/_ .0005” relative to each other and the head’s deck. This is extremely important, as we want all the valve heights to be the same in each chamber, yielding accurate chamber volumes and piston to valve clearances. All the porting and asymmetric seat radiusing will now take place. After a couple day’s effort, all the porting / chamber work is complete and the seats are machined again and dropped .001” referenced from their original pre-ported locations. The head’s now ready for nit picking on the flow bench.

I’ve discussed what we do to the heads on our old BBS enough that I’m not going there in this article, but I am including the flow rates with our highly modified intake manifold and 64mm throttle body attached. The exhaust flow was also measured with 10” long primary tubes attached, which are the exact diameter of their counterparts on the real Hy-Tech header.

The flow numbers are corrected and rated at a pressure drop of 28” H20, which has become an industry standard in the racing community over the last 30 years. Just as a point of interest, much of the intake port and manifold development in NASCAR and Pro Stock these days is done using test pressures of 100” H2O (or more) for greater validity in the real world.

In our development on these pieces we’ve used a low pressure of 14”H20 and a high of 68” H2O for testing. The lower end of the scale is meaningful for low rpm operation, while the higher test pressures show a lot more about what the air and fuel mixture will be doing in the higher rpm ranges.

We’re using .5mm oversize intake and exhaust valves in this head, with the seats machined to relative heights that will cause the intake and exhaust valves to just “miss” each other during overlap with the camshafts we plan to use. These valves have flat combustion chamber sides and are the same pieces we sell customers.

The combustion chambers volumes after rework are 42.4CC, which is small for a head with this sort of chamber rework, but the head had been milled about .010” by it’s previous owner. I want to see a chamber volume of 41.0CC to achieve the compression ratio I’m after, so we’ll mill the head to obtain this chamber volume. Final static compression calculates to 13.44-1 for this combination.

While we’re working with the head, it’s time to check the clearance between the underside of the spring retainers and the top of the valve seals. If we run camshafts with more than .515” lift at the valve, there’s not sufficient space for the seal atop the guide, so we’re the using Serdi and tool we made that machines the top of the guide (and the seal’s step) to a reduced height by .045”. This will insure that the combination is safe with any of the cams we may run, and it still maintains enough guide length for good valve stability, heat transfer, and excellent wear-ability.

The springs I’m using are some of our new pieces that use an exceptionally clean Japanese wire. These springs can live at over 11,000 rpm with camshafts that have lift in the .550” range and brutal acceleration ramps. These springs also require a set-up height of 1.410” to achieve the seat and open pressure we’re after.

We’re using some of Crower’s +.060” retainers on this head to gain the additional set-up height, but we’re still .025” short of what we need. To remedy this situation, we’ve machined .027” from the under-side of the stock Honda spring seats before treating their head-contact sides to the same ceramic coating that we used on the piston skirts for better lubricity.

Once assembled, the spring height is exactly 1.410” on each valve.

The +.060 retainers present an interference problem with the rocker arms, as their raised edges contact the bottom side of the engine’s rockers, potentially leading to a catastrophic valve train failure (and a ruined engine). To eliminate this situation, each rocker arm is carefully ground and polished beneath the VTEC piston bore to achieve a clearance with the retainer of .040”. The rework of this high-stress area is accomplished so that all grinding and polishing marks run with the length of the rocker arm, rather than across it, which could lead to stress-fracturing.

We’re also installing the camshafts I plan to use in the head prior to final assembly to check their clearances in the cam bores and caps. It’s essential that the caps be torqued for this operation. The cams should spin freely with only some light oil between them and their bores. If the cams are hard to rotate, we locate the offending areas with some machinist’s bluing and massage, or align-hone the bores until the cams are absolutely free.

Now, for all of you who think that we’ve assembled and torn all the parts down “excessively”, let me remind you that we’ve never experiences a seized cam, broken cam, broken retainer, valve, or any other related failure in a Honda head we’ve assembled. You either check all the places where problems could occur, or break parts on down the road, take your pick. While most of the parts we’re using can be easily “bolted-on”, they’re a long way from being “plug-and-play”, just remember that the next time your local shop does a two-hour cam swap. If you don’t check all of these things carefully, you’re setting yourself up for a disaster. Haste makes waste…..and so does inexperience.

With the head’s machining out of the way, we’re going to assemble the number one chamber with valves and a set of our flow bench springs for checking piston to valve clearance once the short block’s assembled.

Prior to assembling the short block, we’ve assembled the rods to the crank for a final check of bearing clearances using Plastigage for verification. It’s essential that all the parts (crankshaft, rods, and bearings) be at room temperature (72-75 degrees), or this type measurement can be severely flawed in its results. We’re using a crude wooden fixture to hold the crank while doing this operation, as it’s a hell of a lot easier than doing it with the crank in the block. The Plastigage verifies that the clearances are exactly .0015”, which was what we’d calculated by measuring the crank journals, and bearings. We typically split bearing colors on both the rods and the mains to obtain the clearances we’re after. This is acceptable and preferred practice, unless you “skip” a color, which can lead to problems.

The rods and bearings are numbered for their respective cylinders. Next the pistons’ wrist pins are fitted to the small ends of the rods. All of these rods require some bushing honing to obtain the .0005” that I’m after. After pin fitting is complete the rods are disassembled and thoroughly cleaned along with the pins and bearings.

The crank is bearing fitted to the block in a similar manner with clearances of .0015”. We’re using a modified Z10 girdle, so it’s installed during the bearing fitment process. We’re using new main bolts for final assembly of the bottom end. At the same time we’re checking the fore-and-aft crank travel…..which oddly enough brings up the subject of clutches. Since this will be a high rpm engine and at this point nobody knows whether the clutch used will finally end up being a ClutchMasters low-pressure twin-disk carbon unit, or a CM high-pressure double diaphragm single disk (Kevlar / Ceramic) piece, I’m looking to make the life on the thrust bearings as easy as possible.