nuts and bolts in the engine compartment

[Scott Will]

This may seem like a dumb or newbie question - but I here it is...

What are the guidelines concerning what type of substances to use on fittings and nuts, especially firewall forward? When do you use Fuel Lube or anti-seize or nothing at all? What products should be used and where I guess is my main question.

I've been using Fuel Lube on my pipe threads (nothing on flared fittings). But in some pictures I've seen a white substance used and I'm not sure what it is. Fuel Lube is like a thick, gooey, creamy substance.

Do you use anti-seize on all other 'normal' nuts in the engine compartment?

When do you use steel AN fittings vs. aluminum?

Sorry if it seems like lots of questions but I just want to ensure all my connections are up to snuff in the hot compartment.

I appreciate your help.

[f1rocket]

Great questions. Here's what I did.

1) I use only steel AN fittings firewall forward for fire and vibration reasons. You will see a lot of aluminum fittings in the engine compartment, but generally, if you are hanging a hose that vibrates to the fitting, you should use a steel fitting. This is especially true if your hoses are using stainless fittings.

2) For nuts, I never use nuts with fiber inserts in them. I only use the locking steel nuts. Again, you'll see these alot as well, but I don't like to use them.

3) I only uses anti-seize compound on the exhaust system, spark plugs, and any bolt that screws into the engine block. The white stuff you see might be pipe thread tape and you should not use it. Pieces of it tends to break off and clog things like fuel filters, injectors, etc. I don't know the particulars of Fuel Lube. I use Form-a-Gasket as a pipe thread compound.

One thing you didn't mention is your firewall. There was a great thread on this before in the archives. Drill as few holes as you can and make sure that everything you fill the hole with is stainless or at least, steel.

[osxuser]

Fuel lube (or seal lube) is fine for the pipe threads. Most everything goes on dry (I don't use antiseize on engine bolts). Exhaust with antiseize, I don't use it on my spark plugs either. You can spray most gaskets with Hightak, although leave induction gaskets dry. Magneto gaskets get smeared with loctite 518 when I have it available. It makes them easier to get off later and prevents those annoying oil seeps.

I agree, use Steel fittings where ever possible.

[Davepar]

Has anybody used aluminum fittings around the engine and had them crack? Vans puts Al fittings in the firewall forward kit. And Mattituck uses Al fittings on the engine itself, e.g. the cylinder oil return line (although not on the prop oil line). I doubt these two reputable companies would do that if there were a known problem with Al fittings.

Dave

[sf3543]

I would say that most engines do have aluminum fittings installed on the engine. For example, the oil return fittings on the cylinders and case, breather line fitting and usually the oil cooler fittings on the accessory case. (The oil line for the prop governor requires steel fittings.)
All of these aluminum fittings work fine, but when it comes time to remove them, at OH, the aluminum fittings gall (spelling?) and are EXTREMELY difficult to remove.
So, either steel or aluminum is acceptable, but steel is a lot more expensive. Pay now, or pay later in getting the aluminum fittings out, if you ever need to.

[osxuser]

Aluminum is perfecty acceptable, but steel is even more betterer...