Zinc additives for flat tappet lifter break-in

Zinc additives for flat tappet lifter break-in has been recommended by most engine manufactures for years.

There have been a lot of conflicting opinions in the last few years about the lowering of zinc and phosphorus levels in modern oils and how these lower levels relate to classic and performance engines using standard flat tappet lifters.

The concern involves the use of the new lower zinc/phosphorus-content ILSAC (multi-viscosity) oils, and how compatible they are with these older engines.

Worn cam and lifters
Worn cam and lifters

There are several theories as to the primary causes of these failures, and with all the usual finger pointing and blame game such unfortunate episodes inevitably generate, the result has been a muddying of the waters that’s left average hot rodders confused and uncertain as to the best course of action.

What’s the real source of the failures, and more importantly, rather than whining over spilled oil, what can be done to minimize the occurrence of these failures? Various parties have blamed camshaft manufacturing quality control, inferior flat-tappet lifters, the aggressiveness of today’s modern cam profiles, and engine oil formulation as the primary factors behind the failures.

What we know for sure is that the most serious complaints have cropped up within the last three years or so, around the time that major changes occurred in both the flat-tappet manufacturing industry and in the formulation of passenger car and light-duty truck motor oils.

What was discovered through oil testing by several engine component manufacturers is that many older engines experience a short period of time during engine start-up where critical lubrication is insufficient between metal-to-metal lubrication points when using modern oils with reduced amounts of ZDDP/ZDTP.
Camshaft Damage
Camshaft Damage
Most engine and engine component manufacturers recommend Zinc additives for flat tappet lifter break-in; in fact, many will void warranties on camshafts or crate engines if this minimum is not found in the oil sample you supply when returning broken parts for warranty. For this reason, many manufacturers produce their own zinc additives or oils with supplementary zinc included; GM offers its own EOS break-in oil with additional ZDDP.

Experts say that the additives in API blends will no longer cut it in a racing or performance engine. There is no denying that API oils for the most part work very well in late model engines where there are roller cams and much less friction than in high powered racing engines

Experts say that the additives in API blends will no longer cut it in a racing or performance engine.

ZDDP is the predominant anti-wear additive used in crankcase oils, although it is a class of additive rather than one particular chemical.

Not all Zinc (ZDDP) additives react under the same level of heat and load. Zinc has different “Burn” rates.

Some Zinc additives have slower “burn” rates that require more heat and more load to activate than other Zinc additives. For example, Passenger Car Motor Oils (PCMO’s) typically feature a faster burning Zinc than Diesel Engine Oils due to the lower compression ratios found in gasoline engines compared to compression ignition diesel engines. As a result, not all “High Zinc” oils have the same activation rate.

Detergent additives “compete” against Zinc in the engine. Detergents are additives that clean the engine, but detergents don’t distinguish between sludge, varnish and Zinc – it cleans all three away.


The “old school” theory on engine break-in was to run non-detergent oils, and this allowed for greater activation of the Zinc additive in the oil.

Characteristics of Zinc and Detergents determine how quickly and to what extent an oil will provide sacrificial boundary film protection for your engine.

So after all this confusion what do you do !!

In my opinion if it was a late model engine with roller tappets use the factory recommended oil and always keep up to dated with your maintenance.

If this was a newly rebuilt engine with flat tappets and stock parts I would make sure it was assembled with a hi-Zinc additive and broken in with a good quality racing oil. Once the engine was completely broken in I would switch back to the recommended factory oil or a racing oil with the same specs.

And finally if this was a newly rebuilt performance engine with flat tappets I would break it in with stock valve springs first and only after complete breaking then switch to the higher pressure springs.

After that I would only use the best racing oil I could find.

There is a long list of great racing oils out there and they are Not all the same. I would think if your are looking for a great racing oil you must have a lot of friends and colleges out there doing the same thing so ask the guy beside you as they have gone through it and probably learn from someone else’s mistakes.

Every oil producer out there will tell you that theirs if the best, but seeing is believing and not all applications require the same oil.

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