Head Gaskets - Achilles Heel of 3.0L Engines

[latzke]

Nope- I confirmed in the 1997 manual. The M/T spec is 71 ft/lbs. Since that is for the metal gasket, I will go with that number and we will torque to 25, 56 and then 71.

Thanks. You've tipped the scales back. I've re-edited the torque section of OP to again indicate 71 as the spec.

Also, a word on the NSX head bolts. After discussing with several NSX experts and Honda engineers, the NSX bolts are not torque-to-yield (TTY) and are designed to be re-used. TTY bolts are designed to stretch and provide spring tension to provide the required clamping force. Many Ford and Chevrolet products use TTY bolts.

Interesting contribution.

I will try to grab a pic of the gasket.

Looking forward to it.

 

[Honcho]

What would be cool is if someone could measure a brand new bolt (they are the same for 3.0 and 3.2) to give us the proper spec. I think they are 114 mm but not sure.

 

[latzke]

Or just use new bolts every time out of preponderance of caution. $152/set makes it a relatively cheap piece of mind thing to add on (like replacing t-belt) to this procedure.

 

[Mac Attack]

Standard bolts like the NSX bolts are designed to use friction (along the inclined screw plane for you mech engineer folks) to provide the clamping force and are designed not to stretch. This is why both the 1991 and 1997 service manuals do not require replacement of the bolts.

Still, the experts advise to inspect and measure the bolts before re-use. Check the threads for any obvious signs of stretching or damage. Measure the bolt to make sure it has not elongated. If it is ok, you can re-use it without any problem.

I will try to grab a pic of the gasket.

The head bolts stretch, but you can't measure it. Stretch is fine, as long as the stretch is in the elastic range and not the plastic range where permanent deformation occurs.

This is shown in the other non-TTY re-useable bolts Honda uses (main cap bolts, rod bolts, etc). Even though it doesn't mean anything since I don't know the bolt material properties, I measured the OEM rod bolt stretch and got 0.008". The rod bolt returned to it's pre-stressed length when I removed it again (and again and again with my painful engine build). Therefore, the rod bolt stretch was within the elastic range of deformation, and no permanent plastic deformation occured. Unless you can measure the new bolt length and re-used lengths, it's hard to tell permanent deformation. Thread galling is important too.

There is one major benefit to going to head studs, and that is reducing the galling that occurs when tightening the OEM head bolts into the aluminum block threads. Instead, you nominally tighten the head studs into the weak aluminum block threads, and then torque the like stud material to achieve the desired tensile load.

FYI - Most European automakers do TTY too. Maybe the latest Japanese brands do too - I don't know. TTY is more consistent and provides a better clamping load. Of course, the downside is that you can only use them once.

Dave

 

[RYU]

I'm now researching Head Gasket replacement options for my 91. Some questions please.

1. Is there anyone out there who has successfully incorporated a thicker head gasket in an FI application?
2. ^^ Notice any difference in throttle response with the lower CR?
3. Notice any change to timing due to the farther cam gear lenght?
4. I believe a .051 thick HG will yield approx a 9.6:1 CR. Can anyone help me confirm this? My math seems incomplete but if the stock CR is 10.2:1 with a cyl bore 90.5mm and .030 OEM HG thickness...I don't know the piston stroke and combustion chamber volume (my search skills are failing me tonight)

 

[latzke]

I'm now researching Head Gasket replacement options for my 91. Some questions please.

1. Is there anyone out there who has successfully incorporated a thicker head gasket in an FI application?
2. ^^ Notice any difference in throttle response with the lower CR?
3. Notice any change to timing due to the farther cam gear lenght?
4. I believe a .051 thick HG will yield approx a 9.6:1 CR. Can anyone help me confirm this? My math seems incomplete but if the stock CR is 10.2:1 with a cyl bore 90.5mm and .030 OEM HG thickness...I don't know the piston stroke and combustion chamber volume (my search skills are failing me tonight)

When I asked SOS about thicker HG, to lower compression since I'm FI, response was they, "recommend against this (depending on thickness) as it will negatively affect the 'quench burn' in the cylinder."

 

[RYU]

I wonder what is "too thick".

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Great post BTW latzke

 

[michaelbrat]

Very helpful thread. Thanks.

Mike B