Any of you guys have the lifter bores checked for alignment on your BBCs?

Bob, I am quite curious to hear. Hypothesize that many bbc cam wipe outs may be due to flexing in the web area, and this machining operation would square that away. Thats what Crane suspected was the culprit in my 427s case after they examined the "forensic evidence". The new cam they ground eliminated the prob. Core shift in the web area, they suspected.

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Gene Chaas
Gold Member 62/ACES 3112
67 SS 427 (http://www.chevelles.com/feature/october2000.html)
"Be big. Be a builder."

[This message has been edited by 427L88 (edited 04-21-2001).]

I still don't buy this theory. Was the original cam that came out of the motor wiped ? If not, why should you have a problem with the new one ? This problem always seems to arise after a cam change. I suspect either installation problems, especially valve spring settings, or start up procedure.
Just my opinion,

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

<BLOCKQUOTE>quote:</font><HR>Originally posted by 427L88:
The new lifters they ground eliminated the prob. Core shift in the web area, they suspected. <HR></BLOCKQUOTE>
Now I'm confused, why would new lifters solve a core shift problem?

Bill, thats why I say hypothesize. I wasnt there, but trust my buds ability since he has done it successfully all other times, and then Crane's diagnosis.....

Sir, what would it take to "blueprint" the bores? Assume they'd have to be enlarged( bored true to cam centerline), lined and then honed to spec. Prolly alot of dough , huh?

Be a bear to measure centerline to boot.

EDIT: Bob, they gound an additional 1-2 thou of taper into the cam lobes to ensure the lifters keep spinning. Assume then, that out of round, or out of angle bores would stop the lifters from spinning properly. I say again, ASSUME.

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Gene Chaas
Gold Member 62/ACES 3112
67 SS 427 (http://www.chevelles.com/feature/october2000.html)
"Be big. Be a builder."



[This message has been edited by 427L88 (edited 04-21-2001).]

427---- My understanding is that you would over bore the lifter bores and insert a "sleeve" that would then be bored and honed off of the main bearing center line.

[This message has been edited by d1_bradley (edited 04-20-2001).]

substitute the word "lobe" for the word "lifter" in Gene's posts above and they'll read better.

And, core shift does not affect the location of machining, poor machining does that. If there's core shift, the machined hole is still in the same place, but the boss it's bored in is off-center around it. This is just like a thin cylinder wall problem.

Tom

BHJ makes a tool called the "lifter true" that is used to properly locate all the lifter bores. It involves boring out the original holes, sleeveing them and reboring the sleeves. It is not however designed to fix camshaft problems, it is designed to make certain that every valve is opened at the precise time it is supposed to. This is important in very high output class motors such as in NHRA Stock Eliminator where the camshaft is limited by the rules and you have to make sure to get all the lift / duration at the correct times.
Also, Tom Is very correct in saying that "core shift" is not the correct description for the problem. I still do not personally believe that this is the cause of the many wiped cams you hear about.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

[This message has been edited by BillK (edited 04-20-2001).]

They make a very nice and expensive fixture, a block true, that attaches to your block and allows all of these precision machining processes possible. The hosed lifter bores on a rat are more common that most people think but don't seem to surface in stock or modest performance applications. All out race motors with 800 and 900 lift cams and 8 million pounds of valve spring pressure are more likely to have a problem if the lifter bores are in the wrong place.



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Wally
www.muncie4speed.com (http://www.muncie4speed.com)
Gold #67
2001 Chevy Silverado LT
67 Malibu "Small Block" second owner
90 SS454
71 Malibu "Small Block"

I have a 454 block that has had the exhaust lifters on the passenger side bank look different than all the rest every time I changed cams, about 3 times now, I think. Never flattened a lobe or wore the lifter excessively, just looked "different" than the rest. I chalked it up to running 1.8 rockers on the exhausts.

The last time I freshened the block I used a BHJ lifter fixture and checked the lifter bores. Sure enough, the passenger side exhausts were all off. We then bored the bores and bushed them and the lifters have looked fine ever since.

Regards,
Gary Anderson

As Bill suggested, the main reason for lifter bore alignment is to insure correct valve timing. If a lifter bore is higher or lower, in relation to the cam, it opens or closes at a different time that speced. A low lifter bore on the passanger side, will open the valve early, a low lifter bore on the driver side will open late. Not a problem for most of use but in a maximum effort engine it is.

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Pat Kelley
66 El Camino, daily driver
67 El Camino, STRIP/street
Pat's Page (CR Calculator, Utilites, car specs) (http://cochise.uia.net/pkelley/)

[This message has been edited by Pat Kelley (edited 04-20-2001).]

There was a discussion on this at Chevytalk.com about a month or so ago in the performance section.

Intersting...Tom thnx I changed it to lobes which is clearly what is ground with an additional taper....I see Bill's point. E.G., the original L88 block which I'll use for the next and final rebuild has probably 500 hours of run time, didnt have a cam problem, and has been stored for the last 20 years. It should not have any problems. But the 454 2 bolt casting i run now did. I'll stop calling it "core shift" but it is bore misalignemnt of some sort.

Kinda makes you want to run a roller to elim the problem huh? http://www.chevelles.com/forum/smile.gif

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Gene Chaas
Gold Member 62/ACES 3112
67 SS 427 (http://www.chevelles.com/feature/october2000.html)
"Be big. Be a builder."

Yes, this topic has come before on ChevyTalk and I initiated one of them (http://forums.chevytalk.com/forums/Forum64/HTML/001454.html). The other thread (http://forums.chevytalk.com/forums/Forum64/HTML/001194.html) discussed lifter bore alignment as an alternate explanation to cam failure when the poster asked about a cam oiler(http://www.off-road.com/chevy/reviews/bbc_oiler/).

Sorry to have asked such an open-ended question, but there are a lot of guys on TC that didn't see the ChevyTalk threads and I was curious what the response would be w/o biasing the question.

Bill, I agree in principal that if the engine did not experience a cam failure why would replacing the cam do so (assuming the install and break-in was done correctly). But doesn't longevity become an issue? If the lifter bores are out a small amount, won't it just take longer for the failure?

The consensus on ChevyTalk seemed to be that checking for lifter bore alignment is only done for high performance applications and not for street or mild performance situations. Why shouldn't this be checked like all the other clearances we check for? Perhaps the answer is the cost. I have not found anyone around here that has the BHJ fixture or would quote me a price, but $350 was mentioned on one of the posts I referred to.

I eventually found out that the exhaust bore is 45 deg from the crank-cam centerline and the intakes are 38 deg 45 min. BHJ didn't know how far out was acceptable only that it should be corrected.

I also don't understand why using a roller cam seems to make the alignment issue mute. If the bores are out slightly, say forward or backwards relative to the block(but at the correct angle to the crank-cam centerline) wouldn't the roller not sit square on the lobe and create unnecessary stresses and premature wear?