Stripped head threads for center cam tower

[Ben's Z]

Things were going great. I got my 77 cam out of my old engine and had it moved over to my P90. Had some of the bolts reasonably tight using my 1/4" drive, went to torque the cam towers to 30 ft lbs. and whamo the short side bolt stripped out the threads in the head. Took everything off and all the other threads looked great. Please tell me this head is not trash now? Heli-Coil? Machine shop to TIG and re-tap? Thank god I have a beautiful family and don't have cancer because my world of all things Datsun is taking large dumps on me right now.

[Tony D]

Yes.

[Z Greek]

30 sounds way too high, Ben. 15 or so should be fine for an 8mm bolt.

[Tony D]

Argh... "Yes"

 

http://www.classiczcars.com/forums/thread3174.html

[NewZed]

Burned by the Page 94 typo? "How to Rebuild..."?

[Tony D]

Standard lubricated M8 torque is less than 30 ft-lbs...

Try to torque a bolt with oil on it to that and it will pull out of most steel sub assemblies!

 

But yeah, brake cleaner cleaned 12-15 ft-lbs is more than enough (144 ~ 180 in-lbs, actually...if you're using a ft-lb tool on cam tower or front co er bolts, I don't know what to say...)

 

"Head work is a precision bit of work, best accomplished without large hammers and I-R Thunderguns..."

 

Just curious, anybody look what the diamond/circle/square drawing in the FSM calls for in EM section?

Edited November 24, 2012 by Tony D

[Ben's Z]

Burned by the Page 94 typo? "How to Rebuild..."?

Yes I am using the "how to" manual. With the crap this dude has taught in this book I should burn this blasphemy. From now on it is the FSM on my laptop. Thanks guys.

[Ben's Z]

I will step it down to my inch pounds 1/4 drive wrench Tony. I should have trusted my instincts that felt like an awful lot when I was doing it. Luckily I have a Heli coil from a previous job I found in the tool box.

[NewZed]

Just curious, anybody look what the diamond/circle/square drawing in the FSM calls for in EM section?

 

I looked but couldn't find a reference, in a drawing or in the list at the back of the chapter. I think that Nissan assumed that they would never be removed, indicated by their inspection recomendation that says if wear is found in the bearing surface, "replace cylinder head assembly".

[Tony D]

I was somewhat excoriated by a manager for buying a torque wrench that was 5X the cost of the factory-supplied tool.

 

Now, two years later, and over 100 critical fastener re torque procedures I amaze everybody because my runout specs consistently run 0,01-0,03mm against a range of 0,07-0,25mm using the factory tool.

100+ procedures and not a single broken stud in service...the factory tool kit has something like a 85% failure rate...

 

Sometimes the tool you use DOES materially effect the outcome of the procedure. Torquing fasteners is a terribly misunderstood and overlooked aspect of assembly.

[rayaapp2]

Standard lubricated M8 torque is less than 30 ft-lbs...

Try to torque a bolt with oil on it to that and it will pull out of most steel sub assemblies!

 

But yeah, brake cleaner cleaned 12-15 ft-lbs is more than enough (144 ~ 180 in-lbs, actually...if you're using a ft-lb tool on cam tower or front co er bolts, I don't know what to say...)

 

"Head work is a precision bit of work, best accomplished without large hammers and I-R Thunderguns..."

 

Just curious, anybody look what the diamond/circle/square drawing in the FSM calls for in EM section?

I was somewhat excoriated by a manager for buying a torque wrench that was 5X the cost of the factory-supplied tool.

 

Now, two years later, and over 100 critical fastener re torque procedures I amaze everybody because my runout specs consistently run 0,01-0,03mm against a range of 0,07-0,25mm using the factory tool.

100+ procedures and not a single broken stud in service...the factory tool kit has something like a 85% failure rate...

 

Sometimes the tool you use DOES materially effect the outcome of the procedure. Torquing fasteners is a terribly misunderstood and overlooked aspect of assembly.

 

I prefer my Aircat NitroCat1200 to any of the equivilent IR's... except the new IR IQ20V which is on my christmas list.

My shop had an incident with a Honda 3.5L V6 timing belt replacement. It was a warranty job and being such we had the finger pointed at us until we showed proof that all the fasteners associated with the timing belt and water pump were produced. Luckily we use one of those high end digital Snap On torque wrenches and the tech had the forsight to photograph each bolt being torqued to spec based on the installation proceedure handed to him. Why we ever needed to go that far is beyond me, but the manufacture of the timing kit bought the customer a new engine!

 

As for this thread, Even the FSM can be wrong sometimes. An experienced tech might/might not have thought twice about 30ft/lbs on those bolts in the material they thread into. I would have believed something between 12-15lbs. Or if it was somehow 30ft/lbs then I would have expected steps/incriments. This is not to beat anyone down, but something to think about the next time someone encounters anything similar. If any of the bolts actually tightened down without stripping I would double check the threads in the head. They can be deformed or even compromised so that the next proper torqueing will result in failure!

[Tony D]

Two things:

1) " It was a warranty job and being such we had the finger pointed at us until we showed proof that all the fasteners associated with the timing belt and water pump were produced. Luckily we use one of those high end digital Snap On torque wrenches and the tech had the forsight to photograph each bolt being torqued to spec based on the installation proceedure handed to him. Why we ever needed to go that far is beyond me, but the manufacture of the timing kit bought the customer a new engine!"

 

Welcome to my world, Ray! I have used photographic evidence consistently for warranty validation/denial extensively! It's become standard when dealing with claims overseas or great distances-remotely now since digitalis became cheap. It's why I'm in the Philippines right now. It was all conjecture until the site people showed us two dimensional checks where it became clear it was measured correctly, or even ifit wasn't, doing it the right way would still result in improper dimensions!

 

2) One of the things I stress in my training is common sense. Just because something is written down doesn't necessarily mean you blindly follow it. This is ongoing in the mechanical trades, John Muir in an addendum to "The Idiots Manual" for VW relates a customer upset because they followed directions EXACTLY on a clutch change, and the car wouldn't come out of gear. They found the clutch disc installed in the car still in the cardboard box, staples and all! It never said take the clutch out of the package... I have had knockdown drag out arguments with safety officers who place total dependence on operators writing safety work permits in refineries based on a "checklist" whereby the operator never THINKS about what he's doing, he follows a checklist and that will get people killed.

 

There is NO substitute for a skilled technician or engineer who THINKS about he task at hand, questioning the "checklist items" in a work process when something comes up that isn't taken into account.

 

As someone said, the bolts are similar to others elsewhere, and even in the FSM they make torque dependent on head stamp (4,7,9) for the same thread! Aluminium should not (from an aerospace perspective) have bare threads, rather should be helicoiled for all fasteners. Why? Thread strength primarily, but the realities of field work dictate helicoils in place stop damage such as this happening.