hi guys , i had some issue with my new rebuild engine god dam, it has about 2k on it... i dont know if was happen to some one here but two of the eight arm of the spider plate has bend so the dog bone has lift and two lifter has turn and ruin the lobe cam i gess, metal flake is everywere.... did someone has an idea what did happend here. i dont know why and my engine builder has never see that happen. oh by the way my engine is a 383 strocker with xfi280 compcam 1.6rr have some pic to show... thank all

 

What cam were you running and how much spring pressure? Looks like the cam wore down, but that should never happen on a roller.

 

Have an XFI280 roller with 18k multiple flat lobes

Crap metal.

 

That's usually because the cam has too much lift... the lifters descend into their bores too far at zero lift, and fall out of the figure-8s, and the rest, you know

 

Sofa,
Not questioning your call as you've forgotten more than I'll ever know but I'm confused and trying to learn something here. Wouldn't it take a small base circle cam for that to happen? I had always thought this happens because the spider leg "floats" and allows the lifter to rotate as it's no longer holding the dog bone down properly.

 

THINK about a cam for a minute...

Q1: How "tall" can you make the lobe?

Q2: What is "lobe lift"?

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A1: You can only make the lobe as "tall" as the journal diameter.

A2: "Lobe lift" is THE DIFFERENCE BETWEEN the diameter of the peak of the lobe, minus the diameter of the "heel".

Meaning, every cam you buy (except for small BC ones) has the lobe as absolutely tall as it can be and still be installed, since the larger it is, the more reliable it tends to be; and to make a cam "bigger", you don't make the "nose" taller, you make the "heel" shorter.

WHich is why you can take a cam and EASILY grind it down to make it "bigger", but it's almost impossible to go the other way.

And is also why a "big" cam will let the lifters fall down into the block farther than a stock or other "little" one, at which point one may "fall out" of the figure-8, lift it up, and allow the other to spin.

Then, with the factory roller system, not all lifter bores are the same "height"; the factory's tolerance there isn't very tight (doesn't have to be, and from their point of view would be detrimental if it was... see http://en.wikipedia.org/wiki/Muda_(Japanese_term) and scroll down to the 5th type) and so sometimes ... you can end up crossing over that line.

 

In the first picture, top left most lifter, can't even see the top of it as it is so far down into the dog-bone. Then in the second picture the bottom right most lifter, can see how far down it is.

RBob.

 

Gotcha'! I always, (mistakenly), thought that the BC was "0" lift, that the heel of the lobe was the BC, that was a "hard point" measurement and you went from there. See? Even a fat, bald, old, crabby bastard can learn something!

As a PS, this would mean that once lift exceeds a given point, linked lifters are the way to go, correct?

 

Generally so... they actually make those taller, such that the link bar won't get stopped by the block and not drop the rest of the way down in those blocks, since the boss around the bore is taller.

I'm not really a big fan of that figure-8 deal anyway; just seems too fragile in a general way, not a strong enough retention method, and too many parts. The rest of us have all been using link bars since they invented dirt, LONG before the factory came up with that weird thing they did, without issue. (up until the altered late-model block malfunction) Since what is now referred to as the "retrofit" system is (and was) so well and widely known by all to be bulletproof, I don't even know why the factory decided they had to re-invent the wheel and turn it into that triangle instead of a circle. Oh well.

As an aside, that's why when you use a higher lift cam, you tend to need longer push rods, in spite of the intuitive guess that you'd need shorter ones... because at 0 lift, the lifter drops farther down, meaning the push rod drops too, meaning the rocker tilts too far back.

 

Comp cams did have a note on their cams about the limits of the OEM dog bones in the RPM range. That they had a fix for it and a part number for it. Thing is the last time I looked it was gone and I don't know what happened to it.

 

hi , so xfi 280 is to much for stock lifter reteiner setup... the spec of the cam are

Operating Range:2000-6000 RPMDuration Advertised:280° Intake / 288° ExhaustDuration @ .050'' Lift:230° Intake / 236° ExhaustValve Lift w/1.6 Rockers:.576'' Intake / .570'' ExhaustLobe Separation Angle:113°
so what i should do ? get a set of linked lifters or change the cam ... i know i have to buy an another one already ... thanks

 

Sofa,

It was probably 2 cents a piece cheaper!

And, then that's where the whole size/location of the witness mark comes in, yes?

 

i have stock push rod lengh, do i have to get some longer ?

 

Get a measuring pushrod to be sure. They're cheap.

 

Well, the block has to come out and get COMPLETELY torn down and cleaned out.

In fact, I'd suggest that you have the machine shop tear it all the way down; all plugs out, cam bearings out; and you pick it up in that condition. Then take it to the quarter car wash, along with all your gun cleaning brushes (the sizes you'll need are mostly the .410" and 22ga, but take em all) and a wire brush of the same general shape and size as a toothbrush. Stop along the way and pick up a coupla cans of engine degreaser (diesel fuel in a spray can). Run the brush through EVERY oil passage with plenty of degreaser, and use the toothbrush-like one on the grooves behind the cam bearings.

You're doing this because the vat doesn't dissolve metal chips, any more than it dissolves larger pieces of metal; and if ANY are left in the passages, they will have no place to go except RIGHT STRAIGHT TO your brand-new bearings and crank.

Then oil the bores and the lifter bores, and take it back to the machine shop and have them re-assemble it to your desired level before you finish it.

Yes I would recommend either geting the "special" taller "retrofit" lifters, OR talk to the shop about shaving down the top of the lifter bores so the lifters don't drop out of the figure-8s. Find the height above the crank CL that's .050" off of the one that's lowest now, and make all the rest that same height (as opposed to taking .050" off of all), ought to do the trick.

 

yes i know that i have to clean up everything , but i dont think the lifter are going down too much .. i had ajust my valve by myself and didnt see no lifter going down furtur than the top of the dog bone, all lifter was flush at 0 lash and all time i was turning the crank by hands... so should ben something else or realy bad luck..