manifold studs

[ffrnempt]

I am doing some work on the old girl, '49 8N, later this week including new mainifold, new exhaust/muffler, carb rebuild, fuel system service, ect.

Today I took the manifold off. The rear-most (closest to the exhaust pipe) stud came out with the nut, and behind it came a steady stream of engine coolant. I don't have a detailed enough diagram of the motor to see if those manifold studs extend into the coolant jacket. When I screwed the stud back in, the flow stopped.

Is this normal?

 

[Dell (WA)]

ffrnempt......yep, SURPRIZE!!! all manifold studs are "wet" and when you screwed the stud back in, guess what??? it stopped peeeeing on yer toes. Most engine head studs/bolts are also "wet". (just the 4-corners are dry) And yes, most of us use a block sealer on wet studs altho they are supposed to self-seal with the barrel in the middle of the stud. And manifold studnuts are supposed to be BRASS (torque 17ft/lbs) Brass is soft and will strip instead of "freezing" to the stud and causing the stud to unscrew. Definitely use BRASS studnuts!!! .......Dell

 

[ffrnempt]

Thanks. Yeah, it was a surprise! The old nuts are not brass, but the new ones are. There is also a lock washer on two of the four. Is that needed?

Another shock for my marine mechanic self--the carb is made of IRON?

 

[Bruce (VA)]

The nuts are brass, 7/16-20 x 5/8, NAPA part number STN104X, 27 lbs of torque. A bag of 10 from Fastenal is less than $8; part number 1175115. OEM studs are 1-5/8 long 7/16-14. NAPA doesn’t stock the 5/8’s length, but part number RFD 86644, 1 ¾ inch, works as does part number 86632, 2 inches. These studs are “Handi-Pack” items. (I’ve used these longer studs on my 50 & 51 N’s, but you should make sure they do not bottom out in the block on your N as they are longer than OEM). If you don’t get them at NAPA, make sure that the stud has an egg-shaped center between the different threads. Use washers under the nuts.

Clean all the threads in the block w/ a thread chaser. If you are reusing old studs (and I never would) clean them well w/ brake or carb cleaner.

There are two distinctly different recommendations on tightening the studs in the block. Because the stud goes into the water jacket & is constantly undergoing extreme heat & cooling cycles, some folks like to double-nut them & tighten them down at 37 lbs of torque. Others say that it’s a stud & should only be finger tight w/ a good dose of thread sealer or high temp silicone on them.

I’ve replaced the studs on 3 of my 4 N’s w/ no leaks; I finger tighten the studs then take a ¼ turn on them w/ vice grips.

Yep, that's an iron carb.
50 Tips

 

[ffrnempt]

Replace all four studs? Use lock washers on all four?

 

[Tim PloughNman Daley]

If the stud didn't come all the way out, no need to replace it. Studs have a coarse thread on one end ( 7/16-14; this end screws INTO the block ) and a fine thread on the other end ( 7/16-20; this end accepts the brass nut to secure manifold to block. Use the lockwashers and a torque wrench too. Manifold studs are technically called 'interference fit' fasteners whereby they are designed to cause the female thread to get pulled down as they are screwed into the block. It acts sort of like an NPT thread, meant to help form a seal to prevent leakage. The length is important also. Don't toss your old ones out - make sure you take the old one to NAPA or wherever to get a replacement - nnalert sells the correct ones. A longer stud may bottom out or cause the barrel middle section to protrude beyond the manifold spot-faced boss thus causing the brass nut to not secuerly seat properly. You also have a paer gasket between the block and manifold -use a NEW one and be sure to scrape off all the old materila before applying the new one. I would inspect the manifold too at this point and decide if it should be replaced -you have everything off so why not? They usually fail at the exhaust port side around #4 cylinder. HTH

Tim Daley(MI)