I have a 2015 GMC Silverado with the 6.2-litre engine. It has recently developed a tapping sound (like a bad lifter). Having done some research, it looks as if this model with this engine has a bad history (as do other engine sizes with cylinder deactivation). Apparently, the sound I’m hearing could be from a broken pushrod. I have more than 160,000 kilometres on the engine. Is this something the dealer should fix? – Hank R.
While GM may have eliminated the previous valve train problem, it appears they may have another issue to contend with now.
I’m not an engineer, but here is my layman’s understanding of the problem. The pushrod and lifter were redesigned for model years 2015 onward to combat the previous generations cylinder deactivation lifters collapsing.
The older design saw a pushrod and lifter that were lined up with each other. The geometry in the newer generation motor sees the pushrod sitting at a slight angle in relation to the lifter.
When the engine is running, harmonic vibrations naturally occur and cause the pushrod to flex slightly. When the pushrod flexes it can sometimes contact the side of the lifter because of the above mentioned angle difference. Obviously, unintentional contact can yield unwanted bending problems. A bent pushrod will cause a tapping sound as you have witnessed and lead to a misfire in the affected cylinder.
This is not to be confused with older engines that sometimes developed bent pushrods because of heat. When an older pushrod engine is running even slightly hot, thermal expansion occurs and the pushrod becomes slightly longer sometimes causing it to bend as it struggles within the now shallower space.
In your case, 160,000 kilometres is a respectable distance to go before seeing this problem as a quick internet search shows many owners complaining of this same problem at a quarter of your mileage.
I also can’t find any literature suggesting that this part has been redesigned. Therefore, any qualified automotive service facility should be able to easily repair this for you. While this is an unwelcome repair, it shouldn’t be too costly.
Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.
Shopping for a new car? Check out the new Globe Drive Build and Price Tool to see the latest discounts, rebates and rates on new cars, trucks and SUVs. Click here to get your price.