Re-Torque Head Bolts on Z24

[spddm0n]

I was just reading another thread about re-torquing head bolts on the Z24.  This scares the crap out of me. 🙂  I have been working with the VG33E engine a lot, and this engine is notorious for the head gasket failure.  

 

Many Nissan enthusiasts ask me about whether or not my 720 has ever blown a HG, and I still find myself wrestling with how common this seems to be with Nissan (or maybe it's just that I have 5 of them). 🙂

 

I read about re-torquing them and I thought I'd just post this up for some thoughts, since I left my FSM in the shop and I won't get to it until tomorrow.  

 

The only thing I found unclear about the procedure is whether or not to actually remove each bolt, entirely, from the block.  Normally, when I install head bolts (after removing the cylinder head), I always make sure the holes in the block are clean and the bolts have just a tad of fresh oil to ensure proper torque is reached without binding. 

 

I re-torque head bolts on my race car, but this does NOT include loosing the bolts.  I simply check torque and add more if they have lost some (ARP hardware that is not torqu-to-yield).  I only do this once after a few heat cycles of the newly installed cylinder head.

 

Does the FSM call for removing the bolt, or simply loosing it some?  In the thread I read, a guy said he loosened it a "quarter stroke", but I can't figure out what that might mean. 🙂

 

Thanks!!

[datzenmike]

Before loosening I would try tightening them to spec just to see if the bolt is actually loosened and will turn. Then loosen fully and re-torque to 60 ft lbs.

 

I think the Z24 engines are NOT (they better not be!) TTY bolts. All you need do is loosen a turn or two after that snap sound when they loosen and then tighten directly to 60? foot pounds. If the head gasket has never been changed then the threads and holes should be clean.  Only one bolt loosened at a time will allow you to do in any order you like.

 

Re-torque refreshes the clamping pressure on the gasket.... which seems to slowly fade. I've heard people say they have found head bolts so loose they can turn with their wrist. I can't see why a gasket would continue to compress and I don't think the bolts loosen. I have noticed that the Z24 block threads start deeper down into the block than previous blocks like the L20B. Whatever the cause, clamping pressure is lessened over time and you can imagine where that will lead. There are limits to how many times you can add more tightening to a gasket. I should imagine once re-torqued the problem lessens and may even stop. If you check it once or twice a year with your oil change and it hasn't changed, you could extend your checks. 

[spddm0n]

Wow. Great advice. 

Good questions about what’s happening with the gasket and it’s crush. Hard to say. I like that somebody else is thinking about it though.

 

As I’ve worked toward identifying the many aspects of head gasket failure in the VG33E, one thing I noticed is the TTY bolts often fail on installation. I notice when I “add” some torque to existing factory installed bolts, they don’t increase in torque resistance when 

I add torque. They simply “turn”, indicating they have already been turned past their highest torque resistance point in the plastic range of the bolt’s deformation range. I imagine this happened at the factory. 

 

I also found this to be the case when using new TTY bolts (made by Victor Reinz - well, who knows who actually makes anything these days).  I decided to use non -TTY bolts. I cut my own to length, from a class 12.9 bolt. Saved hundreds compared with ARP.  But then again...I’m building several of these engines. 🤓

 

I love the original idea of uniform clamping force and no need to re-torque TTY bolts, but I fear they are tougher to make than people think. Quality these days is questionable in new auto parts. 

 

 

[datzenmike]

I built up a Z24 with an L20B head last fall. I did the same thing with 10.8 threaded stock to make studs. As mentioned the Z24 block has the threads deeper. I was afraid the L series bolts were not going deep enough to get all the threads. 

 

TTY.... just another way to make something cheaper. If the head comes off you have to buy new ones. Win win for the car maker.

 

 

[spddm0n]

18 hours ago, datzenmike said:

I built up a Z24 with an L20B head last fall. I did the same thing with 10.8 threaded stock to make studs. As mentioned the Z24 block has the threads deeper. I was afraid the L series bolts were not going deep enough to get all the threads. 

 

TTY.... just another way to make something cheaper. If the head comes off you have to buy new ones. Win win for the car maker.

 

 

Agreed.  The VG33E is the same way (threads deeper in the block and the holes in the block do not stay threaded all the way to the surface.  I did a lot of math to try and utilize as many threads as I could without bottoming out.  Studs (instead of bolts are better for this reason.  Did you use a stud or a bolt?

[spddm0n]

Does anyone know why this procedure is not described in the general maintenance schedule in the FSM?  I did find this little blurb in the EM section describing the process to install the cylinder head.  It suggests doing this when "performing normal maintenance and inspection".  

[wayno]

I just don't see manufacturers pointing out a flaw in their engines in the factory service manual. 

 

[spddm0n]

2 hours ago, wayno said:

I just don't see manufacturers pointing out a flaw in their engines in the factory service manual. 

 

Agreed.  Hmmm...Well, I jut re-torqued them.  Interesting process.  It took quite a bit of torque to loosen them, after all these years (likely the original bolts).  I loosened the bolt until it was "free", then I re-tightened it until it was strongly snug, then I loosened it again just a bit (it didn't break completely free), and then I torqued it in one final movement to spec.  The problem with this sort of procedure is the amount resistance on the threads that accounts for loss in overall torque (when both sets of threads are not clean and new 🙂 ).  A torque angle gauge would be better for this procedure.  I wish I had one of those. 🙂  Being a 90 degree turn, I probably could have estimated pretty close.

[datzenmike]

On 7/14/2019 at 4:34 PM, datzenmike said:

I built up a Z24 with an L20B head last fall. I did the same thing with 10.8 threaded stock to make studs. As mentioned the Z24 block has the threads deeper. I was afraid the L series bolts were not going deep enough to get all the threads. 

 

TTY.... just another way to make something cheaper. If the head comes off you have to buy new ones. Win win for the car maker.

 

 

 

6 hours ago, spddm0n said:

Agreed.  The VG33E is the same way (threads deeper in the block and the holes in the block do not stay threaded all the way to the surface.  I did a lot of math to try and utilize as many threads as I could without bottoming out.  Studs (instead of bolts are better for this reason.  Did you use a stud or a bolt?

 

 

I've been giving that advice for almost 15 years I think. So long ago I don't quite remember where I got it, 720 forum most likely. It may be a service bulletin for dealers to re-torque any Z24 in for tune ups? Simple and easy enough an as they tend to blow around 100K it cheaper than replacing one.  

[spddm0n]

1 hour ago, datzenmike said:

 

 

 

I've been giving that advice for almost 15 years I think. So long ago I don't quite remember where I got it, 720 forum most likely. It may be a service bulletin for dealers to re-torque any Z24 in for tune ups? Simple and easy enough an as they tend to blow around 100K it cheaper than replacing one.  

Yeah.  Interesting.  I will say that my experience with Nissan and blown head gaskets (well...I buy a lot of them with blown head gaskets anyway, made me really nervous to perform this type of procedure.  I'm super anal putting the heads back on my VG33E's.  This is also the first time I've seen a 4 cyl (or any inline engine for that matter) require a head bolt torque procedure that requires tightening to some intermediate level of torque, loosening them, and then torquing to the final spec.  I thought that might have been due to the lower intake manifolds on those engines (V6 or other V-engines), but perhaps it's simply due to getting a better crush on the gasket so that you don't have a bit of "spring" in the gasket itself.

 

Interesting.  Thanks for the advice through this procedure.

[datzenmike]

To be clear... when installing a new gasket, they are all torqued in sequence, to 20 then 40 then 60.

 

R A D

8....7

4....3

2....1

6....5

10..9

 

Re-torque is simply loosening and immediately tightening to 60, each bolt one at a time. As only one bolt is loose at any one time you can do in any order you like.  

[spddm0n]

27 minutes ago, datzenmike said:

To be clear... when installing a new gasket, they are all torqued in sequence, to 20 then 40 then 60.

 

R A D

8....7

4....3

2....1

6....5

10..9

 

Re-torque is simply loosening and immediately tightening to 60, each bolt one at a time. As only one bolt is loose at any one time you can do in any order you like.  

Cool diagram!  🙂

 

Yeah, the FSM gives a bit more detail, as does the FSM for my Frontier/Xterra VG33E's.  For the Z24, they tell you to tighten to 22, then 58, then loosen them all the way.  Them go to 22 again and if you have a torque angle wrench to turn clockwise another 90-95 degrees (54-61 if you don't have the torque angle wrench).  I have found that due to the irregularities with fasteners, the gaskets, and the surfaces themselves, the resistance to torque is significant at higher torque levels and in order to actually get accurate "clamping force" on the head/block, it's best to turn each bolt the same amount, measured by the angle turned.  I usually mark and measure my bolt heads against the interior of the head and I can get pretty close.

 

Head studs seem to eliminate a lot of the resistance to torque and provide a more uniform clamping force when all torqued properly.  Those manufacturers typically call for a torque spec and not an angle.