How to Diagnose Diesel Engine Noise: Valve Train
We've recently talked about how to diagnose engine noise while your diesel is under load and noise due to engine belts. In this post, we're going to be looking at another possible cause of your diesel engine noise—your valve train components.
Think you might be having a different problem with your engine? Take a look at the common diesel engine issues.
Your Valve Train
The valve train consists of quite a few components, meaning your engine noise could come from several places. Your valve, valve guide, spring, the retainer located on the top of the valve, the cross head, cross head guide, the rocker arm, push tube, and then the cam follower and camshaft all make up the valve train.
If any of these components have wear, the tolerance or clearance that is usually measured in this location will grow or be exaggerated. For instance, the nominal setting might be 27 thousandths of an inch between the rocker lever and the cross head. When these components wear at any given point, that tolerance increases.
There is a minimum and maximum that that tolerance might be. For example, if 27 thousandths is the nominal setting, the minimum might be 23 thousandths and the maximum might be 31 thousandths. That's tolerable. If it's beyond these dimensions, then an adjustment needs to be made to put that back in its normal setting.
If you go through and you make the adjustment on the valve train, you'll need to bar or rotate the engine to set the engine in a specific orientation to make the adjustment.
When you go to make the adjustment, the engine should be in a position with the valves closed and the rocker arm located furthest away from the crosshead.
You make the adjustment by loosening a lock nut, turning the adjustment screw, checking it with a feeler blade, and then locking down the lock nut. Normally there are twelve rockers on a 6-cylinder engine that need to be adjusted.
If you go through and make those adjustments, restart the engine, and the kicking is still there, then you'll need to stop the engine and check the components that are all integral parts of the valve train: the crosshead, the rocker lever, the push tube, the cam follower, and the camshaft.
Identifying Wear on Valve Train Components
With these vital components, you want to make sure that their integrity is good.
For instance you need to make sure that the crosshead, when it's sitting on the guide pin, isn't excessively worn. It should move—it needs to have clearance—but it shouldn't rock.
The same thing is true of the rocker lever. If you can twist it sideways excessively, then it's worn and needs to be replaced.
Push Tube/Push Rod
A push tube or push rod can be bent or cracked. If it's bent, it needs to be replaced. If it's cracked, some are welded. The push tube has a hardened surface on the top and bottom that are affixed by a brazing or welding that can break. It can still sit there and move up and down and cause a ticking noise.
If the camshaft lobe becomes worn, or chunks are missing, then that can lend to the ticking noise. In that case, the camshaft would need to be replaced, or even the cam follower.
At both ends of the cam follower, it's like a rocker lever that's located right on the camshaft. It has a roller that's like a tire. It rolls on the elliptical portion of the camshaft, which makes the cam follower move up and down. Because it's like a tire, it rotates on an axle, called a pin.
If that pin or roller is worn, this again would cause an excessive amount of clearance that can cause the ticking.
On the other end is a socket where the push tube rests. Wear on that socket can also lead to the ticking noise.
If you find any of the components are defective, you'll want to replace them.
Resolving Your Diesel Engine Noise
If you've gone through and made the adjustments across the valve train and the noise goes away, then the problem is solved. If you start it up and the noise happens again, that's when you want to check the crossheads and the push tubes (to see if they're bent). the cam followers are a little harder because they're usually buried a little deeper in the engine. But, you can take a mirror or a little hook to help. You can make a little hook out of a hanger and pull on it to see if it has any excessive play, but it can be done. You can also take your mirror and look down with a flashlight to see if you see any excessive wear.
Engine noise can indicate a larger problem in your engine, so it's important that you identify the cause.
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