Impromptu Overhaul

**jcwright** · 10-27-2021, 03:21 PM

Hello Greg.

MMI has the ‘small’ nuts listed below in its catalog; these might allow you to use the socket you already have. A thin wall socket is another option.

——-

Head nut (small), 3/8″ by 9/16″

SKU: OBLK_07_187.
$0.50

Head nut – 3/8 by 9/16 hex head fine thread, used for thermostat housing studs.
Sold individually

**GregH** · 10-27-2021, 04:15 PM

Originally posted by jcwright View Post

Hello Greg.

MMI has the ‘small’ nuts listed below in its catalog; these might allow you to use the socket you already have. A thin wall socket is another option.

——-

Head nut (small), 3/8″ by 9/16″

SKU: OBLK_07_187.
$0.50

Head nut – 3/8 by 9/16 hex head fine thread, used for thermostat housing studs.
Sold individually

Thanks. I'll dig around the bits n bobs I have to see if I have a smaller nut from other engines.

**jcwright** · 10-27-2021, 08:21 PM

If you don’t have any luck finding the nuts you need, another option would be to sacrifice an old socket and grind it down to make your own thinwall.

I hope the rest of your overhaul goes well.

Jack.

**sastanley** · 10-27-2021, 10:13 PM

You could go old school and use an open end wrench.

You just need enough torque to keep it from leaking fluid.

**ndutton** · 10-27-2021, 10:25 PM

Socket head cap screws will solve your problem.

Attached Files

**indigo** · 10-29-2021, 04:33 PM

Get the small nuts or sacrifice a socket by grinding it down to fit. The thermostat housing studs are head studs just like all of the others except a little longer. Using a socket head capscrew is like using a hex head bolt in lieu of a head stud - a no no. The design of the head stud is such that the thread within the block is a coarse thread and the thread on the other end where the nut goes is a fine thread. With such a design, you seat the stud in the block, then you torque up the head using the fine threads and thus avoid putting any rotational stress on the somewhat delicate threads in the block.

Stick with head studs!

**ndutton** · 10-29-2021, 08:27 PM

The instructor of the Perkins Diesel class I took many years ago did not agree:

The different head bolt torque enigma - Moyer Marine Atomic 4 Community - Home of the Afourians

https://www.moyermarineforum.com/forums/showthread.php?p=82367

**indigo** · 10-29-2021, 11:16 PM

I do not get your point.

I concur that you get greater vertical force from a fine thread stud than from a coarse thread stud for the same amount of torque applied to the nut.

The issue that one often encounters when torquing an A4 head is that of a stud pulling the threads out of the block. The threads in the block are typically foreshortened by corrosion on the water passage side and are thus more susceptible to damage via the torquing process using a bolt as opposed to a stud. The issue at hand is that of torquing up a true bolt in the block as opposed to torquing up a nut on a stud already seated in the block.

The more gentle you can be with the block threads, the more likely you are to get a well torqued head gasket that does not leak.

Stick with the studs!

**ndutton** · 10-29-2021, 11:27 PM

My point was according to the Perkins instructor as well as the Perkins 4-107/4-108 manual, Perkins did not put such importance on the coarse block thread - fine top thread of their studs. Their later model 4-108 (newer and therefore improved? I dunno) had coarse threads at both ends of the head studs.

I'm not advocating one or the other, just relaying from a personal experience that an engine manufacturer had different thoughts on head studs than what was presented here.

**Dave Neptune** · 10-30-2021, 11:42 AM

The torque values between fine and coarse threads is far different for the same clamping pressure.

A stud with coarse or fine threads at "BOTH" ends can easily be swapped out for a bolt but not recommended.

Most stud applications are of a course thread in the block and a fine thread for the torqueing. The clamping pressure is greater for a given torque value than the "same" torque value on a course thread due to the greater leverage of the finer thread.

I have seen a few heads come loose because they torqued the coarse bolt at the same torque value as the fine threaded end they replaced by using a coarse bolt loosing valuable CLAMPING pressure.

Dave Neptune

**GregH** · 11-01-2021, 07:46 PM

I found the narrow nuts from the donor engine and used them. All the head nuts are currently sitting at 20ftlbs since I have to remove the thermostat housing at some point soon to paint and add hose fittings.

About the valve cover gasket, the instructions says to use sealer on both sides due to the late model cover potentially not sitting well. I have the valves/lifters adjusted to spec but thinking I will most likely have to get in there to tweak things once in tune-up mode. Will it be ok to only use sealer on the cover side of the gasket for now?

**sastanley** · 11-02-2021, 05:58 PM

Greg, There is not a lot of oil in that area splashing around, I think it is fine to seal the gasket to one side for now, and then you can easily pull the cover and adjust the valves.