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Crush washer vs. flat washer
- Thread starter Bavafa
- Start date
Split washers (lock washer) and flat washers do nothing to seal. Split washer is used to help keep nut tight by adding a force to increase the friction of nut threads to bolt threads. Flat washer is used to keep from galling the surface of the part when tightening and to be a spacer to ensure the nut tightens on the part and not bottoms out on the bolt threads before getting to proper torque. Proper grip of bolt has no threads in sheer inside hole of parts.
A true crush washer is like used on the oil pan plug for the screen. It is used to seal. It is made out of copper and meant to crush under the head of a bolt, typically used when internally threaded and therefore no nut on something with fluid on the inside. It does not provide the locking feature of a split washer as it crushes and provides no axial force on the bolt to help increase thread friction
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Philip,
When I used "split washer" I was not referring to the type that is used for locking mechanism but the type that you are referring to and the same as crush washer. I have seen it in some advertisement/publication referred to as split washer since there is a split line in the washer.
The flat washer that I am referencing is the type that you will see under spark plug or other area and can be either copper or aluminum. You see it a lot more in cars, break/fuel connections also.
With that said, when is it applicable to use crush washer and when to use copper/aluminum flat washer and if they are interchangeable.
koupster
Well Known Member
Lycoming calls the AN900 annular copper-asbestos gasket used to seal the plug that secures the oil suction screen a "Gasket, annular". These gaskets are tightened a certain number of degrees after contact is made.
Flat copper or aluminum crush washers are usually tightened to a specific torque value.
Personally, I would not substitute flat copper or aluminum crush washer for an AN900 except in an emergency and replace the substituted part at the first opportunity. The AN900 gaskets are only rated to 200 psi and should never be used as a replacement for an AN4027 copper spark plug gasket.
Cheers, David
RV-6A A&P
Flat copper or aluminum crush washers are usually tightened to a specific torque value.
Personally, I would not substitute flat copper or aluminum crush washer for an AN900 except in an emergency and replace the substituted part at the first opportunity. The AN900 gaskets are only rated to 200 psi and should never be used as a replacement for an AN4027 copper spark plug gasket.
Cheers, David
RV-6A A&P
There is your operations guide, and the overhaul manual, or the manual for whatever accessory you might be working with. Other than that it's hard for me to imagine any other guideline for substitutes and the like that would be safe to apply.
I don't ever plan to overhaul my own engine but I bought the overhaul manual and glad I have it, as I have found it useful to refer to for various things over the years. And as it turns out, I did end up doing a partial top OH recently.
