Manifold Torque?

J

jeepguy1948

Well-known member
What is the proper torque for the manifold studs? I believe that I read somewhere that 55# is the proper torque. Is 55# correct?
 
Those are (probably) brass nuts, 55 ft-lbs will torque the heck out of them. 55 ft-lbs is what you're supposed to apply to steel head nuts to contain 5,000 lbs of explosive combustion force.

Les Andrews says 45, I know P.S. does 40 and many folks do less (but some have reported the nuts loosening at less than 35 ft-lbs). Reproduction concave washers seem to be a problem point because they deform inelastically, as opposed to the originals which compress elastically, maintaining the pressure on the manifold gasket.
 
I do it same at 400A. Nice and tight, then after about 30 minutes, then after a few errands. After that I leave em alone.
 
Jeepguy1948 you ask many good questions on this forum but many of the answers to these can be found in Les Andrews MODEL A MECHANICS HANDBOOK VOLUME 1 BOOK. If you do not have a copy I would recommend you get one as it has good graphics and clear and concise explanations of repairing and restoring the mechanical and electrical components in the Model A.
 
Whatever torque you use, it is important to re torque after the first heat cycle and thereafter when you re torque the head nuts.

If you have steel nuts and the intake and exhaust manifold surfaces are co planer and flat, you can use 55 foot pounds. Use the conical washers with the concave side toward the manifold. Also good to have the same thickness on the ears for the intake and exhaust manifolds.
 
I'm totally with Alexiskai #2 on this one, and putting my head above the parapet here....but I don't think it's necessary go over 40 ft lbs for the manifold studs or nuts... simply no need to, why invite potential problems by overtightening?
 
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There are hundreds of folks on the Barn and elsewhere complaining of manifold leaks so that’s a good reason to get em tight. I have grade 8 nuts and the studs are the same size as the head studs so should be able to handle 55# easily. I’m not sure that there is a downside for the higher torque (I can understand it if there were brass nuts but they’re not.
 
I never EVER go over 40 ft/lbs on manifold. I aim for 40. Usually ends up around 35 after some heat cycles. If so, be happy and leave it there.
 
jeepguy1948 said:
There are hundreds of folks on the Barn and elsewhere complaining of manifold leaks so that’s a good reason to get em tight. I have grade 8 nuts and the studs are the same size as the head studs so should be able to handle 55# easily. I’m not sure that there is a downside for the higher torque (I can understand it if there were brass nuts but they’re not.
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This is a common misconception. Dialing up the torque on a fastener is not a foolproof way to stop leaks. You can easily tighten a fastener so much that it distorts the thing it's clamping on. That's how water outlets break.

The Model A manifold assembly is notoriously under-supported, i.e., the four studs aren't really enough to properly secure the manifold. This is one of the reasons the exhaust manifolds droop. The gaskets are not clamped on their outer edges. If you over-tighten the nuts, you can "bow" the manifolds and the gaskets inward, increasing the risk of leaks at the edge.

The ideal amount of torque to apply is the minimum amount needed to seal the gaskets and clamp the manifolds flat against the block. Torque above this amount places unnecessary stress on the joint.
 
I have seen an exhaust manifold with one ear broken off because the bolt was torqued to 55 lbs. Granted , it was probably warped & they tried to fix the leak by over torquing. 35 has been plenty for me as you're not dealing with the high compression. Just be sure BOTH manifolds are surfaced flat together!
 
I'm in the 40 ft/lbs camp and use the two piece copper gaskets. I check them every oil change and usually get another 1/6th of a turn to get them back to 40 ft/lbs.
 
Just a note, like Most things very few are "perfect". There are some errors in Les Andrews books. They are by far in my opinion excellent manuals. But a bit of common sense goes along way also. I did try to order some common sense but all the vendors are out of stock. If it calls for a high torque on a small fastener-be aware. Ya still have to engage the brain.

I also have 4 or 5 different published manuals, so I tend to get multiple viewpoints on my subject. Especially front end work and brakes where you could be in the news. Mistakes are costly and aggravating.
 
I think it is a good shop practice to hand tighten some fasteners on a practice piece of equipment and then check with your torque wrench to get a good feel of tightness by hand, as the mechanics did back in the day. Use a shorter handled wrench on smaller nuts/bolts and longer handle for larger ones. Maybe it would be insightful to find some scrap and twist bolts and nuts with your torque wrench to breaking and get a feel for disaster also.
 
The cylinder head & manifold studs should go into the block only hand tight. If you torque the studs, there is a danger of busting the bottoms out of the blind stud holes that will leak coolant.
 

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