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Like some other fellow Chevelle nuts, I have flattened cam lobes again on my 454. I have read in various posts that I am not alone with regard to this problem. I have been told that going full roller will solve my problem. But I keep seeing posts that talk about big block core shift. Would someone mind telling me what this is, is it correctable, and how it is corrected. Would like to know before I step up (again) for another go around swapping camshafts. Thanks
 

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Core shift is a condition in which the interior cores (for casting) will shift their positions relative to the exterior cores. This results in non-uniform cylinder wall thicknesses and so on. Your cam situation is not affected by core shift, as the machined locations of your cam and lifters is determined by the machining of the block.
 

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The stuff about core shift causing causing cam problems is just wishful thinking, IMO. What actually matters is that the lifter bore holes are machined in proper relationship to the cam, not how much iron is left over on the bosses afterwards. Core shift does not affect this in a meaningful way. I've seen people complain about this but in 25 years of building Chevy V-8's I've never seen anything that could be called lifter bore mis-alignment.

Now, in recent years B&J came out with a jig fixture that will allow a good machine shop to rebore and bush the lifter bores in a *smallblock* for theoretically perfect alignment, this was developed for Winston Cup motors where they absolutely have to have everything perfect regardless of cost. Remember, they run oversize lifters and valve springs that really belong only on a roller cam. Ever hear a competent machinist with one of these tools talking about how far off the bores are before they're machined? Don't hold your breath waiting for this, nobody even checks.

I haven't seen this type of tool for a BB, doesn't mean there isn't one, but I'll predict you'll have a hell of a time finding somebody that has one. Remember, this is a compound angle on these bores.

Think about how many BB's have been built up over the years since 1965-- most do just fine. If you really want to buy some insurance, have the cam hardness tested on every lobe, this will show the real problem, poor quality control on the part of the cam grinders. Also there are available TRW lifters that have a dry film lubricant on the base, I've seen a set of these out of a 60,000 mile engine that literally looked like new, so did the cam.

I really wouldn't spend too much time sweating this, just do your break-in stuff right and go. This is a trouble shooting and problem solving forum, you're going to see the posts of the guys that have had trouble and not the posts from the many that don't have problems.

Roller lifters will solve the problem, but other problems could crop up along the way in the various clearances involved in the reciprocating parts.

Just my $.02, YMMV. Tom

[This message has been edited by Tom Mobley (edited 08-30-99).]
 

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I agree with what Tom says. I have experinced cylinder bores off as much as .015-.020 from the factory. When you consider the tools involved in putting in lifter bores in a mass production environment then they probably have the same sort of tolerences and if one was way off a simple caliper check would revel that conditon. I have checked a few "cam eaters" for bore and location relitive to each other and found not more that a .001 or so variation. Best to just chalk it up to **** happens tear it down, clean it up, replace the bearings and such and get on down the road.

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Harley
69 461 El Camino Nitrous Model
69 Chevelle coupe
71 SS Camaro
75 L-82 Corvette
71 Gremlin X
Kerrville,Tx.
 
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