Tale of an Engine Build, Part 4

Tale of an Engine Build, Part 4

There wasn’t supposed to be a part four to this series.

But there is. Sadly.

After getting about fifty miles on the car and changing the oil three times, even stepping up to 15w40 truck oil, I still had an oil pan full of metal, a tick I didn’t like, and really low oil pressure at hot idle. Like 4-6psi low.

So I pulled the engine out and took it back apart. The source of the problem was located inside the oil pump.

Pump gears. Note the scoring on the right hand gear tooth that’s pointing straight up.

Evidence of contact between the pump cavity and pump gear

Pump filter adapter thrust surface

I’d fallen victim to complacency. I didn’t check the pump cover before installing it. The guys that built it for me had already packed the pump gears with Vasoline and I didn’t want to take it apart and repack it after checking it. That was a mistake.

Line indicates axis of cam sensor and pump drive

Line indicates axis of cam sensor and pump drive

The oil pump on a Buick V6 is driven off the camshaft by the cam sensor. In a carbed application, this same hole would house the distributor. Like many other engines, the cam sensor/dristributor has a tab in it that fits into a slot on the pump drive shaft. If this alignment is not spot-on, the cam sensor and camshaft side-load the pump shaft, which rocks the pump gears into the sides of the pump cavity and into the thrust surface. If the clearances are too tight on one side of the gears, that means they’re going to be too loose on the other side. Oil bypasses the gears through this extra clearance, and voila! Low oil pressure.

The pump gears also ground against themselves and the pump cavity, releasing metal into the engine.

Most of the bearing shells were scored, as were the cam bearings. The crankshaft was unharmed.

So, the entire thing went back to the machine shop to be cleaned and have new cam bearings installed.

I also went back to my friend’s shop and we pulled his entire stock of brand-new timing covers. We checked them all with a set of new pump gears and my cam sensor. All of them had bore alignment problems. Every. Single. One.

So, don’t trust the new pump covers. ATP, Pioneer, Silver Seal, TA? All of them use essentially the same casting from China. Some of them spot-check their incoming stock to see if they’re junk or not. Some don’t. And even the ones that do can miss a batch. If you buy one, put it together on the bench and make sure the assembly turns properly. My friend had a used original GM cover that checked out. I’ve already ported it. Once I get it tanked (it’s pretty grimy) and painted, I’ll be able to finish putting the engine back together.

I also resurfaced the filter adapter.

Resurfaced filter adapter. Mucho  better-o.

And the short block is back together already. Once the timing cover gets back from cleaning, I can re-set the cam endplay, assemble the oil pump and pack it with fresh Vasoline, and finish assembling the engine. Again.

Mostly assembled engine

Andrew

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