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Do not stud a Northstar

26K views 51 replies 18 participants last post by  Submariner409 
#1 ·
Does everyone understand why putting studs in the Northstar deck is not good?

I have been over this many times. Studs are too hard. The Head grows in size and the factory bolt are designed for this.

Say the head grows .5mm at 225 degrees from 50 degrees F. You stud the block and this cause the head gasket sealing ring to be compressed. What do you think will happen when it is 0 degrees out? What do you think it will do to the treads in the block?
 
#2 · (Edited)
Re: Do not stud a northstar

There's nothing wrong with studding itself...it's just a matter of whether or not the studs are produced with the same yield strength and modulus of elasticity as the factory head bolts (which they aren't). That said, I've been through this already in a discussion about whether or not overheating can cause a head gasket leak (and it can, for the same reasons you've just posted - the rate of expansion increases more than designed as temps rise higher than spec'd range - which crushes fire rings, stretches head bolts, and scrubs gaskets). I have found that most here think thermal expansion is a myth, which inherently tells us we don't need gaskets at all and should have no problem with todays manufacturing process machining the surfaces perfectly flat, torquing the heads down with 400 pounds on super hard fasteners, and installing 300 degree t-stats for ultra efficiency. But for some reason, no one does it!
 
#3 ·
Re: Do not stud a northstar

There's nothing wrong with studding itself...it's just a matter of whether or not the studs are produced with the same yield strength and modulus of elasticity as the factory head bolts (which they aren't). That said, I've been through this already in a discussion about whether or not overheating can cause a head gasket leak (and it can, for the same reasons you've just posted - the rate of expansion increases more than designed as temps rise higher than spec'd range - which crushes fire rings, stretches head bolts, and scrubs gaskets). I have found that most here think thermal expansion is a myth, which inherently tells us we don't need gaskets at all and should have no problem with todays manufacturing process machining the surfaces perfectly flat, torquing the heads down with 400 pounds on super hard fasteners, and installing 300 degree t-stats for ultra efficiency. But for some reason, no one does it!
Have you looked at the quality of the aluminum?
 
#5 ·
Re: Do not stud a northstar

AJ in your example even the highest expanding cast aluminum alloy's can not grow 0.5 mm. I don't have the measurement but "let's say" seems to work for you. If the compressed head thickness was let's say 3" and we torqued the heads down at 50* F. Then at 225* F the expansion under the head stud would be, remember worse case scenario, 0.176 mm (0.00692"). I myself believe this to be within the elasticity of the gasket materials and the castings. In fact I would say the pressure against them generated by torque is much higher than that increase by temperature.

I'll go with the prevailing wisdom on this one, in fact I already have. Also when I torqued my heads down I'm pretty sure it was warmer out, probably at least 70*F LOL.

Bolts are an accountants choice, an engineer will choose studs. I don't want any give with my gaskets, so the harder the better for me. Also I don't put my engine to the test before reaching normal operating temperatures. No need to temp fate unless lives are on the line.

Vernon
 
#8 ·
Re: Do not stud a northstar

Stoveguyy, what the discussion is about it not the expansion of the fastener length, though that is a good point. Rather it's about the expansion of the cylinder head itself, which is clamped down under pressure by said bolts or studs. AJ beleives that the studs won't stretch as much as the OEM bolts and therefore the heat induced expansion will crush the gaskets or pull threads out because the studs don't give. I think he overestimates the expansion of the heads. A five minute Google search provided me with the expansion rates of aluminum alloys per inch by degree F, Onlinecoversion.com allowed me to scale it back to mm. The reality is that's it's less than 20% of his guesstimate.

I think it's a long and thouroughly proven commodity and don't see any reason to fight against known reality's on this.

Vernon
 
#9 ·
Re: Do not stud a northstar

I worked at a Standalone Cadillac dealer for almost 6 years and then went to a Caddy chevy dealer. Just between those 2 GM dealers I have amost 10 years working on Caddy's and I have been with GM since 1999. I have repaired well over 100 Northstar's and I have never had a failure using GM bolts

GM bolts are Torque to Yeild
Some Studs are Grade 8
Other Studs are Tool Steel

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This is another issue
The casting have a tendency to shift or warp.
I have ran the GM tool down the bolt holes. This tool is a REAM type. You will some that are straight and other hole on the same block on the same bank that are bowed.
Now say you down have that long ream type drill bit. You drill the holes out and they are off a little bit. The Studs are too hard to flex.
And another issue
Some studs are placed up at the deck. Everyone should know that you would NEVER want to do this. It can distort the deck surface after torqued or even when going through a heat cycle
Studs are great for race engines, but what is the expected life of a race engine? 20k?

----------

I have a brand new set of 1999 cylinder heads. I will pull a head off the shelf and running it in my parts washer. I will mic it out before and after.

BTW these head are an alloy and not 100% aluminum.
 
#10 ·
Re: Do not stud a northstar

Digital thermometer says 74 deg
Digital Caliper shows 4.5645



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Digital thermometer read 121 degrees. It feels hotter, but my parts washer uses a home hot water heater element and thermostat.
The digital caliper read 4.5895

temp only went up 47 degrees and the head grew .025"


 
#11 ·
Re: Do not stud a northstar

I'd like to see you take a head bolt and a stud, compare lengths at room temp and 200F.

Another thought: Bolts are torque to yield, they stretch some during installation when approaching the intended clamping force. So, if the head grows .030 in height wouldn't the torque to yield bolts be subject to additional stretching, losing almost if not all clamping force when the engine cools?
 
#15 · (Edited)
Re: Do not stud a northstar

I'd like to see you take a head bolt and a stud, compare lengths at room temp and 200F.

Another thought: Bolts are torque to yield, they stretch some during installation when approaching the intended clamping force. So, if the head grows .030 in height wouldn't the torque to yield bolts be subject to additional stretching, losing almost if not all clamping force when the engine cools?
deformation is elastic - like AJ said, like a spring, and that keeps the clamping force very even and uniform across the whole head. If the yield strength is surpassed, the deformation is plastic and permanent.
 
#12 ·
Re: Do not stud a northstar

They work like a spring hose clamp instead of a worm/screw hose clamp. That is a very big part of my point.

The Main Bolt are hard and sound like you are breaking glass when you crack them loose and the main bolts are reusable.
 
#16 ·
Re: Do not stud a northstar

They work like a spring hose clamp instead of a worm/screw hose clamp. That is a very big part of my point.

The Main Bolt are hard and sound like you are breaking glass when you crack them loose and the main bolts are reusable.
If the main bolts are reusuable, why does the fsm call for replacement upon "removal" pertaining to the bottom end? This was a question that I pondered when resealing the mid case seal? Did the dealership replace bolts when a mid case reseal was performed or just reused the old ones?
 
#14 ·
JoeTahoe said:
I am on my 4th studded northstar with Northstar Performance studs, the first three are doing fine the first one I did was over three years ago. Mine was done two years ago and I have beaten the crap out of it with no problems. This has been my experience
I also have studded several, more the 20 with zero failures. Northstar performance has sold several thousand kits with zero failures. They also have the best warranty available on their rebuilt northstar engines which are studded with a 5 year, 100,000 miles warranty. Theories are one thing, but I go by real world performance and from what I've seen, studding is the way to go
 
#18 ·
Re: Do not stud a northstar

It might be instructional to spend some time doing Google searches of the world's engines - powering every type of conveyance imaginable - that use studs for iron, iron-aluminum and all aluminum engines - for cylinder heads, cylinder jugs and block assembly.

Properly designed and machined, it makes not one whit whether the fastener is a bolt or stud - they are both dynamically elastic over a specific range of tension and stretch. Both Jake and Tim have done their metallurgical homework ..................By all that's holy, a stud is nothing more than a bolt without a permanent head. The ONLY reason to use a stud in a Northstar block repair is to eliminate another set of threads in an insert.

I'm not knocking studs (or bolts) or their proper application - Just how long do you figure the cylinder studs are on this 18-cylinder 2800 hp air cooled aircraft engine (Super Constellation) considering that the engine is almost 6 feet in diameter ? (or the incredible range of temperatures over which it operates ???)
 
#27 ·
Re: Do not stud a northstar

It might be instructional to spend some time doing Google searches of the world's engines - powering every type of conveyance imaginable - that use studs for iron, iron-aluminum and all aluminum engines - for cylinder heads, cylinder jugs and block assembly.

Properly designed and machined, it makes not one whit whether the fastener is a bolt or stud - they are both dynamically elastic over a specific range of tension and stretch. Both Jake and Tim have done their metallurgical homework ..................By all that's holy, a stud is nothing more than a bolt without a permanent head. The ONLY reason to use a stud in a Northstar block repair is to eliminate another set of threads in an insert.

I'm not knocking studs (or bolts) or their proper application - Just how long do you figure the cylinder studs are on this 18-cylinder 2800 hp air cooled aircraft engine (Super Constellation) considering that the engine is almost 6 feet in diameter ? (or the incredible range of temperatures over which it operates ???)
I'm not sure if I totally understand him, but I don't think he's knocking the studs vs bolts thing - he's arguing that the studs currently available aren't the same elasticity as the factory bolts. He's arguing that Jake and Tim have done their metallurgical homework incorrectly...I think?
 
#19 ·
just another anecdotal reference point

we've been using time fastener bigserts and stock head bolts ever since these repairs began
we've probably done over 1000 of these jobs ... from what i understand the only ones that have come back were some of the very first ones before the bigsert were used and regular timeserts were used
(that was before the thread pitch was found to be the main source of the failure ... and the bigserts fixed that)

just fyi
 
#21 ·
I'm sure OP point was that the studs and headbolts are not spec'd the same. I don't agree, proper studs and installation using either is critical. Incorrect torquing of studs can cause issues for sure and in my opinion require more attention to installation, but so can bolts. If studs are a problem and will cause me issues 75k miles down the road big whoop. car's going to be junk by then anyways.
 
#22 ·
To reinforce Sub's aircraft engine point and to question the validity of AJ's "racecar" engine point. Here's what I say, look at every Piston driven internal combustion engine designed to travel over a million miles or log thousands of hours at max torque. Tractor, Semi, train, ships, submarines, construction equipment, industrial engines, ad-nausia. What do they use? They use studs. The type of metal is accouted for in design specs but otherwise irrelevant to choice of head fastener.

Bolts for heads are for costs or ease of service in applications where a fastener caused failure doesn't cost lives or significant relavent currency. The car is warrantied for 100K or less after that if your car breaks down, fix it or buy another one, otherwise nobody cares. So they get head bolts. I have to fork out bucks and spend a ton of time fixing this Caddillac if the head seal fails again. So it got studs.

That being said I don't think a Norm's or Big-Serted block with new bolts is a problem. Those solutions should work great.

Vernon
 
#25 · (Edited)
The Lower Crankcase Installation document that you posted Id #169055.

That one especially I was concerned with because if you reseal the bottom of the motor, the main bearing bolts are broken loose. At that point bearings were to be replaced along with the bolts. I'll have to find the page in my manual.

Yet, if there are revisions and certain procedures aren't deemed necessary anymore I guess that's a good thing.

It's a good motor with some unfortunate issues......

Thanks again AJ for the detailed information.....
 
#26 ·
Just for future reference, when I went through my Northstar I had issues with the main bolts. While loosening them by hand, with some quick tugs, I broke three of them. One was snapped in two with the lower half stuck in the block to the point I had to take the short block to a welder for extraction. After the first one broke I proceeded with extreme caution on the others and found two that had cracked to the point they were visibly twisting apart. Keep in mind this is not my first engine overhaul, I didn't go ape on it. These bolts are very hard, think brittle, and very thin, like a pencil. Because of my experience I will always replace them once removed. I believe it's not worth the risk trying to determine if the popping I hear coming out was threads or bolt shanks. I think I spent under $70 wholesale for all new main bolts. In any case never use power tools to remove or install them.

Vernon
 
#29 ·
The distinct snapping noise of those bolts breaking loose is bone chilling.....

I said to myself....DAMN what in the world did they use to install these bolts?

I like Vernon, decided after that adventure not to reuse the old main bolts.

Again, no power tools for insertion or extraction.......
 
#30 · (Edited by Moderator)
Hey guys,
This is Tim, interesting conversation, hats off to AJ for his theories.
However, as good as he sounds, he is incorrect in theory. Having a few years as a Cadillac mechanic does not one make an automatic engineer.
Whether you ask me or Alan Johnson with CHRFab, you will find we have done our homework, we are engineers it is what we do.
GM's reason for torque to yield bbolts was for the weight and nothing more, they use minimum weighted material in a lot of different areas of the car, likewise this was the purpose of the aluminum engine.

One more thing, it is true that studs should never be at the deck surface, this is common knowledge
AJ is correct on this issue. Our studs have been engineered to go to the correct depth and we provide replacement dowels
for this purpose. Alignment studs are above the surface and will in facr distort the deck and should not be used.
Using correctly engineered studs will far out perform torque to yield bolts, hands down.

We have zero failures, but we have had to repair many after Cadillac dealers service departments sert jobs have failed.

The big Serts I just read about is also a set up for failure, and once they fail? The block can never be repaired again.
Big Serts should never be an option.
 
#31 · (Edited by Moderator)
I have been a GM trained Cadillac Tech since 2003. 6 years of that I was at a standalone Caddy dealer.

I have misspoken here. The OE bolts are not Torque to Yeild. I have posted this on the forum many times since 2007. OE Northstar bolts are reusable per GM's documents, but you need to clean the bolts, reapply the threadlocker, and apply sealer to the washer to keep fluid out of the bolt holes.

I have use the GM big serts 1 time and I have to plans on ever doing that again. I have used the NS300L inserts and feel they are the best choice.
 
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#32 · (Edited)
FWIW ............

Tim Carroll is a Northstar repair mechanic and operates a shop in Texas. He has a vested interest in engine studs.

AJ is/was a Cadillac Tech who also does engine and PCM work on the side.

Neither of these businessmen is currently an authorized vendor in CF, so plan your communications accordingly.


........ and here's a BIG quote from the 2002 GM/Cadillac service manual:

Engine overhaul, cylinder head bolts ......... procedures -
Left bank cylinder head ........ (italics mine)

Removal:

4. Remove and discard the ten M11 internal drive cylinder head bolts.

Installation:

2. Make sure any old thread sealant material is removed from the cylinder head bolt holes in the block (Is this the source of AJ's advice ?)

5. Place the cylinder head on the deck face
IMPORTANT: Do NOT reuse the old M11 cylinder head bolts......
6. Install new M11 cylinder head bolts in the head."


I have not found the TSB that reverses this procedure i.e. - Use the head bolts over again - and my TSB list dates back from 01/28/13.
 
#34 ·
You are correct and you need to go back to the original training manuals to find the information. The bolt part number did not change

Now the Felpro and Engine tech bolts state that they are Torque to yield bolts.
The OE bolts per GM are not Torque to Yield.

I recommend replacing the bolts every time
 
#35 ·
People have been studding engines since the beginning of high performance building ( including aluminum block engines since 1990 in the old DOHC 349 Cubic Inch in the Corvette ZR-1). any time a real mechanic puts real horsepower in an engine one of the very first things done is studding.

Tim i know our companies dont have the greatest terms but you have to agree that studs are the only way to go, especially in these northstars.
 
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