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Discussion Starter #1
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

See a picture of my Camaro here:

http://temp.corvetteforum.net/c3/1970corvette//view.jpg
 

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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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'69 RS Camaro
355 5-speed 4.11
 

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Discussion Starter #6

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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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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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Discussion Starter #9
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? :confused:
 

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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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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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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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Discussion Starter #15
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. :confused: 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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Well this falls in the category of "do as I say not as I do" but, I wiped out a cam two three years ago. I didn't use the right lube and spent too much time setting valves. I wasn't in a position to pull the engine so I just got a new cam and installed it without checking anything. Three years later, driving to and from work everday and it's still in good shape.
 

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Bob, HotRod69Camaro hit the nail on he head with the rear cam lobe problem. That's the same lobe that went on mine. The old 2000 RPM for 20 minutes rule can contribute to the problem. Most of the cam MFRs now say to VARY rpm between 1500 and 3000 RPM (or something like that) for 20 minutes --- that changes how oil is slung around in the engine so no one lobe stays dry for very long. Rear lobes, especially #8 exhaust, seem to be the most susceptible to going flat due to a lubrication problem.

ps. On the hardness thing. There are only a few manufacturers of camshaft cores --- Comp doesn't make their own cores, so I wouldn't blame Comp for a soft core . . . they just sell more cams than anybody else, maybe that's why you hear about more Comp Cams going flat.
 

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I have had 2 lobes wear down in my pickup. The first cam was what was in it when I got it (I believe a crane...don't know much about it). I then changed to a Comp XE268, and wore down a lobe on it in about 2 years and 5000 miles. I think this was caused by electrical problems (engine not firing right away while cranking the engine with little to no oil pressure)

I changed to a HE268 and haven't had any problems, but I've also sorted out the electrical problems. I probably won't by another comp hydralic cam though.

I'll have to try that EOS next time I build an engine.
 

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Comp doesn't make their own cores (hardly any of the cam manufacturers do), but it's the induction-hardening and heat-treat process AFTER grinding that determines the case depth from the surface, and this is done by the cam grinder. With all the complaints recently about wiped Comp Cams, they may have had a process control problem with their hardening/heat-treat process, assuming people followed the directions for installation and break-in (which isn't always the case).
 

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Discussion Starter #20
Well, the cam was changed out and got the factory 396/375 hp solid lifter cam in. I did a cold lash setting as per Team Chevelle tech notes and the engine started right up. The valves adjustments sounded very close but I went a little loose and will fine tune them after break-in. I primed the engine oil pump for about 5 minutes before start-up. I also added EOS to the engine. I ran it a 2000 rpm for about 30 minutes and did a little varying of rpm during this time. No leaks and no problems. The cam sounds good and engine feels good.

During tear-down, I had checked/inspected the cam bearings and they looked good. I had drained the oil and found a little metal on the magnetic drail plug. I removed the filter, cut it apart and found some very fine metal dust in filter. It looks like filter hopefully caught all or most of the metal from the wiped lobe.....

Well, back on the road again
 
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