D&D Custom Cam Problems?

Well?It?s been almost a year and a half (and a little over 10,000 miles) since I rebuilt and installed a 4.6 with a D&D custom cam, and the motor seems to be running well?.

BUT?

I have noticed a RANDOM knock/tapping (only noticed at idle) that sounded internal to the motor. I had just gotten rid of a knock that the cat was making when hitting the frame, by replacing the motor mounts. I was hoping this other knock was somehow related, but after replacing the mounts, it is still there.

I finally had a chance this past weekend to tear into it to determine where the knock was coming from.

The only things I could imagine it could be were:

Slipped liner
Cam shaft end-float causing the cam to tap on the front of the block (I?ll explain later)
Rod or main bearing (although unlikely as they were just replaced last year)
Oil pump gears getting ready to shatter (maybe that?s a stretch)
Broken valve spring (again, maybe a stretch)

My first thought was a loose liner, but I my gut feeling was that it was not, as I had just rebuild this thing and it seems unlikely that both myself AND the machine shop would not have noticed a short liner. I dropped the pan and could not see evidence of a slipped liner. The rods seemed not to have any play in them either.

I wanted to check end-float in the cam, so I then tore in far enough to remove the rocker shafts (as they were holding pressure on the cam).

Using a screwdriver from underneath, I could then (carefully) move the cam front to back. It was hard to tell exactly how much float I was getting because there was just no practical way of measuring it, but it appeared to be at LEAST 2-3mm. (which is pretty much for at least the OEM cam which calls for .075 to .25mm). This end-float was evident when I first installed this custom cam year and a half ago (can?t remember just how much, but probably about the same though).

And here is where I think I found the cause of the knock:

When moving the cam from the front to the back, there was a definite tap/knock as the flange at the front of the cam (thrust surface), came into contact with the front of the block. Evidently the cam is floating and the tap I am hearing is when it floats back into position against the front of the block.

A while back when Mark was developing the cam, I questioned how the cam was going to be retained and keep it from floating front to rear. Here is a link to the original thread.

http://discoweb.org/forums/showthread.php?t=19343&highlight=custom+cam

Dan Erickson said:

When I talked to Mark the other day, I told him that I was still pretty confused about the way the new cam was going to be retained from moving front to back.

I know the stock cam had the trust plate attached to the front of the block and rode in a groove machined in the cam. This kept the cam from moving in either direction.

I understand that this thrust plate will not be used in the setup for the new cam.

When I talked to Mark, He said something like the cam did not need to be retained from waking forward because the turning of the cam would always sort of "screw" it toward the back.

I still would very much like to know what in the hell keeps the cam from moving too far back.

I did not see any other sort of thrust type surface that would keep it from moving too far back. What would the cam finally hit to stop it?

I thought I read somewhere that the thrust surface was a part of the new cam assembly, but what would IT contact: The soft surface of the front of the block?

I'm obviously just not getting it.

Is there a drawing or picture anyone has that could maybe set my mind at ease?

Dan

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Now I certainly could be wrong about this, but I am 95 % sure the knock is being made by the cam floating at idle.

I?m going to call Mark at D&D today, and see what he thinks about it.

Just wondering what other problems this might cause (like screwing with the knock sensors) and If I should just button it up and ?go with it?.

Anyone else with a D&D custom cam (no distributor) experience anything like this?

Pretty damn random.

Intervals can be anywhere from 3-4 up to 10-15 seconds (sometimes even longer).

AlaskaBound said:

Dan:

Hunter here. The only tapping I've noticed seems to be from the noisy lifters. Could that be it?

I will take a close listen for the next few days and report back. Definitely let us know what Mark says about it.

-H

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Naaa...This is a much deeper (and more hollow) sound than lifters would make.


Just talked to Mark no long ago.

He does not think it is the cam doing that.

He wants me to check the sides of each push rod to make sure they have not been rubbing the sides of the holes in the heads.

I will do this when I get home, but it just does not seem like they would make the same noise as I'm hearing.

scottjal said:

I thought all these engines had lifter tic?

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From all the ones I have heard, they do, but this does not seem to be my problem.

ptschram said:

I spoke with Crower about the cam retention and was told not to worry about it.

Any evidence on the front cover of contact?

Any difference in appearance on the rocker arms where they contact the pushrods/valves?

PT

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I have not taken the front cover off yet, but I can tonight.

Having said this, when manually pushing the cam forward, it does not feel like it hits the front cover (as there seems to be no hard, stopping point). What it feels like, is the timing chain begins to bind from side deflection and keeps it from making it all the way to the front cover.

I will inspect the rockers more closely tonight, but again, the sound seems much deeper than what lifter or rocker noise would be (not to mention very random).

Yea I do have the tighter set of valve springs.

Looking back, I'm not so sure I really needed them though.

I will take a fresh look at things when I get home today.

I was not able to do anything else last night as I ended up having to take care of other business.

I did get to talk to my local machine shop guy and he suggested a button on the front cover may help to prevent the cam from walking too far forward (or at least rule out that this is the problem).

He also suggested I push the cam all the way back into position, and then turn the motor over by hand to see if the cam is walking forward (I have the plugs out already). This seems like it would take an awful long time by hand and may not even prove anything as it may only do it at idle speed (which I obviously can’t attain by hand).

So if it does walk forward it would prove this could be the problem, but if it does not, it doesn’t necessarily prove anything at all.

Like PT suggested, I need to get that front cover off to see if maybe there is evidence of contact.

I will try to do this tonight, but my GF just texted me that she wanted to give me a night of pampering and also wrote something a bit naughty, so I am now torn between the Rover and an evening of…well…you know…

D Chapman said:

Dan,

I've found the lifters D&D supply suck monkey balls. They're noisy as hell, more so on start-up.

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Yup…definitely noticed this. I was thinking of going with different ones, but seems a waste of time until I’m in there for something else.

D Chapman said:

I have a hard time believing that the cam is walking. These motors barley see 4k RPM's at the most. And a cam walking at idle is questionable.

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Well…Admittedly it took me a while to understand it was the grind of the cam lobes (slightly higher on the side of the lobe toward the back of the motor) turning on the bottoms of the lifters that is supposed to justify (push) it toward the rear, but I still have a REAL hard time believing this is an acceptable method for retention, but, then again, I am certainly no expert. I guess if the lobes ever wore flat (I don’t mean off I mean front to back), there would be nothing to screw it to the back anymore…dunno.

D Chapman said:

Something we found at MAR last week, though. I was changing an intake plenum and one of the horns in the intake was just loose floating around in there. It had been like this for quite some time as the bore was all wallowed out.... We re-set the horn and got everything back together. When the engine was restarted a "tapping" noise was gone the owner said had been there since he's owned the truck. That might be worth a look.

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This is good news to know for my daughter’s D1, but since my D2 is a Bosch engine with the big ass octopus looking upper air intake, it couldn’t be that.

D Chapman said:

That said, I've got the same set-up as you and I too have a "knock". But, mine is coming from the rear of the engine or the front of the transmission. I'm pretty sure mine is transmission/torque converter related, but I'm not 100% sure, yet. It's been doing it for about 2k miles now.....

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I originally thought the knock might be coming from back in that area (and thought it could be the flex plate), but thought it might just be resonating through the motor. After I dropped the pan, I spun it around, and the flex plate seems to be tight. I could not see any cracks, but I have read they are hard to see sometimes.

The fact that we both may have the same knock, really gets me wondering.

To attempt to describe the knock a little better: It sort of sounds like someone is taking a hammer and tapping the engine (just a little on the dull side though, like the hammer face had a thin coat of rubber on it).

How many miles do you have on your engine now?

D Chapman said:

I've pulled the inspection plate and checked and re-check all the bolts. Everything looks normal.

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Same here.

D Chapman said:

Knocking is at idel. Speed the motor up slightly and it goes away. Weird.

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Same here.

D Chapman said:

just can't wait for it to break so I can fix it. At least then I'll know what it was.

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LOL!!!

Same here?.well?sort of.

ptschram said:

Disconnect the torque converter so you can see where the flexplate attaches to the crankshaft. You might have broken the flex plate at that point.

For your sake, I hope not, but it isn't THAT bad to slide the tranny back and reach up in there. I hate undoing the torque converter bolts. If I'm even the slightest bit tired, they piss me off badly!

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I realize this is a possibility.

Not too crazy about the idea of having to do this.