Wiped cam lobe? - Team Camaro Tech
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post #1 of 22 (permalink) Old Sep 14th, 02, 05:18 PM Thread Starter
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In my Camaro, I am running a 396/375 short block with a Comp Cams XE274H (Intake.552/230
Exhaust.555/236) with headers. The engine has about 500 miles on it and it has began to backfire thru the carb on acceleration. I checked the timing and it is right on. The plug wires are correct and the plugs look good. There seems to be a rattle or noise in the lifter/cam area. I am about to tear into it and take a look.......any ideas? thanks

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'69 SS 396/375hp L78 M21 3.73 Fathom green/medium green interior

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post #2 of 22 (permalink) Old Sep 14th, 02, 05:27 PM
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Pull the valve covers and see if you have a rocker that's barely moving. It's a dead giveaway for a bad lobe.

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post #3 of 22 (permalink) Old Sep 15th, 02, 03:22 AM
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I second that motion, flat cam.

-Mark.
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post #4 of 22 (permalink) Old Sep 15th, 02, 06:57 AM
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Don't forget pushrods bend before they break. A rocker not moving as much as the others deserves a look at the pushrod/s.

Good Luck,
John
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post #5 of 22 (permalink) Old Sep 15th, 02, 07:59 AM
 
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Tips can come off the end of pushrods as well (if they are the pressed in type, instead of the one piece type).


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David
Camaro - '68 327 Coupe, '86 Z-28 IROC 305 TPI
Corvette - '73 Mako Shark II, '82 Cross-fire, '01 Coupe
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post #6 of 22 (permalink) Old Sep 30th, 02, 08:57 PM Thread Starter
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Following my trouble with the Comp Cams XE274, I have been following this post and reading his problems with Comp cams:
http://www.chevelles.com/forum/Forum4/HTML/011659.html

Interesting findings on the rockwell numbers for his cam....

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'69 SS 396/375hp L78 M21 3.73 Fathom green/medium green interior

See a picture of my Camaro here:

http://temp.corvetteforum.net/c3/1970corvette//view.jpg
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post #7 of 22 (permalink) Old Oct 1st, 02, 07:44 AM
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I had a Comp go bad late last year, but thought is was due to a bad contamination of the motor oil. Had a second go bad, in a different motor, this one died because of the distributor gear. This time, I bought a Crane....
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post #8 of 22 (permalink) Old Oct 1st, 02, 11:38 AM
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I just had a 294s go bad during breakin in my 383. The odd thing was that it was the rear most lobe on the cam - #8 exhaust and the rest of the lobes looked absolutely perfect. The lobe was completely gone after the 30 minute break in and about 50 miles of "figure out what's wrong" driving.

I assumed the problem was initially caused by me not following the directions. I was using a tall 1.47" dia single spring with specs very similar to the 986 springs with the cam that failed. But Comp wants you to break the cam in with only the outer spring and 1.5 rockers, I used the single spring equivalent to their double spring.

I since have installed a new cam (they still replaced it for free) following Comps instructions EXACTLY and it is running fine after 75 miles with 1.6 rockers.

I have also heard about others that have installed Comp roller cams that have wiped multiple lobes during breakin, but in each case Comp's break in instructions were not followed exactly. I'm not defending Comp here, just emphasising how important it is to follow the procedure.

What a PITA to replace a flat cam !
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post #9 of 22 (permalink) Old Mar 1st, 03, 06:43 PM Thread Starter
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Thumbs down

Well, I finally got around to tearing down the motor today and found #8 exhaust lobe wiped pretty bad and the lifter kind of wore on the bottom. All the other cam lopes looked perfect and the other lifters also looked like new.
I was running the Comp Cams XE-274 cam and
began to have backfiring thru the carb after about 500 miles. I am now going to the 396/375 hp solid lifter facory blueprint cam from Crane.
I was wondering why all the other lobes look great if I may have done something during the break-in to cause this as Comp says??? I would have thought if one lobe was damaged, others would have been similar? Could it have been the hardening process at the factory?

'69 SS 396/375hp L78 M21 3.73 Fathom green/dark green vinyl top, medium green interior
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post #10 of 22 (permalink) Old Mar 1st, 03, 07:38 PM
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Next time, try adding a can of GM EOS Engine Oil Suppliment. It is made for new engines and eases cam break-in.
David
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post #11 of 22 (permalink) Old Mar 3rd, 03, 06:45 AM
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To chime in on what David said, In the late 60's and early 70's, I worked at a chevy dealership. I rebuilt and installed a lot of engines and short blocks. During this same time, i was also building quite a few race engines. I must say, I have NEVER had a cam go flat. I can't contribute it to any one thing or any specific cam. I cannot say I never made a mistake, as I am the KING of crossing plug wire #5 and #7. All in all, All my engines had one thing in common. Each engine I did had a can of EOS in it. Whether it was a dealership job or a race motor, none ever went out the door without EOS. I was taught (by the best mechanic I ever knew) to add it and I did. I learned very on in my career to never question my mentor. Rest in peace David.
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post #12 of 22 (permalink) Old Mar 3rd, 03, 06:54 AM
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Actually I am suprised it took 500mi. Make sure there isn't another problem like coil bind or rockers hitting the studs. You must get all of the ground up cam out of the motor. It usually requires a complete teardown to do it correctly. Definately use EOS it is the best you can use.
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post #13 of 22 (permalink) Old Mar 3rd, 03, 11:49 AM
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I was talking to Comp about a tick. Turned out not to be a lobe. But they said the lobes at the rear of the motor tend to have more problems because the sling of oil off the crank is hindered by the oil pump getting in the way
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post #14 of 22 (permalink) Old Mar 3rd, 03, 06:40 PM
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The oil restrictors are for keeping more oil down below. They are for solid lifters not hydrolics which need the oil. Good luck.
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post #15 of 22 (permalink) Old Mar 4th, 03, 03:30 AM Thread Starter
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I drained the oil and didn't really find any metal. I also run a drain plug with a magnet. I had some really fine metal dust particles but no large pieces. I looked at the cam bearings and they looked really good. I plan on cutting the oil filter open to see if it caught all/most of the metal.....also, several weeks ago I purchased a few bottles of EOS, I plan on using it.
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