BodybyFisher

Head bolt torque, NS

Recommended Posts

The prooer head bolt torquing method uses a combination of traditional torque tightning in combination with torque angle.

My uneducated quess is that this methodology removes the potential for over torquing a head bolt due to oil on the threads thereby stripping the threads out of the hole due to overtightening because the threads slip easier giving a reduced false torque indication.

Question 1:

Has anyone estimated what the equivalent traditional torque is of this prescribed methodology?

Question 2:

Before torquing the head bolts or any other bolt for that matter, should the threads be cleaned and dry or lightly oiled?

Question 3:

Why is it necessary to tighten the headbolts to the point of stretching? Expanding and cooling of aluminum heads?, to maintain clamping force?

Question 4:

Why didnt GM specify a specific torque like the old days on the NS? This may have been answered above already.

Thanks, I am trying to learn more about clamping force, aluminum, expansion, etc.


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

The prooer head bolt torquing method uses a combination of traditional torque tightning in combination with torque angle.

My uneducated quess is that this methodology removes the potential for over torquing a head bolt due to oil on the threads thereby stripping the threads out of the hole due to overtightening because the threads slip easier giving a reduced false torque indication.

Question 1:

Has anyone estimated what the equivalent traditional torque is of this prescribed methodology?

Question 2:

Before torquing the head bolts or any other bolt for that matter, should the threads be cleaned and dry or lightly oiled?

Question 3:

Why is it necessary to tighten the headbolts to the point of stretching? Expanding and cooling of aluminum heads?, to maintain clamping force?

Question 4:

Why didnt GM specify a specific torque like the old days on the NS? This may have been answered above already.

Thanks, I am trying to learn more about clamping force, aluminum, expansion, etc.

GM's torque specs. for the head bolts are dry. The new bolts have a microencapsulated thread locker applied that acts as a thread locker and an anti-seize compound. The bolts should NEVER be oiled.

The head bolts do not stretch per se. - microscopically, yes but the Northstar head bolts are not torque to yield bolts. The only reason you cannot reuse the head bolts is that there is no practical way to re-apply the microencapsulated thread locker in the field so it is easier to specify new head bolts.

The torque-angle method is far more accurate in consistent clamping force as it takes friction out of the equation. With a conventional torque spec. (ft.-lbs. only), there is a great deal of friction that develops the tighter the bolt is tightened. By torqueing to a low initial torque to set the baseline, friction is at a minimum. By torqueing three passes at 60° for example, the gasket compression distance is known to be half the distance between threads.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Thank you, I followed you till this point:

"By torqueing three passes at 60° for example, the gasket compression distance is known to be 1-1/2 times the distance between threads."

I understand the 3 passes at 60 degrees or a total of 180 or a half a turn, but why is the next statement important?, can you explain?

"the gasket compression distance is known to be 1-1/2 times the distance between threads."

I am not clear what you mean by that.

Have you ever tried to estimate a final traditional torque equivalent after the 3 passes? For curiosity purposes?

Thanks Kevin,


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

Thank you, I followed you till this point:

"By torqueing three passes at 60° for example, the gasket compression distance is known to be 1-1/2 times the distance between threads."

I understand the 3 passes at 60 degrees or a total of 180 or a half a turn, but why is the next statement important?, can you explain?

"the gasket compression distance is known to be 1-1/2 times the distance between threads."

I am not clear what you mean by that.

Have you ever tried to estimate a final traditional torque equivalent after the 3 passes? For curiosity purposes?

Thanks Kevin,

My mistake - it should be 1/2 turn or half the thread pitch. I edited my post to correct it.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Kevin why is half the thread pitch relevant? Thx Mike


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

Kevin why is half the thread pitch relevant? Thx Mike

It is just the distance the gasket is compressed. It is a relatively constant number compared to a standard torque value.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Oh I understand now thanks


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

I hope I don't sound like too much of an idiot for the following:

These numbers are not at all realistic, I am going to use them for simplicity. If the head gasket were 2" thick and each thread on the bolt represents 1", when done turning the bolt you would be compressing the gasket 1/2" correct? So my question is what is the clamping force being applied by? if not bolt stretch, is it the aluminum trying to decompress, the gasket trying to decompress? From reading the previous posts I understand the reason for using the degrees is, it is more accurate way to reach desired compression of all parts involved right? Having asked these questions, then why not a lock washer under the bolt as many parts use throughout a car?

Anyway thanks to whoever responds for the education.

Share this post


Link to post
Share on other sites

I hope I don't sound like too much of an idiot for the following:

These numbers are not at all realistic, I am going to use them for simplicity. If the head gasket were 2" thick and each thread on the bolt represents 1", when done turning the bolt you would be compressing the gasket 1/2" correct? So my question is what is the clamping force being applied by? if not bolt stretch, is it the aluminum trying to decompress, the gasket trying to decompress? From reading the previous posts I understand the reason for using the degrees is, it is more accurate way to reach desired compression of all parts involved right? Having asked these questions, then why not a lock washer under the bolt as many parts use throughout a car?

Anyway thanks to whoever responds for the education.

Correct - 1/2 turn (180 degrees) in your example would be 1/2" of compression. It is the tension of the head bolts that provides the clamping force. In traditional torque specs., there is so much friction once the bolt is tightened that it can result in more variation in the clamping force. In an iron engine, it is not that big of deal but in an aluminum engine, it is more critical.

When a critical fastener needs to be prevented from coming loose, it is usually a thread locking compound that is used and is more effective than a lock washer.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Good stuff, thanks

So, if you were to purchase new head bolts, since oem are microencapsulated with thread locker would you stay with oem or is a brand like fel-pro or other after market bolts sufficient?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

You can't go wrong with OEM. Fel Pro is good also - they might even make the OEM bolts as Federal Mogul is a huge OE supplier.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Thanks

PS, airmike, the only bad question is the question not asked.

I have experienced people who think that asking questions is a sign of weakness or a lack of experience on a subject. Sometimes questions are asked to embellish, confirm or explore ideas and understanding.

Ideas I postulated 10 years ago on the Northstar have only recently been confirmed to be true and only deepens my understanding of this awesome engine.

Ill be learning till the day I climb in my casket


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

When AJ was around, we had discussions and photos of deteriorated aluminum that was obvious when drilling the block for timeserts. The material was dusty and powdery instead of metal filings and the damage was caused by electrolysis and most probably coolant intrusion into the threads accelerating the problem.

1) the head acts as a ground for the high voltage applied to the spark plugs. Unfortunately the head bolts probably carry some if not all of that ground between the head and block where most of the ground is. I do not notice any heavy grounds between the head and the block. Does anyone think that a strong copper ground on each side of the heads between the head and the block, would lessen the potential for electrolysis?

This may have to do with current taking the path to least resistance and that may in fact be the head bolts and it is not preventable

2) Given the potential for deteriorated aluminum does anyone think that bigserting a block the first time makes more sense as the hole that is drilled is larger ensuring that you get deeper into the aluminum material? Now I think that leaves you with no place to go if a bigsert pulls but the chances are the bigsert will grabs healthier aluminum.

Just thinking here and interested in ideas thx


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

Pretty sure there's a ground strap on the rear head. I don't recall if there is one on the front. I don't think that would have an effect on the block deteriorating or not.

You could use Bigserts but you'd need to buy that kit also. That's a pretty big expense only to find out the weak material exceeds the diameter of the Bigsert.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Pretty sure there's a ground strap on the rear head. I don't recall if there is one on the front. I don't think that would have an effect on the block deteriorating or not.

You could use Bigserts but you'd need to buy that kit also. That's a pretty big expense only to find out the weak material exceeds the diameter of the Bigsert.

Interesting Kevin about the weak material exceeding the diameter of the bigsert.

Ok, now consider this, my inclination is that weak material would increase resistance if you were to test it with an ohm meter, what do you think?

I am thinking that bad material would be obvious as it would show increased resistance. I would need to develop a probe for the purpose that maybe contacted the hole at a single point after drilling, then test the hole at 12, 3, 6 and 9 o'clock. What do you think?

When a hole that is being drilled emits bad powdered material shows up, this premise could be tested


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

The weak material in the block may exceed the diameter of the Bigsert. There is really no way to tell other than to drill but then then you need to buy the Bigsert kit plus the oversized head alignment dowels which is a significant expense.

I'm not a metallurgist by trade so I can't really speak to it's properties. A metallurgist would be able to identify the specific cause of the failure. I suspect if the material is oxidized, the resistance would increase but what would be the acceptable limit of the resistance? That is the key unknown. Then you'd need to consider the accuracy/precision of the test device.

Have you run across a block that has the powdery material?


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Not yet, but once one starts to timesert these engines its something to keep an eye on. I am just exploring things that are on my mind.

My gut is that if there is bad material it will be obvious during the drilling process.


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

My gut is that if there is bad material it will be obvious during the drilling process.

That is correct. When drilling there will be a LOT of chips - you will know if the material is not sound.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

My gut is that if there is bad material it will be obvious during the drilling process.

That is correct. When drilling there will be a LOT of chips - you will know if the material is not sound.

Terrific, thanks Kevin. I imagine the block scrap at that point?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

My gut is that if there is bad material it will be obvious during the drilling process.

That is correct. When drilling there will be a LOT of chips - you will know if the material is not sound.

Terrific, thanks Kevin. I imagine the block scrap at that point?

If the regular Timesert drill produced powdery crud and it won't clean up with the Bigsert drill, the block is scrap.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Share this post


Link to post
Share on other sites

Thanks


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

On my 1997 ETC, the battery ground cable is double. One cable runs to the engine block, the other to a chassis ground (not the cradle). I never found an engine ground strap, so I think that the double ground battery cable *is* the ground strap.

I have the FSM for all GM cars and light trucks for 1998 through 2012 if anyone has a serious question about engine grounding on a particular model and year.


CTS-V_Dashboard.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

Share this post


Link to post
Share on other sites

On my 1997 ETC, the battery ground cable is double. One cable runs to the engine block, the other to a chassis ground (not the cradle). I never found an engine ground strap, so I think that the double ground battery cable *is* the ground strap.

I have the FSM for all GM cars and light trucks for 1998 through 2012 if anyone has a serious question about engine grounding on a particular model and year.

That is true Jim. My reasoning for asking about grounds is not related to the ETC, its related to the ground between the head and block, the bolts are in effect the ground between the two. The current produced by the coils flows through the bolts potentially encouraging electrolysis. I was thinking that placing copper grounds between the head and block on each side would lessen the current flow through the bolts.


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

It never occurred to me that there would be any significant resistance between a mounted head and a block.

The spark current circuit on an early Northstar is through the coils and wires, through the two plugs on each coil, and grounded through the heads, so the circuit is closed by spark current passing between the heads.

One current path would be at the compression sealing rings at the bores. These should provide excellent electrical contact. But even if that is a good electrical path, the head bolts probably are too, and fast electricity like spark currents tends to do what it wants to do, not what you think it will do.

The bypass seems like a good circuit but that is going to have bolts with threadlock and a gasket, twice. The biggest and best circuit is going to be through both head gaskets and the block.

I didn't find anything quickly on the WWW about how sensitive Loktite is to electric currents, or whether it maintains a film like oil that interferes with electrical contact.

It seems to me that a ground couldn't hurt. The simplest thing to do to help with the spark grounds would be to add a wire that goes between the heads.


CTS-V_Dashboard.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

Share this post


Link to post
Share on other sites

Jim, my thinking process also identified the sealing rings, and I especially do not want those completing the circuit to ground.

You know, I am simply exploring here, kind of brainstorming ideas with the guys. My thinking may be flawed, and if it is, I know the guys will set me straight, the designers may have considered it, there may be no way to remedy my concern and I may be worrying about the deck chairs while the Titanic sinks, but, I am just thinking out loud, in a way.

We all here have differing experience, I miss, JimD, Ranger and others to extensive to name off the top of my head. You describe this an a gentleman's board, I like to think of it as a thinking man's, opps, person's board. We will see things happen as the Northstar ages that the original designers, those who validated it, will never see. Things will happen no one has encountered before, that will cause a cascade affect. I heard a new one from our friend barczy01 they other day, where a cheap secondary tensioner was used that collapsed and blew out a bank of valves because the cam jumped teeth, WOW... that is a new one on me, that is terrific to know about. I plan to go really deep with this engine if things go right for me. I think its an engineering marvel. I don't think that a lot of people really understand it or know how to maintain it, plus I believe 100% that most mechanics are a compromise between doing it right and the time is money reality of earning a salary. I have seen so many bad, unethical, careless and abusive mechanics in my life but on the other hand I have seen some of the best. Unfortunately the first type are all too common and for an engine like the Northstar that requires specific care, they all too often mess it up, misdiagnose it or have a negative bias toward it.

You mentioned quick high voltage being unpredictable and nearly uncontrollable and yes, I agree with that, but in spite of that thought, if you control it, you can direct it. Think lightning rod, no lightning rod, the lightning WILL find ground when it hits your house, I have seen lightning enter/exit and travel down walls, though a house till it does find a ground, I did not experience that first hand thank heavens. The lightning rod provides it with a definitive path to ground, saving the lightning from searching.

Here is an interesting story, my cousin has a house in Mantoloking, NJ between the beach about 2 blocks to the east and on the bay with a dock on a dead end canal. Let me tell you about the lightning the summer I worked there, serious lightning. She has a 40 foot wide trex deck with a 40 foot wide removable canopy that has a 2 1/2" galvanized pipe structure that is bolted to the house and bolted to the deck. Its a big structure that is about 15 feet high, 40 feet wide and 20 feet deep. One day I am sitting there and I notice that, its NOT grounded. I called the installer who puts up the canopy material in the late spring and asked him, 'shouldn't the steel structure be grounded in multiple places"? And he said, you know NO ONE has asked that question before, you are the first.......>insert shocked baby face here< that is a huge structure a big steel 'umbrella' on the water in a high lightning area just looking to be struck by lightning. IF it is struck by lightning, that lightning WILL find a ground if it needs to blow through the house and kill someone. My daughter works at a summer camp that has a huge covered open metal structure and EVERY leg is grounded, so my thinking is NOT so far fetched. You have to ask yourself why was the installer 1) never asked that question before and 2) why doesn't the municipality require grounding?

Back to the Northstar, each spark plug is grounded to the head, the head gets its ground through the head bolts and fire ring. A ground at either end of the head would be too far away, the charge would go to one of the 4 bolts that surround the cylinder and not necessarily pass one of those, and go to the end ground. I even considered that aluminum is less conductive and poses a higher resistance than copper. And it would find the least resistance of copper, but its too far, I think

Metal%20Conductivity_zps1qyb4gpt.jpg

Reference: https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

But in the end, I think the nearness of the bolts to the high voltage discharge to the ground provided by one of the 4 surrounding headbolts would be near impossible to attract away from the head bolts using copper grounds between the head and block to minimize electrolysis of the block material. So, we must pay strict attention to the coolant PH to discourage electrolysis which is the reason why maintaining the coolant is so imperative. It may make sense to think about grounds that need restoring once in a while to minimize electrolysis. I have a salt chlorine generator and to stop electrolytic corrosion I installed a grounded anode in line bonded to the pool, I considered a skimmer basket sacrificial anodes as seen on boats but opted for the inline anode.

Hope I am not appearing to chase my tail

Interesting that others think of this, I just found this

http://www.autowerksofamerica.com/article/tech/tech-articles/general/electrolysis.htm


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.