Manifold Stud Success

[S30Driver]

Late last year, I started developing an exhaust leak from the number 6 port which was... of course, broken off flush with the head. Probably has been broken for many years before I got the car. With the nice summer weather, I decided to replace the gasket & install all new high grade studs & bolts. Let PB Blaster go to work for a few days and went to work.

I removed the manifolds and used left hand drill bits to extract the broken studs. (number 1 was also broken off - discovered when i removed the manifolds) Number 1 backed out by the time I got up to about a 3/16th bit. Number 6 refused to comply, so I drilled it out and re-tapped for the stud.

Patience is definitely the key - accurate center punch mark, slow drill speed, cutting oil, don't overheat the small bit sizes.

Chased all the threads and prepped the head for the new gasket. All is looking very good so far.

Tomorrow, or the next day, will pick up the new stud & bolt hardware. Going to try and get grade 10.9 for the studs and 3 middle exhaust bolts. Grade 8 at least.

Also, have the main heat shield and some other stuff at Performance Coatings for ceramic exhaust coating - Chromex. Should be ready in 3 or 4 days.

Will be interesting if it has any impact on the minor heat soak issue I experience occasionally.... Will report back on that.

[siteunseen]

I put 4 of these on my N42, 2 on the ends and 2 in the middle. Came from my Nissan dealer, I think they're for a Titan pick up.

[S30Driver]

Thanks siteunseen. I will keep those in mind, depending on what i find at the industrial fastener place i go to.

[Zed Head]

You can get Nissan factory-quality manifold studs from the dealer. Designed for the application. High numbers in a bolt or stud grade doesn't mean that they're better. Just that they're different. You don't need super-high yield or ultimate tensile strength, you need fatigue and heat resistance. Constant bending and heat-cycling is what breaks the studs. Better to get a stud that's been tested for the application by the factory.

You can get the part numbers here, and your dealer will have them. If you get a good parts guy he can find them on his own by car model. They're common and cheap.

Datsun 280Z Cylinder Head, Rocker Cover & Thermostat L28E

You can get the nuts also. Notice that there are no lock washers.

Datsun 280Z Manifold, Egr. L28E (From Aug.-'76)

Edited July 9, 2014 by Zed Head

[Hardway]

I used the MSA stud kit when I installed one of their ceramic coated headers on my '72 240z a few years ago. All of the hardware was well made and was complete with nuts and lock washers. I put a little anti-seize on all the studs before installing them, just in case they ever needed to be removed in the future.

I agree, I don't see why high grade fasteners are needed. The components being bolting to the engine should be at the correct torque and not "cranked" on.

[siteunseen]

My last hole at #6 was so wallerd out I had to go bigger and the 1st hole at #1 under the thermostat housing had a heli-coil in it that I drilled out and went bigger. Do you have the N47 intake manifold? If you do, does it have any rot around the EGR tunnel where the tube from the exhaust manifold connects? My '77 did and another guy, Rossi, had the same problem with his. Here's a picture of mine after I sawz-alled the EGR mount hoping I could have it welded up. No way said my welder so I lucked up and found an early edition N47 without the EGR openings.

Oh yeah, I'm pretty sure the OE size studs for our cars is what's on 4cyl. Altimas, at least that's what I remember the parts guy saying when he was trying to find the larger ones.

Edited July 9, 2014 by siteunseen

[S30Driver]

Thanks for the insight you guys. I want the high grade studs for number 1 & 6, heat treated, for exhaust use. Nissan used grade 7 studs. The others don't suffer from the tension - breakage problem. Am replacing all the studs & bolts (except for the big intake bolts) because they were in poor shape and I don't want any issues with removal in the future.

The last thing I would do is over tighten steel stud in a aluminum head beyond factory spec.

I think Nissan used pinch nuts instead of washers - except on 1 & 6 which had washers.

[S30Driver]

Site - yes, my intake is N47 and the egr portion of the manifold was in good shape. I am deleting the egr however.

Ya - Rossiz's intake was interesting, glad I didn't have to deal with that.

Come the think of it - all his threads are interesting.... waiting to see how his new head works out.

[Zed Head]

I want the high grade studs for number 1 & 6, heat treated, for exhaust use. Nissan used grade 7 studs. The others don't suffer from the tension - breakage problem.

I think Nissan used pinch nuts instead of washers - except on 1 & 6 which had washers.

It's not a tension problem. The threads would probably pull out of the head before the stud failed from tension. But it sounds like you've made up your mind. Probably not a big deal either way.

Why are you following Nissan on the nuts, but not on their stud grade? Don't you want to use lock washers and threadlocking compound?

Just curious about the logic path.

[S30Driver]

Hi Zed, I know you have a high level of knowledge on Z cars, maybe I was not clear with my intent previously. I assumed most everyone is familiar with why the number 6 stud always shears off flush with the head.

I believe it is due to the long length of the 6 cyl manifold which bows over time causing it to put extreme tension or pressure on the 2 end studs in the vertical direction. The stock grade 7 stud can't handle it, the nut is fine.

Nissan used pinch nuts which are 1 use only, eliminating lock washers, if you take them off - you are supposed to replace them.

Pallnet sourced & used to sell a kit with 10.9 grade studs due to this problem. (I have his fuel rail on my car)

I just hate fixing things twice, and my goal is to end up with good quality hardware that won't corrode, has extra strength for those extreme end studs, installed with some anti-seize so I will never have to worry about them.

[Zed Head]

I was just wondering what your reason was. I have a bowed exhaust manifold that I bolted on to a head and found that it doesn't take much force at all to bend the manifold down to the mating surface. Probably a millimeter gap closed up. The surfaces may not be parallel but the tension applied by the ends of the manifold are not much different than in the middle. Not extreme, for sure.

But that's the advantage of having a collection of parts. Even the defective ones are useful.

My theory is that the three bolts in the middle of the exhaust manifold hold it tight to the head and that the ends of the aluminum head expand away from center farther than the steel manifold. Aluminum has a higher coefficient of thermal expansion than steel. In other words, if they start out in the same spot cold, the aluminum will grow more than the steel when hot. The hot-cold cycles bend the stud back and forth farther on the ends.

That's my thinking anyway. Really, the 10.9 grade might have similar fatigue strength to a grade 7 or grade 8. It's a property that's not considered much.

How do you know the Nissan studs are grade 7? I'm no bolt-stud expert, but that's an odd number. 2, 5, and 8 seem to be the common ones, American. 10.9 is a metric standard. And seems to be identical to Grade 8, property-wise. So we've probably been talking in circles..

http://www.tessco.com/yts/customerservice/techsupport/whitepapers/pdf/bolt_grade.pdf

That's the beauty of the forums - you have to go learn some new stuff just to keep up. Here's an interesting book on fasteners that I browse through when things start to fade.

Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook (Motorbooks Workshop): Carroll Smith: 9780879384067: Amazon.com: Books

Might be cheaper here but it looks like his web site is screwed up. It's missing.

www.CarrollSmith.com -- Purchasing

[S30Driver]

Hey Zed, i like your theory.... Also, I think Nissan knew they had an issue, but it didn't show up until years down the road - many heat cycles and fatigue setting in. If you look the later ZX manifolds, they modified the design, slotted the ends to allow for some expansion and give.

When I was still in Denver, I had a good friend that was an old Nissan service manager - he gave me the stud grade info and was generally a very knowledgeable guy. Wish he was out here.

If I have to settle for grade 8 - then I can live with that.