The Little Rollers That Changed Engines Forever
The design and construction of the engines that power automobiles have evolved by both evolution and revolution over the nearly 140 years since Karl Benz’s Patent-Motorwagen chuffed about the countryside. Benz’s single-cylinder required numerous steps just to start. It could only run for so long before requiring at least some amount of fiddling. In comparison, modern engines are comically complex in their operation but wildly simple to maintain. What changed?
Well, lots of things. Material science has progressed leaps and bounds in the last 100+ years, but all the formulations of steel and aluminum in the world would be useless without precise control of an engine’s internal systems. That’s why so many revolutions in engine design centered on the orientation and actuation of the intake and exhaust valves—together known as the valvetrain. However, the key to a reliable and dependable modern valvetrain boils down to a simple roller.
The roller in question sits at the tip of the lifter, a key piece that translates the rotational motion of the camshaft into the linear motion of the pushrod, which acts on the rocker arm to open the valve. Spring pressure keeps the valves closed and, as engines have adopted higher and higher redlines, spring pressures have increased to better control the valves and ensure proper cycling of fuel and air. (Yes, I know desmodromic valvetrains exist, but they are relatively uncommon compared to traditional spring closures.)
That additional spring pressure has turned out to be the root of some interesting automotive developments. As these spring pressures were increasing, governments began to mandate emissions equipment. The addition of catalytic converters, and other tailpipe-emissions monitors and cleanup efforts, conspired to take certain additives out of regular engine oils. The main additives that got removed belonged to a family of compounds (zinc dialkyldithiophosphates, or ZDDP) that are critical to cushioning the connection between the lifter and the camshaft. Jason Fenske of Engineering Explained recently covered the topic in-depth, and his YouTube video is worth watching:
Lifters have a slight dish on the face that rides on the cam, but to the naked eye they look flat—hence the name. Without proper lubrication between the cam and lifter, those flat tappet lifters would either be eaten away by the cam, or the lifter would wear away the camshaft. Either way, not good.
While ZDDP was common in fuels, flat-tappet lifters worked great for decades, but when those zinc compounds were removed, and as spring pressure increased and camshaft profiles grew more aggressive, damage to the lifter or camshaft became significantly more common. Replacing the flat tappet lifter with one that incorporated a roller that rode on the camshaft solved many problems and eliminated the need to change your oil formula.
These simple rollers changed the game and even opened the door to more performance. Since the reduction in friction lowered the risk of wiping material from the lifter or camshaft, the profile of the camshaft lobe could be altered in ways previously unimaginable. Higher lift with a more aggressive ramp than ever was not an issue, since the roller rotated with the cam. No additives were needed, so the emissions systems functioned as intended and maintenance intervals could stretch ever so slightly.
Friction is the enemy of an engine. Friction takes horsepower and turns it into heat and destruction. Essentially we have found two ways to reduce friction in the valvetrain: Oil additives like ZDDP and lower-friction components like roller lifters and rocker arms. Luckily now we have access to parts that can retrofit vintage engine designs with roller valvetrains, and we can purchase specially formulated oils or additives that will keep our engines running for a long time—as long as we maintain our vehicles properly and choose the correct oils.
Roller lifters may be more common now, but they aren’t new. Hudson, among others, used them in the 20s.
They were widely used in German and US aero engines in WW2. The Merlin engine did not have them and suffered rapid tappet wear.
Amazing how sone of this tech has come to help more HP but has also changed things to hurt older cars like oil not up to flat tappets anymore.
Same with Direct Injection. It adds more HP but we have seen new issues on some engines.
Now wet cam belts will be a new major issue.
The original Gray Marine two stroke diesel engines (which became Detroit Diesel) used both roller tappets and direct injection back in the ’30’s. Just about all of the “new” technology has been around for a long time. I was a fan and user of Schubeck technology that employed a spherical nosed lifter made of a proprietary material that slightly less hard than a diamond. Joe applied a similar coating to the cam and just about eliminated wear that area. The rumor was, an engine could be lubricated with water and experience no cam and lifter failures. That probably wouldn’t help the rod and main bearings, but Schubeck had a wonderful product that was so advanced, NASCAR and NHRA banned it. The two engines we built ran for many years with no issues.
Kyle, Great explaination. I always look for your interesting stories. Thanks
No question roller lifters are a tremendous leap in advancement but “flat” tappets aren’t as bad as most people think. The cam lobes are ground with a very small taper making them just a touch taller at the rear than the front. Also the lifter bores are not centered over the lobes. These two features cause the lifters to spin in their bores so they are indeed rolling on the cam, not simply scraping on it. If you’ve ever run your OHV motor with a rocker cover off you may have noticed pushrods spinning. This also keeps the cam sprocket pressed against its thrust bushing and not walking in and out wreaking havoc on ignition timing.
Yup, I’m the only one in the house still awake. Am I posting the first comment of the year?? Happy New Year either way everyone!
No question roller lifters are a tremendous advancement but “flat” tappets aren’t as bad as most people think. The cam lobes are ground with a very small taper making them just a touch taller at the rear than the front. Also the lifter bores are not centered over the lobes but are significantly offset. These features cause the lifters to spin in their bores so they are rolling and not simply scraping the cam lobes. If you’ve ever run your OHV motor with a rocker cover off you may have noticed pushrods spinning. This also keeps the cam sprocket pressed against its thrust bushing instead of letting it walk back and forth wreaking havoc on ignition timing.
Yup, I’m the only one in the house still awake. Am I posting the first comment of the year?? Happy New Year either way everyone!
Well the double post proves you were up. But were you awake?, that’s up for debate 😜 Happy New Year!
Little too much Egg Nog, maybe? I don’t personally know Tinkerah, but I kinda suspect he might be an Egg-Nog-on-New-Year’s-Eve kinda guy… 😉
Proper lubrication!!!
There is no substitute, thus no failures!
Unfortunately, the vehicle manufacturers sabotage the engine life with false maintenance schedules. In no world should an engine go. 10k or more miles on an oil change! Chrysler can’t get it right and their schedules conflict between dealer and factory. Toyota ended up changing their recommended schedules maintenance from 10k to 5k! Vehicle manufacturers know that the vast majority of new car owners only keep their cars to maybe 50k miles and then trade it in for a new one so if the manufacturer says a $250 oil change only needs to be performed 3 times before you trade it in, you will feel good about the brand because your costs to own the car are low. If the oil is changed at the logical limit of 5k miles, that’s 10 oil changes at $250 per.. so the cost of ownership is the difference between $750 or $2,500! Which one would you feel better about owning? The car manufacturers dont care about the second owner… They make no money off of them. This is evident in a recent ruling in California where it was determined that lemon law buy-backs do not apply to the second or third or whatever beyond the original owner. The manufacturers spent a LOT of money fighting that.
I’ve roller rockers and roller cam followers on my Big Block Chevy engine I’m building I’ve been socking the followers/ rockers in oil for months in these winter months. They will give me more power !!!
Unfortunately, one only has to Google the phrase “hemi tic” and you’ll see a major problem with the roller lifters in use today. This malady afflicts all modern V6 and V8 engines. Toyota, GM, Ford and Chrysler all have this similar issue. And it’s not cheap to fix! In the 5.7L Hemi, $4k minimum… And then it’s not a guarantee fix. If any of the metal shavings from the worn cam make it into the bearings, you’re looking at a total engine replacement… And that’s about $10k! I remember back in the 80s swapping flat tappet cams and lifters with roller equivalent and those engines being run very hard. And this didn’t happen to them. Something is really wrong with today’s designs for this problem to be so universally prevalent across all manufacturers