Flat Tappet Cams - PeachParts Mercedes-Benz Forum

JHZR2 · #1 03-07-2010, 09:13 AM

Hello,

There is a lot of oil misinformation on here. Zn is not the end-all, be-all additive that some make it out to be, and in reality, the new chamistries not only hold TBN longer (despite lower starting point), but protect better.

The one place where we have not seen a better additive than Zn is in applications which use a "flat tappet cam". Generally this seems to be older domestic large V8 engines, but I am not clear if one would consider the engines used in older MB diesels, e.g. the 616/617, and its predecessors, as having a "flat tappet cam".

If so, it could drive the oil selections that are relevant for these engines.

Thanks!

Matt L · #2 03-07-2010, 09:45 AM

Yes, those are "flat tappet cams" as they lack rollers.

vstech · #3 03-07-2010, 10:40 AM

Quote:

Originally Posted by tangofox007

Those engines do not have tappets.

they have cam followers which are essentially "tappets"
meaning the cam does not a. hit the valves themselves, nor b. hit a roller follower or "tappet"

most call a tappet or lifter the device that the cam hits to move a pushrod... this car being an overhead cam design, has not pushrods. but it does have a rocker / cam follower, that pushes on the valve assembly...

Oldwolf · #4 03-24-2010, 10:01 AM

I am thinking a flat tappet is an old term used for engines that had solid lifters.

Are our engines really "flat tappet" or are they more accurately described using some other term (that I do not now know)?

compress ignite · #5 03-24-2010, 12:35 PM

That's why I've run the Rotella Synthetic 5W40 (Zn Package)

Howeveah, I've been converted to the Redline 15W40 scenario for Oil Film
Thickness concerns @ Summer Temps.

Oldwolf · #6 03-24-2010, 01:55 PM

Some expert in another forum is telling me they are not. I just wanted to be sure I wasn't going to be proven wrong there on some type of Engineering technicality.

rscurtis · #7 03-24-2010, 05:52 PM

AFAIK, flat tappet refers to a valve train where the cam slides on its mating surface, regardless of solid or hydraulic lifters or followers. Roller tappets refer to the cam lobe riding on a wheel.

DSlater · #8 03-25-2010, 12:36 AM

Found this at http://www.cam-shield.com/acatalog/FAQ.html:

* How do I know if I have a flat tappet cam and that this problem affects me?

Virtually every American-made vehicle, and many foreign-built vehicles manufactured before 1975, has a flat tappet cam engine. The tappets are also known as lifters and can be either hydraulic or mechanical (solid). Flat tappet cam engines are also known as overhead valve engines. Modern engines with overhead cams or roller cams are not affected.

Hit Man X · #9 03-25-2010, 01:35 AM

Uh oh... I foresee an oil thread starting!

JHZR2 · #10 03-25-2010, 07:56 AM

Quote:

Originally Posted by DSlater

Found this at http://www.cam-shield.com/acatalog/FAQ.html:

* How do I know if I have a flat tappet cam and that this problem affects me?

Virtually every American-made vehicle, and many foreign-built vehicles manufactured before 1975, has a flat tappet cam engine. The tappets are also known as lifters and can be either hydraulic or mechanical (solid). Flat tappet cam engines are also known as overhead valve engines. Modern engines with overhead cams or roller cams are not affected.

So this isnt the most insightful, IMO. What about modern OHV engines, like GM V8 engines? OHV yard equipment? I think that the language there is a bit too expansive.

vstech · #11 03-25-2010, 09:38 AM

bottom line...
if the cam lobe is riding on a valve lifting device that does not have a rolling device it is a flat tappet cam.
nearly every motor built before 1985 is considered a flat tappet cam motor.
there are MANY motors built before that that had roller cams, but the "norm" was flat.

vstech · #12 03-25-2010, 09:42 AM

Quote:

Originally Posted by Oldwolf

Some expert in another forum is telling me they are not. I just wanted to be sure I wasn't going to be proven wrong there on some type of Engineering technicality.

whoever is arguing with you is technically correct. there are no tappets in an overhead cam engine.
a tappet is a piston like device in a pushrod style motor.
overhead cam engines have no pushrods, hence no tappets.
the 603 has hydrolic "lifters" but they are actually called cam followers.
the 617 has an adjustable rocker arm that rides on the cam, and it is not a lifter, but the CAM is a "flat tappet cam" because of the profile and it's surface that it rides on is not roller designed.

4x4_Welder · #13 03-25-2010, 02:01 PM

Actually, a tappet is a grouping term for any device that rides on the cam, and originated with the old flathead engines. In those, the cam was situated directly under the valves, and the valves had a cap in between them and the cam that rotated as the cam swept past. This setup was nearly identical to the newer OHC engines that use a bucket shaped cap over the valve, usually with shims under it for adjusting. This unit would rotate to distribute the wear, and that is the problem- all the force for lifting the valve goes into a very very small spot the edge of the cam, and the cam is ground with a very slight taper to it. Sacrificial zinc is used as a lubricant, since it gets crushed and squeezed out building a film to keep the parts from actually contacting.
Engines that use roller lifters, and OHC engines that use slipper type rockers like these are not as affected by the zinc because the contact surface is spread out over the whole width of the cam lobe, but it is still generally advised to use the recommended oil- Newer is not always better.