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Category: Categories > Engines > Engine Building > Tech Tip
|BUDGET BIG BLOCK PART 3, HEADS, updated!
Posted: Sat Mar 15, 11:36 PM EST
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|Author's Username: KAM||Ask the Author a Question or View Answers|
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Recap so far
We started with a $500 rebuildible core and have spent almost $600 to put the short block together complete with cam lifters and timing chain. This included having having the crank cut and a rod reconditioned.
The heads we are working with are the oval port 049 castings. similar to 781 castings both of these are some of the better oval port heads that GM produced. The heads came through with 2.025 intake valves and 1.72 exhaust valves. The small valves are good for low end torque and response
The heads were in surprisingly good shape. The valve guides were tight and the seats intact. The valves had only about .001 wear.
If we REALLY wanted to keep the cost down I probably could have just done a quick valve job. Assembled the heads with new springs keepers and seals. Im sure the combo would have performed just fine.
We have kept expenses low enough so far that we decided to spend a little more money and modify these heads to perform better.
The first step was to port the heads. The heads were pocket ported with a die grinder and carbide burrs. Starting below the seat the bowls were opened up for larger valves and smoothed. The big ridge was removed in the bowl area and the short side radius were cleaned up. The larger valves let you clean up the shortside with a nice gentle contour. be careful as there is water behind that short turn. you dont need to remove a lot of material, just make a nice gentle contour. The valve guides were not shortend in the bowls. The chambers were lightly polished with sanding rolls. The chambers were swept out slightly to un-shroud larger intake valves. Very little was done to the intake runners. The entrance of the ports was matched to the intake gasket and blended about 1 in. Any obvious casting flash was removed and thats about all.
Similar clean-up was done to the exhaust runners.
The work was cleaned up with 60 grit sanding rolls.
Some searching on the web turned up some decent prices on parts for the heads. A company called Century had a closeout on a ton of Erson valve train parts. We purchased springs-retainers-keepers-pushrods and Racemaster exhaust valves for $213. Ebay turned up good stainless intake valves and some new long slot rockers for another $56.
Valve sizes are 2.19 intake and 1.88 exhaust
Now the fun part. The valve job. This is how to do this with conventional high speed stone equipment. I use Kwik-Way valve and seat grinding equipment. My first step was to see how the larger valves looked in the heads. This also meant checking the installed height before starting any grinding. Next thing was to take a large stone and remove all the casting flash and uneveness around the valve seat areas. Then the three angle valve job was performed. The angles are top cut of 30*// a seat cut of 45* //and a bottom cut of 60*. Below the 60° cut a 70 or 75 and blend into the bowls. When creating the new seats, make sure you bring them to original depth or you will lose installed height for the srings and may have valve/piston contact issues. I like to have the seats toward the outer edge of the valve, but there must be some margin left on the exhaust valve.
ENLARGING VALVE SEATS
The basic method to enlarge valve seats on cast iron heads without inserts is this.
With a 45* stone grind the seat until it becomes the full width of the valve face o.d.
then with a 30* stone you will grind the top angle until there is a small margin around the outer edge of the valve. Then with a 60* stone narrow the seat to its actual width.
the seat width for racing is intake .060 and exhaust .060
for street use make seats .020 wider.
A set of dividers and a dial caliper is very helpful. Once you make the first seat the dividers will help you to rough in the others faster.
A trick I use to help me narrow and move seats around is to paint the seats with black magic marker or blue machinist layout fluid. Then when you cut the angles its easy to see what your removing. I will use a little prussian blue to see how the valve hits the seat. I also lap with compound to see the actual width and location of the seat on the valve.
The new valves were cut with a slight interference angle. The front face to margin was radiused and the seat was back cut with a 30* angle. The heads were thoroughly cleaned. A last step before assembly was to make sure that there would be adaquate clearance between the valve guide and retainer at maximum lift.
The heads were assembled with plenty of oil on the guides and stems. No rotaters were used. The final installed spring height is adjusted by shims under the springs. Actually one shim proved sufficient on these heads.
That pretty much wraps up the cylinder heads for this engine. There are many ways to go here. It depends on many things. Your budget and how much you can do yourself. How good your cores are. How much performance you want. The aftermarket gets better and better for cylinder heads. New heads may be the way to go for some projects.