Some engine builders like to use API CJ-4 diesel motor oil as a break-in lubricant for new engines. That’s because it contains plenty of zinc (ZDDP) to protect flat-tappet camshafts. Apparently this oil is being replaced with a new formulation, API CK-4 and CK-4/SN (SN means the oil meets current year API standards). And just like today’s gasoline engine motor oils, CK-4 has much lower levels of ZDDP, on the order of 800 parts per million (ppm).

That’s not good news for folks using diesel oil to break in gasoline-powered engines.

Since gas engines operate at higher rpm than diesel engines, they typically have higher valve spring pressures. That puts high loads on the contact area between the cam and the lifter. These higher pressures require higher levels of anti-wear additives to prevent scuffing and premature cam failure.

Driven showed us testing by an independent lab.

It revealed a 100-percent failure rate when attempting to break-in a flat tappet cam using a CK-4 diesel oil, even when adding a bottle of ZDDP additive. The chart shows the average cam wear of two different CK-4 oils compared to two different break-in oils. The testing was based on an engine with valve spring pressures of 145 lbs. closed/340 lbs. open—pretty stout, but not a radical valve spring by any measure.

Camshaft wear from using wrong break-in oil

Camshaft wear measured in microns. (Chart/Driven Racing Oil)

CK-4 oil could also be trouble for diesel engines.

Ford Motor Co. has issued a service bulletin stating not to use CK-4 formulation oils as its testing showed increased camshaft wear in engines using it.

[See Understanding the New CK-4 Diesel Oil Specification (Video)]

There are several brands of specially formulated engine break-in oil, diesel motor oil, and gas engine motor oil enhanced with ZDDP to protect your camshaft from damage.

ZDDP levels by oil type

(Chart/Driven Racing Oil)

Author: Alan Rebescher

Editor, author, PR man—Alan Rebescher has done it all in a 25 year career in the high performance industry. He has written and photographed many feature stories and tech articles for Summit Racing and various magazines including Hot Rod, Car Craft, and Popular Hot Rodding, and edited Summit Racing’s Street & Strip magazine in the 1990s. His garage is currently occupied by a a 1996 Mustang GT ragtop.