Cams, cams, cams.. While camshafts can and do “go out,” something other than a bad core more often than not is to blame. Below are 10 things to think about before calling foul on your cam.
Coil bind is when a spring compresses solid before or during full camshaft lift. This stack of metal stops the valve train motion, usually breaking the weakest link. This can result in bent pushrods, dropped valves and flattened cam lobes.
There is a formula to make sure they won’t bind, if you are technically minded:
Valve spring installed height on seat – minus – (cam lobe lift x times x rocker arm ratio) + plus + valve lash – minus – safety margin = equals = remaining open spring length.
Basically, subtract the total of how much it’s going to move, the lash and the safety margin from the installed spring height.
That difference should not be less than the spring’s published coil bind height. If it is, you have problems. When in doubt, call the CAM HELP line, 1-800-999-0853.
The “safety margin” is generally around .060 inch, though some modern spring and cam lobe combinations can now vary from .015 to .120 of an inch. They utilize coil-to-coil interaction to dampen spring surge, but the bottom line: Coil Bind is bad and can wipe out a camshaft and other components.
RETAINER TO SEAL BIND
Just as coil bind turns a spring into a solid stack of metal, retainer to seal bind can do the same damage. The distance from the top of the valve seal to the bottom of the retainer must be greater than the valve’s lift or the seal and retainer will hit. If it is less, the guide must be machined. This is a very common cause of early camshaft failure. (See Diagram A)
For more info on springs, click here: http://www.compcams.com/Pages/415/truth-about-valve-springs.aspx
IMPROPER VALVE TRAIN CONTROL
Improper valve train control can also cause damage. The valve train is an intricate system of perfectly timed moving parts under great stresses and high RPM. Any weak link or incorrectly matched component can cause harmonics and pound parts into junk.
Incorrect springs are often the culprit. Make sure they are the right ones for the job and work with the cam and cylinder pressures.
The pushrods are the longest gap in the valvetrain and usually the first to distort. While the springs may get the blame, increased cylinder pressures push back on the valve and cause pushrod flex. They need to be thick enough for the load and RPM.
Too much lash or plunger preload can also cause damage. Since it determines how much “run” components make before contacting, the faster the “hit” or contact, the more abusive it is on parts.
IGNITION CUT REV LIMITERS
While “banging off the rev limiter” may sound cool, it’s rough on the valve train.
Most modern rev limiters intermittently cut spark to the cylinders, usually on every other cycle. However, fuel delivery continues and overloads the cylinder with twice as much fuel by the next spark. This volume greatly increases cylinder pressure and creates a rich condition that burns poorly, throwing off the rotational balance.
The increased cylinder pressure also slams the valve back, stressing the spring, rocker arm, pushrod, lifter and the cam. The adverse effects in Spintron testing suggests staying off the rev limiter is a good idea for longer engine life.
IMPROPER CLEANING OF ROLLER LIFTERS
Debris is the number one cause of roller lifter failure. Since they rely on oil flowing through tiny passages, pieces of debris can hurt lifter operation. Clogged passages can stop the lifter from pumping up and cause excessive noise. The increased play in the valve train hinders valve motion.
When installing lifters, make sure the engine block and passages are as clean as possible. Inspect the lifters for shipping damage and rinse them in clean mineral spirits to remove any residual manufacturing contaminants. Once thoroughly cleaned, soak them in engine oil to recoat and lubricate the surfaces prior to installation.
Watch the Lifters 101 video for more information.
An engine can never be “too clean” during assembly. While properly cleaning a block is a time-consuming activity that usually requires specialized equipment like a hot tank and a heated parts washer, there is no getting around the bottle brushes. Bearing failure can often be traced to a build-up of dislodged sludge BEHIND the oil opening left over from an improper cleaning.
Dirt and grime accumulates throughout the oil passages, especially in engines that suffered an internal failure. It hides in nooks and corners, and simply blowing the passages out with compressed air can compact the grime even more. They must be thoroughly rinsed and scrubbed until no trace remains. Any and all oil galley plugs must be removed (even if they have to be drilled and tapped for NPT plugs) and the passages brushed out, as they offer access to critical debris collection points. Floss all crank oiling holes and rinse out pushrods, even if they are new.
Cams, lifters and bearings rely on a microscopic film of lubricating oil to keep them from galling, and any debris or grit suspended in the oil becomes an abrasive that quickly destroys their surfaces or gets stuck within the close clearances. Block those life-giving oil passages and the bearing or lifter begins to fail. This is especially true of silicone contamination left over from gasket surfaces, or excess material pinched at installation that drops into the block.
Bottom line, if you want your cam and lifters to live, it has to be clean, clean, clean!
INSUFFICIENT OILING OR HIGH OILING TEMPS
Proper oiling is key to cam and lifter life.
The “Four Rs of Proper Oiling” are the Right oil, at the Right place, at the Right time in the Right amount. Under normal operating conditions, oil temperatures do not spike. A rise in oil temperature is usually the result of a mechanical bind or blockage causing excess heat, such as a lifter sticking in a bore or a clogged passage.
ZDDP wear additives need heat and pressure to release the zinc molecule and form the protective phosphate coating in an even and calculated amount. With excess heat, the chemical reaction that forms the film doesn’t occur and the additives then become antioxidants and instead get consumed. This translates into the oil “breaking down” or losing its ability to “pad” the metal contact surfaces, and damage will occur.
Low oil pressure doesn’t create enough “padding,” or oil depth, between the moving parts. This allows them to touch and generate heat and begin to fail. A good rule of thumb is 10 lbs of oil pressure for every 1,000 RPM. A high-volume oil pump is wise when increasing RPM.
IMPROPER BREAK-IN OF FLAT TAPPETS
An unforgiving nature and high spring pressures make flat tappet camshafts the star of cam failures. Failure to follow the proper break-in procedures is a recipe for…well, failure.
Since flat tappets are metal cylinders that ride directly on the cam lobe, a properly-formulated break-in oil is essential. Even today’s “high zinc” oils lack the right additives to withstand the abuse. A dedicated break-in oil contains the proper amounts of Zinc and Phosphorous to coat and protect wear surfaces.
In addition to proper oil, there are several other areas that need attention. Spring seat pressure is often overlooked. An ideal break-in seat pressure is around 80 lbs and not exceeding 100 lbs. Dual springs must be run-in with just the outer springs or replaced with “softer” break-in springs with less seat pressure. Low-ratio rocker arms that reduce spring loads during break-in are also available.
Since they wear, or “mate in” together, never re-use lifters with a new cam, or if keeping the same cam, never change the lifter order.
Coat all contact surfaces with the proper assembly lube after a thorough cleaning.
Prime the oiling system before starting, and rotate the engine in the process to assure all rockers are oiling and surfaces are coated.
Correctly set the timing to reduce heat, and load and prime the carb for a fast startup. The engine needs to start quickly and run at 2,000-2,500 RPM to allow oil to splash on the valve train. Low-speed cranking does not throw enough oil around and can wipe out lobes.
Once started, run the engine for 20-30 minutes, slowly varying the engine speed between 1,500 and 3,800. Restart immediately if it stalls, to continue oil flow. Replace the oil and filter after the break in and again after 500 miles.
Check out the flat tappet break-in overview video.
For more detailed instructions, read COMP Cams Installation Instructions, Part No. 145 at http://www.compcams.com/catalog/COMP2012/pdf/COMP_Catalog_2012_404-407.pdf
IMPROPER BREAK-IN OIL FOR ROLLER CAMS
Particulate contamination is the number one cause of roller bearing failure. While break-in damage on a flat tappet is obvious, roller cam break-in damage may take a few thousand miles to fully fail. Proper procedure and oil is essential.
Dedicated break-in oil has two jobs: protect the valvetrain and allow the rings to seat. If there are friction modifiers, as in regular oil, the rings won’t seat. If it’s an aggressive break-in oil, the rings will seat too quickly and generate higher levels of particulate wear metal — that’s bad news for roller bearings.
A proper break-in oil like those available from COMP Cams has high levels of ZDDP that create an anti-wear film to fill in the microscopic peaks and valleys on the surface of roller wheels and needle bearings. A smooth surface carries a greater load.
Another overlooked area is mechanical interference. When building a high-performance engine, the “mix and match” process offers plenty of room for binding and rubbing. Carefully inspect pushrods and rockers through the full range of motion for signs of contact. Rocker arm geometry and pushrod length should be checked for proper alignment and range of motion.
Pushrods need to be matched to the RPM and load range, as inferior ones can “hula” around and deflect as much as half of an inch. Make sure they are seated and staying in the lifters and rockers and not stressed to any odd angles.
Make sure rocker arms clear all stands, valve cover rails, girdles and springs, as slight milling or clearancing may be needed. Never just “bolt and go” with the valve train.
Additionally, check any re-used components for wear, making sure round things are still round and openings like lifter bores are true and correct. A worn lifter bore will cause the lifter to shift and possibly stick with disastrous results. Make sure all used and new components work together and are within spec.
Check the camshaft play where necessary, as well as the position of the lobes in the bores. Some very-centered lobes might not put enough spin on the lifters.
Properly building or upgrading an engine is a complex and precise adventure. There are many places where things can go wrong, and double-checking specs and following proper procedures will always save time in the long run. Don’t rush to race, or immediately blame the cam core when disaster strikes. While they can go bad, cam failure is usually for another reason.