One of the advantages of modern-day social networking is that engine builders and others now have the opportunity to share experiences. We’ve noticed a recent rash of comments and videos from enthusiasts accusing cam companies of flooding the market with low-quality flat-tappet camshafts and lifters. These comments inevitably stem from losing a cam lobe or two during a cam swap. We recently read a comment where an enthusiast claimed he’d killed four cams in a row on the same engine!
This pushed us to do a little digging into the process of why flat tappet cams fail and how to minimize this. Along the way, we uncovered several processes that will help improve the chances of a successful break-in process on a new flat tappet camshaft.
One part of our research led us to an insightful discussion with Bob Cook, who works with John Callies, Inc , the go-to people for Morel lifters. Morel does not sell flat tappet lifters, but Bob was willing to share some of his industry knowledge. The whole process of breaking in a flat tappet lifter, either mechanical or hydraulic, must start with one overriding fact — all flat tappet lifters must spin in their respective lifter bores.
You Spin Me Right Round
This concept is built around several key aspects of cam and lifter design and machining. Each lobe on a flat tappet camshaft is machined with a specific amount of taper as viewed from the side. This taper works in conjunction with a slight crown on a flat-faced lifter, that together induces each lifter to rotate inside its lifter bore. This spin ensures that the majority of the lifter face is in contact with the lobe.
As Cook succinctly put it, “If the lifter does not spin, it will not survive.” So this then should be the very first test an engine builder should perform on his engine. At the very least do this test before installing the pushrods and rocker arms with the new cam and lifters in place. It might even be a good idea to perform this test before removing the old cam. This will identify a possible bad lifter-cam interface before the engine is reassembled.
The test is simple and easy. Mark each lifter with a marker at the 12 o’clock position and then turn the engine by hand so that the camshaft rotates four to five full revolutions. Each lifter should rotate roughly one-quarter turn in its bore. If you find a lifter that does not turn, make sure it is not hanging up or stuck in the bore. There are several reasons why a lifter may not spin in its bore. But after several tests, if one or more do not spin, then it’s likely that the lifter and lobe will fail if the engine is reassembled and run as-is.
Diagnosing A Non-Spinning Flat Tappet Lifter
If you find a lifter that does not spin, you might try this simple solution. COMP Cams and others offer a brass shim that is placed between the cam gear and the block. This will move the cam forward in the block and re-position the camshaft lobes relative to the lifters. The small-block Chevy shim from COMP, for example, is around 0.030-inch and this small movement may be enough to help with lifer rotation.
The problem of no lifter spin could also be the result of a poor angle of the lifter bore to the camshaft. This can also be identified with a different, simple evaluation called the lift at top dead center (TDC) test. In this case, you merely set up a degree wheel on the engine so that TDC is accurate. Then measure the lift at TDC of each intake and exhaust lobe and compare all eight intake lobe lift numbers to see if they all are within roughly 0.003 to 0.005 inch of each other. The less variation there is, we can assume the lifter bores are accurately positioned relative to the camshaft. If the lift numbers vary by 0.008 to 0.010 inch or more, this is an indication that the block, cam bore, and lifter bores are not accurately machined. It would also be wise to check all of the exhaust lobes as well.
We recently tested a badly machined small-block Chevy that offered as much as 0.015-inch spread on the eight different intake lobes tested and none of them came close to being within 0.003-inch of each other. Clearly, that block exhibited very poor alignment of the lifters to the cam centerline.
Beyond the lifter position in the block, it’s also a good idea to check lifter-to-bore clearance. A high-mileage engine will probably not be troubled with a too-tight lifter bore but it may have burrs or restrictions that could prevent the lifter from rotating. So it’s a good idea to carefully check each lifter bore for obstructions. A more likely scenario is that the lifter bore is tapered or worn excessively, which would produce excessive lifter bore clearance.
The acceptable clearance range for a flat tappet GM 0.842-inch lifter is in the range of 0.0012 to 0.0019 inch (note the extra zero in there). Excessive clearance can allow the lifter to cock or become angled in the bore and this can potentially lead to a damaged cam lobe and a destroyed lifter. We’ve read examples where the builder claims the exact same cam lobe failed twice in a row. This would suggest excessive lifter bore clearance which could lead to that failure.
Slicking Everything Up
Assuming that all the lifters spin freely in their bores and the clearances are acceptable, there are several other approaches you can take to help the camshaft achieve a proper break-in. Among those ideas is to have the new flat tappet camshaft nitride hardened. This is a process also offered by COMP called Pro Plasma that subjects the camshaft to a nitrogen ion hardening process.
This requires the cam to be completely clean, heated to a preset temperature, and then bombarded by nitrogen gas that forms a hardened surface on the camshaft — especially the lobes. This surface finish is much more resistant to wear and helps allow it to successfully survive the break-in process.
Another potential move to give the lifter every chance to survive the break-in process is an electrical discharge machining (EDM) option where a high-intensity electrical beam is used to drill a small hole (generally 0.024-inch) in the lifter face to force pressurized oil onto the area between the lifter and the cam lobe. Several companies offer this option and these lifters do cost more, but offer direct lubrication as opposed to relying on splash oiling from the crankshaft.
Another step in this direction is a process that applies a diamond-like carbon (DLC) that forms a very slick coating on the lifter. This process has become so popular that COMP, for example, offers this for only a small increase in price over its more traditional non-coated lifters. This DLC-coated lifter combined with a nitriding process on the camshaft would offer the ultimate in protection to ensure a proper cam and lifter break-in process.
Another option is lifters fitted with a separate chilled-iron foot. These lifters can be quickly identified by a seam located roughly one quarter of the way up from the bottom of the lifter. This seam separates the chilled-iron foot from the rest of the steel lifter. The chilled-iron process creates a more durable material that is compatible with traditional cast-iron flat-tappet camshafts. Several companies offer this option including Chevrolet Performance, COMP, Crower, and others.
Proper Flat-Tappet Break-In Procedures
Of course, all of these ideas or processes should accompany the classic break-in rules that obviously still apply. To give the camshaft a chance, the valvesprings for that new cam should not test more than 90 to 100 pounds on the seat. Performance big-block engines, for example, often demand dual springs — except for break-in. At the very least the builder should remove the inner springs to give the cam every opportunity to survive.
Next, the engine should be pre-lubed with high-pressure oil fed to the entire engine just before startup. Of course, this also demands quality break-in oil. There are several good break-in oils on the market but note that diesel oil is not an acceptable break-in oil. While this idea has worked in the past, all current diesel oil formulations have changed dramatically and diesel oil now offers roughly the same minimal ZDDP as current gasoline engine oil. So the diesel engine oil trick does not work anymore.
Another reason to avoid using diesel oil is that it contains higher detergent values than gasoline-engine oil which only makes the situation worse for your flat tappet cam. Detergents work to remove the ZDDP protection from the parent metal, which is why most good break-in oils minimize or eliminate the detergents altogether.
A new flat-tappet cam’s initial start-up also calls for a quality tune where there is fresh fuel in the carb and the initial timing is set at roughly 15 degrees before top dead center (BTDC) to ensure the engine will start on the first crank. It does the cam no good to crank the engine excessively in an attempt to start it.
All cam-in-block engines lube the lifters by splash oiling, so once the engine fires with a new flat tappet cam, immediately bring the engine up to a minimum of 1,500 rpm and constantly change the RPM (no lower than 1,500) to ensure all the lifters are continually splash oiled. Don’t just set the fast idle cam at 1,500 rpm and let it run at a constant speed. Check your ignition timing and continue to vary the RPM for the first 10 minutes and then let the engine cool down. Then repeat the process at least once more for another 10 minutes.
Listen carefully for any telltale noises. After the first cool-down, pull the valve covers and check for loose rocker arms. If you assembled the valvetrain correctly you should not find any loose rockers. If you do find a loose rocker arm, that’s often the classic indication of a flattening cam lobe.
If you do your homework and ensure that the lifters all spin correctly and all the right parts are working together, you will have a far better chance of a content flat-tappet camshaft at the end of the break-in period. Many things have changed in the last 20 years but failing flat tappet cams should not be one of the legacies of a 21st Century high-performance engine. Use good parts and perform the break-in process correctly, while avoiding the shortcuts, and your engine will have the best chances of success.