Flat Tappets and ZDDP

[raffy]

I'm not very knowlegeable on the engineering in small engines, but I was told the other day that most of them have flat tappets and therefore should not use the newer lower viscosity oils that have lower levels of ZDDP. Is this true? I'm not too concerned about our push mower as it's not very expensive but more about our riding mower. The rider has a 13.5 hp single cylinder Briggs flathead on it. I've put Amsoil 5W-30 (which I use in our Saturn car) for years in it and have had no problems. Now I'm told that ZDDP levels have been reduced in the latest automotive oils to protect catalytic converters and that I ought to consider using a 10W-40 oil that has higher levels of ZDDP for the mowers.

So what's the verdict? Can I keep on using 5W-30 (which Briggs says is OK to use in the manual, along with 10W-30) or should I switch to something higher viscosity with more ZDDP? Are there any instances of valve tappet failure due to these lower levels of ZDDP?

 

[oliver88]

If you are worried use any 15w40 Heavy Duty oil such as Rotella or Chevron Delo...available at Autozone or Advance.

 

[Familyguy]

Tolerances are so loose on a typical lawn mower engine that I doubt it will make any difference whatsoever. If you change the oil at the beginning (or end) of each season, I think even the cheapest "whatever is on sale" oil is going to be more than adequate for this type of motor in a typical once a week lawn mowing duty cycle.

 

[JAG]

The widespread fear of lower ZDDP oils in stock engines is way overblown.

 

[bepperb]

If you're concerned, you can certainly use a HDEO. But I really doubt it will matter, the way these engines are built with splash lubrication and no filtering.

 

[StevieC]

Originally Posted By: JAG
The widespread fear of lower ZDDP oils in stock engines is way overblown.
+1 It's only engines with heavy duty valve springs pushing down on the cams creating pressure of metal on metal.

Stock engines with lower pressure valve springs and lower ZDDP levels in modern oils are just fine.

 

[Nayov]

You could run olive oil and it would be fine. In my mower I use Super Tech synth 10-30 which is treating it like gold compared to the average lawnmower owner who probably never changes the oil.

 

[OilNerd]

Check out this thread: Unkillable briggs

Enjoy!

 

[Brett Miller]

Small engines have so little valve spring pressure that it means nothing.

 

[Pablo]

Not really a concern, but since you use Amsoil you may want to run the small engine oil, ASE or even ACD.

 

[raffy]

OilNerd, that is an awesome, and rather funny, video to watch. It looked like one of Briggs and Stratton's "classic" engines. I'm not so sure that their larger engines can tolerate such abuse. Maybe someone on here has a riding mower that's about to bite the dust that could be used in a similar experiment!

I must say that Tecumseh engines aren't as immune to abuse. I had a Tecumseh push mower quite a few years ago that had a manual throttle and was a bit underpowered for the lawn. I ran it at full throttle most of the time, ran it through wet grass sometimes, basically just abused it. It developed an engine knock after several years. Never killed it, though, as I sold it off for a song and got a new one. Now every four-stroke small engine that we use regularly is a Briggs.

I guess the message I'm hearing is that engines with heavy duty valve springs (which are often used to control "valve float" at higher rpm's, as in racing applications) put high pressure on the valve tappets and followers and are the ones most susceptible to damage from lower ZDDP.

 

[OilNerd]

Thought you'd enjoy that. I stumbled upon it while staying up late and it put me on the floor laughing.

Yes, it was a "classic" engine, but most lawnmower engines can still take a fair bit abuse and be forgiving, though I don't recommend it, or the olive oil

, though I now believe it could be done.

My '70s lawnmower/pest controller runs quite nicely with synthetic SM oils. I use whatever synthetic oil I have leftover, but the small engine oil (ASE) Pablo mentioned does look like great stuff and well designed for the application. It depends on budget and what things are worth to you.