Last year a client reached out when his engine developed what sounded like serious issues. We gave him a quote for a full performance engine build based on a worst case scenario. We provided realistic expectations, clear pricing, and a conservative timeframe. Ultimately, our client was swayed by a promotional quote from another shop trying to get their name out. They promised the moon: absorbing all the labor costs and delivering in half of our timeline.
Fast-forward 10 months. The engine was built, pulled out once for problems, reinstalled, and then suffered a complete failure. That’s when the customer finally had the car transported to us. Within a couple weeks we were able to get the engine out and started the inspection.
Bank 1
When we opened Bank 1, we immediately saw evidence of the first failure of the built engine. There was severe damage to cylinder one’s valve train. Witness marks revealed a head stud nut had come loose, bounced around inside the cylinder head, and was eventually smashed between the exhaust cam lobe and the head casting, cracking the head clean through the camshaft saddle.
Both the intake and exhaust cams showed damage to the noses of their first lobes. It was also evident that one of the finger followers (which should be DLC coated for wear protection) had been replaced with a severely worn, older-style non-DLC coated part.
Every cam cap bolt had Loctite applied, despite McLaren specifications calling for them to be installed dry. This created multiple problems, including incorrect clamp loads due to the Loctite acting as a lubricant on the threads.
We were shocked when we found several of the head stud nuts were barely finger-tight. The studs themselves unthreaded inconsistently—some easily, while others dragged coming out. We also noticed that none of the studs had ARP Ultra-Torque lube applied, which is essential for achieving the correct torque and proper gasket clamping. Then there was the head gasket. Instead of the correct three-layer gasket, the previous shop had installed a thinner two-layer version. That reduction in thickness increased compression ratio in an already high-compression, high-output engine—a recipe for disaster.
Bank 2
Bank 2 was no better. When we removed the exhaust manifold, coolant poured out of Cylinder 8’s exhaust port, clearly indicating a massive head gasket failure. The exhaust cam caps had been installed in the wrong positions, with their numbers ascending back to front rather than front to back. That wasn’t just sloppy—it changed the oil clearances and caused scoring on both the cams and the cam tunnels.
Six of the ten head stud nuts were finger-tight, and three more required less than 100 lb-ft to remove—far under spec. The Bank 2 head gasket was blown in multiple places, with Cylinder 8 the worst. Unlike Bank 1, this side did have the proper three-layer gasket.
When we started removing the head studs from Bank 2, we finally had our “aha” moment when one of the studs came out with aluminum threads attached. Testing other head stud positions confirmed that simply threading a stud in and pulling lightly would pull the threads out. This was the smoking gun that allowed us to determine how this snowballed into the engine’s ultimate demise.
The previous builder had installed ARP CA 625 Plus head studs. These are extremely strong fasteners with very high tensile strength that require exceptionally high torque to achieve the proper stud stretch. These were not a good match for an all-aluminum block. With the combination of high torque, thermal expansion, and extreme cylinder pressures, the studs had literally pulled the threads out of the block. This caused a loss of clamping force which was the cause of both failures of this engine. With the studs not properly stretched, the insufficient friction allowed the stud nuts to loosen, this allowed the nut to come off causing the first failure, and the head to lift, blowing the gaskets on the final failure.
Because of the extent of the damage—and because some of the affected parts aren’t available individually from McLaren—there was no way to repair this engine to get this customer back on the road quickly. The only viable option was a brand-new McLaren crate engine at about twice our original quote.
Unfortunately, this story isn’t unique. We see this pattern over and over again: shops overpromising to get the work, then cutting corners or simply lacking the knowledge to do the job correctly. In the end, the client pays far more than just money—they lose months of time and deal with the massive frustration that comes with this.
If you’re considering an engine build for your McLaren or any high-performance car, do it right the first time. Bring it to a shop that understands these engines inside and out, follows the proper procedures, and uses the correct parts every single time.
At Cannonball, we don’t cut corners. And we won’t compromise your car just to save a few bucks. Trust us the first time, and you’ll save yourself months of headaches, thousands of dollars, and a lot of regret.
See you next time