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The
Simple
Stuff
MGCCWDCC Logo by Bob Vitrikas

What's that Racket!?

Hydraulic Tappet ComponentsMost of our old British cars use a valve lifter to transfer movement from the camshaft lobe to a pushrod to a rocker arm to the valve stem resulting in the valve opening and closing as the camshaft pattern commands. Metal expands as it is heated, so all these mechanical parts have a tolerance or gap to allow for this expansion. As the parts expand, the gap decreases along with the ticking or tapping sound you may hear, especially when the engine is started from cold. Hmm “tapping sound,” guess that’s why they are sometimes called “tappets,” eh?

As an aside, some of you may recall an NPR show called “Car Talk” hosted by “Click and Clack, the Tappet Brothers”. I have fond memories of listening to “Car Talk” on Saturday mornings while working on my Mini Cooper race car with the late Tom Howen. Tom passed February 16th this year and was a legend in racing circles for his engineering, fabrication and driving ability. Tom could do it all and was one of the most widely read and brilliant minds I have ever known. Over the years, he hosted tours of his Charlottesville shop for the SVBCC. I will miss him dearly.

Valve lifters come in two “flavors,” solid and hydraulic. Hydraulic lifters were introduced on production cars in 1930 by Cadillac on their V16 engines. Not a typo, Cadillac and Marmon featured V16 engines in the 1930s, in the darkest days of the Depression. Hydraulic lifters have the advantage of using engine oil to automatically adjust the lifter gap, eliminating the need for valve gap adjustment and quieting the engine when first started. Which is great until they don’t…

If your engine suffers from noisy lifters there are several possible causes.

  • If you have a solid lifter motor or an overhead cam engine that requires periodic valve adjustment, it may need to have the valve gap adjusted.

  • If you have a pushrod motor, you may have a bent pushrod. Not so good! This will require a deep dive into the internals of the engine to replace the bent pushrod.

  • If your engine employs hydraulic lifters, it may simply be you are low on oil or the oil has become contaminated and the dirt has allowed one of more of the lifters to leak hydraulic fluid as it sits overnight. If this is the cause, the racket will go away in a few seconds after start up. The cure could be a simple as pouring an oil additive, such as Risolene into the crankcase. NOTE: This is not an endorsement of Risolene! If this doesn’t cure the problem, the engine may need to be opened up and the faulty lifter(s) cleaned or replaced.

Now that you know where that racket is coming from and why you can make an informed decision as to what action to take. Hopefully it’s a simple one!

 


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