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What type of cam core? HR? Flat? Billet? iron dizzy gear? etc.
Not sure of all those details (been too many years, probably cast core) other than it is a HR, had to use a hardened gear for the dizzy and could not use the stock fuel pump pushrod. Pretty sure it's not a billet cam however. I tried a bronze tip first and when the fuel pump failed the first time, the tip had started to mushroom. That's when I got the polymer rod.
The polymer rod showed no wear itself. So the wear had to occur to the cam lobe. Poorly hardened perhaps? I decided it was easier/cheaper to go electric pump than change the cam.
Last edited by REELAV8R; Jul 25, 2024 at 08:27 PM.
That spec is not really possible to find on line, at least I couldn't. And good luck contacting the manufacturer. I measured the throw on my old original cam and it was .330"
So with GKulls and Reelav8r experience, both on HR cams, it sounds to me like the hardened cast cam core has fuel pump lobe problems, even with a polymer pushrod. and the billet core cam is OK with the polymer pushrod.
10+ years in both cases!
And both guys had bad experiences with the bronze tipped pushrods. Cast cam core and billet core.
I found this BBC oiling diagram which shows an outline of the pushrod going thru the block.
You can just see the fuel pump pushrod on the lower left.
For the OP it shows that only a little bit of the pushrod sticks out of the block to grab from below.
Based on Reelav8rs measurements, it needs to be at least .330"
And the top portion get almost completely buried in it's tunnel at the same time, and if it has a bronze tip, that is getting mushroomed, I could see how easily it could get stuck in the tunnel.
Now without pulling the manifold I am not sure how you could confirm what is happening up top.
If you have a borescope, it is probably long enough, you could snake it thru the distributor hole, and all the way to the other end of the cam, and find the pushrod tip, and maybe see what is going on.
2nd choice is to pull the closest pushrod and go in that way thru the valve cover.
That one sounds easier to me.
Or yank the intake.
This the borescope I bought. Because you can aim the tip, you can get it into very tight places. I used it to inspect my cylinder bore and the bottom of the valves, thru the sparkplug hole. Pic on my phone. It could easily find the fuel pump pushrod. link
So with GKulls and Reelav8r experience, both on HR cams, it sounds to me like the hardened cast cam core has fuel pump lobe problems, even with a polymer pushrod. and the billet core cam is OK with the polymer pushrod.
This may or may not be true in regards to the cast cams. If I were a gambling man, I'd say someone failed to harden the lobe adequately. All the valve cam lobes have survived and they undergo a much rougher life as far as pressures are concerned. The fuel pump lobe however sees wear similar to a flat tappet cam. So that may be a factor as well.
The only way to find out or sure is to remove the cam and have a hardness test done on the fuel pump lobe.
Good point.
I find it interesting, yet problematic, on these HR cams, with the different cam cores.
And their various lobe wear issues.
Lifter lobe wear, distributor gear wear, and then the fuel pump lobe wear, which seems to be at the bottom of the list.
Last edited by leigh1322; Jul 26, 2024 at 09:52 PM.
I’ve had bigger priorities but finally got back to my stuck fuel pump rod. I decided to fit a piece of pipe and JB weld it into place. Both ends were cleaned well and the pipe has a few holes to attach a slide hammer if needed. The rod is stuck fairly well so I give this about a fifty fifty shot!
I wasn’t very clear, I bought a cheap fuel pump rod for fitment. No, the rod isn’t out yet. The engine was built by a reputable builder , the reason I requested a few dyno runs wasn’t for tuning but to verify everything before installation. When I went back thru my pictures and video I seen that the builder used an electric fuel pump for the dyno test. Lesson learned!
if I have success getting this out I’ll call Comp Cams and get their input for the correct rod. I’ve seen several post concerning mechanical fuel pumps that have different “arm” geometry causing bent pump rods. It seems impossible to bend rods that are almost fully supported but it happens.
Concerning why this rod was not coming out? I don’t know, I’m thinking it has been sticking for a while. The new engine only has a few miles on it, making great but inconsistent power. I thought (and more experienced owners here), that it was a bad fuel pump from setting so much. I hooked up a fuel pump gauge and noticed low pressure. When I removed the suspect pump it looked like new, I now think it was the pump rod sticking.
KC
SUCCESS!! I got my stuck fuel pump rod out this morning. I’m not still 100% sure why it was stuck but you can see some wear on the sides. I think the scratches are from me trying to get this out with tools. The bronze tip doesn’t appear to be mushroomed but does have a fair amount of wear on the flat portion relative to the low engine hours (<25).
i welcome input but my plan is to call Comp Cams to verify this is the correct part for my cam. I’ll probably remove this around 5000 miles to make sure it’s not mushrooming or galling. If I have to I’ll replace every 10,000 miles as I don’t put many miles on this rig.
KC
I'd go with the polymer rod or convert to electric. If you do go electric the internal pump is going to be better. The external pumps make so much noise.
putting another of those rods in and then getting it stuck permanently doesn't seem like much of an option.
Fantastic news!
Have you checked for a bend by rolling it on a flat surface (like plate glass or cast iron tool top)?
For those more familiar with these things, is the pump rod supposed to rotate like lifters? This rod appears to have the cam mark in only one orientation.
All good questions, I’ll check the end for mushrooming by measuring although it doesn’t appear with the eye. Same for the straightness. To respond to another question, yes, I am concerned about going thru all of this and having the same issue again! It’s kind of frustrating to have a very original Vette and not be able to have it function as Chevrolet designed it.
I was a bit concerned about the wear pattern on the soft tip with so few miles, this part from Comp Cams has been superseded by a new part number.
KC
The 4607 push rod has been “superseded” by 4610 which is a different design. It looks like the bronze end has Ben replaced by a coated end. We will see how this plays out, hopefully this doesn’t wipe the cam lobe. I’ll take this out after 5000 miles and take a peek at it.
KC
Just a thought and dont remember if this was mentioned. These are made by humans and sometime we do miss stuff.
How does the OD compare to a known new/good used one?
Chance that just a few thousands to big causing a bind.
