Automotive or S&S Tappets in Your Harley

Hi, I'm Bruce from S&S Cycle. In this video we're going to talk about hydraulic tappets. The S&S tech department gets a lot of calls from writers with valve train questions. One of the more interesting ones is about using tappets for Chevrolet V8 engines in their Harley Davidson engines. First of all, you may ask, why would anyone want to do that? Well, mostly it's about saving money. These tappets for Chevy V8's are pretty cheap. Of course, you'll probably have to buy a set of 16 to get the four tappets you need. The second question you should ask is will these tappets fit in your Harley Davidson engine? Absolutely. This is a tappet for a Chevy V8 engine, and this is an S&S premium Tappet for 1999 and present Harley Davidson big twins, and 2000 and later Sportster models. Dimensionally they're identical. This Chevy tappet will fit, but the next question is, will it work? And here's the big one, is it going to screw up my engine? That my friends is exactly what we're going to find out. In order to demonstrate how these listers function in a controlled and repeatable environment, we're going to use the S&S End-of-Line engine testing machine. A powerful computer controlled electric motor spins the engine up to various RPMs, simulating actual running conditions. We use heated oil to simulate conditions in a running engine. We're going to use this machine to demonstrate the most important difference between a Chevy lifter and an S&S tappet. Or a stock Harley tappet for that matter. Namely, top end oil delivery. As a happy coincidence, motor oil glows under ultraviolet light. So we can use UV to detect where the oil starts feeding the top end. This little hole in the end of the rocker arm is where the oil comes out to lubricate and cool the valves and valve springs. We'll keep an eye on the end of the rocker and the top of the valve spring during the test, so we can tell when oil is available to the top end of the engine. We're working with a special engine that has S&S premium tappets in the tappet guides for the rear cylinder, and tappets for a Chevy V8 in the front. With the top rocker covers removed, we're using two cameras to compare the oil delivery of the S&S tappets and the automotive tappets. We're going to turn out the lights and shine these ultraviolet lamps on the rocker arms and valve springs as the End-of-Line tester turns the engine at idle speed. We'll know when the oil starts coming out of the rocker arm since the oil glows under UV light. If you're in the same engine, they're seeing the same oil pressure, with the same oil, at the same temperature. The engine is turning at idle speed of about a thousand RPM. And we're waiting for the oil to show up at the tip of the rocker arms. The oil temperature is about 175 degrees. We have about 13 pounds of oil pressure. It's been about 30 seconds, and no oil from either rocker arm yet. This should be a good illustration of why you shouldn't rev your engine right after you start it. Okay. It's been 42 seconds and we can just see the oil starting to come out of the rocker arms on the rear cylinder. That's the one with the S&S tappets. Nothing yet from the cylinder with the automotive tappets. Well, the engines been running for about six minutes without enough oil to the front rocker arms to lubricate the springs. And it doesn't look like we're going to get it. You may be surprised by the difference in top end oiling, but we've actually done some research ahead of time, and this is about what we expected. We tested the oil flow through a number of tappets, and this chart shows what we found. Here are the S&S premium tappets flowing about 80 cc's per minute. And the tappets for GM V8 engines flowing only about four cc's per minute. Wow, a pretty dramatic difference. Does that mean the tappets for V8 engines are inferior? Not at all. They're just not made for this application. Consider this: an automotive tappet is designed to run in a liquid cooled engine, where the temperature is pretty well controlled. An air cool engine experiences a much wider range of temperatures. Another consideration is that the oil pressure in an automotive engine usually runs about 50 PSI and seldom less than 20, even at idle. But in a V-twin motorcycle engine, oil pressure could be as low as 20 PSI on the highway, and often less than five PSI at idle. To make matters worse for your motorcycle, the oil specified for a modern GM V8 engine is 5W-20. So when you start trying to feed 20W-50 oil to the top end with a tappet designed for 5-20 oil at a lower pressure, you just aren't going to get as much oil. So, considering the lack of oil to the top end, do you think that using automotive tappets in your Harley Davidson motorcycle is going to save you money? We presented the facts, but it's your bike and we'll let you decide if you want to go with the automotive route. Besides, we sell replacement rocker arms too. So it's okay.