I have a survivor ‘66 Corvette 427. I selected the Factory Muscle solid flat tappet cam as I was trying to stay as true to the original build as possible. I am searching for a solution due to a cam/lifter failure during initial break-in.  Not too many people have good things to say about the flat tappet cams available today, and several have suggested using a hydraulic roller instead. I really don’t want to spend the extra money on an entirely new hydraulic roller valvetrain but I also don’t want to lose another cam. The jury is still out on how much metal went through the rest of the engine. Do you have any recommendations? I’d appreciate your help.


Jeff Smith: It appeared from J.C.’s email that he would prefer to stay with the flat tappet cam, but was prepared to go with a hydraulic roller if necessary. We contacted him to obtain more information in order to properly answer his question. We wanted to find out what valve springs and break-in oil he used and what the break-in procedure was.

J.C.’s break-in procedure was good–he pressure lubed the engine before starting and used a high-zinc oil, a Valvoline VR1 10W30 racing oil. I think that the culprit for the lifter failure might be the valve springs. J.C. used COMP Cams’ CCA-26120 beehive spring, It would normally be a great choice, but not during break-in with a flat tappet cam. That’s because these springs offer a seat load of 155 pounds with an installed height of 1.880 inches, which is a bit too much load for a flat tappet cam.

Compounding the issue is the cam’s 0.520 inch intake and exhaust lift. This creates almost 350 pounds of load on the lifter at maximum lift. This combined load probably contributed to three of the cam lobes going flat. Recommended loads for a flat tappet big block Chevy cam during break-in would be closer to 100-110 pounds of seat load with a maximum peak lift load of 300 pounds or lower.

This is a photo of the lifters that failed on J.C.’s engine. Taking the time to break in the engine correctly with the right spring pressure, the correct oil, and a proper break-in procedure are the things a modern engine builder must do to be successful.

Many engine builders use a dual spring but remove the inner spring before starting the engine. That places seat load around 100 pounds for the duration of the cam break-in period. Once the cam and lifters are thoroughly seated, the inner springs can be reinstalled. This is more work, but less than replacing the cam and lifters after a failure.

COMP generally recommends using the CCA-911-16 spring for its flat tappet cams. This spring is rated at 122 pounds of load at 1.900 inch installed height and 309 pounds at 0.500 inch valve lift. This is substantially lower–14 percent–at maximum lift, which would make things much easier on the lifters.

J.C. provided photos which showed excessive wear on only three lifters. That means 13 lobes appeared to have survived. This could be evidence that he was right on the edge of this cam surviving the break-in period. Reducing the spring load is an excellent way to ensure the cam will survive the break-in process.

Another variable was the Valvoline VR1 oil. This is a good race oil with a high 1,300 parts-per-million (ppm) count for phosphorous and an even higher 1,475 ppm count for zinc. The zinc and phosphorous are better known by the term ZDDP, which is an acronym for zinc dialkyldithiophospate. However, the VR1 oil also has nearly 1,100 ppm of calcium as a detergent. Normally, detergents are a great addition to oil because they help keep the engine clean. However, one aspect of detergents that is generally not well known is that they also attempt to clean anti-wear additives like zinc and phosphorous off of the metal parts they are trying to protect.

The best oil to use during cam break-in is one with high ZDDP levels but very low or no detergent. This way, the ZDDP remains on the cam lobe and bottom of the lifter where it belongs, minimizing excessive wear and allowing the lobe and lifter interface to create the necessary wear pattern.

The old mechanics from the 1950s and ‘60s recommended a 30-weight non-detergent oil for cam break-in on new engines. I’m old enough to remember those days, and I always wondered why (and frankly didn’t believe) a non-detergent oil was the best choice. But now that I understand how detergents interact with ZDDP, it is now clear why these mechanics made this recommendation. It worked!  

Oils I think would offer the best chance for a proper break-in would be COMP’s Break-in Oil, Driven Racing’s Break-In (BR) Oil, and Lucas Break-in Oil. All have sufficiently high levels of ZDDP while minimizing the use of detergents.

We’ve found a company called Speediagnostix that has performed a series of tests on new oil to determine their actual chemical makeup. This sheds light on some oils that have the proper chemical makeup, and also reveals oils that are perhaps fine for a late model engine, but a terrible choice for breaking in a new flat tappet camshaft. The information we’ve placed in the accompanying chart has come from this Speediagnostix testing.

We’ve listed five oils in the second chart to illustrate that looking at only zinc and phosphorous levels does not tell the whole story. For example, COMP’s Hot Rod oil has good levels of ZDDP, but the calcium level is also high, which would work against the ZDDP during break-in. The Valvoline oil’s calcium level is not excessive, but still in the four-digit range. The Driven Break-in Oil has very low detergent levels with high ZDDP, a good combination.

Note that we included an API SN category oil just for comparison. Any oil with high calcium and low ZDDP numbers would be a disastrous choice as a break-in oil for a flat tappet performance engine. The trick of using an off-the-shelf diesel oil instead of a dedicated performance oil is no longer a good idea. The CK or the new CJ diesel oils offer very low ZDDP counts.

It’s our opinion that changing to a lower spring rate single spring for break-in and using a quality break-in oil such as the ones we’ve suggested will let you use a muscle car-style flat tappet camshaft and reward you with a much better result.

Once the engine is broken in, you still must use a high-zinc oil to maintain the proper lubrication needed for your flat tappet camshaft. If an occasional quart of API SN oil is needed in an emergency like during a road trip that should not be a problem. But you certainly don’t want to use an API SN oil regularly for an engine like J.C.’s. You will need one of these specialty oils to help maintain the flat tappet cam’s integrity for years to come.

Recommended Break-In Oil for a Flat Tappet Camshaft Performance Engine

This list includes oil that we have had personal experience with. There are likely other oils that will also be successful, but we have not tested them and so are not included in this list.

Description PN Source
Comp Break-In 10W30 1590 Summit Racing
Driven BR30 01806 Summit Racing
Edelbrock 30W 1070 Summit Racing
Lucas 30W Break-In 10630 Summit Racing

Speediagnostix New Oil Testing

Engine Oil Additives Valvoline VR1 20W50 Comp Hot Rod 10W30 Driven Break-In 15W50 Pennzoil APR SN 5W20 Chevron CK Diesel 5W40
Calcium 1,090 3,100    366 2,561 1,324
Phosphates 1,302 1,980 2,713 718 771
Zinc 1,475 1,950 2,090 848 900
This is J.C.’s engine as it went into his Corvette. We expect it will look very similar once he gets it back together with the new cam and more compatible springs.
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.