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Don’t Walk!

How To Set Roller Cam Endplay

Jeff Smith Mar 1, 2000

Step By Step

A roller cam is the hot ticket for high-tech street engines, but it does require care during installation to ensure it performs to the best of its ability. This is one of Comp Cams’ new mechanical Xtreme roller grinds featuring the new Endure-X duty roller tappets with the machined lube groove that pressure-feeds oil to the roller bearings. It’s a great choice for street engines.

Flat-tappet camshafts are machined with a slight 0.0025- to 0.005-inch taper on the face of the cam lobe that spins the lifters. This also imparts a rearward thrust to the cam. Roller cams don’t have this feature, which is why a thrust bearing or washer is necessary.

Comp Cams and BLP offer this trick two-piece timing-chain cover.

It also offers a small hole in the front of the cover that allows you to place a dial indicator on the face of the cam gear to check endplay. The spec is 0.005- to 0.010-inch.

The best cam button to use is this adjustable roller bearing piece, available from just about any cam or valvetrain company. The button uses a roller bearing to prevent wear, and also features a series of washers that can be used to accurately set the endplay. Using a roller cam button will also require three small-head, 12-point bolts to retain the cam since standard head bolts will not easily clear the thrust bearing.

Here we see an aluminum button (1) and a better nylon (2) button.

Cloyes makes this beautiful two-piece cast timing chain cover with a removable insert that allows for cam timing adjustment. The insert also employs a built-in thrust bearing for endplay adjustment.

On the left is a cast one-piece cover from TD Performance. It is inexpensive, works well, and includes a center step. Note that on the stock cover on the right there is a worn mark where an aluminum button galled into the cover. This also bent the cover. We replaced it with a stronger cast-aluminum cover and a roller button.

The guys at Reggie Jackson Performance use this slick homemade tool to establish endplay. What’s missing in the photo is a timing cover gasket on the block. This may be roughly 0.020 inch thick. They set the height of the adjusting pin using a feeler gauge with the proper spec by locking the setscrew.

At the proper clearance, the block will sit flat on the cover while the adjusting pin just touches the inside of the timing chain cover.

Many engine builders prefer these thrust washers instead of the trick roller bearings because if the roller bearing falls apart, the bearings will end up in the engine. The washers measure roughly 0.030 inch and prevent cam gear wear on the block.

BLP sells a series of different thickness cam gear spacers that can help align the cam gear with the crank gear. These fit between the cam and the gear.

The late ’80s GM small-blocks that came with a roller cam also were fitted with a thrust plate that bolts to the front of the block. This takes the place of a thrust button. It also requires the use of a dedicated roller cam with the step in the nose.

Checking endplay with a dial indicator is best done before the cam plug is installed. Set the dial indicator on the cam and gently move the cam back and forth with a long screwdriver. If the motor is in the car, you can use a dial indicator sitting in the lifter valley at an angle onto the cam. This is not the most accurate method but will work in a pinch.

John noticed that his 11-second Camaro was losing top-end power. He checked fuel-pump pressure and initial timing, but the car was definitely lying down at high rpm. After several hours of searching for the cause of the problem, he finally decided to check the timing at high rpm. He discovered that the timing retarded 12 degrees between 4,000 and 6,000 rpm. At first he blamed the ignition box, then the distributor, but all were working fine. Finally, after much head scratching, he discovered the aluminum roller cam button had galled itself against the inside of the timing chain cover, which allowed the roller cam to walk forward 0.040 inch. This cam walk moved the distributor, which retarded the timing.

Roller camshafts are becoming increasingly popular with the high- performance set, but with these trick new parts can come headaches if you don’t know how to properly set up a roller cam. Flat-tappet cams for Chevys V-8s incorporate a built-in feature that prevents cam walk, but roller cams do not. For both the small- and big-block Chevys, cam manufacturers grind a slight taper into each lobe across its face that loads the cam toward the rear of the engine. GM uses a 0.0025-inch taper while aftermarket cams use as much as 0.005 inch. This taper also spins the lifter in the bore, which prevents wear and break-in problems, especially with aggressive camshafts.

Roller cams do not have this tapered ramp design, which means that other external forces can cause camshaft walk. Generally, situations like lifter bore placement, position of the distributor relative to the cam, and other factors affect the fore or aft thrust of the cam. One of the most important considerations is the vertical orientation of the crank gear relative to the cam gear. So if the crank gear is slightly forward of the cam gear, this offset will pull the camshaft forward.

One danger that exists with significant cam walk is the real possibility that the roller lifter could crash into an adjoining lobe. If this happens, catastrophic engine damage is only seconds behind. At the very least, your first indication of a problem will be metal shavings throughout the engine.

The Cure

Now that we know what the problem is, let’s look at a few solutions. All the major cam and valvetrain companies offer several styles of cam buttons that limit cam walk. The spec is to keep camshaft movement to around 0.005-0.010 inch. The best way to do this is with a roller-bearing cam button. This style button uses an internal roller bearing that does not wear into the timing-chain cover. In some cases, the cam gear may need to be machined in order to fit this cam button spacer.

But just installing the button is not enough. Stock small-block Chevy stamped-tin covers are flimsy, and the forward thrust of the cam button can easily deflect these thin covers. It would also be wise to stay away from any thin, stamped aluminum cover. The best plan is to invest in a thick, cast-aluminum cover. Cast covers are far more durable, they don’t deflect like stock tin covers, and they look trick. Several companies also offer two-piece covers in various styles that allow access to just the cam drive, or the entire face can be removed without having to drop the oil pan.

Another option to consider is that many aftermarket aluminum water pumps offer small adjustment bungs at the rear of the pump, which can be used to establish a limiter that rests up against the timing-chain cover to eliminate deflection. This isn’t necessary if you are using a cast-aluminum cover.

Finally, there are also several different styles of cam buttons available. Most of the cam companies have discontinued aluminum buttons, but they are still out there. You should avoid them because the aluminum wears quickly. The next best style is the nylon button that’s available from several companies, including Comp Cams. This piece wears well yet has no moving parts that could fail.

Setting Endplay

Before checking cam endplay, it’s wise to investigate the relationship between the crank gear and the cam gear. Often the crank gear ends up farther forward on the engine than the cam gear. This will pull the cam forward. Use a straightedge to check this gear alignment. If necessary, use a shim between the cam and gear to adjust the gear forward. You can also purchase a crank gear shim from BLP that will move the crank gear forward to prevent rearward thrust, which could cause excessive wear on the gear and the block.

Checking and adjusting roller-cam endplay is best done before the engine is assembled. This way, you can set a dial indicator right on the end of the camshaft before the bellhousing cam plug is installed in the engine. We have photos of a trick tool the guys at Reggie Jackson Performance made that makes checking this endplay quick and easy and requires only a feeler gauge. If the rear cam plug is already installed, the endplay is best checked with one of those trick two-piece timing-chain covers from Comp Cams or BLP. These covers have a plug in the center that allows the use of a dial indicator.

The easiest way to adjust the cam endplay is to use the roller cam button. It offers shims installed on the button to adjust its height. These roller buttons are also available in three different lengths depending upon the application. If you choose to use the nylon button instead, these units are designed to be slightly long, allowing you to sand or grind the button down to establish the proper clearance.

Setting roller-cam endplay isn’t a big deal but it is critical. Like most things in life, it’s the little details that can make all the difference. The bottom line is, if you’re not sure, check it. You might be surprised by what you find.


Crane Cams
Daytona Beach, FL 32117
Comp Cams
Memphis, TN 38118
Cloyes Gear And Products Inc.
Ft. Smith, AR
BLP Products
Orlando, FL 32805
Lunati LLC
Olive Branch, MS

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