This is straight from GMHighTechPerformance Magazine
Nov. 2003 Volume 9, NO.7

Heads should NOT be removed from high-millage LT1's inless the main and rod bearings are replaced. Even engines that seem to be in perfectly fine operating condition.

Quote " LT1 engines can have misaligned main bearing bores from thermal fatigue and that I ( Not myself ) shouldn't try to put new heads or a cam on it. " The tourque from the bolts being tightened can disrupt the block and cause bearing spinnage.

GM High Tech Performance's response to this was " The speed shop is correct we highly do not recommend that you try and replace and internal parts in that engine inless you plan on rebuilding the shortblock. We have witnessed numeruous bearing failures in LT1's from installation of cylinder heads and/or camshaft. It has been our common practice to pull the engine and replace the main and rod bearings with Clevite 77"H" bearings and then reassemble.


So how many guys out there have actually spun bearings directly related to head/cam installs ?

 

Thats the first i've ever head of this.

Let me get this strait. Heat warps the main bearing bores/caps and the bearing/crank/cap wear together in that warped state.

Removing the heads and retorquing the bolts down torques the block and shifts the warped center caps?

I doubt it, highly doubt it for a number of reason that I cant exactly put into words but i'll try.


This means the the head bolts are twisting the block. The bolts would not line up the block was being twisted, even the slightest bit...

 

I will give my input on it.Yes that is probably true to a point.Some of it has to do with the previous maintainence,and cleanliness.Also,people do H/C and go out and rev it to the moon. Having just done H/C myself at 70K miles without problem,I say go for it.

 

I put H&C in on 112k and have about 800 miles on it without any problem yet.

Here is something else to think about when people blow head gakskets on Higher milage LT1's I dont ever hear of anyone having bearing trouble.

IMO I would worroy about it to much.I would have to see some "Facts" to back this up.

GMHTP also said the spec stage 3 clutch didnt chatter

 

wtf... a tad over a 1000 miles on my car and A-OK (knocking on wood). I guess it depends on previous care to the block. I would think.

 

Torquing the head bolts will "twist" the block. This kind of test is performed many times in new engine development at an OE. The cylinder bores distort, main caps distort, etc. Heck, even head gasket design can change bore distortion.

I wouldn't worry about it too much though. I would highly doubt it would cause a failure in many engines unless they already had uneven bearing wear, or were going from 230 RWHP to 400 RWHP on a 100,000 mile engine or the like.

 

So this ONLY applies to LT1's or not and every single SBC, BBC, SBF, BBF, SBM, BBM that anybody has ever put new heads on is at risk? I think not. People that put head and cam on they cars are at risk of ruining the short block because:
1. Spin many more RPM than stock
2. Produce much more horsepower and more torque than stock
3. Usualy don't drive their h/c cars like little girls
( and finally but not least...the most important rule there is)
4. Man Cars Break
So by me torquing my new heads on my car with these sub 100 ft.lbs. of torque I am literally twisting the block. I doubt it. Please pass me what ever that GMHTP guy is smoking because it is some pretty serious stuff.
I blew my head gaskets on my car, replacing the head gaskets turned into "lets dumb a few thousand and make this car fast." So if what this guy is saying every motor that goes into the dealer to replace head gaskets that blew are at risk of letting the bottom end loose. I am afraid not.
:BS:

 

what about cars that blow head gaskets that keep running forever. My old nissan truck blew a head gasket at 20,000 miles (twenty) of solid city driving. Replaced it. 10 years and 180,000 iles later....I sold the car with OVER 200,000 miles and the car ran like a champ. Not a single problem.

 

As I said in advanced tech i think the MAIN cause of it is overrevving the motor on 10 year old bearings. Theres your explanation about the cars getting head gaskets fixed at a dealer.

As far as distorting the block, hell yes cylinder heads and main caps distort the block. If you think they dont, why are blocks bored with torque plates on them? To simulate the clamping forces cylnder heads put on the block.

 

Motor Sport Tech use to say the same thing, I've seen to many camd LT1s to agree with it though. People I knew personaly with cams

JeffStar
Slim
Joe94B4C

Not one spun a bearing due to the cam.

 

I do understand that. But how would it explain that quote? It is basically saying, "remove the heads and you will end up replacing the bottom end" And yes I understand the torque plates.. I just disagree with the first post...

I senses tell me this thread is going to blow up big time... once some of the "big dawgs" see this thread... injuneer, ken, brent... hehe

 

*shrug*

Hell i believe the shop who is saying that does heads/cam swaps on stock shortblocks. Who knows.

i think its just a problem of oiling the main/rod bearings due to the high rpm people turn with their new heads and cam.

 

Actually Jayson Cohen of MTI came up with that response, not some automotivewannabeGMHTPwriter. I imagine he said that for "business reasons".

On a side note, I did my current set-up in my sig with OVER 100K miles, and it runs just fine...

 

werd

 

Hey what the hell.....go for it. I spun my bearings on 4,7 and 8 on the crank and only had 78K on it and didn't do crap except bolt ons. If it goes it goes.