Ferrari 360 Cam Sprocket Locking Tool 3D Printed

 

To change the timing belts on the Ferrari 360, the cams have to be locked in place when the belt comes off. Failure to adequately secure the cams can result in major engine damage. 

The Work Shop Manual for this car uses a pair of vice grips to lock the cam sprockets during the belt change. Unless the Vice Grips are really clamped hard, they can easily pop off. Too much clamping force might also damage the bearings at the end of the cam. I thought I could do something more secure and less damaging. 

My thought was to create a locking mechanism that wouldn't put pressure on the bearing. To do that, the space between the sprockets would need to be filled with the clamp.

I started with a picture and the measurements of the inner diameter of the sprockets and the space between them.

This picture shows the areas the can be used to secure the sprockets. 

Since this is a plastic clamp, the material bends easily under pressure so I had to come up with a way to move the force of the clamp from the edge, where a bolt would secure the clamp, to the back edge of the clamp. If the clamping force is at the end of the clamp, with compression as the dominant force. 

The clamp slips over the inner cam sprocket and fills the space between the cam sprockets.

The clamp has a feature where the top end of the clamp, the part that sticks out, has a slight ramp of 1/10" so that the fender washer pushes at the end of the clamp instead of at the bolt hole. The tension in the fender washer transfers the clamping force to the end of the clamp and adds steel to the strength of the clamp. Plastic is highly failure resistant in compression.

To secure the clamp, a 2-1/2" hex bolt (up to 5/16" diameter) is inserted into the hole with two 1-1/2" fender washers, a locking washer, and a hex bolt. To secure, the hex bolt is tightened so the locking washer is fully compressed, then a bit more, maybe 1/2 a turn. Pull on the lock to verify it is locked in place. If it's not tight, turn the nut down a bit more.

Here's the clamp with the bolt, fender washers, locking washer, and nut.

Here's the lock in place. The lock is 1-1/2" tall and sticks out about 3/4" from the face of the sprocket. 

Epilogue...

I finished installing the new belts, along with new tensioners and tensioner bearings. The cams were locked solid during the belt change. With the first belt, I had to pull and tug on the belt quite a bit to get it to snap into place. For the second belt, I loosened the tensioner bearing just a bit before locking the cams. That relaxed the belt and make it so it doesn't require a lot of force to fit it into place. It took a lot less effort to set the second belt.

Using the tensiometer is a bit tricky and requires some careful attention. I used the Gates Carbon Drive app to read the belts. I came up with these important things to consider.

1. Be as close to the belt with the phone's microphone as possible. The closer, the better.

2. Have the room as quiet as possible. Turn off A/C's, fans, and anything that rumbles or makes a steady sound.

3. This is critical. Clean the openings for the microphone. They are likely clogged with lint and crud. 

4. Plucking the belt should be done with the finger. I got the best readings using the edge of my thumb or index finger. 

It takes some practice but once I figured it out, I could get consistent readings every time.