Flat tappet vs. other lifter types & lubrication

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This is just a curiosity question/post. I've looked at cutaway images that show the difference between flat tappet and roller type cam/lifter setups. The flat tappet has high loading at peak lift, as the cam profile is very aggressive. The roller setup allows the cam profile to be more smooth, distributing the load much more evenly as the cam makes its revolution. This lends credence to why some suggest the use of HDEO and/or oils with good amounts of AW additives (ZDDP for example) for flat tappet applications.

What about OHC engines, especially where the valves act on "bucket" lifters? That setup (which I'm much more familiar with, and have seen on many engines) seems a lot like a flat tappet OHV engine, similar cam profile, or am I wrong? Is there an inherent difference in cam/lifter loading that I'm not seeing that would necessitate an HDEO (or other oil with improved anti-wear characteristics) in a flat-tappet OHV versus a OHC cam-over-bucket setup that traditionally uses normal PCMO?

When did major manufacturers transition away from flat-tappet OHV design? I know my 1985 460 has the setup, but not entirely sure how long this design persevered.
 
Valve springs. Spring pressure, as well as ramp rate, are key components here. A roller can also have a much steeper (faster) ramp than a flat tappet camshaft. So actually, a roller camshaft is generally more aggressive (stock for stock) than the flat tappet. It is just visually it looks different.

But to get to your question, to control the mass of the lifter/pushrod/rocker/valve assembly requires more spring pressure than just a bucket on the top of the valve. Less mass and far fewer components. Subsequently, this also means that lobe profiles for a cam over bucket setup can be more aggressive for the same spring pressure than its pushrod counterpart.

There are of course variations of OHC that use roller followers as well (Ford Modular).
 
Originally Posted By: OVERKILL
Valve springs. Spring pressure, as well as ramp rate, are key components here. A roller can also have a much steeper (faster) ramp than a flat tappet camshaft. So actually, a roller camshaft is generally more aggressive (stock for stock) than the flat tappet. It is just visually it looks different.

But to get to your question, to control the mass of the lifter/pushrod/rocker/valve assembly requires more spring pressure than just a bucket on the top of the valve. Less mass and far fewer components. Subsequently, this also means that lobe profiles for a cam over bucket setup can be more aggressive for the same spring pressure than its pushrod counterpart.

There are of course variations of OHC that use roller followers as well (Ford Modular).
+1 well said
 
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Perhaps OHV is better lubricated which partly compensates for the higher loading?

If not actually immersed, the cam is closer to the oil pump so it might get earlier lubrication on startup, and it'll perhaps get more splash in use.

I like OHV. Seems less chance of timing chain trouble (and generally no chance of timing belt trouble) but I havn't had one since a push-rod Renault 5 sometime in the mid-90's.

Think some Volvo's (140?) were gear driven OHV (which seems optimal) but I've never had one of them.

Doubt there are any pushrod engines for sale on new production cars now.
 
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Originally Posted By: Ducked
Perhaps OHV is better lubricated which partly compensates for the higher loading?

If not actually immersed, the cam is closer to the oil pump so it might get earlier lubrication on startup, and it'll perhaps get more splash in use.

I like OHV. Seems less chance of timing chain trouble (and generally no chance of timing belt trouble) but I havn't had one since a push-rod Renault 5 sometime in the mid-90's.

Think some Volvo's (140?) were gear driven OHV (which seems optimal) but I've never had one of them.

Doubt there are any pushrod engines for sale on new production cars now.


I've got one. So does anybody driving anything GM with a V8. Both the modern MOPAR HEMI and the LSx engine family are pushrod mills.
 
GM still produces high performance push rod engines and actually enjoy a lower CG.
GM light duty trucks use them as well. Despite the cam in the block - they are VVT engines ...
 
I think there were a few pushrod V6s and the Jeep 4.0 that stuck to flat tappet cams for a while. They weren't performance engine (though I'm sure Bubba's stock carbureted 305 wasn't either) and didn't have enough valve spring pressure to wipe a lobe if high zinc oil wasn't used.
 
Originally Posted By: FordCapriDriver
I think Chevy Small blocks went to roller cams in 1986?, most manufacturers moved away from flat tappets in the late 80s- early 90s-


GM made the bulk switch in small and big block engines to roller cams in 1996 with the Vortec SBC and Gen VI BBC. The previous SBC were flat tappet as were the BBC. This is true in trucks, some cars got roller cams much earlier, but the final switch was made in 1995. I can't think of any other US engine that used a traditional cam in block flat tappet later than this. Perhaps the ISB/6BT Cummins used in the dodge trucks which used a mushroom tappet, I'm not sure when if ever those switched over.

I stand corrected as I post this. Miller88 is correct, the 4.0 Jeep engine never had a roller cam and they were built into the 2000's
 
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Originally Posted By: OVERKILL
Originally Posted By: Ducked
Perhaps OHV is better lubricated which partly compensates for the higher loading?

If not actually immersed, the cam is closer to the oil pump so it might get earlier lubrication on startup, and it'll perhaps get more splash in use.

I like OHV. Seems less chance of timing chain trouble (and generally no chance of timing belt trouble) but I havn't had one since a push-rod Renault 5 sometime in the mid-90's.

Think some Volvo's (140?) were gear driven OHV (which seems optimal) but I've never had one of them.

Doubt there are any pushrod engines for sale on new production cars now.


I've got one. So does anybody driving anything GM with a V8. Both the modern MOPAR HEMI and the LSx engine family are pushrod mills.


OK, my non-US perspective is showing. Good to know.
 
Originally Posted By: FlyNavyP3
Originally Posted By: FordCapriDriver
I think Chevy Small blocks went to roller cams in 1986?, most manufacturers moved away from flat tappets in the late 80s- early 90s-


GM made the bulk switch in small and big block engines to roller cams in 1996 with the Vortec SBC and Gen VI BBC. The previous SBC were flat tappet as were the BBC. This is true in trucks, some cars got roller cams much earlier, but the final switch was made in 1995. I can't think of any other US engine that used a traditional cam in block flat tappet later than this. Perhaps the ISB/6BT Cummins used in the dodge trucks which used a mushroom tappet, I'm not sure when if ever those switched over.

I stand corrected as I post this. Miller88 is correct, the 4.0 Jeep engine never had a roller cam and they were built into the 2000's



The Cummins engine is still flat tappet, although I have heard of hot-rodders converting them to roller.
 
Originally Posted By: 92saturnsl2
That setup (which I'm much more familiar with, and have seen on many engines) seems a lot like a flat tappet OHV engine, similar cam profile, or am I wrong? Is there an inherent difference in cam/lifter loading that I'm not seeing that would necessitate an HDEO (or other oil with improved anti-wear characteristics) in a flat-tappet OHV versus a OHC cam-over-bucket setup that traditionally uses normal PCMO?

When did major manufacturers transition away from flat-tappet OHV design? I know my 1985 460 has the setup, but not entirely sure how long this design persevered.



Yes, you're right that OHC bucket lifters are similar in design to flat tappet OHV valvetrains. As long as similar materials are used, the two different valvetrains are designed to the same limits of contact stress between the cam and cam follower. But because the bucket lifter valvetrain has much less mass, it can withstand higher ramp accelerations before reaching the contact stress limits. And additionally, because of the lower mass, a bucket lifter valvetrain requires less spring load to control the valve at peak lift, which also tends to lessen the contact stress.

Most of the transition from flat to roller lifter OHV valvetrains occurred in the late 80's. The big driver was about a 2% improvement in fuel economy. The additional power potential of the roller valvetrain was not exploited until later.

For the most part, roller finger follower valvetrains have taken over the automotive engine market in the last 20 years. The only mass-market engine that I know of in North America to keep the slider bucket lifter was the Ford 3.5L Ecoboost V6, and it has been converted to roller finger follower for 2017.
 
Originally Posted By: OVERKILL
There are of course variations of OHC that use roller followers as well (Ford Modular).


What other OHC engines use roller followers ? (if you don't mind me asking sir)
smile.gif
 
The list would be huge there - anything with a finger lifter is a posibility. The Mitsubishi 4D56 had roller rockers, and the fist symtom of a roller failure was a doink, doink, doink coming out the airfilter. Investigation would show a roller collapse on a rocker.
 
Originally Posted By: Silk
The list would be huge there - anything with a finger lifter is a posibility. The Mitsubishi 4D56 had roller rockers, and the fist symtom of a roller failure was a doink, doink, doink coming out the airfilter. Investigation would show a roller collapse on a rocker.


Yup.

The Northstar V8 (at least the 2004+ version, not sure about earlier ones), the Dodge 4.7 and Pentastar 3.6L, Honda K20....etc.
 
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