Problem found…

and it ain’t good.

They found out the problem on my truck.  It’s been having a high rpm misfire above 4200 rpm, and they haven’t been able to tune it.  Turns out there was a problem during assembly (likely I screwed it up, but it’s possible there was a part failure).

Here’s a picture of the timing cover:

From top to bottom, that’s the water pump drive gear (driven off the camshaft), the Optispark distributor drive interface, and the crankshaft snout.  The Optispark distributor drive interface is really just the front of the camshaft; that dowel pin goes into the Optispark, which is a pancake shaped distributor that sits between this timing cover and the water pump.

Here’s a picture with the cover removed.

Again, a picture of the front of the cam, which drives the distributor:

And now a picture of the back of the Optispark distributor, which is what goes on that camshaft:

SO, take a look at the front of the cam again:

Those two bolts on the sides hold the cam plate against the face of the motor, which holds the cam in.  SOMEHOW, they worked themselves out.  As they did, that allowed the front of the cam to move around a bit, which caused that dowel to break.  The broken dowel caused the opti to not be directly in time with the engine when a high rotational force was applied (high rpm), causing the misfire.  It also caused enough vibration in there to get one of the distributor rotor bolts to back itself out inside the case.  You know, looking at those two bolts, I definitely put locktite on there; I wonder if I didn’t get them torqued right?  Huh.  I’m pretty sure I did; not sure what happened.

I guess it’s good that they found the problem; it could have been much worse if the thing had completely come apart going down the highway.  As it is, the shop is going to try and pull or drill that dowel out, and press a new one in.  Hopefully, they won’t have to pull the lifters and replace  the camshaft.  Then put the timing set back together, then the distributor back on, then the water pump back on.  Gah.  This is going to be EXPENSIVE.  I’m sorta glad they’re doing it though; it’s not fun work at all.

But damn, is it going to be expensive.


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