Ditto to the max, and I have read about the lifters needing to be bored to be true!

 

BBA: First time I ever herd that. Learn something new every day. Thankx

BILLY D

 

your not the first person i've heard say this about retro fits and a short life compared to a block made for roller lifters.

 

Actually, LT4 OEM aluminum roller rockers are made my Crane for GM...:)

I'm guessing if the rocker is in a very stressful situation (full race) then the fatigue factor may be accurate. What does Nascar run?

:)

 

Check out this response!
http://www.chevytalk.org/threads/sho...5&o=31&fpart=1

 

"BBA"

"Bleive it or not, it was due to the design of a flat tappet block. On a flat tappet cam designed block, the lifter bore is not perpendicular to the cam lobe, it is angle slightly to promote lifter spinning which makes the flat tappet cam/lifter last longer. "


thats a common MYTH , ITS THE CAMS LOBES that are ground on a slight angle AND the flat tappet LIFTER BASES that are ground on a very slight curve so that the load on the lifter base is kept slightly off center that causes the lifters to spin in thier bores, IF YOUR BLOCK WETHER ROLLER OR FLAT TAPPET WAS CORRECTLY MACHINED THE LIFTER BORES ARE PERPENDICULAR TO THE CAM SHAFT CENTERLINE,and slightly offset from the cam lobe centerlines, yes it is very true that SOME BLOCKS ARE UNINTENTIONALLY OUT OF SQUARE SLIGHTLY BUT NOT BY DESIGN but only due to MACHINEING ERRORS,Normal FLAT TAPPET lifter face areas have a spherical shape with .002" crown. It is not flat across the contact surface as many people assume. BTW thats one of the main reasons roller cams require cam buttons or retainer plates with no slight angle on the cam lobes to tend to make the cam stay to the rear of the block the roller lifters flat lobes allow the cam to walk back and forth slightly in the block while flat tappet cams tend to have the lifters rideing on that slight lobe angle push the cam rearward, thats why stock flat tappet factory engines require no cam button or retainer plate



http://www.iskycams.com/techinfo_index.html


[Modified by grumpyvette, 10:14 PM 1/18/2003]

 

I remember when the first LT4 motors came out in the 96' Grand Sports, GM had problems with the roller rockers's & had to recall them, I believe it was due to the needle bearings in the roller tip falling out of the vendor (Crane) produced rockers.

 

there is a 30" radius ground on the bottom of the lifter. :chevy

 

Found this at http://www.hotrod.com/techarticles/43418/index2.html

Each lobe on a flat-tappet cam is ground with a taper of approximately .001 inch across it. Also, a flat tappet isn’t flat but actually has a spherical bottom. This compensates for misaligned lifter bores and spins the lifter in its bore. If the lifter contacts the edge of the cam or does not rotate in its bore, rapid wear will occur, causing the cam lobe to go flat and, consequently, the bottom of the lifter will be ground concave by the lobe.


The type of lifter used determines how steep the ramps can be. While a larger-diameter flat tappet allows steeper ramps, roller lifters allow extremely radical ramp angles. Higher valvespring tensions are required to keep the roller in contact with the cam, as the cam profile becomes more extreme. Roller cams do not have a break-in coating and are generally made from billet steel to endure the higher valvespring pressures.


You can see the circular contact patch on this used lifter (arrow) that indicates proper contact and rotation during use. The diameter of the lifter (on a flat-tappet cam) dictates the maximum angle that the cam flank can have. Also, for a given diameter lifter there is a maximum amount of lift you can have per degree of duration. Larger-diameter lifters, such as those in Fords and Chryslers, allow the cam manufacturer to increase the ratio of lift to duration. One trick used in many circle-track small-block Chevy engines is to enlarge the lifter bores to accept small-block Ford lifters to take advantage of the larger diameter. Also, some cam manufacturers offer mushroom lifters, which have a base larger than the lifter bore.

 

Well grumpy...it may be a common myth, but you'd be harder pressed to prove that aftermarket roller cams will be ground with angled lobes.

So...if it is so common that a myth is created...then just maybe the tolerances of lifter bore machining are still to blame?

Don't you think the factory roller blocks have to avoid this problem and therefore will have more precision in lifter bore perpindicularity? Especially to last 100-200K miles.

Never the less, it happenned to me...and it was the fault of lifter bore alignment, not cam. I know of several people who it either happenned to also and/or who know people it happenned to.

So, would you still say I am wrong to tell someone to have the lifter bores align bored/sleeved if they want a retro-fit roller motor to last high mileage?

 

What I find most funny about the Isky article is they say the most common problem is thrust bearing wear, erratic timing and distributor gear wear.

Are they NUTS? Have they ever seen a lifter wheel eat into the side of the lifter body? Looks like the professional Isky storyteller there needs to see reality...I bet even the fellow Isky techs are talking behind his back at how ignorant he is.