Well, after 20 years of futzing with engines I have jsut killed my first cam at startup. Wiped about half the lobes off the cam- mostly exhaust lobes. And I can't figure out why.... so I'm down to weird stuff.

It's a Comp Cams XE282 solid flat tappet cam, straight off the shelf. I have been through the valvetrain over and over and it's not the problem. Valve spring pressure on the seat and open are all just a smidge less than spec for the cam (I'm talking about only 10lbs- and it's LESS than spec, not more, so I doubt that's what killed the cam). Valve spring installed height is dead-on. I'm not coil-binding the springs at max lift (plenty of room before coil bind). Retainer-to-guide seal clearance is WAY more than cam lift. Pushrods are stock length, they aren't bent or worn and rocker geomentry is dead-on. Rockers are just standard 1.5 aluminum Harland Sharp rollers. Valve lash was corrrectly set. Disassembly reveled no bent parts or signs of contact between anything- in the valvetrain or valve-to-piston. Like I said, the valve train is NOT the problem.

THis is an in-car cam swap. The old cam we pulled out (also a solid flat tappet but of unknown origin) was in the motor and running without problems for 2 years. This is not a "new engine" scenario. We just replaced the cam and lifters with new (Comp cam and Comp lifters- not a frankenstein) and screwed it back together, everything else is the same. Something I've done MANY MANY times.

Proper assembly lube was used on the cam lobes and faces of the lifters, engine fired quickly and was brought up to 2000-2500 RPMs for 10 minutes immediately after startup, oil pressure was good from the instant after startup, oil level in the engine was good (even overfilled it slightly to make sure plenty got thrown onto the cam by the crank). In short, it was broken-in correctly, just like I've done MANY times before. And yet the cam was dead in 20 minutes.

I'm down to weird stuff.

I checked, on a suggestion by a friend, the location of the cam lobes vs. the centers of the lifter bores. Sure enough, the cam lobes are slightly to the rear of the block relative to the lifter bore centerline. Further checking reveled that the "cheap old" top timing chain gear only has about .155" offset vs. a new GMPP timing chain that has .120" offset. That's at least part of the reason the cam lobes are slightly to the rear vs. the lifter bores. BUT COULD THAT HAVE KILLED THE CAM?? SHOULD THE CAM LOBES EVEN BE CENTERED EXACTLY ON THE LIFTERS??

I have also double-verified this slight offset situation by looking at the wear pattern on the worst wiped lifter. It had worn down and stopped spinning so the lobe wore a nice stright path across it's face. That path is definitely slightly offset. Enough you can tell just looking at it by eye.

I'm stumped on this one, guys. Am I on the right path or is there something else I may be missing? I am VERY reluctant to stab in a new cam with all the same parts just to chew it up 20 minutes later.

 

One other thing- the lifters that were dead but still spinning were worn down on the OUTSIDE edges. In other words, the face of the lifter was higher in the center, lower around the eges. It was NOT worn "convex" like you see when a high mileage cam lobe goes away and grinds out the center of the lifter face.

 

I'm sorry, but I am having a hard time visualizing this. Anyway, a bad cam core? Did you call Comp? I gotta think about this for a while.

Rich Krause

 

A thought:

Is the lobe wear at the rear edge of the lobe?

With the cam slightly aft, do the lobes go all the way to the rear edge of a lifter bore when you sight down the lifter bore?

If 'yes', the contact point of the lifter to the lobe could be at the edge of the lifter rather than nearer the center. As you know the flat tappet cam lobes are slightly tapered to force the cam rearward and to cause lifter rotation. If the lifter ever gets edge contact that's all she wrote. The same idea limits flat tappet lift/degree (cam velocity) but in the other plane.

At least this would explain the edge wear on the lifters.

Still thinking...

My $.02

 

The location of the cam lobes are just SLIGHTLY to the rear of the lifter bore centerline. Not horribly so, just a bit. With the new GMPP timing gear the're just a SMIDGE closer to on-center. We're talking about a hundredth of an inch, maybe. I've ripped into several other SBCs I have laying around and they're all the same way- cam lobes are just SLIGTHLY to the rear of the lifter bore centerline. Appears to be a normal situation. The cam lobe didn't hook the edge of the lifter. The abnormal wear pattern appears to start about .080" in from the edge of the lifter.

I've been asking around with shops I trust and they're all saying the same basic thing- solid lifter flat tappet cams are a crapshoot. They have several go bad right out of the box every year, despite near-"voodoo" type installation procedures. Planets aligned properly, holy water sprinked on motor, meticulous assembly and blueprinting, etc. Comp Cams is apparently the worst offender in this respect, but no manufacturer is immune. It seems the lifters are more often at fault than the cam, but the result of either going bad is the same- quick cam death. Apparently either the lifters or the cam don't get properly hardened in manufacturing somehow, thanks to spotty quality control. That's their theory, anyway.

I've been over this and over this a THOUSAND times. I've checked and double checked everyting. There's NOTHING wrong with the motor or the valve train. The b1tch just died.

I'm told that in most cases it won't happen a second time. How's that for reassuring?

 

Comp does recommend breaking in flat lifters with the inner spring removed from a dual spring installation. (pg. 410 Step 13 of online catalog).

I can't find an "XE-282" listed cam. The closest I found was a "XS282S" or a "282XOS". With the latter, an Extreme Oval Solid, the exhaust is very aggressive and Comp recommends extra oiling. Even the XS282S, which uses EX lobes, has a pretty aggressive profile.

I'm glad to hear cam centering is good.

Still thinking...

 

What is the exact camshaft PN 12-000-5 or something like that? That's going to help figure out what the lobes are.

Bret

 

Hello people, my 383 is the engine Damon is working on. This has been a "chin-scratching" situation. We both are great meticulous technicians and for us to have missed something so important to have this happen just isn't possible. After hearing about all the horror stories about bad lifters from the manufacturer; I feel confident that we did nothing wrong and should be fine when we reassemble the engine again this week.

I'll be in touch with an update as we get one.

Thanks to all who have voiced their help and wisdom.

PS- the part # with Comp Cams is 12-678-4 (XS282S) and the webpage is....
http://www.compcams.com/Technical/Ca...L/128-169.html

We are using the recommended Comp Cams springs, lifters, retainers, and seals !!!!

Heavy

 

If it were my engine, I would follow the breakin advice from Comp quoted above and remove the inner springs if it's a dual spring.

The chance that you got that many "bad" Comp lifters is S-T-N in my book.

Good luck, and keep us informed.

 

SStroker- yep, that's what we're doing. If all else fails, follow directions.

PS- removing the inner spring is NOT part of the directions. Comp told us this only after we reported the mysterious failure. Frankly, I'm kinda groaning at the thought of doing this. Not that the extra work is a huge deal, but I've done MANY cam swaps and never had to go through these gymnastics. It just leaves me with a sort of "uneasy" feeling about Comp Cams products.

To wit:

Spring specs for this cam: 132# @ 1.75" 280# @ 1.25"
Springs we had in it gave: 120# @ 1.77" (actual measured installed height) 272# @ 1.25"

Taking out the inner spring gives us.... 100# @ 1.75" 210# @ 1.25"

Now look at a typical set of teeny tiny 1.25 diameter flat tappet hydraulic cam springs that I use ALL THE TIME without ever a problem....

110# @ 1.75" 265# @ 1.25"

That's not far from the spring specs for the solid lifter cam and I've never flattened a lobe on a hydraulic cam. Makes me wonder how a crappy flat tappet hydraulic cam can take 265# over the nose but a "performance" solid lifter cam can't take 272# over the nose. Like Mark said, it's a chin-scratcher.

Frankly, I'm spooked. I'm now wondering if I've just gotten luckly all these years with flat tappet solid cams. I never went through all these gyrations before.

 

Did you check the camshaft endplay at all. you might have and i missed it.