Just wondering if the drive gear on the front of the pump uses a key to turn the inj pump shaft and if they ever shear off and if the chain that drives the pump is the same one that drives the cam?

 

The pump is turned by a gear that rides on the tapered shaft of the injection pump. The cam and pump are gear driven. No chains in there. If you think you sheared something, odds are the gear slipped on the IP shaft.

 

does the gear come loose often?

 

No,not very often. have you ever had the gear off before???

 

I found that replacing the nut with a new one is really cheap insurance against the IP slipping on the drive gear.

 

The gear only tends to slip on rigs where the gear has been popped off to change the timing and not reinstalled correctly.

Sometimes if the dowel pin comes loose and gets caught in-between the gears it will shear the cam gear off. If this happens valves will crash into pistons, the result often is the entire engine is trashed.