Need timing help, keep breaking pushrods, CAT 3406

Almost done with the in frame rebuild I've been working on for the last month or so and today I'm working on the timing on a 4CK CAT 3406 and having trouble, I keep bending pushrods. So far I've followed the instruction manual to the 'T' in regards to the timing bolt in the flywheel and #1TDC with both intake and exhaust pushrods being able to spin by finger indicating that the piston is up and the valves are shut.

Went thru and set the valve clearances(0.015" intake and 0.030" exhaust) and when I was done I go to crank the motor over by hand and CRACK, pushrod bends out of shape for seemingly no apparent reason.

Only two things I can think of that would cause this would be the valves contacting the pistons or the clearances being set WAY off and the valves bottoming out. According to the manual the pistons should not be contacting the valves because I had the motor properly set at #1TDC and from what I can see the valve springs were nowhere near bottoming out.

Any ideas on what I'm doing wrong? Thanks for the help!

 

The cam did not come out of the motor but the crank did. Before the crank came out I made marks on the crank gear and cam gear with paint then when it went back in they were matched back up.

Just went and played with it some more and came to the conclusion that the valves must be hitting the pistons even though I have it timed properly according to the book. As I was spinning the motor over by hand it would stop rotating for no apparent reason. I released the torque on several valves at the pushrods one by one and problem solved, at least that problem. The engine will spin all the way around by hand now no problem.

I thought about the possibility that I may be 360* off. You can only set the valve clearance when there's no pressure on the pushrods, correct? If that's the case then it can't be 360* off because the valves for #1 are engaged while #6 is at TDC and vice versa.

It kind of makes sense to me at this point that the cam would be off...Any way to check it while the front cover is still on the engine?

 

How would I go about checking those with the engine still in the truck and both the cylinder head and front cover installed?

Thanks!

 

I was under the impression that I had it timed correctly but I guess not. It's gotta be an issue with timing the gear train the more I think about it and all of the other stuff that has been done. Looks like I will be yanking the front cover back off of the motor, after I get it back off what is the best way to ensure that everything is timed correctly? I don't remember seeing any timing marks on any of the gears but I could have been looking in the wrong areas.

Thanks again for helping this newb out!

 

The push tubes all look to be identical as far as I can tell. So far I've busted 3 and when I ordered new ones thru CAT they only listed one part number. The more I think about it the issue has to be with the gear train. Gonna yank the front cover off and see what I can see.