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#4777426 - 06/04/18 04:28 PM Flat Tappets: Observed Failures
Building3 Offline


Registered: 04/30/17
Posts: 82
Loc: Michigan
In reading the recent Pennzoil forum on this site, they make it clear that their new SN oils are backward compatible with all prior designations. So that means even though the ZDDP is less, some other substances must compensate for the loss of the ZDDP to protect flat tappet engines. However, with so many reports of flat tappet engine failures using SM or SN motor oil, what I'd like to know is this: Has anyone on this forum actually had a failure? Not one that you have heard about but a failure of an engine that you had in your car, or one that you built. There's lots of hearsay on all of the oil blogs and forums about flat tappet engine failures using newer oils but is there any real documentation? Thanks in advance.

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#4777432 - 06/04/18 04:37 PM Re: Flat Tappets: Observed Failures [Re: Building3]
skyactiv Offline


Registered: 03/02/13
Posts: 4392
Loc: The Midwest
If you really wanna make your head spin, Google 540ratblog. Lots of people disagree with the guy because of his one arm bandit machine, but he provides detailed personal knowledge on the subject aside from the engine oil testing he does. I think some oil makers market on public perception of high zinc oils so they can sell a niche product.
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#4777447 - 06/04/18 04:53 PM Re: Flat Tappets: Observed Failures [Re: Building3]
Lolvoguy Offline


Registered: 02/06/14
Posts: 2328
Loc: Canada
Anyone have a tl;dr version of 540ratblog?

I find good 'ol diesel oil works great in my BMW thumbsup
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#4777477 - 06/04/18 05:27 PM Re: Flat Tappets: Observed Failures [Re: Building3]
ka9mnx Offline


Registered: 05/21/18
Posts: 50
Loc: South Carolina
Originally Posted By: Building3
In reading the recent Pennzoil forum on this site, they make it clear that their new SN oils are backward compatible with all prior designations. So that means even though the ZDDP is less, some other substances must compensate for the loss of the ZDDP to protect flat tappet engines. However, with so many reports of flat tappet engine failures using SM or SN motor oil, what I'd like to know is this: Has anyone on this forum actually had a failure? Not one that you have heard about but a failure of an engine that you had in your car, or one that you built. There's lots of hearsay on all of the oil blogs and forums about flat tappet engine failures using newer oils but is there any real documentation? Thanks in advance.


I have a flat tappet engine and have used SN oils with no problems.

When this issue cam up I did A LOT of research on the subject. Back in the 50's and 60's ZDDP was used as a detergent. The boundary lubrication properties were discovered later. Most oils in the 50's, 60's and 70's had a ZDDP level of 600 or less. Late in the 70's and into the 80's they began to bump up the levels for better, overall, engine protedtion.

A broken-in flat tappet cam in a normal street car or truck will have no problems with SN oil. Where the problem comes in is with high valve lift, high valve spring pressures in hot rod engines.

Most cam failures in the 90's was later discovered to be with inferior camshaft and lifter materials and hardening. Present day failures are attributed to import lifters.
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#4777518 - 06/04/18 06:19 PM Re: Flat Tappets: Observed Failures [Re: ka9mnx]
Ducked Offline


Registered: 10/25/12
Posts: 4334
Loc: Taiwan
Originally Posted By: ka9mnx


Most cam failures in the 90's was later discovered to be with inferior camshaft and lifter materials and hardening. Present day failures are attributed to import lifters.


Ah, So if that's true, IOW there were failures, and there still are.

Doesn't entirely fit the "non-issue" line you came in with,

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#4777528 - 06/04/18 06:30 PM Re: Flat Tappets: Observed Failures [Re: Building3]
aquariuscsm Offline


Registered: 12/30/06
Posts: 18150
Loc: Dallas,Tx USA
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#4777563 - 06/04/18 07:04 PM Re: Flat Tappets: Observed Failures [Re: Building3]
JeepWJ19 Offline


Registered: 09/09/15
Posts: 932
Loc: PENNSYLVANIA
My flat tappet 4.0 has had some pretty loud lifter tick on cold starts regardless of ambient temperature. It's been like this for the past 60k miles I've had it. If it was a failure attributed to SN oils, I'd have a hard time believing it'd still be running to this day. JMO
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#4777569 - 06/04/18 07:10 PM Re: Flat Tappets: Observed Failures [Re: Building3]
JeffKeryk Offline


Registered: 01/09/10
Posts: 248
Loc: Los Gatos, CA
A mild camshaft should be OK. If you get into higher spring rates, ZDDP becomes more important.
I run Rotella 15w40 in my 68 L36 Corvette Roadster and 65 4-4-2.

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#4777620 - 06/04/18 08:01 PM Re: Flat Tappets: Observed Failures [Re: Building3]
ZeeOSix Offline


Registered: 07/22/10
Posts: 17767
Loc: PNW
Almost all modern engines are essentially "flat tappet" since a cam lobe actuate a shim on top of the valve stem bucket. It's still a cam lobe swiping motion over a flat surface just like a cam lobe on a hydraulic lifter.

In order to achieve the ILSAC GF-5 rating the oil must pass certain wear tests, and I'd think doing wear measurements on "flat tappet" type of valve train would be part of that.

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#4777639 - 06/04/18 08:15 PM Re: Flat Tappets: Observed Failures [Re: Ducked]
BrocLuno Offline


Registered: 09/06/15
Posts: 5511
Loc: Kalifornia Kollective
Originally Posted By: Ducked
Originally Posted By: ka9mnx


Most cam failures in the 90's was later discovered to be with inferior camshaft and lifter materials and hardening. Present day failures are attributed to import lifters.


Ah, So if that's true, IOW there were failures, and there still are.

Doesn't entirely fit the "non-issue" line you came in with,


OK, cam and lifter failures are two different things. Obviously they relate to each other, but they come from different causes.

Most cam failures are caused by incorrect heat treating of wrong alloy selection and then poor surface hardening. The big failures (by numbers) were/are GM and Comp. Both were attributed to soft cores.

Lifters failures are related to one of three factors. Lifter face hardness, lifter face radial geometry, and poor bore fit. So something like the Delphi or Johnson lifters were well made and held to very tight tolerances. Then along came the off-shore copies ...

So the Aussies had/have to buy OEM lifters from the USA when GM and Ford were still building cars down under. Lifters were an expensive import item for the hot-rod community. So they got good at regrinding the faces and reusing them. Same quality metal throughout. They claim to be able to get three re-grinds and are still selling known good USA lifters as re-grinds around the world with decent results.

A cam will fail by wearing the nose off, usually through spalling. A lifter will fail by cupping or failing to spin. If a lifter skids (not spinning) it will die quickly. It's prolly dead in 100 Revolutions of the cam lobe, but if it starts spinning again, it'll limp along for a while. But the death knell is set.

The way you know which is which is by looking at the carnage. If the cam is flattened, but the lifter is mostly intact, you have a soft core /hardness issue. If the lifter is cupped or oddly worn, but the cam lobe looks about right, you have a bad lifter.

OEM spring pressures, even say Z-28 springs will not really stress a cam/lifter combo. But you start getting past say .550~.580 lift on a BBC (fairly mild hot cam) and say 350#s over the nose to control valve float above 5,000 RPM and you are goinna stress the materials. If they are not right, it'll die. >1,000 PPM ZDDP is mandatory as the spring pressures go up. Above these numbers and things just go sideways quicker, if not all correct.

Comp lost a lot of cam/lifter sets and did everything they could to blame the end user. Howards and Crower have had very, very few failures. Howard's offers a 5-year warranty if you buy their whole kit and follow instructions. Comp wouldn't do that if you paid them ...

Ford and Chrysler have had few cam/lifters failures running even their most aggressive factory grinds. Practically none of their daily driver combos have failed. And this is with average Joe doing spotty maintenance, etc. GM has not been so fortunate ...

So we need to know exactly what scenario you are interested in? I still will not buy much from Comp (mostly just rockers) and their other brands like Lunati. Howards or Crower - no question about their reliability as far as I'm concerned.

Oil pressure does not fix this. 60 PSI at 6,500 is plenty, more than enough. Bad oil and bad metallurgy will get you every time. It's up to the builder to get things right. Break-in right. Pop the valve covers and make sure every push rod is spinning as it should after initial fire-up. No start stop, or herky jerky allowed. It's either right, or shut it down and fix it ...

Cam on shim/bucket is a type of flat tappet. But not the traditional push-rod configuration that had all the issues ... OHC engines have different lube strategies and lighter valve trains, so they have milder spring pressures (no need to control as much inertia). Push-rod engines have cam lobes lubed by sling oil off the crank. Hit and miss at best ...


Edited by BrocLuno (06/04/18 08:23 PM)
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#4777641 - 06/04/18 08:16 PM Re: Flat Tappets: Observed Failures [Re: ZeeOSix]
OVERKILL Offline


Registered: 04/28/08
Posts: 36428
Loc: Ontario, Canada
Originally Posted By: ZeeOSix
Almost all modern engines are essentially "flat tappet" since a cam lobe actuate a shim on top of the valve stem bucket. It's still a cam lobe swiping motion over a flat surface just like a cam lobe on a hydraulic lifter.

In order to achieve the ILSAC GF-5 rating the oil must pass certain wear tests, and I'd think doing wear measurements on "flat tappet" type of valve train would be part of that.


Quite a few of them are roller. I'd say quite a few, perhaps even the majority are cam-over-bucket, but there is certainly a significant percentage that are roller.
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#4777703 - 06/04/18 09:16 PM Re: Flat Tappets: Observed Failures [Re: OVERKILL]
Shannow Offline


Registered: 12/12/02
Posts: 39846
Loc: 'Stralia
Originally Posted By: OVERKILL
Originally Posted By: ZeeOSix
Almost all modern engines are essentially "flat tappet" since a cam lobe actuate a shim on top of the valve stem bucket. It's still a cam lobe swiping motion over a flat surface just like a cam lobe on a hydraulic lifter.

In order to achieve the ILSAC GF-5 rating the oil must pass certain wear tests, and I'd think doing wear measurements on "flat tappet" type of valve train would be part of that.


Quite a few of them are roller. I'd say quite a few, perhaps even the majority are cam-over-bucket, but there is certainly a significant percentage that are roller.


Different kettle of fish...

"Flat Tappets" weren't flat, they were convex, and worked on a quite narrow lobe, offset with a slope on the lobe so that they would rotate...contact surfaces comparatively tiny, and the rocker arms amplifying the movement at the valve a the valve end, and thus the contact forces at the other. Being required to be slid into the block, to get the lift meant a reduction in base circle, and more contact pressure.

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#4777780 - 06/04/18 11:13 PM Re: Flat Tappets: Observed Failures [Re: Shannow]
turtlevette Offline


Registered: 12/24/13
Posts: 3559
Loc: Massachusetts
Now. I wonder. How much sliding do roller lifters do. There has to be some.

How much sliding do the needle bearings within the roller lifter do? I would think ep and anti wear additives are still important in a roller cam system.

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#4777781 - 06/04/18 11:19 PM Re: Flat Tappets: Observed Failures [Re: ZeeOSix]
1JZ_E46 Offline


Registered: 04/04/16
Posts: 1220
Loc: Oregon
Originally Posted By: ZeeOSix
Almost all modern engines are essentially "flat tappet" since a cam lobe actuate a shim on top of the valve stem bucket. It's still a cam lobe swiping motion over a flat surface just like a cam lobe on a hydraulic lifter.

In order to achieve the ILSAC GF-5 rating the oil must pass certain wear tests, and I'd think doing wear measurements on "flat tappet" type of valve train would be part of that.


The pressure is far less, though, in bucket-style valvetrains. Push rod and rockers have a very high pressure spike as the cam rolls past peak lift due to the push rod/rocker design.

And most modern engines have migrated to roller valvetrains for fuel efficiency.
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#4777822 - 06/05/18 01:18 AM Re: Flat Tappets: Observed Failures [Re: Building3]
Silk Offline


Registered: 07/26/03
Posts: 4552
Loc: New Zealand
It's more of a 2 valve pushrod problem, heavy valves, heavy springs to control them. And not all lifters rotate, some are fixed in their blocks. Here are some Triumph twin followers...they would get a groove right in the center when worn. You could grind it out, but the radius was important...a flatter radius on R lifters.

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