Is the cure more painful than the cause?
By Chuck Lynch
A common complaint that we field on the AERA tech line is LS hot idle oil pressure issues. We start down the list of the typical things to check off.
- Did you use mechanical and vehicle gauge?
- What is the main bearing clearance?
- What is the rod bearing clearance?
- Is the oil pump correct for application?
- Is the pick-up tube installed correctly with correct O-ring and not sucking air?
- Are all oil line plugs installed?
- Is the barbell oil diverter installed?
- Is the VLOM filter contaminated?
- Is the AFM by-pass functional?
- What is the lifter to bore clearance?
- Does the engine have piston cooling jets?
If we get beyond these checks, you have to start considering that camshaft oil clearance may be an issue. This is usually an unpopular discussion because we have little control over cam clearances with the processes that we practice in most shops. If you look at the oil flow illustration below, you will see that lifters and cam bores will see oil before the mains, which then supplies the rods.
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2024EPQ2/#p=24
If we get beyond these checks, you have to start considering that camshaft oil clearance may be an issue. This is usually an unpopular discussion because we have little control over cam clearances with the processes that we practice in most shops. If you look at the oil flow illustration below, you will see that lifters and cam bores will see oil before the mains, which then supplies the rods.
We often use the analogy that people are like liquid as they will follow the path of least resistance. Well, that is exactly what we are often dealing with in some instances with modern pushrod engines because they still have a camshaft in the block. This is challenging to us in the repair industry because the OE’S do not install finished inside diameter cam bushing/bearings like we practice in the aftermarket. They install green bearings into the block and then bore the inside diameter to establish the proper alignment and oil clearances.
Take a look at the snip below that is captured from Prosis, and you will see that there are different diameter cam housing bores for different locations. In addition, you will see that the tolerance of the diameters is large. If we consider the tolerance of a crankshaft housing bore or a connecting rod housing bore, the tolerance of the cam housing bore is at least double, if not more than double. If there is that much tolerance on the housing bore, how do you think that the cam bushing/bearing is going to respond? It will not be consistent. The bearing supplier has to accommodate the largest bore to ensure enough interference fit for bearing retention which is not going to be the best accommodation for the tightest bore dimension allowed.
When you consider how most camshaft housing bores are machined you will understand why not only the variation in bore diameter can be challenging but alignment may be poor as well. At the OE level, many blocks have some cam bores machined from one end of the block and others machined from the opposite end of the block. This creates an opportunity for misalignment.
So, if you couple the variation in housing bore diameter and possible misalignment, how do you accommodate camshaft installation? You have larger clearances built into the bearings. This is not the fault of the aftermarket cam bearing supplier. This is the result of machine shops requesting adjustments so that the camshaft will rotate in the block.
Now, fast-forward to an era of 0W-something oil and we are still producing cam in block engines the same way we have for 80ish-plus years. What is going to happen with oil pressure? I revert back to the statement early in the article, “fluid flows in the path of least resistance.” Pressure is the measure of restriction to flow and when the fluid flows easily because of viscosity and chemistry, pressure can be more challenging to produce.
What is the fix? Well, awareness is half of the battle. You do the easiest things first. You start by measuring. Many folks don’t want to measure cam housing bores because they are different sizes which means a lot of set up changes of the bore gauge.
➤ Measure the installed bearings and see how they reacted to the amount of interference fit that they have. If the block sizing is good but the bearings seem to be coming with excessive clearance, then that is truly something the vendor can address. There are undersize options, coating, etc.
➤ If the clearances measure good but the cam will not turn, you likely have an alignment issue. This could be due to the installation of the bushing or the misalignment of the bores. Remember, variation in the ID of the cam bearings and variation in the journal diameters will present itself as misaligned. Look at where the bearing and the journal are showing signs of rubbing and polishing.
➤ If you find that the bores are misaligned, align boring may be the only answer. We have accepted that reality with crank housing bores but fight that notion when it comes to cam housing bores. You can bore the blocks and correct the housing bores, or you can buy green bearings and bore the ID.
Over the past couple of years, I have discussed this challenge with engine builders in custom machine shops, high-performance only machine shops, production engine rebuilders and every type of shop has battled this issue. I myself remember dealing with this 30 years ago. We had reamers, roller-burnishers, a bar to bang on to displace the material so the shaft would turn and so on. The difference is the oil and the engine management of today does not allow what we “use’ta could.” The ECU will say no way and you are in protect the engine mode if you even get that far.
I have mentioned green bearings earlier in the article. When I was a sales engineer at MAHLE, I managed accounts that used green bearings due to contract requirements. Knowing this was sometimes the case, I asked Aaron LaRose at SRC Automotive what they were doing with their LS program and if I could share his comments. Aaron stated that they sell their LS engines into the direct aftermarket, and they have determined that they are time and money ahead to install green bearings purchased from Dura-Bond and align bore. That statement means that they are not being forced to practice that by an OE, they have found that to be the most repeatable and reproducible process for them to be successful at building that engine family.
There is a supply of unfinished or green bearings available to the aftermarket. There are machines that can align bore cams just as well as crankshaft main housing bores. Does the rework justify a different process, or do you continue to fight these as they come along? A close evaluation of true cost and profitability holds the answer and that varies from shop to shop.
So, back to the beginning, is the cure more painful than the cause?
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2024EPQ2/#p=24