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Discussion Starter · #1 ·
After re-doing my timing gears and buttoning the whole thing up I took the truck (93 f250 w/460 EFI) for a gentle spin to make sure everything was working well. It started running rough, then stalled out in front of a mechanic's shop (small favors?).

Examination showed that the camshaft nose sheared off. The rear link-path of the timing chain is (currently, anyway) riding on the front set of sprocket teeth. Mechanic theorizes that somehow it crawled forward and exerted the wrong kind of force on the gear, and consequently the camshaft nose, causing it to shear after less than ~30 minutes of running time.

And, joy of joys, there's also fine metallic dust in the oil--looks like aluminum and copper (silver and yellow sparkles). The oil was fresh and clean, and the filter brand new, when I backed out of the driveway.

So, here's my questions:
1) Mechanic is urging me to do an engine swap on the grounds that he believes the timing gear shaved aluminum off the inside of the timing cover, which then got into the crankshaft bearings and rubbed the copper in them down. Is this a legit diagnosis, or is this an up-sell from a camshaft job? What risks to I run if I just have him do the camshaft?

2) I was very meticulous when I put the timing gears, harmonic balancer(s), timing cover, etc. back on, following all the torque specs in the shop manual. It does not appear that any of the bolts backed out or came loose (the crankshaft bolt is still fixed firmly in the broken camshaft nose which is itself still firmly fit inside the top timing gear). What could have caused this problem? Is this the result of me overlooking something due to not having done a timing gear swap before? Is this a normal wear failure mode that simply happened due to unlucky timing? Did taking the camshaft bolt out and then putting it back in put too much stress on an aging camshaft nose? It's an expensive lesson no matter how this shakes out, but I'd very much like to learn the lesson rather than just having the expense.

Thanks much for your thoughts!
 

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It sounds like the wrong bolt may have been used to attach the timing gear to the cam. This can happen when the bolt it too long. The bolt bottoms out in the hole and then consequently donesn't provide the clamping force and the pin on the front of the cam ends up getting sheared off. Either that or the bolt just wasn't tight enough to begin with. I'd start with that.
 

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Discussion Starter · #3 ·
Definitely wasn't the wrong bolt, and it was torqued to spec at 45ft-lbs, with the original washer. When it broke, the nose broke off but remains pinned through the sprocket. It's as if somehow the bottom sprocket was too far forward and pulled the whole chain forward. I just can't imagine how that could possibly happen.
:-/

Any opinions on whether the glittery oil means the crankshaft bearings need replacing?
 

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Definitely wasn't the wrong bolt, and it was torqued to spec at 45ft-lbs, with the original washer. When it broke, the nose broke off but remains pinned through the sprocket. It's as if somehow the bottom sprocket was too far forward and pulled the whole chain forward. I just can't imagine how that could possibly happen.
:-/

Any opinions on whether the glittery oil means the crankshaft bearings need replacing?
If it didn't shear the alignment pin and it broke between lobes or between the front of the cam and the first lobe it almost sounds like you just had a bad cam core to start with. It probably chunked & chipped the heck out of the front cam bearing so that could explain the metal glitter. If something heats up in the front it will usually shear the pin first. Breaking where it did is unusual from my experience. Do you see any heat discoloration in the front bearing or bearing journal on the cam? Could have possibly been lack of oil on the front cam bearing........ask me how I know.....
 

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Discussion Starter · #5 ·
The broken part is standing proud of the engine, like so. Vertical punctuation is the front of the engine as viewed from above. This is what I can see with the timing cover off:
|[SNAPPED OFF][Bolt end] [Camshaft Nose] [Timing Gear] [Washer] [Bolt head]

The alignment keyway and everything else are still all together with the bolt, the camshaft nose, timing gear, washer, etc,it's just that the camshaft sheared clean off just hair proud of the engine block.

No heat discoloration visible--can't seen the camshaft bearing as it sits, would have to pull the camshaft to see it.

What would cause the front cam bearing to stop getting oil?
 
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