Potential Cam Failiure?

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Alex.Sciortino

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I've got a 360 that when built, the machine shop had the exhaust valve guides too tight. During cam break in, it hung an exhaust valve, and bent a few push rods on the exhaust. I put a different set of heads on the motor, and ran it, because the lifters looked OK at that time. The car was then driven about 150 miles. At this point, there was a bit of valvetrain noise. I have 273 rockers, figured they loosened up a bit, and readjusted them. I was also fighting an issue where the engine was breaking up pretty bad over 3000RPM. Put another 100 or so miles on it. At this point, the voltage regulator went out, and I parked the car until last week. This week, I have put maybe 10 miles on the car, and it developed a pretty bad clunk in the top end. I have the rocker as tight as it will go, and there is still play. It also happens to be the exhaust on the cylinder that had the valve hang. Car runs like garbage, and there is glitter in the oil. I'm fairly confident that I have a flat cam lobe, but I won't be able to pull the intake and get a good look until I am home from school over Thanksgiving. Any good ways to tell for sure? If it is a flat cam lobe, I'd like to start looking for a 5.9 Magnum to drop in the car over break, so I can drive it until I have the time and money to build something a little hotter.
 
Pull a valve cover turn it over and see if one valve moves much less than the others. If you have one of the cheap harbor freight bore cameras you might be able to fish down through the oil drains in the head to peek at the cam
 
Pull a valve cover turn it over and see if one valve moves much less than the others. If you have one of the cheap harbor freight bore cameras you might be able to fish down through the oil drains in the head to peek at the cam
Not that I can see, but it is hard to tell.
 
I'm going to say this not to be demeaning, but because I've seen this so many times its second nature.

An machinist is getting called out because he set the guide clearance too tight. While this is possible, that machinist would have to be stupid, lazy or both. It's not that hard to do.

What most likely happens is guys *THINK* it's better to use very late (slow, retarded...whatever you want to call it) timing on intial start up because it's "safer"

Well, it ain't safer, it's more likely to cause an exhaust valve to stick that anything else and it needs to be corrected.

When starting any fresh engine, you want MORE timing than you would normally run, or at least the same amount of timing you would normally run.

For example, if you normally time the engine at 35 total and it's all in by 3000, and you fire this new engine with only 10 degrees on it, and you set break in engine speed at 2000, depending on the timing curve you may only have 15-18 degrees on it.

And that, makes a huge amount of heat. And that heat goes right into the exhaust valves and IDK if you set the with .005 clearance that will stick. Every single time.

What happens is you are delaying combustion so late (and there for you complete combustion late) that combustion is still happening, the exhaust valve opens into all that heat and it gets over heated. And it's happening so fast that the valve can't possibly dump all that heat through the seat. Next thing is the valve gets hotter and hotter, the stem gets bigger and bigger and boom, it grabs the guide.

I'm not saying this is your issue. I'm saying I've seen this happen so many times its criminal. If a machinist sets guide up too tight he should quit the business, because as I said, he is either stupid or lazy.

Just a FYI.
 
Yeesh, I'm already cringing... I can guarantee with 100% certainty that it wiped out all the lobes that had bent push rods. There is absolutely zero tolerance for that type of error during a camshaft break in...
 
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I would pull the cam to be sure. Its worth it for peace of mind to know for sure. Some metallic flaking can be normal during break in so dont be too alarmed with that. You still need to investigate it for sure.
 
I would pull the cam to be sure. Its worth it for peace of mind to know for sure. Some metallic flaking can be normal during break in so dont be too alarmed with that. You still need to investigate it for sure.


Not on my stuff. It better be damn little. And it should look like it came off the springs and retainers and nothing else.
 
About the only two things it can really be are the cam is going flat(most likely), or the adjuster screw/pushrod is wearing out.
Compare the length of the adjuster screw to one of the others.
If it’s the same, the cam is done.
 
Why? He already sees glitter.


It’s tells the true story. I cut all my performance filters apart. Some kinds of oil including brad penn that I use has some crazy coloring at times and under different lighting. I’ve gone to friends houses to cut their filters apart when they thought they saw things. Not a big deal
 
It’s tells the true story. I cut all my performance filters apart. Some kinds of oil including brad penn that I use has some crazy coloring at times and under different lighting. I’ve gone to friends houses to cut their filters apart when they thought they saw things. Not a big deal

I agree 100%, but he already has evidence. You know, the stuff they slap ignored in the OJ case? lol
 
I agree 100%, but he already has evidence. You know, the stuff they slap ignored in the OJ case? lol



I try to diagnose my issues even if I am planning on a rebuild. Example: before I pull my small block that I’ve races for four years I will do a compression test, leak down test, filter will be cut apart, and I will even check and redegree my cam. 45 minutes of testing gives me a lot of future data.
 
I try to diagnose my issues even if I am planning on a rebuild. Example: before I pull my small block that I’ve races for four years I will do a compression test, leak down test, filter will be cut apart, and I will even check and redegree my cam. 45 minutes of testing gives me a lot of future data.

I cannot agree more. But a tear down is a tear down. And that's what he's lookin at. lol

When was your last race?
 
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