I have a .040 over 350 that has been running kinda funny lately. I just installed new headers on it and I noticed that the paint burned off all the primary pipes except #3. It's been a few weeks, and it still hasn't burned off. I checked the rocker arms and they were secure, and the springs didn't seem easy to compress or anything. This motor is carbed, so it's not a bad injector. The plugs and wires were just changed and can be ruled out. I didn't see any metal shavings in my oil. There's no smoke in the exhaust or gas in the oil. I noticed that when I get on the gas too quickly, it pops (through the intake) before reving. Does this sound like the cam failed?

 

sound like a bad cam to me backfire through carb is the tell tale sign to me
chack compression on number three that will tell the story

 

it is pretty hard to wipe a lobe on a roller cam now if you did it is because of lifter failure or a spun lifter which would probably mean 2 spun lifters i would probably guess that you have way to much preload on those lifters that is holding the valves well at least the intake valve open

 

I forgot to mention that it's a hydraulic flat tappet cam. Sorry.

 

sounds like a wiped lobe

 

try a CR check on that cylinder too, could even be a ring sealing issue


if the lifters are traveling and rockers moving in an expected range of travel then it will be something else, you should remove the valve cover and observe rocker motion

good luck

 

if you did wipe a lobe and there wasnt any shaving in the oilpan then they will be in the filter think about how much shavings there would be after "wiping" a lobe if you did you would see it in the oil

 

Yea, that sounds exactly what my car did when I wiped 4 lobes.

Remove your valve covers, and fire it up and check the rockers. It'll be spurting oil like crazy, so move fast. This is a SUREFIRE way to check if you've wiped a lobe.
I made a video and posted it here last summer when I wiped my cam, I wanted someone to confirm it for me. I'm very leery of making decisions for myself. Watch this video if you want to see, watch the second from the back rocker on the drivers side, and I think the 3rd and 4th rockers back on the passenger side...
https://webdisk.ucalgary.ca/~jmknopp...l/rockers.divx

 

Like Sonix said, they only way to know for sure is to pull a valve cover and watch the rocker arm motion - or lack thereof. If a rocker appears to be moving less than it should compared to others, you have a problem (could still be a collapsed lifter or bent pushrod).

A compression check will tell you nothing - its a waste of time!

 

trick tuners keep a set of old stocker V8 cover around with the centers cut out. So you can run the motor without spewing to much oil all over the place, also lets you watch how things work and adjust as needed with attlot less mess.

Or get some 2 piece covers made

 

If that cylinder isn't firing, then you should have a very noticealbe miss vibration. Could be caused by a vacuum leak to that cylinder. Check the runner for any vacuum ports. If there are rubber hoses pinch the hose and listen for a noticeable change in the RPM/smoothness of the engine. You may have to check every hose, and don't forget the brake booster.

 

I'm gonna try looking under the valve cover in a few minutes to see what the rockers do. If they seem ok, I'll get a compression check. As far as leaks, I think I have a small vacume leak at the brake booster.

 

A vac leak anywhere above the intake will cause all cyls to lean out....

Could be the intake gasket torn at that runner or something though.

Spray a little carb cleaner around there while the engine is running (but not hot!) and see if the idle changes. that will tell you if you have any vac leaks.

 

Well, it looks like the rockers are operating the valves like normal. And there is small metal shavings in the oil after looking harder. Does this still seem like the cam failed? I'm already in the process of finding a replacement motor. I was really hoping to keep this one working since it was such a good foundation - high nickel block (4bolt), bored .040 with forged pistons and PM rods and steel crank.

 

Did ya go with a hi volume/psi oil pump?
cam could be walkin on ya making them shavings.

Allot of folks get in trouble by just slappin in one without pre thinking, they can also oil starve the motor easy if you didn't do oil return mods.

Best to get an adjustable one.

 

If it looks like all your rockers are moving the same amount, then you're probably right. It might have lost some lift, but usually you lose A LOT.

You said the paint didn't burn off one header, vs the rest. That's a red flag. Check those rockers very carefully. Then when it's idling, pull the plug wire on that cylinder, and shove another plug into the wire, and hold it against the block - make sure it's sparking. Also pull the plug and make sure it doesn't look super carboned and caked on.

Either the ignition on that cylinder is bad, or the cam lobe(s) is gone. Not much else would cause it to be a dead hole.

 

couldnt it be firing into the intake do to open valves?

 

Well, I'm pretty set on replacing this motor after seeing the shavings in the oil. I'm sure changing the oil/filter won't get the shavings out, will it? If not, I plan on finding a roller cammed 350.

 

no.. that only happens if your timing is really off.. valves usually dont stick open unless you have a bent valve.. not likely in this case

gunz4life2, a oil/filter change will not get all the shavings out.. its all in the oil galleys and i bet you still have a load in the oil pan.. even the lifters might have some in them

 

sorry what i meant was could valve lash be set to tight holding a valve open...

 

So this motor definately needs to be taken apart and rebuilt, right? If I can find a good replacement motor, I won't bother with this one anymore.

 

check that.....if you dont hear knocking or anything coming from the motor chances its not a bad lobe.......in normal situations you would know right away if you wasted a lobe. it would not be hey this is running funny, it would be ooooooohhh shhhhiiiiiiiiiiiiiiiitttt and you would pull over and have the car towed.

 

Well no, it's kinda like - gee, what is that? No matter what tuning I do to the carb, it seems to get slower...? If I give it too much throttle it backfires? What the heck is going on here? etc etc.
I drove mine for about a month with it getting slower and slower before I realized I had lost 4 lobes.

It's not like the shortblock is toast when you get a bad cam. New bearings and a clean up will save you. You don't need new pistons, new crank, or a bore job. I'd just clean up that block.

But! If your rockers are moving the same amount, i'm thinking your cam is ok. Check the plugs to see if one shows a bad cylinder. If you're pretty sure it's a hard part that's bad (ie, requiring a rebuild, and not just a new gasket or plug wire), then pull the motor and tear it down and find out what's up. Bearings and gaskets are CHEEEP compared to pistons, crank, block, machine work - etc.

 

well yea
it could be rounding slowly
too bad we havent invented x ray vision yet ha ha
sonix makes a good point gaskets are cheap and you get to spend a few days with your motor!

 

i was in the EXACT same situation before.. car was going for about a month with the downed cam.. lost 7 lobes.. tried tuning and lowend was pretty good for only 7 cylinders.. still had a healthy chirp in third.. but top end just seemed to get weaker and weaker.. tapping occured again and i got a remote starter and finally found the #4 cylinder closed shut

 

Well I think I'm gonna take your advice and pull it apart/inspect it and clean it and install new bearings and rings if needed(along with a new cam). Thanks for the help guys.

 

That's a bummer, make sure n take lots of pics for us.

Next time around I dunno, maybe revamp your start up n break in.

use more fancy break in products or less depends on how ya did it the first time and or what stuff ya used?

 

maybe look into a hydraulic roller so you dont have this problem again

 

Easy way to see if you rolled a lobe is to remove teh rocker and put a good dial gauge on the pushrod and measure the lift at the lobe. Good as X-ray vision.

 

I looked into a roller setup, but it's more than I want to spend right now, but it's definately in my future plans for the next motor. I ordered a cam for this motor, but now I realized that I ordered more cam than my valvesprings will handle. My valvesprings are supposed to be rated at .525 lift, but my cam is gonna come out to .526lift. Can I get by with them until I buy new springs? Thanks.

 

whoa whoa, .001" over? Nuh uh.

Yea, you'll be fine. You'll only have .074" clearance rather than .075" or so. No biggie.

 

Roller cams are capable of wiping too. This was my LT1 with around 100k on it, and ive seen other lt1 doe this too, always occurs within the first 4 lobes.

The nose has wore down around 1/8 inch, and the opening ramp has a divit in it.

 

I agree with this. A nearly round lobe will still feed the cylinder at cranking rpm. I do think you should do a compression test before you pull it down. Everyone seems to have forgotten what the symptoms of a burnt exhaust valve is.

 

How do you burn an exhaust valve? Someone else suggested I pull the heads and check the vavles, thinking I had a damaged valve. I'm gonna try to get a compression test on wednesday. The cam is on it's way already, so we should have it here soon.

 

Either a defect in the valve (bent) or seat or something mechanical that prevents the valve from closing completely such as a clogged lifter that pumps up and won't leak down or binds in the bore on the way down. Let us know the results of the compression test. If it's low, do a pressure test before you tear it down to pinpoint where it is leaking to.

 

I wouldn't 2nd guess anything if you don't find much and just swap in a new cam. If yout not 100% sure on them springs pull me out, still new and are sellable. Get some fancy oval springs. Spring material isn't round but oval, better newer design. Hope ya do new lifter too.