In GM hightech MTI stated that the LT1 is especially prone to spinning a bearing after cam and or heads install..
Now i know this has been covered in the LT1 tech before. Most of the arguements have been toward inproper torquing of the Head bolts and contamination.
But MTI knows there sh*t and highly recommend a rebuild before heads and cam are attempted. But they also have incentive to say that cuz they sell rebuild kits and bottom ends..

Im trying to bring up the article but i cant find it. My bro read it to me over the phone. If anyone can put a link up here on it that'd be nice. Suppose to be September issue of GM high tech "bearing the truth"

I'd really like to injuneer's and other engineer opinions on this. Im not sure who to believe since some opinions are based on profits... Im just looking to add some power safely and cheaply with a very low risk.
Found it

Q:I have a 1994 Caprice that I purchased from the sheriff's office with 180K on it. It pulls 20" of vacuum at idle and seems to be in good condition.The local speed shop told me that LT1 engines can have misaligned main bearing bores from thermal fatigue and that I shouldn't try to put heads or a cam on it. They say the torque from the bolts being tightened can disrupt the block and cause me to spin a bearing. Now I do believe the block has been through a lot of heat cycles, but no more than any other older L98 car or 70s/80s car. What is your take on this?
A: You local speed shop is correct. We highly do no recommend that you try and replace any internal parts in that engine unless you plan on rebuilding the short block. We have witnessed numerous bearing failures in LT1 engines after the installation of cylinder heads and/or camshafts. It has been our common practice to pull the entire engine, replace the main and rod bearings with Clevite77 "H" bearings and reassemble with performance cylinder heads and camshaft. If you choose this route, you will not be running a high risk of destroying your crankshaft from a spun bearing and you will have a fresh short block to get the most potential from you new heads and cam.


also
http://www.impalassforum.com/cgi-bin...c;f=1;t=006047

 

I have found there are two main reasons this happens.

First. Many people get to much garbage in the motor while intake is off. I can not count how many people have pulled there motor apart to see the Oil pickup tube full of silicone or other garbage.

Second. After installing a cam many will over rev there cars or run it lean with out tuning.

I remember the artical but not sure when it was sorry.

 

MTI does head/cam swaps if im not mistaken, without building the bottom end. hmm.....

I think the number one cause of failure is overrevving, the bearings cannot handle the stress and fail.

 

The cam bearings on an LT1 are no different than any other of the gazillion SBC's out there. If you mess up the bearings or get crap in the motor when doing heads and a cam, you may have a problem. Otherwise, you won't.

Rich Krause

 

I'm number 3 on the dirt issue.

Before you work on your car, make sure you go to the car wash and clean out the engine bay! Engines are senstive to dirt, and the dirt in the engine bay and on the motor will get everywhere so if you can get that out of there BEFORE you take it apart that's going to save you alot of hassels down the road.

Bret

 

analyze that q & a section a bit. maybe i'm misreading this but follow along with me. they don't recommend you pulling the heads and replacing them yourself because "lt1's often suffer from misaligned main bearing bores... thermal fatigue". but they do reccomend letting them rebuild the engine, replace the bearings and put the cylinder heads and camshaft in. where in there did they correct the "misaligned main bearing bores"? maybe they just forgot to mention that but it really stuck out in my head when reading that.
do the lighter blocks distort more? absolutely. but to help the situation you should be using a head stud, not a bolt. so then we come to factory buildup practices and the question... what does swapping the head bolts for studs do to the motor? bottom line is, i would never build a performance engine with a head bolt but it's your call. you should see the lifter bore indexing on these motors, if you have the tooling, it's easy to see how bad they are and why correcting that situation is a good call. most don't though...

cleanliness is next to godliness when working on any engine so that's a really good point being made. just some random thoughts.

JB

 

On the lifter bore alignment issue, are LT1s any worse than other production blocks? I have seen the misalignment on standard blocks using the BHJ setup... and it's amazing. They must machine these things with a drill and grinder

 

I just picture'd a line worker rolling a round rasp file between the plams of his hands like the caveman starting a file....doh

 

some of that might have been influenced by bucks.

I recently wrote to an editor of SuperChevy, Mr. Randy Fish.
long email and responces here
http://web.camaross.com/forums/showt...ghlight=rotors

Nothing that great in it, didn't even include half the stuff I really should have so you dont have to read the whole thing, just skim through it to get the gist. 85% of that info can be found in that "crossdrilled vs blank rotors" thread in here a few months ago.

To save you some reading; here are the main points; his two responces.


Here was my responce



quote:
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Trey --
Thanks for forwarding your thoughts and comments. In today's world of enthusiast publishing, the editorial and advertising balance is more delicate than ever. Often times, sales reps are forced to negotiate a "story for ad" program, where the advertiser gets a tech story supporting his product line in exchange for spending dollars on an ad campaign. I can certainly understand the cross-drilled and slotted rotor theories you provided. However, there are times where some of our editorial "slants" are dictated by the particular advertiser in question. If they promote their product as offering additional cooling, they expect us to promote it in the same way.

Thanks for reading, and it's great to know there are talented car guys out there among our institutions of higher learning.

Randy Fish
Senior Editor
Super Chevy Magazine
(xxx) xxx-xxxx

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and


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Pretty harsh comments. The reality is, if there were no ads there would be no magazine. So, I guess you feel as though our leaders in Washington always tell the whole story and nothing but the story. Advertisers have been involved in editorial ever since enthusiast publications began.

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Most production blocks are machined on a transfer line with hard-mounted drilling, boring, milling heads. The lifter bores are probably very accurately spaced with respect to each other. Some of the problem is locating the block at each machining station. Generally there are machined angle pads near the front and rear cylinders. These are very obvious on a LS1 block. That's the first thing machined, and other surfaces are located from those pads.

Unfortunately, the lifter bores are probably NOT located from the camshaft bearing bores in production. More's the pity.

Even a BHJ's "Lifter-Tru" locates from the main journal saddles and the front cam bearing saddle only. If there is any "cam skew" in the block (cam bearing saddles not parallel in two planes to the crank main bearing saddles), you'll still have incorrect lifter bore location with the worst being at the rear.

Lacking a good, big, CMM (coordinate measuring machine) to check actual lifter bore location with respect to the cam bearing bores, I think I'd check cam skew before I moved any lifter bores.

CNC Bowtie or other blocks are better, but not perfect in this respect.

I guess you could build a fixture similar to the "Lifter -Tru" which locates off the cam bores and references the front or rear main instead of the other way around. Maybe someone has (other than Smokey 25+ years ago!) . Just guessing on that one.

So, if cam bores are skewed, and that's not too easy to correct, how about just rephasing the cam lobes the appropriate number of degrees as you move along the cam. That may be costly, but moving cam bores could be much more so. Hey, how fast do you want to go? You know the rest...

Oh yeah, if we drive the cam from one end, and it has a torsional vibration mode that changes the relative phasing of the lobes at high rpm, do we compensate? How?

My $.02

 

It would take one hell of a CMM to measure lifter bores with respect to main bearing bores! I guess a little fancy placement and suspension of the block would help... but i'd love to see that.

 

It wouldn't be that hard to fixture this, and many tool & die shops would have a CMM big enough to handle something block-sized.

Per what Old said, it's very unlikely that the lifter bores are located off the crank or cam bore; however, from what little I've seen of GM's transfer-line operations, it's going to vary extremely little once set up. I have no idea what the print tolerance is on this dimension, so it could be off a bit, but I think it'd be very consistant.

With regards to the GMHTP letter and response, I think they're full of it. If the motor got hot enough to cause any sort of block warpage, sorry - it'd be toast well before anyone decided to do a heads/cam swap.

It's just a matter of keeping things clean, and making sure the engine's in good health before beginning any mods. While modern SBCs sure can last a long time, I have noticed that oil pressure seems to drop off as the engine ages - and there's not really that much of it to begin with. My wagon, with 225K on the stock LO5, will flicker the oil light at low revs - clearly, this would not be a good candidate for a head/cam swap. I've seen the same thing on higher-mileage Vortecs, as well, and I'd have to assume that LT1s may very well follow the same tendency. I've also seen some bearing wear on high-mileage Vortecs that caused absolutely no problems at the time the motor was disassembed (i.e. no noises or serious loss of oil pressure), but if you've got a few rod and/or main bearings showing copper, it might be a terrible idea to stick in some monster bumpstick and decide to rev it up to 6500 RPM a few times.

 

Maybe the LT-1 is a different animal than earlier engines BUT......... I've done heads/cam on a LOT of older small blocks. Not like I build engines for a living but I mean a HELUVA LOT for a weekend wrench. When bearings spin after a cam swap it almost always happens for one basic reason- you've changed the basic RPM range of the engine. If you spin a motor to 6500 that has spent it's whole life (tens of thousands of miles) at only, say 5500 maximum, you're GONNA break it. Spun bearings, broken rod bolts, broken rings, you name it.

So how do I know that the mains being out of alignment wasn't the problem? Because I rebuild that same motor WITHOUT EVER TOUCHING THE MAINS OR CAM JOURNALS and it lives for another billion miles with the same big cam and high-flow heads. Go figure.

I dunno. Maybe I'm missing something here.

 

I don't think you are missing anything.

 

Since I think the theory of all of our points has been well-versed, I'll just try to ease the original poster's mind by saying that I've never had a LT car spin a bearing immediately after I've installed a cam/heads......or even within 10K miles. You have to use an accurate torque wrench, keep operating-room clean, and use fasteners just as hi-performance as the parts that they're fastening. If a block distorted...nevermind, that's a bunch of crap. RPMs and low oil pressure kill engines.
Can't you just see someone taking this GMHTP article as fact back when you could take your LT1 powered car in for a warranty due to that notorious intake manifold leak?...."Yeah, uh, Mr. Goodwrench, I want you to fix that oil leak but I want you to rebuild the whole motor while you're at it. According to a magazine, you untorquing the intake manifold bolts will disrupt the harmonious balance."