Fuel pump cam lobe problem
Safety Car
Joined: May 2004
Posts: 4,363
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From: los altos hills california
Difficult to say for sure but I mostly blame the Mobil 1 I was using at the time. Lack of ZDDP and the cam mfgr (CROWER) said the fuel pump lobe was not hardened properly. They gave me a $100 rebate on another cam. I stopped using mobil 1 and went to a pushrod with softer tips. Might have been some composite tipped rod, don't remember for sure.
What amazed me was the motor kept running right until the cam went completely round. I had a very hard time initially believing this was the problem until I got a dial indicator in there.
This might be about 10 years ago now. I assumed all that metal was captured by the oil filter, never really had a problem changing out the oil and filter with the new cam installed.
You might want to send your cam back and see if they will compensate you somehow.
What's your story?
Last edited by ignatz; Jul 14, 2018 at 07:30 PM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I find it hard to believe that oil / zinc is to blame here but maybe. As far as pressures, when installing a fuel pump the arm is forced down a bit when you easily tighten up the pump bolts. And you can take a SBC fuel pump and force the arm down with one hand. There is not a lot of pressure in the spring. Nothing like what a valve spring exerts on a cam lobe.
I would suspect an oil passage was blocked and it ran dry. Or that slim, very slim chance that the soft tip pushrod was installed up-side-down.
I would suspect an oil passage was blocked and it ran dry. Or that slim, very slim chance that the soft tip pushrod was installed up-side-down.
Last edited by HeadsU.P.; Jul 14, 2018 at 08:45 PM.
Safety Car
Joined: May 2004
Posts: 4,363
Likes: 1,587
From: los altos hills california
I find it hard to believe that oil / zinc is to blame here but maybe. The composition of the oil at that time was low on ZDDP, I checked As far as pressures, when installing a fuel pump the arm is forced down a bit when you easily tighten up the pump bolts. And you can take a SBC fuel pump and force the arm down with one hand. There is not a lot of pressure in the spring. Nothing like what a valve spring exerts on a cam lobe. That's right.
I would suspect an oil passage was blocked and it ran dry. Nope Or that slim, very slim chance that the soft tip pushrod was installed up-side-down. Originally the hardened steel pushrod was in place I only installed the softer tip after this occurred
I would suspect an oil passage was blocked and it ran dry. Nope Or that slim, very slim chance that the soft tip pushrod was installed up-side-down. Originally the hardened steel pushrod was in place I only installed the softer tip after this occurred
Safety Car
Joined: May 2004
Posts: 4,363
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From: los altos hills california
Yes we all know that, that fact has been stated. "It's not from the oil" is your opinion. A fact, the mfgr stated they didn't ordinarily need to harden that lobe. Another fact, this happened after I switched to Mobil 1. The motor ran fine before that. Correlation is not causation but those are my circumstances.
We need to hear the OP's circumstances. Meanwhile you might want to do a search on the subject, here is a quote from "The Economist" from back a few years.
That leaves only one other suspect—the oil used to lubricate the engine. To prevent excessive wear of the valve gear, motor oils have traditionally contained a fair amount of a zinc and phosphorus in the form of zinc dialkyldithiophosphate (ZDDP)—with typically 1,700 parts per million (ppm) of zinc and 1,600 ppm of phosphorus. The ZDDP additive works by getting the zinc to react with the iron of the tappet surface and cam lobe, creating a glassy sacrificial barrier between the two. As the barrier wears away, it is replenished constantly by the ZDDP in the oil. The phosphorus plays a similar, though lesser, role in protecting the engine's valve gear.
We need to hear the OP's circumstances. Meanwhile you might want to do a search on the subject, here is a quote from "The Economist" from back a few years.
That leaves only one other suspect—the oil used to lubricate the engine. To prevent excessive wear of the valve gear, motor oils have traditionally contained a fair amount of a zinc and phosphorus in the form of zinc dialkyldithiophosphate (ZDDP)—with typically 1,700 parts per million (ppm) of zinc and 1,600 ppm of phosphorus. The ZDDP additive works by getting the zinc to react with the iron of the tappet surface and cam lobe, creating a glassy sacrificial barrier between the two. As the barrier wears away, it is replenished constantly by the ZDDP in the oil. The phosphorus plays a similar, though lesser, role in protecting the engine's valve gear.
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Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
I agree, the pump has no where near the spring pressure of a valve spring...and .its not the oil.. or lack of zinc..its the wrong type pushrod for the type cam used.. Pushrods are not UNIVERSAL.. they need to be matched to cam material .. as far as ."it ran fine before Mobil One".....you stated it was "running fine" as we see the cam now.. if it was the oil, ALL the lobes would be worn out.. They are not. ..Tens of millions of motors running on Mobil One.. how many cams look like yours?? . Find out what the Cam maker recommends for pushrods on THAT SPECIFIC cam. .. they come in about a dozen compositions and configurations. INCLUDING a roller tipped one .. Matched components is the key to longevity
Le Mans Master
Joined: Oct 2007
Posts: 7,451
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From: RI, Now Franklin/Nashville TN
I have to agree, I seriously doubt that Mobil 1 oil caused that rounding when the cam lobes with MUCH higher pressures on that cam look fine. I vote for a mismatch of fuel pushrod material for that cam or lack of oil to the section of the cam......
The one question I do have is for both with rounded fuel pump cams is what type of fuel pump pushrod was used. Was it the OEM GM fuel pump pushrod or if aftermarket, what type? OEM, Composite, roller tipped, hardened??? On my howards roller cam, I specifically asked howards about using my 1978 OEM GM fuel pump pushrod and the answer was absolutely and I could also use my my OEM Distributor GM gear. 5 driving seasons now and BOTH are perfect...BTW..I have used Mobil1 oil either 15W-50 before the 2014 rebuilt and Mobil1 0W-40 European Formula since 2014 and all is good with the motor and the oiled components.
I have said this before many times but will share once again that every car I own, new and old, every piece of power equipment I own including generator, lawn tractor, snowblower etc uses Mobil 1 0W-40 European formula synthetic oil regardless of the weight specified by the OEM manufacturer for about 20 years now. If Mobil 1 oil was a problem with its lubication ability I would be up the creek without a paddle................
The one question I do have is for both with rounded fuel pump cams is what type of fuel pump pushrod was used. Was it the OEM GM fuel pump pushrod or if aftermarket, what type? OEM, Composite, roller tipped, hardened??? On my howards roller cam, I specifically asked howards about using my 1978 OEM GM fuel pump pushrod and the answer was absolutely and I could also use my my OEM Distributor GM gear. 5 driving seasons now and BOTH are perfect...BTW..I have used Mobil1 oil either 15W-50 before the 2014 rebuilt and Mobil1 0W-40 European Formula since 2014 and all is good with the motor and the oiled components.
I have said this before many times but will share once again that every car I own, new and old, every piece of power equipment I own including generator, lawn tractor, snowblower etc uses Mobil 1 0W-40 European formula synthetic oil regardless of the weight specified by the OEM manufacturer for about 20 years now. If Mobil 1 oil was a problem with its lubication ability I would be up the creek without a paddle................
Last edited by jb78L-82; Jul 15, 2018 at 08:09 AM.
Safety Car
Joined: May 2004
Posts: 4,363
Likes: 1,587
From: los altos hills california
In no particular order to your comments, let me restate what I know
Thank you all for your comments. It would be nice to hear from Shayster he's probably out in the garage switching cams and scratching his head
- the only lobe worn out was the fuel pump lobe
- the mfgr stated that wasn't hardened and ordinarily wouldn't be, of course all the other lobes were hardened
- this is a roller cam
- the steel pushrod was in the motor for years with that cam running on conventional oil. I still have it
- this was ten years ago and there were numerous instances of failures reported at that time from lack of ZDDP
- it wasn't just me, oils were being reformulated at that time because of problems like this
- the lobe went flat after I switched oils
- there were no lubrication problems, of course I looked
- got a new cam from the same manufacturer, switched pushrods and oil and ran the motor for about seven more years
Thank you all for your comments. It would be nice to hear from Shayster he's probably out in the garage switching cams and scratching his head
Le Mans Master
Joined: Oct 2007
Posts: 7,451
Likes: 974
From: RI, Now Franklin/Nashville TN
In no particular order to your comments, let me restate what I know
Thank you all for your comments. It would be nice to hear from Shayster he's probably out in the garage switching cams and scratching his head
- the only lobe worn out was the fuel pump lobe
- the mfgr stated that wasn't hardened and ordinarily wouldn't be, of course all the other lobes were hardened
- this is a roller cam
- the steel pushrod was in the motor for years with that cam running on conventional oil. I still have it
- this was ten years ago and there were numerous instances of failures reported at that time from lack of ZDDP
- it wasn't just me, oils were being reformulated at that time because of problems like this
- the lobe went flat after I switched oils
- there were no lubrication problems, of course I looked
- got a new cam from the same manufacturer, switched pushrods and oil and ran the motor for about seven more years
Thank you all for your comments. It would be nice to hear from Shayster he's probably out in the garage switching cams and scratching his head
Safety Car
Joined: May 2004
Posts: 4,363
Likes: 1,587
From: los altos hills california
Thread Starter
Heel & Toe
Joined: Mar 2004
Posts: 17
Likes: 0
From: Waukesha Wi
Thanks to all of you that have responded, and sorry for the delay in sending this. I have been in contact with Comp engineers regarding the issue and I believe the problem lies with the push rod. The factory says there are a few different materials used in the core of the cams and a corresponding rod tip must be matched up. It appears the rod used originally was a metal tip but the one that goes with my cam should have been a brass tip. In addition, related to the problem was the failure and lockup of the fuel pump causing the catastrophic lobe wear. All corrections are in motion so the future looks good. As a matter of point I also use Mobil1 on every internal combustion engine I own. Thanks again everyone.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Wow! Never heard of that: Lockup of the fuel pump arm. The engine would continue running until the fuel bowls were empty. But I guess that's long enough to do some major damage. You would never see it or hear it.
I guess one could say that with some soft materials of aftermarket pump pushrods, they would be considered "sacrificial rods". Meaning that the rod should wear out first and would be cheaper / easier to replace than a cam any day. A 20 min job as opposed to an all day job.
I guess one could say that with some soft materials of aftermarket pump pushrods, they would be considered "sacrificial rods". Meaning that the rod should wear out first and would be cheaper / easier to replace than a cam any day. A 20 min job as opposed to an all day job.
Thread Starter
Heel & Toe
Joined: Mar 2004
Posts: 17
Likes: 0
From: Waukesha Wi
I probably had 3 or 4 thousand miles on the cam and it would have run quite a bit longer from what the engineers said but the life was cut short due to the pump locking up. I'm busy right now trying to get my motor back in and hooked up but when I have some time I will split the pump to see how and why it failed like that.
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
Thanks to all of you that have responded, and sorry for the delay in sending this. I have been in contact with Comp engineers regarding the issue and I believe the problem lies with the push rod. The factory says there are a few different materials used in the core of the cams and a corresponding rod tip must be matched up. It appears the rod used originally was a metal tip but the one that goes with my cam should have been a brass tip. In addition, related to the problem was the failure and lockup of the fuel pump causing the catastrophic lobe wear. All corrections are in motion so the future looks good. As a matter of point I also use Mobil1 on every internal combustion engine I own. Thanks again everyone.
Safety Car
Joined: May 2004
Posts: 4,363
Likes: 1,587
From: los altos hills california
Five years later I got my Z06 which recommended Mobil 1 (that is five years running on that steel pushrod). I figured that must be really good oil for that big motor so I switched over. My mistake certainly but don't discount the oil deficiency as formulated at that time so quickly.
This hasn't come up either but I also remember switching to a composition distributor gear when I first installed the cam. I can't find any notes on that subject.
Finally on a slightly different synthetic topic, my local and very experienced Corvette Repair guy (Dave Herlinger, very OCD guy) told me in no uncertain terms to never use synthetics in my manual transmission as the synchro wouldn't like it.
So yes you are right about matching the pushrod with the cam (and which I did check on) but I would also add with the correct oil.