Understanding Harley Valve Train Tuning

Understanding Harley Valve Train TuningThe Harley Davidson “valve train” begins with the cam and ends with the valve itself. Along the way many problems can occur. Tappets consist of a tappet body with a small hole in the side that admits oil to the lifters. A lifter is a device that sits within the tappet body and transfers the motion of the tappet body to the pushrod. The tappets are equipped with rollers that rest on the cam lobes and transfer the positions on the lobes upward to the pushrods, then to the rockers, and finally to the valves.

You can run hydraulic or solid lifters. Hydraulic lifters have been stock in HD bikes since 1948. Hydraulic lifters receive oil under pressure (12 to 35 psi) from the engine and use that oil to damp the motion of a small piston that is connected to a pushrod. The small amount of oil in the hydraulic cylinder provides a cushion against shock as well as thermal expansion compensation. As the motor heats up the cylinders and heads expand upward. So does the oil in the lifters. With hydraulic lifters you get increased reliability as well as less wear and tear on the valve train – up to a point.

Hydraulic lifters are just the ticket for average street cruising and touring, but look out when you roll on the throttle and rev that engine! You can exceed the lifter capacity, forcing the oil out of the hydraulic cartridge and possibly damaging your engine. The solution, if you want to push the motor to its limits regularly, is to install solid lifters.

Whether you install solid lifters or convert your hydraulic lifters to solid, you will be able to run a more aggressive cam, and you will be able to twist that throttle as much as you like. However, you will need to adjust those pushrods more often, and you will need to deal with damage due to increased stress on the valve train.

It’s all a matter of what you want to do with that bike. If you want to spend time on the drag strip and street riding isn’t important, you will want to run a high lift cam, and use solid lifters. In fact, if you run an Andrews 3 grind or an S&S 514 on up (for example) you MUST use solid lifters. If you use your bike on the street or for touring you will want the reliability and decreased maintenance requirements of a hydraulic lifter set.

Shovelhead riders may be interested in upgrading to Jims Powerglide tappet blocks. These blocks are machined to accept Evolution tappets, so you get the benefits of Evo technology, including higher revs and lower maintenance in you shovelhead motor. The kit comes with hydraulic tappets and lifters ready to install. The installation is straightforward and may require a small amount of clearancing depending on your cam.

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  1. Rob Fleming - August 30, 2011

    New blog post: Understanding Harley Valve Train Tuning http://t.co/Tf1g94R

  2. Rob Fleming - August 30, 2011

    New blog post: Understanding Harley Valve Train Tuning http://t.co/Tf1g94R

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