Relationship Between Camshaft, Oil Pump, and Distributor?


#1

I was reading about a car problem where the distributor gear kept getting stripped in a souped-up Ford small block vintage 1970, apparently due to some kind of incompatibility w/a special high volume oil pump previously installed. I got to wondering – in general – what’s the purpose of combining both distributor and oil pump functions like that? Is it an engine-saving feature so that if the oil pump fails, so will the distributor, then the car won’t run? And how exactly does it all work? Does the cam drive the oil pump which then drives the distributor? Or does the cam drive the distributor, which then drives the oil pump? Or neither?

One more related question. The article seemed to imply the fuel pump cam (eccentric) wasn’t machined into the camshaft (after-market) , but instead a replaceable bolted on part. Are oem camshafts on engines w/mechanic fuel pumps usually configured like that too?


#2

The cam shaft has gear the drives the distributor gear.

Out of the distributor shaft is a rod that goes down to the oil pump.

In the case of your Ford pickup, this rod is hexed shaped between the distributor shaft and the oil pump.

Tester


#3

There is one gear on the camshaft that drives a gear mounted a little off vertical. The oil pump is attached to the bottom of the gear and the distributor is attached to the top. The fuel pump has an arm (or lever) that rides on a cam lobe, but the lobe round but its center is off set from the cams center.


#4

The fuel pump is driven off an eccentric on the crankshaft.

Tester


#5

Ford used 2 different distrubutor/oil pump gear sets and missmatching the gear on the distributor to the cam resulted in gear failure.

And while Chevrolet V-8s and I-6 engines had the fuel pump eccentric ground into the camshaft Ford and Mopar V-8s used a ~4’ bowl mounted off center onto the front of the camshaft to actuate the fuel pump. But I don’t recall any common domestic carbureted engines that drove the fuel pump off the crankshaft @Tester. I’ve been told that my looks and memory are fading though.


#6

Any old V8 engine used the crankshaft to operate the fuel pump.

On GM’s, you had to hold the fuel pump push rod up so the pump could be installed.

A dab of grease on the push rod would hold the push rod up.

On Fords, you just turn the crankshaft until the fuel pump can be installed without effort.

Now! We’re talking about the days when vehicles didn’t have computers.

Tester


#7

I remember on the Pontiac V8s there was an eccentric cup bolted to the front of the camshaft sprocket that drove the fuel pump. I did many timing chain jobs on these because the nylon camshaft sprocket teeth would split and break. They were molded onto an aluminum hub. The replacements were always all metal.

Edit: to change nylon hub to aluminum hub. Getting careless in my old age.


#8

Tester: You are 100% correct.


#9

The fuel pump eccentric is integrated into or bolted onto the camshaft on those old engines.


#10

Here’s an illustration of how Pontiac did it. I just dug out an old Chiltons manual and photographed it.


#11

I remember fuel pumps always being driven off camshafts.
I never saw one driven off a crankshaft.


#12

Why was it done?? My guess; The oil pump adds steady drive load to the camshaft to dampen the pulsations from the crankshaft. The old timing chains didn’t have any guides or dampers to keep the chain from rattling itself to death. The oil pump added that load. Notice new cars with crank driven oil pumps have all kinds of guides and tensioners to control the chain or chains.

Apparently there are different philosophies regarding a broken oil pump shaft and the distributor. Most that I’m familiar with (Fords and GM) would keep running if the oil pump shaft failed because the gear was on the distributor. A foggy memory tells me some Chrysler products had the gear on the oil pump shaft so the engine would stop. This was how my old Datsun OHC 4 cylinder was, too.


#13

On Fords at least, the fuel-pump eccentric bolts to the end of the camshaft…So, with a single power take-off point, the camshaft chain, four engine functions are accommodated: The cam, the distributor, the oil pump and the fuel pump all operated off a single PTO point…


#14

Every fuel pump I have changed on a domestic pushrod engine, the mechanism that activates the pump, whether it is just a pump arm or includes a pushrod, angles up to the camshaft, not level toward the crank. That includes Chevys,Mopars, Fords, Studies, And Nashes


#15

Every mechanical pump I’ve changed worked off of the camshaft.

Besides, the cam runs at half speed. Imagine a mechanical pump lever operating at full RPMs off of the crank… :frowning:


#16

I have to confess that I have only changed one mechanical fuel pump on my 59 Pontiac. I had no idea what it ran off of but checked my Motors book and it runs off the eccentric on the cam gear. That’s the extent of my knowledge.


#17

I’m pretty sure – ok, this is just a guess – but on my early 70’s Ford V8 truck my guess it runs the fuel pump off an eccentric on the camshaft. At least that’s what it looked like when I looked into the hole where I bolted the replacement fuel pump when I replaced it a couple years ago. I didn’t take the engine apart of course, so maybe what I was seeing wasn’t the camshaft but something driven by the crank via a pushrod. But it sure looked like a camshaft eccentric I was seeing inside that hole where he fuel pump bolts.

A person could argue that since the camshaft has no power on its own, but instead is driven by the crankshaft, then the fuel pump is driven by the crankshaft.


#18

Yes, Fords have an eccentric on the end of the camshaft.