Corvette Magazine (July 2007)

Magazine Site: Corvette Magazine

AVOIDING THE DAILY GRIND

Think you have a better cam grind to put in your LS? Jeff Glen doesn't exactly believe you, but he'll walk you through an LS-series shaft swap regardless. Photographs by the author and Synergy Motorsports.

Looking for more performance? The cam often sounds like a good place to start. After all, it determines how air and fuel move through the cylinders; what could be more central to engine performance than that?

Well, the reality is the cam swaps should never be taken lightly. Precisely because this piece is at the heart of the operation, any little change can have far-reaching and often unpredictable effects. Unless the new cam has been correctly engineered to work in harmony with the precise heads, intake, exhaust, and management systems on that very engine, you're playing with forces you don't really understand. Fortunately for me, the process of selecting a cam isn't this article's focus- I'm just here to show you how to yank out the old one and drop in its replacement after that choice had been made. In politics, you'd call it "plausible deniability."

In the layout of a traditional pushrods V8, the cam isn't just central to functionality but geographically central as well; in other words, it sits smack-dab in the middle of the block. On the plus side, once everything is out of the way, sliding out the old cam and slipping in the new one isn't that much harder than moving two wine bottles around in the rack. The trouble is, as modern Corvettes become ever more complex and tightly packaged, just clearing all the stuff out of the way has turned into a major procedure.

Since Synergy Motorsports of Fremont is just a hop down the freeway from our Emeryville, California editorial offices, on one warm Monday in June I headed to that shop to participate in a cam swap on a mildly upgraded C6. While some the packaging details are different, most of the processes I'm going to talk about are common to C5's and even most earlier cars. Everything can be done with the cylinder heads and intake systems in place, meaning we're mostly just talking about the nut-and-bolt tasks here. Two notes: First, you'll appreciate having a lift, and some specialized tools for this job, but it's not mandatory. Second, I always think taking stuff apart is easier than coaxing it back together, so instead of showing you the breakdown process and then saying "assembly is just the reverse," I'm going to explain it the other way around; the meat of the story will cover reassembling everything after it's been taken apart.

A) Before even raising the hood, straighten the wheels and rig up a jig to keep the steering wheel in it's current position-the easiest tricks are to hang a weight from the rim with a short piece of string or to tie a wire between one spoke and the shift lever. If the steering rack and steering wheel aren't reassembled in their original relationship later, the steering-angle sensor inside the rack tells the car's main computer that the front wheels are turned when they actually aren't; it drives the traction-control system completely bananas.

Next, break the front wheel lugs and the main crank-pulley bolt before raising the car off the ground. A good impact gun is best for the latter, but a gigantic cheater bar will get you there, too. (On automatic cars, it's a good idea to take out the starter and install a proper locking tool onto the ring teeth.) Once these tough fasteners have been softened up, take off the plastic engine covers, unhook the battery, unplug the MAF sensor and main air intake hose, remove the alternator, and loosen and slip off the serpentine belt. Pop off the sparkplug wires, the coil packs, and the valve covers. Remove the top radiator shroud and disconnect and pull out the fan.

Working underneath the car, drain out the coolant and power-steering fluid and unbolt the antiroll-bar mounts. Once the antiroll bar is hanging loose from its end links, most of the cooling apparatus can be slipped out through the bottom. Remove the air-filter housing and then disconnect the coolant hoses from the water pump.

Unbolt the pump housing and take it off the front of the engine, then carefully take off the rockers on top of both heads.

B) Now comes the most frustrating part of the whole silly job-extracting the steering rack. Undo the balljoints at the far ends of the tie rods and free up the steering-shaft mount. Next, unplug the rack-position data wire and loosen the hydraulic lines where they enter the rack. When that's done, undo the main rack-clamps bolts, one of which holds down the ABS modulator's bracket. While the bracket is unbolted, keep the modulator and all of the brake lines intact and in place.

With everything disconnected, lean into the engine bay from the driver's side and shift the rack forward and away toward the passenger's side. Once the tie rod is finally convinced to clear the driver's-side frame rail, the whole unit will come up and out of the top. This is easier said than done, but it's possible- just be patient and try not to herniate too many discs in your spine.

C) With the rack out of the way, there's now enough room to pull off the a/c belt. The crank pulley comes off next, a job that's easiest if you use the special tool that grabs slotted holes, rather than the edge of the belt surface. A regular puller tool will still do in a pinch.

Undo the bolts and take off the timing-chain cover, exposing the chain and the cam sprocket. Unbolt the sprocket, then pull it away leaving chain simply dropping in place. The bolts of the cam-retainer plate are now accessible; take off the plate.

D) If you haven't already, go ahead and yank out the radiator now. Leave the a/c condenser intact and in place; protect it with heavy cardboard or blankets if you're worried about skewering the fins.

E) Before sneaking the cam out of the engine, the lifters need to be held up in place. Synergy fabbed up some rods which slide into the oil galley for that task; you can get professionally built versions of the same tool online or make your own. Either way, the rods are inserted into the gallery hole over the cam and slid home.

F) To help get some purchase on the cam, tech Rodney Roland likes to thread the timing-sprocket bolts back into the nose. It also helps to have a second set of hands available to hold the a/c condenser out of the way while you're working. To draw out the camshaft, grab the front of the cam and gently rotate the unit while pulling backwards. If you feel any lobes getting caught on the way out, don't force it-just ease the cam back into the block a little, start spinning it again, and try gently drawing it forward again.

G) Once the old cam is out, take the new one and give its journals a good dose of assembly lube. Bolt the sprocket onto the new cam finger-tight, then push the shaft into the block again rotating constantly and easing up if it seems to get caught. Once the shaft is fully home, take the sprocket back off and reinstall the cam-retainer plate. Torque down its bolts to 18 lbs-ft each.

Now put some threadlock on the sprocket bolts, reinstall the sprocket, and quickly-before the good sets-ease the timing chain back on the teeth. (The space here is tight and there's just barely enough play in the chain, so this takes steady nerves.) Once you have everything put back together, final-torque the sprocket bolts to 26-lbs-ft.

H) Thread the crank-pulley bolt into the crank, then rotate the crank with a wrench to put it at Top Dead Center. Now, this is as good a time as any to replace the original timing chain and sprocket, but very few C6s have racked up enough miles to require that kind of thing yet. In any case, when installing either a new sprocket or the original, the dimple on the face should point straight down to TDC. Since our cam was ground to a Synergy design and inspected on-site, we didn't have to degree it to ensure its position relative to the timing gear. If you're pulling a new cam right out of a box, though, it's usually worth the additional step just to be on the safe side.

I) Even if you're just lining up the sprocket's dots, it's worth doing a compression check to next ensure everything's gone back together correctly. Reinstall one cylinder's rocker and pushrods, take out the fuel-pump fuse, and then check the numbers on that cylinder. With a good 200 psi showing, we knew we were in business.

J) Now the reassembly process really kicks into gear. Carefully wipe down the block face and front cover, removing all oil and grit. Then grab the timing cover, pop the old crank seal out with a rubber mallet, and gently tap in a new one.

To remove the cover, dab a smooth bead of gasket compound around the periphery, concentrating a little bit more in the corners, and then line up the bolts. Snug down the bottom ones first to seat the gasket compound, then cinch down alternate-side bolts until the cover us held evenly all around.

K) LS-series crank pulley, unlike those found on most older engines, don't use a key but just press on the crank hose however they like. Use a long bolt/washer combo of the proper thread pitch to force the pulley onto the nose initially; once it's been driven far enough, back out the long bolt and put it back into your toolbox. Replace it with the stock fasteners and, using an impact gun or that super-mondo cheater bar, torque that bad-boy to 240lbs-ft.

Now you're on the home stretch. Slip the air-conditioning compressor belt onto the rear most groove of the main pulley and the compressor, then sit back for a minute and take a hard-earned break.

L) Refreshed? Well, good, because it's time to stuff that damm steering rack back in place. Standing again on the driver's side, aim the tie rod into the gap and jockey the rack as far toward the passenger's side as possible. Eventually, with some noodling and smashed fingers and foul language, you'll just barely get the left tie rod in the past the frame, at which point you're home free. Lower the rack into place and center it; you may need a buddy to help it placed. Once it's there, push in the mounting bolts, reattach the steering shaft, and gently thread the hydraulic fittings back into the rack. Now you can crank down the main fasteners; don't forget that the ABS-modulator bracket is incorporated into one of the rack mounts. Reattach the balljoints to the steering arms on the uprights, then tighten up the hydraulic lines. Plug the data wire back in before leaving.

M) The water pump is next on the list. Line up the gaskets on the back of the pump assembly and slide the bolts into the housing. Refit the cover, making sure not to knock any bolts back out as you go. The coolant joints are sealed via O-rings, so don't use any gasketing compound when reinstalling this part.

N) Refit the radiator from the bottom, making sure the mounting holes and a/c condenser are correctly aligned when you're done. Next, drop in the fan, bolt it down, and reattach its wiring harness. Reattach the antiroll-bar brackets after that, being careful to evenly sandwich the soft brushings between the brackets and front crossmember . Reattach the over-flow-reservior hose next, snapping it into the upper clip on the side of the radiator. Reattach the upper radiator cover to the frame after that, then reinstall the upper air-filter housing.

O) Whenever installing a new cam it's a good idea to change pushrods as well, but if for some reason re-using the old rods is part of your plan, make sure they go back into the same bores they came out of. As with most internal pieces, you'll avoid lots of wear issues later by putting everything back in the exact same location it came out of.

P) Put the rockers into place next. To tighten them down, technician Andrew Mota cranks each one in turn to 22 lbb-ft after making sure that its lifter is sitting perfectly square on the back of its lobe. To achieve that, he has a helper rotate the crank until the rod is completely relaxed. Once he feels it slide down off its ramp, the engine is cranked a little bit further so that the lifter rests fully on the back of the lobe. After that he tightens the stud and moves on.

Q) We're getting close. Reattach and re-wire the alternator and then snake the serpentine belt back into position. Using a socket wrench for leverage, move the belt tensioner toward the alternator until you're able to muscle the belt onto its pulleys. Align and re-tension as needed.

R) Refill the radiator, reattach the primary air duct, and plug the MAF sensor back into its harness. Refill the power-steering reservoir and then snap the plastic coil covers back into place on top of the engine. Last but not least, reach up from the bottom and replace the bolts holding the lower part of the airbox. Now check your watch: Pretty shocking how long it took, yeah?

With a professional lift, lots of practice, and some specialized tools, a seasoned technician can knock this job out in a day. Most of this task is just straight nut-and-bolt labor, and the steps move along smoothly when done by well practiced hands. Doing all this for the first at home with a jackstand, though…well, you ain't gonna be loving life. The packaging makes it a major slog. Don't worry, you'll get it done-like I said at the beginning, just don't take the whole cam-swap thing lightly.



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