skinny z

What's the word on the street for a bronze tipped fuel pump push rod for this cam?
I recall that the cam was a casting (not billet steel) although now I can't recollect. The advice at the time was that it wasn't necessary. Neither was a different distributor gear. It's been in for over 25 000 (hard) miles without a hint of trouble however now I've got a so far undiagnosed clatter that can be heard above the rest of the engine noise. Very much like a rocker/lifter tapping however on an initial inspection and running the valves again, there was no indication of anything out of adjustment. It's barely noticable when going through the rev range with the hood up but quite apparent when driving. There's a load element to it as well in that it's more defined when accelerating (lightly) than when cruising steady state.(it's definitley not detonation or preignition).
I'm thinking about the fuel pump rod possibly getting wiped out or perhaps I've damaged the cam pump lobe. I use a Carter M4891 fuel pump which is nothing out of the ordinary. Oil pressure and fuel pressure are fine and the car performs as it always has (although I'm hesitant to get my foot in it with this problem).
Any experiences?

skinny z

To complicate things a little more, I'm getting conflicting information regarding an aftermarket push rod. One camp says, a hardened tip to prevent push rod wear. The other says a soft tip to prevent cam lobe wear.
I've got a call into Comp to determine if the cam is cast or billet.

305sbc

iTrader: (3)

The key to bearings is to have dissimilar metals in contact. Bronze makes an excellent bearing surface.
The push-rod should be slightly softer than the cam lobe.

I would use a stethoscope to try to pinpoint the sound. Sounds are usually caused by clearance/slop, or a part resonating.

skinny z

I used a stethoscope however it was ineffective in that the tapping is inaudible unless you're driving (unusual I know). I couldn't persuade my buddy to sit on the fender with the hood up while I drove down the road!
Good idea though.
I would think that a steel cam would wipe out a standard push rod (which is ok in that the cam lobe should be intact). I'm trying to source a bronzer tipped part locally and then I can investigate further.
I haven't received an answer from Comp regarding the cam material. Pretty sure it's a casting.

305sbc

iTrader: (3)

Have you tried pulling the accessory belt off and then driving for a short distance?

I wouldn't think that the cam lobe would eat into any type of pushrod as long as the contact end of the rod is properly convex shaped.
Have you pulled the rod to inspect it?

skinny z

I'll go through another round of tests and inpsections when I have the chance. I suspect I'll ultimatley pull the intake and the entire valve train to inspect each piece. Run the lobes as well to see if anything has come off. I found a couple of frightful pictures.

skinny z

Here's the reply I received from Comp regarding the composition of the cam I have.

"The cam is a Austempered Ductile Iron material. It is the same thing that
the factory uses on OE Hyd. Roller motors. It is not the same thing as a
cast flat tappet cam but it is not steel."

Aaron Mick
COMP Cams Technical Consultant
amick@compcams.com

Still leaves me wondering what type of fuel pump rod I should be using.

87IROC-DAN61

Hello skinny z!!

Usually the fuel pump push rod is made out of a softer material than the camshaft, as it's easier to replace the fuel pump push rod, than the camshaft!!

I had a 1970 Plymouth Roadrunner with a 383 4bbl, with a suspected fuel pump problem!! Turned out to be the fuel pump push rod was a tad short, by about an inch, and wasn't working the fuel pump through it's complete pumping stroke, causing a fuel starvation problem!!

$35.00 vs $500.00 or more nowadays!!!