Valve cover screws with external tooth lock washers

[bruceh]

On my Lycoming IO-320 the screws that hold the valve covers in place have external tooth lock washers that are basically threaded on to the screws so tight that I can't unscrew them. These are 1/4" screws, but the lock washer inner diameter is less than that. I'm not sure how these got screwed on there, but I'd like to replace them and I can't seem to get them off.

Cut them off and replace, or reuse them? Or is this just a Lycoming "assembly" (screw and lock washer)? Aircraft Spruce sells these Rocker Box cover screws. 24 of these are approaching $30, vs. around $1 for just the lock washers.

I have the MS35335-33 washers from Aircraft Spruce and they have a much bigger inner diameter than the ones on these Lycoming screws, and they slip on the screws like I would normally expect.

Also, is there any general wisdom on using external vs. internal teeth lock wasters? Valve covers have external, and the exhaust bolts use internal teeth (MS35333-33)

[RV6_flyer]

I have Internal Tooth lock washers on Stainless Steel Allen Screws for my valve covers for about the past 3 years.

I prefer to NOT use External Tooth lock washer unless there is a REQUIREMENT for them. When Lock Washers are called out, I lean toward the Internal Tooth lock washers.

[az_gila]

Originally Posted by RV6_flyer

I have Internal Tooth lock washers on Stainless Steel Allen Screws for my valve covers for about the past 3 years.

I prefer to NOT use External Tooth lock washer unless there is a REQUIREMENT for them. When Lock Washers are called out, I lean toward the Internal Tooth lock washers.

The "requirement" is that it is a Lycoming part # STD-1925 - SCREW, 1/20 x 5/8 long, pan head, self-locking and it is called out in the Lycoming Parts Manual...

But, what the heck, we are experimental.

I believe it works and is reusable because the torque specified for the valve cover screws is a mere 50 in. lbs. for a cork gasket and an even lower 35 in. lbs. for a silicone gasket. At these torques the "teeth" in the external built-in lock washer won't get squished down flat.

[dpansier]

Always wondered why valve cover screws did not require safety wire, must be some reason why it?s not used in this application.

[JonJay]

Originally Posted by dpansier

Always wondered why valve cover screws did not require safety wire, must be some reason why it?s not used in this application.

Simply not necessary.
I have never had the need to replace them, nor have I had any back out beyond a very slight bit that gets taken up at the CI, and that is usually only a couple that need that, and it is very slight.
Valve cover leaks are not catastrophic. They show up well before any significant issue in my limited experience.
My opinion, don't mess with something that works (unless you have the experience of someone like Gary, then all bets are off .
If you torque them to the correct value, cork or silicon, they should make TBO.