The Ferrari 360 is one of the first of that brand where changing the timing belts can be performed in the car, without having to remove the engine. This opens up this important task to the DIY owner and makes maintaining the car simpler.
One of the tools required to perform the belt change is the Crankshaft Locking Tool (AV 3207), which allows taking off and torquing the crankshaft pulley nut.
The tool is available for purchase from several outlets with the Hill Engineering (HE) label, and it's a beautiful tool. Cost is considerable for a tool that's used exactly twice every three to five years. I'm certainly not one who scrimps on tools and I typically would buy such a thing. However, it looked like a part that could be 3D printed.
Here's AV 3207. This tool protrudes into a gap in the clutch housing.
The first consideration is strength. The Ferrari style tool has a single protrusion that interferes with a single point on the clutch housing. That point has to take all the torque in one plane, which is a horizontal force. A 3D printed part is weak in this plane since 3D printing assembles the part in layers. A horizontal shear force would likely cause a 3D printed part to fail, or stretch. The protrusion also is fairly long, so there would be a large moment generated by the torque on the protrusion. That would cause a twisting force in the base of the part and flex in the tool.
If the tool is made from aluminum, as is the case of the HE tool, it wouldn't matter as the material is quite strong and resistant to bending and twisting.
The weakest part of the Ferrari part design is that it uses the same tiny screws (3mm hex) to hold the tool in place. The tool comes with a set of special screws that have an unthreaded portion that's larger in diameter than the threaded part. Lose one of those screws and guess what? You're <**>.
One heavy limitation of the Ferrari tool is that clutch housing has a limited number of ports where the Ferrari tool will fit and from what I've read, none of them line up with Top Dead Center (TDC). So once the bolt is loosened on the crankshaft pulley, the locking tool has to be removed to line the engine up with TDC, then after the belt job is finished, the tool has to be reinstalled to torque down the flywheel.
When I first looked at making a tool, I thought the geared tooth on the flywheel would be a much better choice because it's close to the edge of the inspection cavity and the toothed nature allows multiple points to take the stress and the stress is distributed out in multiple angles. This is far better for plastic than a single fault point.
Additionally, since there are a lot of teeth on the flywheel gear ring (64), the tool can be locked very close to, or at TDC and left on until the last steps of the job. This assures that the crankshaft won't move unexpectedly. This would be a rare thing, but it could happen and it would be bad if the timing belts were off.
The body of the tool was fairly easy to model since I had excellent access to the inspection port, but the locking part, the "grabber" had to fit the teeth of the flywheel. I tried to measure the diameter of the flywheel and could only get a best estimate of 12". I looked online and couldn't find a better answer so that was my starting point. Then, on a whim, I asked both ChatGPT from AI Open and Bard from Google and those entities both said 10.5". AI's have a weird habit of making stuff up if they don't know, but when two different AI systems come up with the same answer, it's probably a good one.
After I had the flywheel, I modeled up a thin bit that would be the biting end of the tool and the first iteration fit perfectly. So Bard and ChatGPT were correct, or correct enough for my purposes.
Here's the tool modeled with the flywheel.
I finished my belt job and torqued up the crankshaft bolt to the right specs. The crankshaft locking tool worked perfectly. I noticed some distortion on the leading edges of the teeth of the tool. It seems like the removal of the bolt took more torque than the setting. I suppose that's from Loctite.
Here's the tool after using it:
This amount of distortion is completely tolerable but since it's plastic, those distortions would be additive and the tool would eventually fail if used often enough. I would suggest a maximum of two belt changes be performed with this tool before discarding and printing another. Since the tool only costs a few dollars to print, I further suggest chucking it in the trash after a single belt change. Just print another when needed. No sense in keeping it around for years.
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