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Old 01-01-2012, 11:06 AM
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400 sbc cam swap problems

I changed my cam out to a little more mild comp 4x4 cam and am now struggling to get it to run right. It just doesn't have any power!

I'm sure that the wires are on correct and that the timing is set correct... I walked away from it the first day and rechecked everything the next day. I also went through and verified the valve adjustment is correct (zero lash plus half turn, studded heads with polylocks).

The engine starts and idles fine, but there is a "diesel" sound that appears to be coming from the passenger bank. It isn't really a "tap" sound like a lose valve but there is definitely some kind of valve train sound.

This engine ran fine prior to swap just didn't like where the power band was. I replaced the cam and lifters, everything else is "as was" condition.

Any help is appreciated!

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Old 01-01-2012, 11:16 AM
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What are the cam specs and did you do a timing chain swap while you were there ?



Cole
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Old 01-01-2012, 11:22 AM
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Before you do anything else, try some better fuel. I suspect that what you have done by using a shorter cam is to raise the cylinder pressure beyond the capability of the fuel you're using and that "diesel" sound you're hearing is detonation. This is what can happen if you don't do the math and just reach out in thin air to pick a cam. I could be wrong, but that would be my best guess.
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Old 01-01-2012, 11:35 AM
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[QUOTE=eloc431962]What are the cam specs and did you do a timing chain swap while you were there ?

It has a comp cam double roller timing chain set in it with less than 20 hours on it, I lined the dot to the zero timing mark (also where key way for crank was).

Cam specs:

.462 intake lift
.480 exhaust lift
111 lobe separation
Full detail: http://www.compcams.com/Company/CC/c...x?csid=96&sb=0
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Old 01-01-2012, 11:41 AM
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Quote:
Originally Posted by techinspector1
Before you do anything else, try some better fuel. I suspect that what you have done by using a shorter cam is to raise the cylinder pressure beyond the capability of the fuel you're using and that "diesel" sound you're hearing is detonation. This is what can happen if you don't do the math and just reach out in thin air to pick a cam. I could be wrong, but that would be my best guess.
This shows my ignorance... I guess I was going with a "lesser" cam so I thought it would Be plug and play. The cam that was in it was a Sum-1107, duration
292/302, Lift .488/.510

My goal was to have more low end grunt with better vacuum...
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Old 01-01-2012, 11:45 AM
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That cam closes the intake valve at 36 degrees ABDC @0.050" tappet lift. An SCR of around 9.5 would be a good match for it.
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Old 01-01-2012, 11:46 AM
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Here is my original engine build with details on engine 406 sbc, build questions

I'm running 93 octane and have heard pre-detonation "ping" before and this doesn't seem to sound the same...
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Old 01-01-2012, 11:48 AM
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Quote:
Originally Posted by techinspector1
That cam closes the intake valve at 36 degrees ABDC @0.050" tappet lift. An SCR of around 9.5 would be a good match for it.
Then I should be ok with my set-up, I'm just a little over 9.5 cr
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Old 01-01-2012, 12:02 PM
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I performed the proper break-in sequence with a good oil additive... Is there a chance that a lifter is collapsed even though they're brand new? I don't believe any of the lobes flattened b/c I went through and readjusted all the valves and they all were functioning... I guess I could use a dial indicator and verify they're all lifting the same? What's a flattened lifter sound like and what are the chances that it could happen from a brand new lifter?
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Old 01-01-2012, 12:07 PM
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Quote:
Originally Posted by manchildau65
I performed the proper break-in sequence with a good oil additive... Is there a chance that a lifter is collapsed even though they're brand new? I don't believe any of the lobes flattened b/c I went through and readjusted all the valves and they all were functioning... I guess I could use a dial indicator and verify they're all lifting the same? What's a flattened lifter sound like and what are the chances that it could happen from a brand new lifter?
All things are possible.
Did you buy the lifters from the cam grinder or did you opt for a "white box special" offered by some other supplier? Warm the motor up, shut it down, remove all the spark plugs, wire the throttle plates wide open, disable the ignition and do a compression test on the motor. Find out what it's doin'. Did you degree the cam when you installed it?
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Old 01-01-2012, 12:17 PM
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Quote:
Originally Posted by techinspector1
All things are possible.
Did you buy the lifters from the cam grinder or did you opt for a "white box special" offered by some other supplier? Warm the motor up, shut it down, remove all the spark plugs, wire the throttle plates wide open, disable the ignition and do a compression test on the motor. Find out what it's doin'. Did you degree the cam when you installed it?
I bought the kit from Jegs, it's all supposed to be comp cam parts...

I didn't degree the cam, I've never done it before, I know it's recommended and wish I would have bought a wheel and learned how to do it...

I'll need to find a compression tester but will follow your guidance.

One thing that I remember is that there was one intake valve that the poly lock set screw seemed to stick out further than the other intake nuts. I remember this b/c I went back through and verified the valve was properly set and after it was still sticking out about an 1/8" further than the rest, could this indicate a stuck lifter?
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Old 01-01-2012, 01:22 PM
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Quote:
Originally Posted by manchildau65
I bought the kit from Jegs, it's all supposed to be comp cam parts...

I didn't degree the cam, I've never done it before, I know it's recommended and wish I would have bought a wheel and learned how to do it...

I'll need to find a compression tester but will follow your guidance.

One thing that I remember is that there was one intake valve that the poly lock set screw seemed to stick out further than the other intake nuts. I remember this b/c I went back through and verified the valve was properly set and after it was still sticking out about an 1/8" further than the rest, could this indicate a stuck lifter?
It would indicate to me that I was using too much valve spring pressure with pressed-in rocker studs. Don't hold my feet to the fire on this info, but I think the limit is somewhere around 250-260 lbs before you begin pulling the studs out of the head. Two ways to fix it:
1. Pin the studs with a Mr. Gasket kit
http://www.race-mart.com/Mr._Gasket-MRG-806G.html
2. Install screw-in studs
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Old 01-01-2012, 02:11 PM
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They're already studded...

I'm running 1.6 ratio crane roller tip rockers on the intake and the same but 1.52 on the exhaust. Same way they were with the last cam (don't have sound logic on the differing ratios, it's just what I have)
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Old 01-01-2012, 04:52 PM
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"The engine starts and idles fine, but there is a "diesel" sound that appears to be coming from the passenger bank. It isn't really a "tap" sound like a lose valve but there is definitely some kind of valve train sound."
You didn't happen to delete a washer you had used previously on the intake installation or use a different length bolt by any chance? In certain locations a bolt that is too long will contact a pushrod and cause problems. I can't remember exactly which locations, but I think they were towards the middle.
You might want to pull the valve covers and set the valves with the engine running at idle. That way you can observe the lift of each valve and see if they appear to be the same to eliminate a camlobe/lifter problem while getting a good adjustment.
Just a thought.
ssmonty

Last edited by ssmonty; 01-01-2012 at 05:07 PM.
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Old 01-01-2012, 05:00 PM
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Thanks for the thought, but i used the same bolts and washers... I know b/c my buddy picked on me about using grade 8 bolts and washers! Good thought though, I used a similar technique intentionally to keep the fuel push rod in place when changing cam... A long 3/8 bolt front front of engine.
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