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#2247542 - 04/30/11 07:28 AM Flat tappet engines
Sierra048 Offline


Registered: 02/26/11
Posts: 264
Loc: Georgia
Can someone explain what a "flat tappet" engine is? Positives or negatives? Is there a better oil to use if you have one? I've got a 3.8L in my Jeep and I believe someone said it was a "flat tappet". Since access to the engine is extremely easy with plenty of room to boot, I want to do all that I can to keep the repairs and maintenance up on it myself. I'm not a mechanic by any stretch of the imagination but pretty decent turning a wrench when I build up enough knowledge on what I'm working on. Any help would be greatly appreciated.
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#2247554 - 04/30/11 07:50 AM Re: Flat tappet engines [Re: Sierra048]
electrolover Offline


Registered: 12/04/10
Posts: 3192
Loc: TEXAS
its an engine where the lifters are just flat metal and they ride on the metal cam. lubrication is an issue because of all the friction.

in later years they have went to roller cams, thats where the lifter has a wheel on the bottom of it to ride on the cam. greatly reduced friction.

if its the 2011 jeep in the sig i would not worry about it. all new engines are designed to run less zddp. so any SN would be fine
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#2247556 - 04/30/11 07:55 AM Re: Flat tappet engines [Re: Sierra048]
electrolover Offline


Registered: 12/04/10
Posts: 3192
Loc: TEXAS
http://cgi.ebay.com/ebaymotors/SBC-CHEVY...sQ5fAccessories

http://cgi.ebay.com/ebaymotors/SBC-BBC-S...=item3362132488

this is a pic of a cam with flat tappets ^^^ notice no wheel
below is a roller lifter, notice the wheel on the bottom

http://cgi.ebay.com/ebaymotors/COMP-Cams...sQ5fAccessories
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#2247557 - 04/30/11 07:58 AM Re: Flat tappet engines [Re: Sierra048]
jorton Offline


Registered: 07/04/03
Posts: 2726
Loc: San Antonio, TX
I think a flat tappet engine is an Over Head Valve engine. Not Over Head Cams. If valve spring pressure or tension is very high camshaft lobes wear too fast when 20 or 30 multi grade energy conserving motor oil is used. Some folks who expect to keep the vehicle for many years use 40 multi grade, or heavy duty oil instead.
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#2247558 - 04/30/11 08:04 AM Re: Flat tappet engines [Re: jorton]
electrolover Offline


Registered: 12/04/10
Posts: 3192
Loc: TEXAS
Originally Posted By: jorton
I think a flat tappet engine is an Over Head Valve engine. Not Over Head Cams. If valve spring pressure or tension is very high camshaft lobes wear too fast when 20 or 30 multi grade energy conserving motor oil is used. Some folks who expect to keep the vehicle for many years use 40 multi grade, or heavy duty oil instead.


not all overhead cam engines are roller. the gm quad 4 for example has flat tappets that just sit ontop of the valve springs
my modular on the other hand has roller followers instead of lifters.
the grade of oil isnt going to make a whole lot of difference, its the zddp your looking for. for a flat tappet you need atleast 1200 PPM of zinc. that being said if its a stock cam and springs, once its well broken in you can get by with new oil like SM with out problems
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#2247569 - 04/30/11 08:39 AM Re: Flat tappet engines [Re: Sierra048]
Astro14 Offline


Registered: 10/10/10
Posts: 4446
Loc: Virginia Beach
The flat tappet (or lifter) was simpler to manufacture...and the cam required careful break in if you installed a new cam. The lifter "foot", that rode against the cam lobe, rotated slightly as it went up and down. The lifter would break in with that particular lobe, so if you ever pulled the cam or lifters, you better have them labeled so that they go back to the paired set. For most V-8s, a very high moly content lube was put on new cams, that then had to be run 20-30 minutes at 2,000 - 2,500 RPM right after start to establish that lifter rotation and break it in right, otherwise, you risked abnormal cam wear and poor performance. The higher the lift (and valve spring pressure) the more critical this step was....

There were some very high performance engines built with flat tappet engines. Flat tappets fell into two categories: hydrauic and mechanical. The hydraulic lifters used oil pressure to "pump" them up to establish the valve train clearance. This was the most common and required no maintenance, as the valve train wore, the clearance was maintained by the lifter itself. For high profile cams, like the early 60's fuelie V-8s from Chevy for example, or the 327/365 in the '64 - '65 Vette, the hydraulic lifter would not work well under the high lift of the cam, so they went to a "mechanical" lifter, which was really just a metal foot under the pushrod. The clearance had to be adjusted on these periodically to keep the valvetrain right...and they would clatter a bit until the engine was warm...

Just to complicate (or clarify) the discussion a bit more, while OHV engines (think American V-8) used to be flat tappets - many are now rollers...

However, the 1932 Packard 8, which is a flathead (valves in the block, adjacent to the cylinders) has roller tappets on the cam...

So, you can't always tell by engine configuration or age of the car whether it's flat tappet or roller...

Roller or not, the Packard gets an HDEO for a variety of reasons, ZDDP among them...


Edited by Astro14 (04/30/11 08:52 AM)
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#2247608 - 04/30/11 09:44 AM Re: Flat tappet engines [Re: Sierra048]
440Magnum Offline


Registered: 02/01/09
Posts: 6237
Loc: Texas
Originally Posted By: Mfrank84
Can someone explain what a "flat tappet" engine is? Positives or negatives? Is there a better oil to use if you have one? I've got a 3.8L in my Jeep and I believe someone said it was a "flat tappet". Since access to the engine is extremely easy with plenty of room to boot, I want to do all that I can to keep the repairs and maintenance up on it myself. I'm not a mechanic by any stretch of the imagination but pretty decent turning a wrench when I build up enough knowledge on what I'm working on. Any help would be greatly appreciated.


The 3.8 is not a flat tappet engine- it has roller cam followers. The 4.0L inline six that the 3.8 replaced WAS a flat tappet engine, and that's where the misconception that "Jeep engines are flat tappet engines" comes from.

Flat tappets just mean that the cam followers are flat-faced hardened metal pieces that slide along the surface of the hardened cam lobes, in contrast to roller followers that, as implied, roll on the cam lobes. As others have said, whether you need anything special in the oil or not depends more on the max pressure that the lifter sees. A high-performance 60s v8 like my two 440s has a whole lot more spring pressure on its flat lifters than my 99 and 01 Cherokees. The Cherokees would be fine on any SN oil, the 440s always get an HDEO like Rotella, or another high-performance oil like M1 0w40, Redline, etc. to get the protection they need.
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#2247620 - 04/30/11 10:01 AM Re: Flat tappet engines [Re: Sierra048]
Cujet Offline


Registered: 02/15/03
Posts: 4124
Loc: Jupiter, Florida
And, of course, there are many overhead cam engines that are not roller tappets, lifters or followers.

VW had a problem with cam wear on Diesel PD engines made around 2005-2006. It was an overhead cam engine with "flat tappets". Sure, it had a roller for the unit injector, and that lobe held up fine. The valve lift lobes are the ones that wear.

It's my opinion that any engine that does not use some form of roller cam follower is a flat tappet engine. Regardless of where is the cam is located.

More important is the load on the cam lobe.
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#2247700 - 04/30/11 12:27 PM Re: Flat tappet engines [Re: 440Magnum]
Sierra048 Offline


Registered: 02/26/11
Posts: 264
Loc: Georgia
Thanks to all. Great info to have. 440Magnum, thanks for clearing up my misconception. It's good to know.
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#2249308 - 05/02/11 11:33 AM Re: Flat tappet engines [Re: Cujet]
440Magnum Offline


Registered: 02/01/09
Posts: 6237
Loc: Texas
Originally Posted By: Cujet
nion that any engine that does not use some form of roller cam follower is a flat tappet engine. Regardless of where is the cam is located.


Absolutely correct. In recent years, there have been far more "flat tappet" overhead-cam engines than there have been "flat tappet" cam-in-block engines. With a few exceptions (Jeep 4.0/2.5, non-high-performance small-block Chevy, Rover v8) the vast majority of cam-in-block engines- for example Ford and Mopar v8s and v6s- went to roller lifters in the 1980s. The rest had pretty much done so before the 2000 model year.
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#2249367 - 05/02/11 12:47 PM Re: Flat tappet engines [Re: Sierra048]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
Cars have either flat tappets or rollers.
[This is the actual contact between the cam and the lifter.]
Older cars used cams with lifters, pushrods , rocker arms, and then the valves. Their heavy loads made them need a high zinc oil.
But even modern OHC engines often use flat tappets.

Flat surfaces slide, rollers roll. Guess which one has less friction?

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