Fuel pump problem after cam change 327/300

[Jeff S.]

A 'Gilbert' (fka Salley) Chevy crate engine take-off cam (14888839) was installed during complete rebuild. First firing operations went fine for 45 seconds or so until fuel starvation shut down the engine when the Holley float bowl priming gas was consumed. Troubleshooting included installing a second fuel pump (known to be good) with the same results on the next attempt. Note: neither fuel pump seemed to offer the typical resistance that is normally felt when the actuating arm contacts the rod. In other words, I was able to insert the pump right up to the mounting plate surface & spin the attaching screws home by fingers without the usual load presented as the arm's coil spring compresses during the last 1/8" or so.

Yes, gas in tank is suffienct w/good fuel supply to pump via head pressure
Yes, the rod is original and unchanged.
Yes, the engine was positioned to #1 TDC firing during pump install(s)
Yes, a pinch bolt was used to keep the rod 'up' during pump install(s)
Yes, the pinch bolt was released & plugging bolt installed after install(s)
Yes, both pumps bench check fine
No, Holley stone filter is not plugged

In between pump installs, the engine was cranked to observe the rod travel while holding it up against the cam with a finger. It did stroke -- thought to 'feel like' about 1/4". I have not figured out a more accurate way to measure this, but will try. If there is no load on the arm at TDC #1, then 1/4" would do little more than compress the spring at max travel -- thus not acheiving any deflection of the pump's diaphragm.

This is what I fear; an incorrect fuel pump eccentric circle size or offset or both on the cam. I know it seems unthinkable, but I'm puzzled as to what else it could be. Gilbert Chevy confirms that the GM Goodwrench cams they take off from their crates do have fully finished pump eccentrics.

What have I missed? Ideas or donations of band aides gladly accepted.

[Duke W.]

Re: Fuel pump problem after cam change 327/300

Jeff and I have discussed this via email. I have the drawings for both the 839/840 and 930/929 cams. The 839/840 is an OE replacement for the 930/929. The only difference is a very slight change to the inlet and exhaust lobe eccentricities. The basic .050" specs are the same with a very slight difference it max lift.

The fuel pump eccentric details on both drawings are the same. It's nominally a 1.500" circle offset a nominal .170" from the camshaft centerline, so total movement of the pushrod should be about .340".

I find it hard to accept that the eccentric could be way out of spec, but we ran out of other ideas and need some help.

FWIW this cam does not have a GM "ID Number" - the last four digits of the finished camshaft part number - 8839 in the casting. (The GMPD "part number" - ...840 and ...929 are the cam/pin assemblies) It appears to be the same Textron CWC blank that the aftermarket uses. My understanding is that this blank arrives at the cam grinder with all machining (including the fuel pump eccentric) completed except final lobe dimensions, which are ground to spec by the cam vendor.

So if the eccentric is "off" the problem is at Textron, and there are probably a whole bunch of defective cams out there from all vendors.

Duke

[John M.]

Re: Fuel pump problem after cam change 327/300

Jeff, I just installed a fuel pump on a 327-300 with a Crane cam and it went on as you would have expected, resistance to getting the bolts lined up because of the diaphragm spring. Maybe your "special" cam has a special lobe for the fuel pump requiring a special rod? I could get some measurements if you get desperate.

[Clem Z.]

Re: Fuel pump problem after cam change 327/300

A 'Gilbert' (fka Salley) Chevy crate engine take-off cam (14888839) was installed during complete rebuild. First firing operations went fine for 45 seconds or so until fuel starvation shut down the engine when the Holley float bowl priming gas was consumed. Troubleshooting included installing a second fuel pump (known to be good) with the same results on the next attempt. Note: neither fuel pump seemed to offer the typical resistance that is normally felt when the actuating arm contacts the rod. In other words, I was able to insert the pump right up to the mounting plate surface & spin the attaching screws home by fingers without the usual load presented as the arm's coil spring compresses during the last 1/8" or so.

Yes, gas in tank is suffienct w/good fuel supply to pump via head pressure
Yes, the rod is original and unchanged.
Yes, the engine was positioned to #1 TDC firing during pump install(s)
Yes, a pinch bolt was used to keep the rod 'up' during pump install(s)
Yes, the pinch bolt was released & plugging bolt installed after install(s)
Yes, both pumps bench check fine
No, Holley stone filter is not plugged

In between pump installs, the engine was cranked to observe the rod travel while holding it up against the cam with a finger. It did stroke -- thought to 'feel like' about 1/4". I have not figured out a more accurate way to measure this, but will try. If there is no load on the arm at TDC #1, then 1/4" would do little more than compress the spring at max travel -- thus not acheiving any deflection of the pump's diaphragm.

This is what I fear; an incorrect fuel pump eccentric circle size or offset or both on the cam. I know it seems unthinkable, but I'm puzzled as to what else it could be. Gilbert Chevy confirms that the GM Goodwrench cams they take off from their crates do have fully finished pump eccentrics.

What have I missed? Ideas or donations of band aides gladly accepted.

make sure the pump push rod moves freely in the block as a bent rod could stick on the return stroke. the stroke should be about .500. remove the pump and check the rod movement with spinning the engine on the starter

[Jeff S.]

Re: Fuel pump problem after cam change 327/300

Clem

I did that. See my post, above, starting with " .... In between pump installs ..."

[Clem Z.]

Re: Fuel pump problem after cam change 327/300

did you measure the length of the stroke and if it is not close to .500 that is your problem.

[Joe L.]

Re: Fuel pump problem after cam change 327/300

A 'Gilbert' (fka Salley) Chevy crate engine take-off cam (14888839) was installed during complete rebuild. First firing operations went fine for 45 seconds or so until fuel starvation shut down the engine when the Holley float bowl priming gas was consumed. Troubleshooting included installing a second fuel pump (known to be good) with the same results on the next attempt. Note: neither fuel pump seemed to offer the typical resistance that is normally felt when the actuating arm contacts the rod. In other words, I was able to insert the pump right up to the mounting plate surface & spin the attaching screws home by fingers without the usual load presented as the arm's coil spring compresses during the last 1/8" or so.

Yes, gas in tank is suffienct w/good fuel supply to pump via head pressure
Yes, the rod is original and unchanged.
Yes, the engine was positioned to #1 TDC firing during pump install(s)
Yes, a pinch bolt was used to keep the rod 'up' during pump install(s)
Yes, the pinch bolt was released & plugging bolt installed after install(s)
Yes, both pumps bench check fine
No, Holley stone filter is not plugged

In between pump installs, the engine was cranked to observe the rod travel while holding it up against the cam with a finger. It did stroke -- thought to 'feel like' about 1/4". I have not figured out a more accurate way to measure this, but will try. If there is no load on the arm at TDC #1, then 1/4" would do little more than compress the spring at max travel -- thus not acheiving any deflection of the pump's diaphragm.

This is what I fear; an incorrect fuel pump eccentric circle size or offset or both on the cam. I know it seems unthinkable, but I'm puzzled as to what else it could be. Gilbert Chevy confirms that the GM Goodwrench cams they take off from their crates do have fully finished pump eccentrics.

What have I missed? Ideas or donations of band aides gladly accepted.

Jeff-----


There is no doubt that the GM #14088839 camshaft is supposed to have a fully finished fuel pump eccentric. This camshaft SERVICES many applications which use a mechanical fuel pump. Also, all of the crate engines which currently use it have provisions for a mechanical fuel pump. So, there's absolutely no doubt that it's supposed to have the eccentric.

Next, of course, comes the question regarding whether it might be defective and not have the eccentric or not have it machined to spec. Personally, I consider this unlikely. For one thing, you have used the "feel test" on the pushrod while turning over the engine and you've found some movement. So, we know the rod is doing something. We just don't know if it's a sufficient movement to operate the pump properly.

It is possible to measure the stroke, but it might be difficult while the engine is installed in the car. However, if you can set up a dial indicator, you should be able to measure the stroke precisely. If you can't do this, you can still get a fairly accurate measurement by using a small machinist's rule and a straight endge. Crank the engine until the pushrod is at it's most inward travel. Place the straight edge against the fuel pump pad mounting surface. Use the machinist's rule to measure the distance between the pushrod end and the straight edge. Then, turn the engine over so that the pushrod is at it's furthest outward travel. Measure the distance as described previously. The difference between the 2 readings is the piston travel. It should be about at the spec that Duke described. If it is, you then KNOW you've got no problem with the cam.

[Jeff S.]

Re: Fuel pump problem after cam change 327/300

Joe

As you know, with the car fully configured for running, there is barely enough room to conduct a 'feel test'. I will figure out something more elegant, but it will require clearing the real estate significantly. However, measuring the stroke will not provide me with information to confirm the circle size -- it will only confirm or deny the accuracy of the offset. If the circle size is indeed too small, the results would be the same as I think I'm encountering.

[Timothy B.]

Re: Fuel pump problem after cam change 327/300

Jeff,
You don't suppose the strainer in the gas tank is getting clogged and not letting a good flow of gas when the engine is running. Just a thought and this would save alot of work.

[Jeff S.]

Re: Fuel pump problem after cam change 327/300

Tim

Wish it were so, but I've got gas a-plenty. Enough head pressure from the tankfull to push it through the pump & up the hard line to the carb inlet. Confirmed that a couple of times during the fuel pump swaps.

I keep coming back to the pump installation situation. Both pumps offered no resistance when offered to their mounting holes with the rod pinched full-up in it's bore and the engine on #1 TDC. I have never encounted this before -- always had to out muscle the last 1/8" or so by evenly tightening the mounting screws as the actuating arm made it's contact with the rod end & compressed the coil spring segment somewhat. Not so in this situation -- acts like the actuator arm is just in there touching nothing, which is not good. Once I get the area cleared, I can use Prussian blue and figure out where my contact surfaces are.

Sigh ...

[Clem Z.]

Re: Fuel pump problem after cam change 327/300

Jeff-----


There is no doubt that the GM #14088839 camshaft is supposed to have a fully finished fuel pump eccentric. This camshaft SERVICES many applications which use a mechanical fuel pump. Also, all of the crate engines which currently use it have provisions for a mechanical fuel pump. So, there's absolutely no doubt that it's supposed to have the eccentric.

Next, of course, comes the question regarding whether it might be defective and not have the eccentric or not have it machined to spec. Personally, I consider this unlikely. For one thing, you have used the "feel test" on the pushrod while turning over the engine and you've found some movement. So, we know the rod is doing something. We just don't know if it's a sufficient movement to operate the pump properly.

It is possible to measure the stroke, but it might be difficult while the engine is installed in the car. However, if you can set up a dial indicator, you should be able to measure the stroke precisely. If you can't do this, you can still get a fairly accurate measurement by using a small machinist's rule and a straight endge. Crank the engine until the pushrod is at it's most inward travel. Place the straight edge against the fuel pump pad mounting surface. Use the machinist's rule to measure the distance between the pushrod end and the straight edge. Then, turn the engine over so that the pushrod is at it's furthest outward travel. Measure the distance as described previously. The difference between the 2 readings is the piston travel. It should be about at the spec that Duke described. If it is, you then KNOW you've got no problem with the cam.

do the late model engines use a longer fuel pump push rod ???

[Joe L.]

Re: Fuel pump problem after cam change 327/300

do the late model engines use a longer fuel pump push rod ???

clem-----

Most of the later small blocks were used with applications using electric fuel pumps, so no pushrod was required. For instance, Corvettes last used a mechanical fuel pump for the 1981 model year. However, the current crate small blocks, when used for a mechanical fuel pump application, use the same 5-3/4" OL fuel pump pushrod as used for all 55+ applications, both small block and big block, alike.

Plus, the GM #14088839 camshaft is designed for SERVICE use with all earlier 1957+ small blocks.

[John M.]

Re: Fuel pump problem after cam change 327/300

Jeff, Any luck figuring out what's going on here?

[Chuck R.]

Re: Only four culprits I can see Jeff

1) Fuel starvation from the tank

2) The lobe on the cam was machined to a smaller diameter than required.

3) The push rod is either too short or hanging up in the bore.

4) The fuel pump arm is bent downward away from the rod.

A question, are you using any type of spacer plate that would hold the pump further away from the block than normal?

I'm done, keep us informed on what you find Jeff. I just love a good mystery,

Chuck

[Jeff S.]

Re: Only four culprits I can see Jeff

Re: Only four culprits I can see Jeff

Chuck & all

Turns out there was a fifth 'culprit'. I was out-smarted by a spider or some other critter that deposited a nasty silk egg sack of sorts in the hard line between the carb and the pump. It was porous enough to allow gas to seep by pushed by the head pressure created by the full fuel tank. It was not porous enough to let a slug of fuel-pump delivered gas by, however.

The line had been hanging on a pegboard in my garage since engine removal in January. I neglected to put a rubber plug in the ends or to bag it up like I did all other parts. During assembly I had fuel present at the carb end (head pressure source), so I never included this in my troubleshooting.

This morning as I was dis-assembling stuff to rig up some sort of pump rod stroke measuring device, I removed the hard line. It was wet with fuel, so with a finger over each end drained gas into a jar, walked to my compressor with the intention of blowing the line dry. After about 1-2 seconds of 60 psi -- SPLAT -- on the garage floor.

Returned line to the pump & tested via a couple of revs with the starter -- nice big fuel pulses issued.

Thanks to all -- glad there's not a bunch of bad cams out there.