Where do flat tappet cams usually fail?

[plovett]

Where do flat tappet cams usually fail?  I mean physically, on the cam itself. Is it on the nose, at peak lift, where the spring pressure is highest?  Or on the intake ramp where the acceleration rates are the highest?  On the base circle because the lifter is bouncing off it while closing?  (I wouldn't think so, just throwing it out there).  The lifter contacts all parts of the cam so it's hard to tell by looking there....

What is the critical area?

thanks,

paulie

[My427stang]

First, always hard to tell because once the lifter stops spinning it takes out the entire lobe very quickly

My hunch would be most failures are not "typical" but would be after the lash ramp as the lifter is accelerating quickly and should be spinning. 

I deduced that by the delta in load, plus the requirement to spin, any other point on the lobe the lifter is already spinning or it has significantly reduced load.

The only clarifying statement I would add is, anywhere on opening ramp or nose could easily take out a lifter if the lifter stalled due to stuck valve, etc. 

One last comment, I have never seen a bad cam (other than the late 70s/80s Chevy SBs) that didn't have a good reason for a failure.  Too much spring pressure before break in, stuck valve, rockers hitting retainers, tight lifter bores, etc.  I am all about the right oil, but if it's in there and you lose one, barring extreme lobe designs, there is usually a reason that could have been prevented.

[plovett]

I think what you are saying is that most cam failures are secondary failures, caused by a separate primary failure?  Or caused by incorrect selection of parts?

I guess what I am wondering is when a cam crosses the line by becoming too aggressive for the associated parts, where is that line?  The opening ramp?  Probably lots of different possible answers.

thanks,

paulie

[My427stang]

I think what you are saying is that most cam failures are secondary failures, caused by a separate primary failure?  Or caused by incorrect selection of parts?

I guess what I am wondering is when a cam crosses the line by becoming too aggressive for the associated parts, where is that line?  The opening ramp?  Probably lots of different possible answers.

thanks,

paulie

Yes I am saying that, but not necessarily a separate primary failure per se, could be assembly error, break in error, wrong parts, poor oiling design, quantity, temperature etc.

I am spit balling, but knowing that the lash ramp is less steep and gets the lifter spinning, the transition to the more aggressive opening ramp would be where I would expect failures happen. Once it's established on that ramp, the spring pressure is increasing but doing so in a linear value unless the lifter goes out of control, but barring that, there are likely less pressure spikes then the initial acceleration off the lash ramp.  BTW that initial load as it starts climbing the ramp spikes far beyond spring pressure resistance and leverage disadvantage.

Harold Brookshire used to talk about famps and how they affected both the lifter and the valve.  Maybe do some searching on old S/T posts under UDHarold.   think the answer for "what is too aggressive" needs to first  identify "for what? 

Too aggressive of an opening ramp can stall a lifter and eat a lifter, then lobe, or can even dig a lifter into the side of a lobe

Too aggressive of a closing ramp can make noise or even cause valves to bounce, correct with spring pressure,back to scenario 1  LOL  Or the floor can drop out below the lifter that it can't follow a cam, that's why rev kits were invented.

If you look at the intensity values of the lobes, you'll see MI which is the difference between advertised (.006 for hyd or for solid cams .020) and .050, but more importantly look at the shape of the lobe with the number broken into two values behind it (at least in Comps catalog)

In my opinion, under 27 or 28 MI and 13/14 on a flat tappet on both sides is getting very stout for something that doesn't get torn down much,  Opening side less of an issue for valve bounce, but more for eating a cam during break in, closing side will affect bounce, but too slow gives you extra overlap

It's funny, for a while we all thought you needed to snap those valves open and shut as fast as you can, limited only by valve control.  Until you cannot meet the valve events you want, there really is no reason to snap them open so hard.  Usually the first cost of too lazy of a lobe is overlap, then you get into valve control and durability  if it's too aggressive.  Always a trade off

[plovett]

It's funny, for a while we all thought you needed to snap those valves open and shut as fast as you can, limited only by valve control.  Until you cannot meet the valve events you want, there really is no reason to snap them open so hard.  Usually the first cost of too lazy of a lobe is overlap, then you get into valve control and durability  if it's too aggressive.  Always a trade off

Good thoughts.   Thanks!

One thing I have noticed many times on cam tests is that when LSA's and ICL's and cams with different "aggressiveness" are tested is that the compression ratio isn't changed.  Not that that would be practical at all, but....

For instance, if you have one cam with an LSA 108 and an ICL of 104 and another with the same lobes, but the LSA is 114 and the ICL is 110, then the one with the later ICL could take maybe 0.6 more points of compression.   That's not a huge amount , but it is something. It could be 4% more power. Usually the tighter LSA (and earlier ICL) makes more torque, but if you estimate what the higher compression ratio would do with the wider LSA (and later ICL) it comes out about the same.

Maybe the same could be said when comparing "aggressive" and "lazy" cam lobes?

paulie

[e philpott]

I had two cam failures back in the days of no zinc in Mobil 1 that nobody new about yet with Schubeck lifters back in 99-2000 , both failures where at the distributor gear to Cam drive gear that initially thought was the caused by the strong oil pump spring but the second one was with stock low pressure spring so that lead to the low zinc problems with oil , and I'm still using the lifters to this day , sloshing  the cam in oil didn't work back then with low zinc oil but obvious not a problem now days , the Cam I use is a Comp 304B , 304 Adv , 266-276 at .050 and 626-659 lift and have roughly 5K miles on it now

[Falcon67]

One last comment, I have never seen a bad cam (other than the late 70s/80s Chevy SBs) that didn't have a good reason for a failure.  Too much spring pressure before break in, stuck valve, rockers hitting retainers, tight lifter bores, etc.  I am all about the right oil, but if it's in there and you lose one, barring extreme lobe designs, there is usually a reason that could have been prevented.

The last one I lost was a previously broken in set, removed and re-installed during a motor fresh.  Three passes before losing an exhaust lobe (#8).  Quality Isky EDM lifters, everything clear as normal - had to be some missed piece of debris or something.  Not spring pressure, etc.  Cam had run for two seasons no issue, all parts went back in the same holes, same block, etc, etc.  After that - no more flat tappet cams.  Done, over.

[wowens]

Cam failures are witchcraft to me. Must be something in the cores now. Back in the preverable day we ran used lifters on used cams  with cheap oil and I never had a failure. Lifters came out of a box full of "used" lifters that "looked ok""  Why so much failure now ? Oh yeah, break in was crank it, adjust valves and run the crap out of it.

[blykins]

Back in the day the lobes weren’t aggressive and the spring pressures were low.  Over the last 30-40 years, cam tech has changed and we run a lot different cam specs and spring pressures.  My 465 that I just built had 165 lbs seat and 440 open.   Now granted, that was a nitrided camshaft and tool steel lifters, but I routinely run more spring pressure on "regular" flat tappet stuff than guys did decades ago. 

[plovett]

Back in the day the lobes weren’t aggressive and the spring pressures were low.  Over the last 30-40 years, cam tech has changed and we run a lot different cam specs and spring pressures.  My 465 that I just built had 165 lbs seat and 440 open.   Now granted, that was a nitrided camshaft and tool steel lifters, but I routinely run more spring pressure on "regular" flat tappet stuff than guys did decades ago.

I'm at 150 lbs closed and 405 open with a nitrided cam and regular EDM lifters.  I feel like I have to adjust the valves just a tiny bit tighter every once in a while.  Makes me skeered.  I am looking forward to looking at my cam and lifters when they come out.

[My427stang]

I'd be inclined to say you have pushrod, rocker, and seats wearing more than cam issues.  If the lobes were wearing significantly, it'd be more than a minor change in adjustment

[plovett]

I'd be inclined to say you have pushrod, rocker, and seats wearing more than cam issues.  If the lobes were wearing significantly, it'd be more than a minor change in adjustment

That's an interesting take and I hope you are right.  I might like to reuse this cam in my 470+cid build I am putting together. 

Thanks,

paulie

[machoneman]

I was 'there' for the many wiped 1st gen. SBC cam failures in the later 70's and early 80's. In hindsight, GM admitted that the rear few lobes at back of the engine did not receive the correct treatment (forget now if it was Parkerizing, case hardeneing, whatever) at the factory. Cost them a ton as failures were very widespread.

Point is, I've wondered about the processes of admittedly foreign made cams these days (blanks at least) and if they contributed to lobe/lifter issues? In fact, even if the cams themselves are o.k., are the aftermarket lifters too soft (or hard) essentially leading to worn-off lobes?  I do remember reading Harvey Crane's old tech data statements that the relative surface hardness of lobes and lifter had to be close to one another to prevent rapid wear. Not easy in my mind as chilled or tool steel  lifters running on cast iron cores must be a pretty good engineering trick.

https://www.scribd.com/doc/83949185/Secrets-of-a-Cam-Designer

First, always hard to tell because once the lifter stops spinning it takes out the entire lobe very quickly

My hunch would be most failures are not "typical" but would be after the lash ramp as the lifter is accelerating quickly and should be spinning. 

I deduced that by the delta in load, plus the requirement to spin, any other point on the lobe the lifter is already spinning or it has significantly reduced load.

The only clarifying statement I would add is, anywhere on opening ramp or nose could easily take out a lifter if the lifter stalled due to stuck valve, etc. 

One last comment, I have never seen a bad cam (other than the late 70s/80s Chevy SBs) that didn't have a good reason for a failure.  Too much spring pressure before break in, stuck valve, rockers hitting retainers, tight lifter bores, etc.  I am all about the right oil, but if it's in there and you lose one, barring extreme lobe designs, there is usually a reason that could have been prevented.

[plovett]

In my opinion, under 27 or 28 MI and 13/14 on a flat tappet on both sides is getting very stout for something that doesn't get torn down much, 

What are you referring to when you say "13/14"?

paulie

[blykins]

The 13/14 refer to the "span" of the intensity. 

When cam designers are willing, they provide you with the major/minor/hydraulic intensity and then can further provide you with how the intensity is biased......i.e. if the opening is rougher than the closing, or the closing is rougher than the opening.  That way you can determine how quickly the valve is opening, if it's getting slammed shut, if it's going to be a spring eater, etc. 

The spans will always add up to the intensity, so that way you can determine where the bias is. 

When dealing with hydraulic rollers, all of this information is extremely helpful, especially with heavier valvetrain engines like the FE.