How to Rebuild a Corvette 454 Engine - Part 10

Well, I managed to make fairly good progress in the last few weeks. Since my last update the parts I ordered came in and I was able to get a decent amount of work done on the motor.

First, before going too much further with my engine build, there is one additional check that needs to be done - check the piston to valve clearance. For obvious reasons this is an important check. If a piston was to make contact with a valve because not enough clearance was provided, or for any reason for that matter, the result could be catastrophic. To accomplish this check I simply used a bit of modeling putty (that's just a fancy name for Play-Doh) placed in areas on the piston where clearance issues may exist. To prevent the putty from sticking to the valves I sprayed the valves and combustion chamber in the cylinder head with WD-40. I also cleaned the piston with lacquer thinner to help the putty stay in place on the piston during the test.

With the putty in place I reinstalled the cylinder head and bolted it down. For this check I left the head gasket off which will give me conservative clearance results. Since I'm still using those checking springs I once again set up my dial indicator to ensure that I was getting full valve lift as I rotated the engine through several cycles. Specifically, I was worried that the valve pressing against the putty would cause the hydraulic lifter to collapse. Initially it did cause the lifter to collapse a bit, but after rotating the engine through several cycles I was able to get full lift.

Next I removed the cylinder head and verified that none of the putty got caught in the valves or was stuck to the combustion chamber. If it had I would have needed to clean it off and start over. With the cylinder head removed it was obvious where the putty had been flattened. To get accurate measurements I used a razor blade to make a vertical cut down the center of each piece of putty. The point of minimum clearance was evident - it occurred at the flat area at the top of the piston. I measured the clearance as 0.060", plus the compressed head gasket thickness of 0.039". Therefore my total clearance will be approximately 0.100", a fair bit more than the minimum clearance of 0.040" (for engines turning less than 7000 RPM). One additional interesting note is that the minimum piston-to-valve clearance occurs at the side of the valve, not at the bottom of the valve as many would expect.

Well, before installing the cylinder heads for the last time I decided to do a bit of double checking. Primarily I was concerned about which valve springs had been supplied with my cylinder heads. After a phone call to Airflow Research I discovered that the valve springs installed on my heads had a seat pressure of 170# and an open pressure of 430#. This was surprising since the pressures are a fair bit higher than the spring pressures I've heard tossed around in the past. Although the AFR representative said these are the springs they like to use with hydraulic roller cams, I was still a little concerned since excessive spring pressures lead to premature valve train and camshaft wear. To see how much spring pressure my new lifters could handle I made a call to Comp Cams. They said that 170#/430# was too much pressure and would probably collapse the lifters. So, I guess I'll be replacing all the valve springs....

Well I wasn't real happy about having to do it, but I ordered some new valve springs from Comp Cams, removed the AFR springs and installed the new ones. I decided on Comp's #928 valve springs. For my setup these springs produce 130 pounds of seat pressure and 340 pounds of pressure at full valve lift. Others I talked to have used this same spring with hydraulic lifters turning up to 6000 RPM without any valve float problems so I felt these springs were a good choice.

Here's one of the new springs in the valve spring compressor ready to be compressed and installed in the block. As you can see it's a dual spring with a third coil separating the inner and outer springs.

So, after several hours of swapping parts I was finally ready to get the cylinder heads installed. After thoroughly cleaning the gasket mating surface of the engine block with lacquer thinner I put the new head gaskets in place. Based on Airflow Research's recommendation, I'm using Fel-Pro's #1017-1 head gasket.

With the head gaskets in place I cleaned the mating surfaces of each cylinder head and lowered them over the head studs.

After lubing each stud with some moly grease I torqued each stud in 10 ft-lb increments using the factory specified torquing sequence.

To be able to torque the head studs I had to remove the rocker arm studs and pushrod guide plates to get enough clearance. The guide plates help keep the valve train in proper alignment by keeping the rocker arms centered (in the front-to-back direction) over the valve tips. With the cylinder heads torqued down it's time to get them reinstalled.

During reinstallation I torqued each rocker arm stud to 50 ft-lbs.

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