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Pilottonny

Well Known Member
Forgive a ?metric-addict? , his ignorance, but I just do not get all this AN, NAS, MS, etc. bolt-stuff!
I need to order 4 bolts, to bolt my prop governor to the back of the engine. So, I started investigating AN-sizes, measured the grip I need, etc. and came up with: AN5H-12A (5/16 dia. 1,1/4 length, drilled head). When the bolts, I ordered from ACS, arrived they would not fit the hole in the back of the engine, because????.. they were fine thread and the threaded hole in the engine is course thread. So I re-ordered the same bolt with ?course thread?. Guess what? After several emails and a telephone call, ACS now tell me they do not sell such a bolt (the? C? after the N-number on their website, turns out to designate ? Stainless steel? not ?Course?, how logical is that?)
They now tell me that they need a ?NAS? or ?MS? number for a bolt that will fit the engine???.
So, I searched the forums, Googeled ?NAS?, etc., but so far: thousands of NAS-Codes, without any logical explanation of dia. and length.
Is there anybody out there that can help me determine what bolt I need?

Thanks in advance for any help.

Regards, Tonny.
 
Hi Tonny,

My (Mattituck-built) engine came with studs already in the engine case to mount the prop governor on.

For my engine (IO-360-M1B) the Lycoming Parts Manual says they are part no. 31C-16, description STUD-5/16-18 x 2.00 long.

Regards,
Steve Hutt
RV-7 G-HUTY
UK
 
Tonny,
I see you have an IO-320.
Just looked in the Lycoming IO-320 Parts Manual, which says:

P/No 67556 STUD,5/16-18 x 2.00 in. long (use in 75153 & 75722)
Used on IO-320-B1C & -D1A & E2A

&

P/No 68316 STUD,5/16-18 x 1-11/16 in. long (use in 75545)
Used on IO-320-B1A, -B1C, -C1A


75153, 75722 & 75545 are part numbers of different ADAPTER ASSY, Prop Governor Drive.

Whether this info is directly applicable to an ECI engine, I do not know but hopefully it may be of some use.

Regards,
Steve

p.s. I believe the 'C' in bolt part numbers refers to 'Corrosion Resistant Steel' i.e. Stainless Steel
 
Last edited:
Bolts

Tonny:

These bolts are a remnant of the engineering that developed aircraft engines in the 1920's and 30'

you can purchase them from the engine builders using the Lycoming part number.

They are common hardware bolts still found in the USA. I believe that the course thread was used to provide just enough clamping pressure at the specified torque so as not to strip the threads out of the aluminum casting.

This stripping, or pulling the threads out of the aluminum would happen with much less torque given the lesser pitch angle of the fine pitch thread. That gives us "ham fisted" mechanics just a little more leeway before we ruin a part!!!!!!!!!:D

Guru's here, correct me if I'm wrong.
 
Sorry, into governor adaptor, not directly into engine case!

Sorry, but maybe I did not explain this properly. It is actually not directly into the engine, that I need the bolts, but the bolts will go in the adapter that the Governor bolts to. The engine came with a little cover plate on the adapter, that was bolted on with 2 ordinary ?house-and-garden? bolts, that I am obviously not going to use.

I tried to get some from my local Spam-Can service centre. He explained that on the engine, studs are used, so the thread in the aluminium does not wear due to numerous dismantling and tightening of bolts. Bolts may be used if the threaded hole has a steel Helicoil installed, which is the case. So that is why I am looking for bolts, not studs. He also could not help me without a part number.

I guess I could use studs instead.

However, is there any way to determine a diameter and length for NAS-bolts, like with AN-bolts?

Regards, Tonny.
 
This may help?

Pilottonny said:
Sorry, but maybe I did not explain this properly. It is actually not directly into the engine, that I need the bolts, but the bolts will go in the adapter that the Governor bolts to. The engine came with a little cover plate on the adapter, that was bolted on with 2 ordinary ?house-and-garden? bolts, that I am obviously not going to use.

I tried to get some from my local Spam-Can service centre. He explained that on the engine, studs are used, so the thread in the aluminium does not wear due to numerous dismantling and tightening of bolts. Bolts may be used if the threaded hole has a steel Helicoil installed, which is the case. So that is why I am looking for bolts, not studs. He also could not help me without a part number.

I guess I could use studs instead.

However, is there any way to determine a diameter and length for NAS-bolts, like with AN-bolts?

Regards, Tonny.
Click to expand...

http://www.gen-aircraft-hardware.com/images/pdf/ms20073_74.pdf

These come in Fine and Course Thread, READ CAREFULLY, the threads are of a specific length and it is the grip that gets longer with each increment.

If you are international you would need to get a quote and place and order by e-mailing your request to [email protected]
Julie will respond as soon as she can.
 
Hi Tonny,
No misunderstanding. Understood you perfectly.
The stud part numbers I gave are the ones shown in the Lycoming Parts Manual for attaching the Prop Governor to the Adapter Assy.
Regards,
Steve
 
Studs it will be.

Thanks everybody for the replies and especially you Steve, for trying to email me the manual. I will see if I can get the studs from the service shop at our field.

Kind regards,

Tonny.
 
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