Disturbing.. GM hightech article LT1 spun bearings

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/ultimatebb.cgi?ubb=get_topic;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.....:confused:

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

Originally posted by ZDriver96
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/ultimatebb.cgi?ubb=get_topic;f=1;t=006047

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:confused:

Originally posted by nosfed
On the lifter bore alignment issue, They must machine these things with a drill and grinder:confused:

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/showthread.php?s=&threadid=165879&highlight=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:
--------------------------------------------------------------------------------
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

--------------------------------------------------------------------------------


and


--------------------------------------------------------------------------------
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.

--------------------------------------------------------------------------------

Originally posted by nosfed
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:confused:

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

Originally posted by OldSStroker
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.

Originally posted by TreySpeed
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.

Originally posted by Damon

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.":rolleyes:

Originally posted by LT1Brutus
According to a magazine, you untorquing the intake manifold bolts will disrupt the harmonious balance.":rolleyes:

I would imagine that having the dealer go anywhere near my car for any reason would disrupt it's "harmonious balance":D

I agree with the other posters that keeping it clean is super important, but also getting the big lobes in there without shaving or gouging the cam bearings is a biggy. Maybe the fact that these cars are physycally hard to work on causes more mechanics to screw up on the basic stuff. In my experience, no other bike or car that I have ever owned ever got me to say the f word so often as my TA.

Originally posted by Kevin Blown 95 TA
In my experience, no other bike or car that I have ever owned ever got me to say the f word so often as my TA.

Couldn't have said it better myself! 4th Gen Fbods are nasty to work on. I swear, everything is a pain in the ass besides changing the oil.

dont worry guys... the magazine has convinced me to not swap heads out... Im just going to go a full forged 383 with heads and cam already on it... :)

Yeah LT1's are a pain in the ass... Worse than TPI's and LS1's.
I wont let the deal touch my car either.... I dont understand how some of those guys are mechanics??? Its ridiculous.

I have seen the results of the "mysterious" after heads/cam install bearing problems. Fortunately, both dealers that did the installs were quick enough to bring me the engines right when they noticed oil pressure problems. on tear down, it was obvious that cam bearing 1 was scared pretty badly and scalloping, causing contamination on the oiling system, therefore leading to bearing failure on the rods and mains (no oilfilter in the world has a chance of catching a piece of bearing moving at 300+ FPS.)


My theory is this.... the late model F-body is difficult at best to do a cam swap, miss alignment when first installing the cam, with an AC condensor wrapped around one arm, one hand under the top core support, and playing a game of twister with your toes, easily leads to a damaged cam bearing.


Dennis
Air Flow Development

On that note, I have noticed some problems w/ the first/front cam bearing that a lot of people don't when doing a head/cam swap. The top 20% of the bearing is often VERY worn when compared to the rest of the bearing. In fact, in my own vehicle which recieved heads & cam @ 107K miles, the top of the first bearing was so poor we decided to replace it. Apparently the added thrust of the water pump being camshaft-driven causes this, particulary if the water pump's rear seal goes out (as they often do) and causes abnormal play. This theory was further proven to me when I did a cam on a 96 SS that had had an electric water pump put in @ only 22K miles. Even at 96K mi. there was very little wear all the way around the first cam bearing.

Anything you want to do major on these motors really requires either to drop the K-member and the whole motor, or to just yank the motor. It's better than risking it and screwing something up. On top of that it's easier to keep the inside of the motor clean in the process.

Bret

Personally, I subscribe to the “they’re full of crap” camp on this one, but those of you that are not so sure yet, I’ve got a question for you:
If torquing the head bolts distorts the block skirts badly enough that it’s going to cause a spun bearing, even if you go through a whole rebuild, install new mains… how are you not going to cause the same distortion torquing the heads as part of the rebuild???

While reading MTI’s comments (and all of GMHTP’s recent tech articles) I feel like I can see the words that were written but they’re really saying “pay us for a full rebuild or we’ll toss rtv chunks in your lifter valley, and then you’ll be sorry.” A bit extreme but when was the last time that they published any decent tech anyway?

Originally posted by WS6 TA
Personally, I subscribe to the “they’re full of crap” camp on this one
Me too...
If torquing the head bolts distorts the block skirts badly enough that it’s going to cause a spun bearing, even if you go through a whole rebuild, install new mains… how are you not going to cause the same distortion torquing the heads as part of the rebuild???
Possibly bolt torque plates or heads on it, then line hone it. But some builders even question the torque plate method of honing cylinders, so which way is right?, and why would it whack the whole block out anyway?
...when was the last time that they published any decent tech anyway?
I had that magazine for 3 years hoping to see some good tuning articles for EFI, but I really think the average guy on the LT1 Edit list knows more than their whole staff about tuning the F-Body...

Originally posted by Kevin Blown 95 TA
Possibly bolt torque plates or heads on it, then line hone it. But some builders even question the torque plate method of honing cylinders, so which way is right?, and why would it whack the whole block out anyway?

torque plate, always. for that matter, you should try to get things as close to operating conditions as possible, if you can get them to do the major machining operations while the block is at operating temps...

Wouldnt the waterpumps force be towards the bottom of the front cam bearing? The pressure would be downward correct? Unless the fit was somewhat scewed to the top putting it in somewhat of a bind. A cam handle (bought or fabbed ) is a very good tool for cam installation it really gives you a better control when sliding it in. I have actually performed several cam swaps on LT1 cars and classic SBC but never have I had one spin a bearing from it....lol. I agree that you should be clean as possible when doing the swap lots of rags and solvent to clean parts and stuff holes while its apart.

Last summer my cat got pluged and my car got pegged in the red. During the winter i put the hotcam + mild ported heads. 200km later 3 mains spun now I have a 383.

one thing i noticed on my new (used) block when they line honed the mains you could tell they were not lined up becuse on one main, one side would be completely honed /shiney while the other side was just touched and the same was true on the next main but oppisite sides.

so if you know the car has never been pegged and i mean pegged in the red you should be allright, but if you know it has I wouldnt bother doing head / cam on it without full rebuild.

these block are probably a lot lighter than old style 350 block hence less webbing and more likely to twist / distort.

Originally posted by ZDriver96
In GM hightech MTI stated that the LT1 is especially prone to spinning a bearing after cam and or heads install..


That statement, especially when widely quoted, requires more qualification and explanation than the magazine provides space for. There are obviously many h/c swaps performed without 'prematurely' spun bearings within 2500 miles, which makes me question the motive or agenda of the folks who say this.

great, more input. my only thought is that an LT1 may suffer from thermal distortion in a different way from a gen I or III SBC due to the direction of coolant flow. if that is the case, it would explain why only LT1's would be at risk of this. considering the angle of the head bolts and intake manifold bolts, its obvious that something is being stressed as an intake manifold is tightened. its a matter of what take the brunt of that stress and is it able to handle that stress.

I got into a discussion with my mechanic about this kind of stuff a while ago. We were talking about what all I needed to do when my motor went in for a rebuild and he was listing all of the machine work that he knew would be necessary to get everything lined up again.

He figures that the reason for most of the blocks being screwed up (as in, needs lots of machining to align everything again) is the difference in the casting/curing process for the LT1s as opposed to "old school" 350 blocks. He said that back in the day, they would cast a block and then stick it on a shelf for 5 years or so before machining it and using it for production. LT1 blocks were cast and then machined ASAP...they really didn't have time to fully cure before they were put together and stuffed in a car.

Anyone have any input on this? I'm not going to pretend to be an expert, I just thought that theory was interesting and it does seem to make sense.

O-neg: I tend to doubt that. Lots of guys doing numbers-matching restorations on older cars search high and low for blocks that have date codes within 3-4 months of the car's manufacture in order to be considered "concours correct". That would indicate to me that the block probably didn't sit around too long before installation in the car, even in the good 'ol days.

There is absolutely no way GM had hundreds of thousands of blocks sitting around aging. I have heard a lot of "old wives' tales", but that's one of the least plausible.

Rich Krause

Originally posted by rskrause
There is absolutely no way GM had hundreds of thousands of blocks sitting around aging. I have heard a lot of "old wives' tales", but that's one of the least plausible.

Rich Krause

I agree

I stopped reading at "GM Hi-Tech article."

:)

It's been said over and over in this thread... the problems are more than likely caused by a bunch of young guys making mistakes & not being as clean as they need to be. Most guys doing cam swaps on these cars are delving into their first real engine modification ever & just dont know better when it comes to certain stuff. Most of the time it works out okay, sometimes it doesnt.

Originally posted by Type_O_Negative_1320
He figures that the reason for most of the blocks being screwed up (as in, needs lots of machining to align everything again) is the difference in the casting/curing process for the LT1s as opposed to "old school" 350 blocks. He said that back in the day, they would cast a block and then stick it on a shelf for 5 years or so before machining it and using it for production. LT1 blocks were cast and then machined ASAP...they really didn't have time to fully cure before they were put together and stuffed in a car.

Anyone have any input on this? I'm not going to pretend to be an expert, I just thought that theory was interesting and it does seem to make sense.


I worked in a GM engine plant in the "old days" (1960's). The foundry where the cast iron blocks, heads, manifolds, etc. were cast was next to the engine plant. There were times when the blocks were barely cool to the touch when they were lifted onto the transfer line to begin machining. Some of them did get to age before being machined....over a holiday weekend was about the longest. :)

Fully "cure"? Cast iron shares very little with fine wine.

My $.02

Originally posted by OldSStroker
I worked in a GM engine plant in the "old days" (1960's). The foundry where the cast iron blocks, heads, manifolds, etc. were cast was next to the engine plant. There were times when the blocks were barely cool to the touch when they were lifted onto the transfer line to begin machining. Some of them did get to age before being machined....over a holiday weekend was about the longest. :)

Fully "cure"? Cast iron shares very little with fine wine.

My $.02

I stand corrected then. You guys know more about this stuff than I do. :)

I so hope this is not true but sadly i think it is.

I have had such bad luck with previous h&c install. after my last failure, I went back to my stock motor again. but this time i put my heads on it(ported ones) and now im pretty sure the mains are on there way out....

read post http://web.camaross.com/forums/showthread.php?s=&threadid=182510

kinda looking for help. will replacing the mains and rods fix the problem

Back to the main topic about the article, I have the article and I didnt see anything about lifter boares or cam berings all it was refering to main boares and it said that heat cycles and highmileage attributed to the the block main boares moving and getting out of line. the point they were trying to make was the heads and cam swap would increase stress and pressures on the crank and main berings witch would lead to spun berings, they recommended the performance bering because it has extra clearence and are therefor more forgiving as far as perfect alignement. I am in the process of building a LT1 for my 82 Z28 and after reading the article I am definatly having the block line honed and would recommend it to anyone planning on makin some horses with any block not just LT1s.
just my$.02 Jim

when i did my h/c swap on my Impala SS, i had very good friends at the dealership do it for me. they gave me a good deal so i couldn't pass up, plus i didn't have the time. anyhoo, they did the whole job and they told me everything looked excellent on the shortblock @ 60k miles. they did the swap with the motor out of the car and since then i've put 3500 miles on the motor and changed the oil about 5 times. running full synthetic seems to have kept it well. i've experienced no problems with anything so far and have been to the 6500rpm mark many times. i will go through my motor this winter and make sure everything is still tight and up to spec just to see how it's holding up.

Well im going to take the chance.. if i spin a bearing i'll just go bigger and better...
The car runs strong now and ive always been good with the synthetic oil changes.

I got a deal on some heads i couldnt pass up... Bad ass heads for 500 bucks from one of our kick ass camaroz28.com head porters. No one I know personally has spun a bearing after a heads/cam swap... I'll have it professionally done so i think the risk will be small..

It'll be done in 3 weeks. I'll let everyone know what happens.