Careful with that camshaft

[XfireZ51]

Busy w “refurbing” the motor this winter. Pete has it and in process of swapping over components to a different short block. During disassembly of the valvetrain Pete loosened the timing gear bolt on the snout, a pretty typical procedure for refurb.
The camshaft snapped into 2 pieces as he applied the necessary torque to loosen the bolt. (See attached). In all the years Pete has been doing this, nothing like it has ever happened. So I decided to ask Marc, given his vast experience, whether he has an experience with a cam breaking that way. Marc said he had never seen that before, but also offered a tip on this procedure. I asked if I could post for the rest of the community and he kindly agreed.

Here is his response:

Hi Dominic,
>
> We have not had that happen. Long ago I would hold the back end of the cam and loosen the cam sprocket bolt. I guess I got lucky and never broke anything. I became concerned about the stress along the cam. For the past ten years or so we let the chain take the load. After removing the cam cover the first thing that we do is loosen the sprocket bolt without holding the cam. This way the torque does not go down the shaft of the cam.
>
> Maybe you found a cracked or weak cam the safe way rather than at 7000 rpm.
>
> Best regards.
>
> Marc

The camshaft of course was never designed to take that type of twisting, and as our components get older, they become more frail just like we do. 😉🤣

So just thought I’d pass along some words of wisdom.

[Dynomite]

Thank you Dominic and Marc for the Information

In "Solutions" under ZR1 Engine/CAMSHAFT

Seems to me that can also be a pretty good load on the chain (maybe not)

[Jagdpanzer]

I hold the end of the cam shaft firmly with a box end wrench and loosen the sprocket retainer bolt with a 1/2” pneumatic impact. The impact hammer blows do a good job of breaking the bolt free of the Loctite without putting an excessive twisting force on the camshaft.


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[Jagdpanzer]

Dom,
What does the fracture area look like? Surprised it broke that far down from the drive end.


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[XfireZ51]

Originally Posted by Jagdpanzer

Dom,
What does the fracture area look like? Surprised it broke that far down from the drive end.


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Phil,

I can try to take more detailed pics of the fracture if that would help. It went on a diagonal. Al Dashto took a look and thinks there may have been an infiltration of oil into the casting. We just don’t know. But perhaps someone like yourself can help in determining whether this could be a singular event or perhaps a leading indicator.

[LGAFF]

Super Brittle.... I had one snap off on the opposite end..... also seen several with snout failures

[grahambehan]

I would also be very interested in looking at the fracture surface. Also were the valve springs compressed on that cylinder, thereby imparting a bending moment also.
Furthermore were the slave caps on at the time, what type of tool was used to hold the rear of the cam.

Graham

[XfireZ51]

Originally Posted by grahambehan

I would also be very interested in looking at the fracture surface. Also were the valve springs compressed on that cylinder, thereby imparting a bending moment also.
Furthermore were the slave caps on at the time, what type of tool was used to hold the rear of the cam.

Graham

Graham,

The cam was out of the cylinder head I believe. I’ll see if Pete can provide further detail.

[Ccmano]

Dom,
Is that camshaft original, reground or aftermarket?
H

[grahambehan]

Originally Posted by Ccmano

Dom,
Is that camshaft original, reground or aftermarket?
H

Looking at the picture, I would say that is not a stock cam.

Graham