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nylocks on firewall fittings

T

tonyjohnson

Well Known Member
I am installing my cabin heat box. Some people use stainless steel rivets to attach the box to the firewall, but I prefer to use screws so that it will be removable later without having to drill out the rivets.

I am wondering if it is appropriate to use nylock nuts on the "cool" side of the firewall to secure the stainless steel screws, the heads of which will be on the "hot" side. I can see a scenario where a fire in the engine compartment would heat the stainless steel screws to the point that it may melt the nylon on the nuts holding the box onto the firewall even though the nuts are on the "cool" side. I don't think the box would depart the firewall even if the nylon melted but I want to make sure that I am in conformance with good practice and safety.

If nylock nuts are not appropriate, what nut would be best?

Perhaps one of the DARs here or someone with knowledge of the subject can help.

Thanks
 
I dont see a problem with what you want to do, the idea of keeping the nylocs out of the engine area is due to the fact that it is hot in there and could melt the nylon out and you would be unawares that whatever you put together with it could be coming loose with no indication to you in the cockpit. Your scenario does not involve a ongoing operation, if there were a fire you would know it and it hopefully wont get too hot by your toes. Even if the nyloc got too hot in that situation the nut is not going to just spin off on its own because it got hot once.
I say go with it if thats what you want to do.
My .02
 
nutplates

Mel,

Because nylocks are so much easier. Having said that, I do not want to comprise on safety. I had not thought of nutplates.

Would you pass a nylock installation on inspection?
 
Stiff nuts

I can't remember exactly when, and it wasn't aircraft related, but a waaaays back we used what were commonly referred to as stiff nuts. I guess because they were, well, stiff! They looked the same shape as nyloc nuts but had no plastic insert. Instead the top bit was kind of 'split' (it had a slot in it) and that bit kind of gripped the threads tight. Sorry the description is so vague, but is was a long time ago. The point is, this type of nut gave the benefits of nylocs without the, er, nyloc bit!
 
tonyjohnson said:
Mel,

Because nylocks are so much easier. Having said that, I do not want to comprise on safety. I had not thought of nutplates.

Would you pass a nylock installation on inspection?
Click to expand...
Yes, nylocks are perfectly acceptably on the back side of the firewall. But, you talk about easier; How much easier would nutplates be for maintenance later on?
 
Stainless Heat Box

I suspect you already have done this; but if not, consider an all-stainless steel heat box, which won't melt like the aluminum ones (leaving those nice stainless steel screws :D )
 
tonyjohnson said:
I am installing my cabin heat box. Some people use stainless steel rivets to attach the box to the firewall, but I prefer to use screws so that it will be removable later without having to drill out the rivets.
Thanks
Click to expand...

I think Harold is on the money when he suggests the stainless steel heat box. The aluminium box will disintegrate in a fuel fed fire.

However I'd like to ask why you think it might be necessary to remove the heat box at a later date.
 
I had the same concerns and used nutplates or all-metal locknuts where it made sense. I purchased a pack of 100 in each #6, #8, #10, and 1/4". Never looked back.

Jerry
RV-8 N84JE, 130 glorious hours!
 
Interesting side note

While in A&P school I also was taught that you didn't use nylon lock nuts in front of the firewall. You might find it interesting though that the Continental (TCM) parts book for the early engines, (O-200, C90, etc), call for nylon lock nuts to hold the kidney shaped oil sump on.
 
AN stop nuts with the nylon are rated to 250F. They should not be used on the engine, but many areas inside the cowl do not ever see 250F. I know many production aircraft use them FWF.
 
stainless steel heat box

Harold, I agree with you completely and yes, my heat box is stainless steel.

Mel, the back side of the firewall is very accessable on the 8A, by reaching inside the forward baggage compartment.

Bob, I do not have a reason to think that I will need to remove the box later....however, I would like to have the flexibility to do so just in case there is a reason that I did not think of.

Thanks guys for your comments. I will look for some of the metal "stiff" or "split" nuts.
 
tonyjohnson said:
Some people use stainless steel rivets to attach the box to the firewall
Click to expand...

Anybody know where you get stainless steel rivets? I've wondered about the value of using aluminum rivets with a stainless steel heat box because I figured the rivets would melt if you had a bad fire and the box would no longer be attached to the firewall.
 
rv9builder said:
Anybody know where you get stainless steel rivets? I've wondered about the value of using aluminum rivets with a stainless steel heat box because I figured the rivets would melt if you had a bad fire and the box would no longer be attached to the firewall.
Click to expand...

Very true, but surely the same could be said of the oil filter recess. Does it make sense to have aluminium rivets there ?
 
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