Now back to assembly. We went...
Now back to assembly. We went with a lightweight Probe SFI race damper-an elastomer unit which uses a steel hub and aluminum inertia ring. For street use, consider the Probe's heavier all-steel damper, which likely dampens better.
As we completed our story last month, our prepped 360 bottom-end was stuffed with a Mopar Performance stroker crank and built up into a stout little short-block. The MP crank stretched the cubes to 408, while Milodon four-bolt main caps, Eagle H-beam rods, and a set of Diamond forged stroker flat tops provided the beef.
To show we were serious, we were also packing a serious but sane Crane roller cam, spun by Milodon's excellent gear drive. We had horsepower in mind for this combo, and the top end wasn't going to hold us back. We ground ourselves silly getting huge flow from a set of W-2s (Nov. 2001 p.54), and the ante just kept getting stepped up. Getting ready for this month's installment, we found that Mopar was dealing on tunnel-rams, so we added one to the program-though a more conservative (by comparison) single-plane is also part of the mix for the dyno test to come.
We found that with the pan...
We found that with the pan on, the edges of the tray were pushed in slightly, enough to cause a clearance problem. Some hammerwork with a notched bar of steel backing it up had the tray clearanced for the 4-inch stroke.
Building a hot engine combo gets tougher the more radical you go, and though this isn't an all-out race engine, our 408 is much more involved than screwing together a basic stock-style 360. Therefore, it's up to the engine builder to make sure everything is right, from ordering parts that will complement each other, to making them fit together like they should. We can't wait to hear this one singing on the dyno, but before that happens, it's all wrenching, grinding, measuring, and checking. When all's said and done, and we've buttoned on the last piece, hearing the sweet sound of our "mini-mountain" small-block pull will make it all worthwhile.
Backtracking
Double-Checking Pays Off
We thought the bottom end of our big-inch small-block was sewn up for good last month, but a lucky catch saved us from potential problems inside. We carefully checked and set the clearance between the Milodon windage tray and the moving hardware swinging above, dropped the pan in place, and buttoned it up.
The tray was bolted back in...
The tray was bolted back in and the position of the dimples verified in line with the rods. When you've got 4 inches of crank, sometimes you just gotta make more room.
Here's the deal. The sides of the pan press against the sides of the tray when it's bolted up, squeezing the ends of the tray in toward the crank. This is not a problem with a stock stroke, but with the 4-inch arm, it pushes in the louvers of the tray towards the rods. It may not hit, but it may be too close for comfort. Luckily, we heard a slight interference inside and opened it up to investigate. Pan-off, plenty of clearance; pan on, contact. The fix was simple-we just marked the lower louvers in line with the rods and dimpled for a margin of safety.
Valvetrain Variables
The Ups And Downs of Cam Peripherals
We had milled, long-stem-type Econo W-2 heads, plus solid roller lifters and aluminum rockers. No, there won't be a cataloged pushrod for this combination. The truth is, any time the valvetrain or related components are changed, things have to be measured. For us, a set of custom pushrods were a given, so we tackled the challenge of figuring out what we'd need and then ordered them from Crane.
The piston's deck height is...
The piston's deck height is measured with the engine assembled or mocked-up. We dialed in our machining to give us .005-inch positive, or out of the hole. Calculating that, we subtracted 1.1 cc from our equation.
The pushrod length is measured...
The pushrod length is measured by mocking up the heads with the cam and a pair of rockers installed, and using an adjustable checking pushrod. The final deck machining of the head should be complete, and the head gasket should be in place. We cheat and use some shimstock under the head to simulate the gasket thickness. The valves are installed with light checking springs. To get the pushrod length, first set the rocker adjuster so only the first thread is starting to show under the rocker. This will normally give the best geometry, the most lift, and the least deflection. The pushrod length is then adjusted to give the specified lash. Measure the intakes and exhausts separately, and then order the pushrods to match the length. Crane made us a set in no time. Run the cam through a lift cycle, and check that the rocker-tip travel is well centered on the valve tip and that the pushrod cup or retainer doesn't bind on the rocker body. These fixed pedestal heads have a fixed geometry on the valve side, so little can be done to change the sweep, other than lashcaps or a change in valve length. The Crane 1.6:1 rockers we had swept nicely on the long-valved W-2s.
The chamber volume is measured...
The chamber volume is measured by "cc'ing" the heads. Our W-2's were machined to give 66 cc's. Doing the final math, we had almost 11.7:1 compression.
With the valvetrain functioning,...
With the valvetrain functioning, the valve-to-piston clearance is checked. This really should be done during a trial or mock-up assembly, since the only cure is less cam or pulling the pistons out for machining. With checking springs installed, it's easy to just push the valves down and see how far they will go before stopping against the piston. Rig a dial indicator to the retainer to measure it, and check the exhaust valve every two degrees from 16 degrees BTDC to 6 degrees BTDC. The clearance should decrease and then open up again. The smallest measurement is the valve-to-piston clearance. Repeat the process on the intake from 6 degrees ATDC to 16 degrees ATDC. If a minimum number doesn't fall somewhere in this range, broaden the checking range, and have another look at the camshaft's installed centerline to verify the cam is timed correctly. We had 0.135-inch clearance intake, 0.152-inch exhaust, which is well above the Mopar recommended minimums of 0.090-inch intake, 0.110-inch exhaust.
Though the above check will...
Though the above check will give the clearance, it won't sound an alarm if the valve's radial clearance to the valve relief is too tight. This is normally only a problem when larger-than-normal valves are used. This clearance can be checked by removing the head and laying some clay in the valve reliefs.
With the clay in place, bolt...
With the clay in place, bolt the head back on, set up the valvetrain, and rotate the engine through a cycle. Turn the crank slowly during the overlap phase, where the valves contact the clay. Pop off the heads, and section the clay with a razor to get a good look at how close the valves will get to the pistons. The clay test verifies we have a mile of clearance.