Cam Lobe Help
Thread Starter
Pro
Joined: Oct 2000
Posts: 558
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From: Vancouver, B.C., Canada
Cam Lobe Help
Long story short. I have been chasing a miss for a few weeks now and have had no luck. Been through the ignition at length. Started worrying that a cam lobe (big block) was going south so I bit the bullet and pulled the intake. Took the time to carefully measure the lobes (measurements below). The cam and lifters look pretty good to me but I'm no bloody expert. Thoughts/opinions please.
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All the hydraulic lifters look like this. There in very good shape.
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[/IMG]All the hydraulic lifters look like this. There in very good shape.
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Thread Starter
Pro
Joined: Oct 2000
Posts: 558
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From: Vancouver, B.C., Canada
That is a hard question to answer. Plugs #2 & 3 are a little more blacker than the other plugs. I wouldn't look at them though and say "gees there must be something wrong with that cylinder".
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
it's really hard to diagnose a miss; however, I can tell you the biggest catch that gets me on misses. Improper lash.
I have a thumpr cam in my c3, and it is only marginally good (meaning no intermittent miss, or backfires) with 1/8 turn from zero; I've had other motors where it needs nearly 3/8 turn to get proper lash.
YRMV
I have a thumpr cam in my c3, and it is only marginally good (meaning no intermittent miss, or backfires) with 1/8 turn from zero; I've had other motors where it needs nearly 3/8 turn to get proper lash.
YRMV
Race Director
Joined: May 2006
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Miss
I dont know what kind of wires you are running to the plugs but have you checked the resistance on those two wires compared to the others?
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
A miss without any clatter from the valve train, I'd get out the water bottle and start spraying plug wires and the cap.
With compression readings like that, the ones I'd be concerned about are #3 and #5- exactly the same number in adjacent cylinders is not noted for being a good thing. Time for a leakdown test.
With compression readings like that, the ones I'd be concerned about are #3 and #5- exactly the same number in adjacent cylinders is not noted for being a good thing. Time for a leakdown test.
Thread Starter
Pro
Joined: Oct 2000
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From: Vancouver, B.C., Canada
Le Mans Master
Joined: Oct 2002
Posts: 7,098
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From: Las Vegas - Just stop perpetuating myths please.
All cylinders within 10 psi is good. How many miles on cam/car?
If u had a wiped lobe u would have noticed the lifter wouldn't come out. And the lifter face would be concave instead of convex.
My guess from here in California would be a hole in a plug wire (insulation)/burnt wire. Open the hood in the dark and look for sparks with the engine running.
Hope this helps,
cardo0
If u had a wiped lobe u would have noticed the lifter wouldn't come out. And the lifter face would be concave instead of convex.
My guess from here in California would be a hole in a plug wire (insulation)/burnt wire. Open the hood in the dark and look for sparks with the engine running.
Hope this helps,
cardo0
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Advanced
Joined: Apr 2013
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From: newtown ct
just asking ALL spark plugs were removed during the compression test ? what kind of carb and intake set up?open plenum or dual plane.and I have done this my self once with a corrected distributer cap there are wires that can be crossed and not cause backfire but a strange miss that with a performance cam the miss gets flatter with engine load at speed double check fire order and wires good luck
Melting Slicks
Joined: Jul 2006
Posts: 2,291
Likes: 493
From: Salmon Arm, BC
What type of intake and carb?....maybe it's a lean miss....
with 2&3 a little blacker that may be poor or incomplete combustion rather than a rich mixture.
How about the carb base gasket....4 hole or open??
with 2&3 a little blacker that may be poor or incomplete combustion rather than a rich mixture.
How about the carb base gasket....4 hole or open??
Thread Starter
Pro
Joined: Oct 2000
Posts: 558
Likes: 22
From: Vancouver, B.C., Canada
All cylinders within 10 psi is good. How many miles on cam/car?
If u had a wiped lobe u would have noticed the lifter wouldn't come out. And the lifter face would be concave instead of convex.
My guess from here in California would be a hole in a plug wire (insulation)/burnt wire. Open the hood in the dark and look for sparks with the engine running.
Hope this helps,
cardo0
If u had a wiped lobe u would have noticed the lifter wouldn't come out. And the lifter face would be concave instead of convex.
My guess from here in California would be a hole in a plug wire (insulation)/burnt wire. Open the hood in the dark and look for sparks with the engine running.
Hope this helps,
cardo0
Cam has been in for a number of years (approx. 10). Of course this car only gets driven in the summer so we're not talking about a lot of miles here. No racing, just cruising. All the lifters came out very easily and look very good to me, as the photo above shows.
All the plugs were removed for the compression test.
Carb is an Edelbrock 750 with a Performer intake. Been very reliable for 12 years. Car ran well before being put away last fall for the winter.
My decision right now is to I put it back together, as is, or keep going to remove/replace this cam and lifters. It's a lot of work!!
Last edited by Kim72; Apr 27, 2013 at 04:45 PM.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
The choice is yours but u still don't know the miss fire cause. No one else knows but u whether u want to replace the cam. But if your asking if u can reuse the existing cam and lifters - yes u can if u put those lifters in the same holes they cam out of. After that i would take it to a dealer where they have a scope diagnostic machine and are trained how to use it. They should be able to diagnose for 1 hour labor/$100. Your getting to where its becoming expensive and time consuming looking by disassemble.
cardo0
cardo0