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Did you know that the small engine in your generator, mini-bike, go-kart or whatever other contraption you have, is actually likely a flat-tappet design? This applies to Predator, Tillotson, Honda, and many other small engines.
Old school muscle car heads will know what flat tappets are. Just in case you aren’t aware though, flat tappet engines mean that the lobe and lifter are right up against each other. This means that the lifter is in direct contact with the camshaft.
While a great and reliable design that has stood the test of time, this design does have one major drawback if it is not properly cared for. The lifter and cam being right smack up against each other means that the oil in between the two metals needs to provide extra protection, above and beyond what newer engine designs need. Otherwise your cam can see extreme wear under heavy loads.
Because of this, in a flat-tappet engine like a Predator, Tillotson, Briggs and Stratton or other small engines, it is critical that you use a high zinc additive, especially during break-in. Ideally, it is best to use an oil or an additive in these engines all the time, even more so if you’re pushing it hard. You can find the right additive and oil to buy simply by finding out how much ZDDP or Zinc that it contains.
How ZDDP Prevents Wear
What is ZDDP you ask? ZDDP is an acronym that is short for Zinc Dialkyl Dithiophosphates. The primary role of ZDDP is to create a protective film to help stop the wear caused by direct metal to metal contact inside of your engine.
ZDDP does this by creating a phosphorus coating at the molecular level that physically separates the metal parts from each other. Being silicate-based, which is great for lubrication, means that ZDDP is regarded as possibly the best existing additive for curbing metal-on-metal engine wear.
Why Doesn’t Oil Contain Zinc Anymore?
The problem with ZDDP isn’t that it is bad for your engine internals, quite the contrary. The issue stems from emissions control device on modern car engines. Zinc additives in oils can negatively affect the catalytic converter in modern cars, reducing the capacity for it to convert emissions into something less harmful.
Being that we only advocate using ZDDP in small engines and in classic cars, this becomes a non-issue for this application, in fact we highly recommend it.
Top ZDDP Oils and Additives
We have put together a list of what we believe to be the best oils and additives to run in your small engine to combat the negative effects of metal-on-metal wear in flat-tappet designs.
1. Lucas Oil 10063 Engine Break in Oil Additive
This is possibly the best additive that you could use for small engine break-in after a rebuild or right out of the box. Simply add to the existing oil that you already have to infuse it with ZDDP.
The dosing suggestion of the label on the packaging will not work for small engines, as it is design for a full size car engine. Instead, we would recommend that you mix it with your oil in a ratio of 2oz per 1 quart of oil.
2. Amsoil 10W-30 Synthetic Small Engine Oil
The perfect oil for your flat tappet small engine, Amsoil Small Engine specific oil has everything you need to break-in and run your small engine with peak protection built right in.
Unlike the other available additive options, there is no need to measure and dose out anything, Amsoil has mixed in the perfect amounts of all protective additives directly into this oil. Simply fill your small engine to the manufacturers’ recommended capacity.
Note: For the Predator 220cc the oil capacity is 0.5 quart and the 420cc takes 1.16 quarts.
3. EASTWOOD ZDDP OIL ADDITIVE
We have used the ZDDP additive from Eastwood on quite a few engine break-ins, and have had excellent results. It’s fairly similar in its zinc content to the Lucas break-in additive, so no surprises there. Sometimes it can be found for a bit cheaper though, so it deserves a mention.
For a small engine the amount that you will add will be much smaller than a full-size car engine. With that in mind, our recommendation is that you mix it with your small engine oil in a ratio of 2oz per 1 quart of oil.
Hopefully this article has helped you to choose the best small engine additive to keep your small flat tappet engine running for many years to come. If you have found this information helpful, please be sure to let us know in the comments below. Don’t hesitate to ask us any other additive questions you may have, we will always do our best to answer!
Doug is our resident mechanic and automotive expert. With over 20 years of wrenching under his belt, he is our go-to for any question we have about additives and cars.