ok so one of the dog bones that hold the stock roller lifters true with the cam popped up somehow and allowed two lifters to spin and chew up my cam... what would cause it to do that????

 

Welcome aboard.

The reason I've heard is having a cam with so much lift that the base circle has to be reduced to get the required valve "stroke", if you will. The lifter drops down so far in the bore that the dogbone gets lifted off and things get ugly quickly.

The other possibility is that the lifter actually failed and did the same thing.

 

it was only a hot cam? the spider keeper was still tight? could there be something wrong with the dog bone?

 

Not really.
Are you using a roller block?
Hot cam w/ 1.6 rockers?
What springs do you have?
Is the lifter wheel still intact?

 

its a true lt4 with a hotcam.. i don't think that the lifter wheel is in any kind of usable condition now, but it was all brand new two days ago when i put the cam in...

 

Do you have pictures? That's a really uncommon failure.

 

i see you have AFRs...

by anychance are you spinning this engine over 6500?
every stock retainer failure ive seen envolved high RPM.

 

nope stock rev limiter cuts off at 6350.. its got the stock lt4 heads... i spin the other engine with the afr's to 7000 without a problem.. i hardly revved this engine out cause its still not tuned.. but it looks like its getting the stock cam back..

 

i will take some today cause i haven't taken it all apart yet just the valve cover. but i plan on getting on doing it in a minute. i am going to change out the spider and all the dogbones... do you think it would help if i bend the new spider so its got a little more preload on the dogbones????

 

Checking for bent pushrods or other valvetrain damage would be a good idea.
Possibly there was an interference issue somewhere, and that snowballed to cause the dogbone to let go of the lifter.

 

Get the AFR "Rev Kit"; which replaces the stupid weak factory dogbone crap with MUCH more beefy dogbones. Theirs is the only one on the market I know of that works that way. Their springs will then be in the center of the dogbone,which will help keep it from ever coming off the top of the lifters again.

There's no way that any kind of interference higher up in the motor can cause the lifter to drop out of the dogbone. Forget that possibility. Which is not to say that there's not interference or whatever; only, that it can't cause the catastrophe at hand.

What most likely happened, is that the dogbone stuck to one lifter when that lifter got lifted (probably the exhaust); and that lifted it up off the intake lifter a little bit when it was all the way down in its bore, such that it then was able to turn; and then when that one lifter the next time, in its turned position, it lifted the dogbone completely up off the exhaust one too. It's mostly because the "spider" thing is so weak.

Or, get yourself some REAL roller lifters, with link bars. I believe they have started making them now in an extra-tall version, to retrofit the original "sensible" design back into blocks with the factory's "stupid" design. Hard to say which one will cost less, that or the "Rev Kit".

 

Interference up top could bend a pushrod, allowing the lifter to float off the toe of the cam lobe high enough to hit the dogbone on the underside, and lift it up to the point where it was no longer engaged on the lifter. From that point, Murphy's law is in full effect.

 

I don't see anything in his post about a bent push rod.... especially not one bent enough to cause this.

And of course, this is all on ONE cylinder; if the engine was built wrong somehow, wrong valve springs or whatever, all 8 cyls would have similar problems.

Which, again, does not mean that there isn't an interference problem or other malfunction of that sort; only, that it DIDN'T cause the issue at hand.