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Symptoms of a flattened cam?*UPDATE*

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by muddin4fun, Nov 20, 2001.

  1. muddin4fun

    muddin4fun 3/4 ton status

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    <font color=red>Update-go to last reply</font color=red>
    Gawd I hope not. &lt;img src="http://coloradok5.com/forums/images/icons/frown.gif"&gt; But can someone give me some symptoms?
    I've got a carb I can throw on it tonight and I'm also going to check the plugs (again) to see if they're fouled out. I've got some major backfiring and it's falling on it's face when you accelerate. Right now, if I keep it under 25, it won't backfire. How tight would the valves have to be to flatten the cam? I've got hydraulic lifters.

    Peace and stuff &lt;img src="http://coloradok5.com/forums/images/icons/tongue.gif"&gt;,

    Muddin

    &lt;a target="_blank" href=http://www.geocities.com/muddin4fun79blazer&gt;www.geocities.com/muddin4fun79blazer&lt;/a&gt;
    <P ID="edit"><FONT class="small">Edited by muddin4fun on 11/26/01 07:29 AM.</FONT></P>
     
  2. Rob 85K5

    Rob 85K5 1/2 ton status GMOTM Winner

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    Re: Symptoms of a flattened cam?

    Listen for a rattling sound inside the valve covers. If the lobe is flat, the rocker arm may be off of the pushrod and be moving around.

    Rob

    <font color=orange>Bleedin' Chevy Orange</font color=orange>
     
  3. RedDwarf

    RedDwarf 1/2 ton status

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    Re: Symptoms of a flattened cam?

    My guess is that you have made an accurate diagnosis. Cams are cheap though. Auto Zone has a Melling cam with good torque for 90 bucks. Add 25 for a new double roller chain and you're in business.
     
  4. jimmyjack

    jimmyjack 1/2 ton status

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    Re: Symptoms of a flattened cam?

    Take of your valve covers and look for a rocker that isnt lifting. Thats a dead giveaway! Is your distributor good and secure? Plug wires burned at all? My blazer ran great at 40 and under but if I stomped on it it was horrible. Turned out I had 3 burnt wires. Couldn't see them til I removed them and really checked them out though! Good Luck, hope its nothing big

    That jeep thing? Yah I understand it....... Like my Blazer? <a target="_blank" href=http://community.webshots.com/user/blazerk5>http://community.webshots.com/user/blazerk5</a>
    Jim
     
  5. K5Jimmy

    K5Jimmy 1/2 ton status

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    Re: Symptoms of a flattened cam?

    I like the burnt wire theory also, 'specially with headers.....you can sometimes feel "hard" spots on the unblemished wire that's burnt.....I've had a bad coil act weird like that also, although it was non-HEI....I had a burnt wire that would backfire like hell when I romped it, but acted ok if I just rolled smoothly on the gas.....I'm havin' a hard time gettin' to a flat lobe on a motor as new as yours.....isn't it still in warranty?....I'm takin' a hard look at the NAPA motor you got as a replacement for mine this spring.....I'd hope it was way more durable than that.......Joleen deserves the best......JD

    Stuck?...Hell no..I still got some gas left..
     
  6. mike reeh

    mike reeh 1/2 ton status

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    Re: Symptoms of a flattened cam?

    I lost a lobe (if i remember correctly an exhaust lobe) on a stock 77 cam.. it idled and stuff pretty good but if you stomped on it it fell on its face and if you kept it at full throttle you could hear metal noise in the engine.. if you babied it, it was definately driveable. drove me nuts, i didnt even consider the lobe.. tried different carbs, distributors, fuel pumps, etc..

    the easiest way to check though is start the engine with the valve covers removed.. might as well adjust the rocker arms while you're there too...

    I got a "rv" cam from a machine shop (generic brand but said it was a bigname in disguise) for cheap... never run used lifters on a new cam.. just get 16 new lifters while you're at it.. and a timing chain would be good too, like was mentioned.. you can have it all fixed in a weekend if you play your cards right. probably for under $150 too..

    mike
     
  7. RedDwarf

    RedDwarf 1/2 ton status

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    Re: Symptoms of a flattened cam?

    You don't even have to start it. You can just turn it over with a ratchet. That's how I discovered a bad cam once. It was completely flat, and the lifter had a big dish in it. It was popping like you described.
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: Symptoms of a flattened cam?

    I definitely wouldn't run a $90 cam in a $3,000 motor.

    If your cam is a Comp, it's pretty typical from what I hear. It will be covered under warrenty in that case.

    If I were you, and I'd payed that much for a crate motor, and it had a flat cam, I'd probably pull the whole motor. God only knows what all those little bits of metal did to that motor when the cam went flat. Sounds like a replacement of the motor is your best bet.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  9. chevyracing

    chevyracing 1/2 ton status

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    Re: Symptoms of a flattened cam?

    could be a collapsed lifter too. If it is an exhaust lobe you can get some popping from the carb. If it is an intake lobe it will run rough and that cylinder will not heat up like the others. Also could be a warped valve. Do a compression check.

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=)

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  10. muddin4fun

    muddin4fun 3/4 ton status

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    Re: Symptoms of a flattened cam?

    I was gonna work on it last night, but decided not to so it's parked. I can get a cam for free. I bought the long block only a few months ago. This weekend I'll look at it. It sure does sound like a bad lifter or flat lobe. [​IMG].
    I'll update ya'll this weekend (prolly friday is when I'll look at it-no work! [​IMG]). Thanks guys! I'll keep ya'll posted.

    Peace and stuff [​IMG],

    Muddin

    <a target="_blank" href=http://www.geocities.com/muddin4fun79blazer>www.geocities.com/muddin4fun79blazer</a>
     
  11. muddin4fun

    muddin4fun 3/4 ton status

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    Re: Symptoms of a flattened cam?

    Oh...I'm also gonna take a good look at the wires...possibly replace them. When I changed the spark plugs a week ago, they looked a little on the crispy side. Is there a good way to do an at home test on them?

    Peace and stuff [​IMG],

    Muddin

    <a target="_blank" href=http://www.geocities.com/muddin4fun79blazer>www.geocities.com/muddin4fun79blazer</a>
     
  12. Butch

    Butch 1/2 ton status

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    Re: Symptoms of a flattened cam?

    If your cam went flat that quickly on a new motor your oil will be shiny. Pull your dipstick and hold it up to a strong light and see if it shines. When I build my motor the cam I got had not been hardened properly and I lost three lobes plus the fuel pump eccentric in about 50 miles after breaking the motor in. If it is the cam make whoever you bought it from stand good for new bearings and turning the crank because they will be toast. Any change in oil pressure?

    I thought I was wrong once,
    but I was mistaken
     
  13. chevyracing

    chevyracing 1/2 ton status

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    Re: Symptoms of a flattened cam?

    You need an ohm meter and just check the resistance in the wires. If you bend them and it sounds like someone stepped on a box of frosted flakes or feel crunching they are shot. Too many people take the wires for granted. They are one of the most important external components of an engine.
    Oh, the resistance should not be over 8000 ohm per foot of suspression wire. On point systems check the wire with the ohm meter connected to each end of the wire, on electronic systems check one end of the wire (spark plug side) and remove the dist cap with wires still attached and check it through the cap at the wire contact where the rotor picks up.
    One more thing to is to make sure you have not routed your wires wrong. (ie:parallel and touching)

    John

    Like to go sloppin' 'round in da mud in a rapid fashion....=)

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  14. Mudzer

    Mudzer 1/2 ton status Author

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    Re: Symptoms of a flattened cam?

    Lara,

    A flattened camshaft is at times difficult to detect. You almost cant detect it just by removing a valve cover. Camshafts almost never completely flatten a lobe (unless it has like 2 million miles on it), it may loose some of the profile, but usually never wear down to completely flat. So, trying to turn over the engine and watching the rockers is difficult unless you have a trained eye! Didn't you just rebuild that engine a while back? Has it always driven this way? I would say either you have a timing issue or carb problem. Your Hydraulic lifters were probably set to zero lash. I woudnt think unless you had an oiling problem or really cheap camshaft, that the lobe was worn flat in that short of time. Give me your info on the type of carb. You say this only happens on acceleration? Is this Hard acceleration or just normal driving? What RPM does this happen at? Does it smooth out after acceleration? How many miles on the rebuild? Did you use a nylon gear on your timing chain?

    Mudzer 1978/91 K5
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  15. muddin4fun

    muddin4fun 3/4 ton status

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    Re: Symptoms of a flattened cam?

    It's a crate motor. It's got about 5000 miles on it. Last week is when it all of the sudden went to the crapper, but yesterday is when it really hit bottom. At first, it was ideling real rough. I changed the plugs and it fixed it for a day, then went back to ideling a little rough, but not as bad. The old plugs were fuel fouled. Then, yesterday driving home for lunch (it made it to work that morning just fine) it would just fall on it's face when you accelerate normal to fast. If you barely touch the pedal, then it wouldn't stumble. Then, when the rpms got to a normal range or high range, it would back fire constanly. You can only hear it out of the pipes. A few times it backfired thru the carb. Not a real loud bang, but that "Pooofst" sound? If I'm on flat land and stay under 25 (TH350 with 33's and 3.73's-I don't have a tach, but with that combo whatever the rpm's would be at that speed) it won't backfire or I'm not hearing it backfire. If I go up a hill and am trying to keep it at least at 25, then it backfires, stumbles, spits, cusses...you name it. The timing is set at 6 degrees and the disty isn't loose or anything. I'm running a 600cfm performer edelbrock. I have a new one in the garage that I am going to put on to rule out the carb. Seemed a little fishy that the plugs were fuel fouled. If I cruise at any speed above 25, it will backfire constantly. The motor was a crate motor BTW. A long block.

    Peace and stuff [​IMG],

    Muddin

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  16. muddin4fun

    muddin4fun 3/4 ton status

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    Re: Symptoms of a flattened cam?

    I'll get the dig cam out and get some video so ya'll can hear

    Peace and stuff [​IMG],

    Muddin

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  17. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Symptoms of a flattened cam?

    Weak crispy wires will do that too...bad miss under load. I used a small inductive lead tester to confirm my then 6 month old Accel wires were crap. My Accels were routed properly and were not burnt...just junk right out of the box.

    Rene

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  18. Mudzer

    Mudzer 1/2 ton status Author

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    Re: Symptoms of a flattened cam?

    Ok, sounds like a fuel problem for sure. I had a street car I used to dragrace. I installed an 850 Holley Double Pumper and had the same problems. At high RPMs the carb would cut out and backfire through the exhaust so bad, I could see orange sparks coming from the exhaust in my rearview mirror. My problem was being too rich. You can get similar reuslts from being lean. Belive me, your 600 may sound a little small for a 383 at first, but it really depends on several factors. I calculated your Optimum Carb Size using a Volumetric Efficiency of 85%, max RPM of 5500, and 383 Cubic inches. This result was 518 CFM. You also probably require about 20 Gallons Per Hour fuel requirement. I think I would try a known working carb, then go from there. Don't throw away that Edelbrock, just buy some new metering rods for the secondaries. Sounds like thats where the problem is. Perhaps the primaries need some fine tuning as well. Secondly, there is a possiblity the accelerator pump is not delivering the proper shot of fuel, whether it be too much or to little, I am not sure.

    Mudzer 1978/91 K5
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  19. muddin4fun

    muddin4fun 3/4 ton status

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    Re: Symptoms of a flattened cam?

    I've got a brand new edelbrock performer sitting in the box in the garage. That's the one I was talking about putting on there.
    My plan of action is as follows [​IMG]:

    1. Test the wires
    2. Pull plugs and look at them-check compression while I'm pulling them
    3. If all that checks out, replace 'defective' carb [​IMG]
    4. If that doesn't work...kick the tire, rant and cuss, have an alcoholic beverage and come back to CK5 for help [​IMG]

    Peace and stuff [​IMG],

    Muddin

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  20. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Symptoms of a flattened cam?

    <blockquote><font class="small">In reply to:</font><hr>

    1. Test the wires
    2. Pull plugs and look at them-check compression while I'm pulling them
    3. If all that checks out, replace 'defective' carb
    4. If that doesn't work...kick the tire, rant and cuss, have an alcoholic beverage and come back to CK5 for help

    <hr></blockquote>

    Sounds like you got it under control...[​IMG]

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
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