Rocker Cover Gasket

[Rjfanjet]

I have old cork gaskets that are seeping. Already have new silicone replacements. Do I need an A and P to sign them off, or is it considered preventive maintenance so I can change them myself?

Thanks.

 

[jetdriven]

I think you need a powerplant  mechanic to sign that off. That said I’m not a fan of silicone gasket’s. Where the bolt holes are, the gasket is narrower there and silicone creeps away from the clamping force. So when you squish it down with the screw and the valve cover it squishes out from between the valve cover and the cylinder head and then you have to keep tightening  it down to account for the squish and then eventually have a warped valve cover,  A leaky squishy kind of semi-gooey silicone gasket. 
Cork gaskets coated with aviation Permatex  sealer do very well however.

[MB65E]

I’ve had really great luck with them. Yes you do need to trim them down to get the baffling to fit correctly but I have never seen them leak if torqued properly. They require 1/2 the torque and are installed on every Lycoming I work on. 

However, I’ll agree that on some TCM 550’s that they not the best fit and I would run cork gaskets on them. 

Seems simple enough task, I feel it would still require a log entry. 

-Matt

[Yetti]

34 minutes ago, jetdriven said:

I think you need a powerplant  mechanic to sign that off. That said I’m not a fan of silicone gasket’s. Where the bolt holes are, the gasket is narrower there and silicone creeps away from the clamping force. So when you squish it down with the screw and the valve cover it squishes out from between the valve cover and the cylinder head and then you have to keep tightening  it down to account for the squish and then eventually have a warped valve cover,  A leaky squishy kind of semi-gooey silicone gasket. 
Cork gaskets coated with aviation Permatex  sealer do very well however.

properly torqued been on the plane for 3 years.  No leaks.  If you crank them down,  seems like they will squish out and leak

[PT20J]

Opinions will vary, so you’ll have to decide for yourself. Here’s the definition from 14 CFR part 1.1:

Preventive maintenance means simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.

I’d argue that replacing rocker cover gaskets fits the definition. However, I’d argue that replacing brake pads does not since removing and replacing rivets might be considered a complex assembly operation.

Skip

[Rjfanjet]

Thanks for all the input.

 

[larryb]

Two tricks:

 

1: blue locktite on the bolts because you cannot tighten them enough to keep them from backing out.

 

2: first trip around tighten to 5 in-lb. Second trip around tighten to 15 in-lb and stop there.

 

[kortopates]

16 hours ago, Yetti said:

properly torqued been on the plane for 3 years.  No leaks.  If you crank them down,  seems like they will squish out and leak

Referring to the silicone gaskets, which I really like and use on my Continental, I found (the hard way I believe) that if the gasket is leaking, its imperative to remove it and clean any and all oil off the metal and gasket and then re-install. Once there is oil leaking, over tightening won't stop it from leaking, it's got to go on clean and torqued per there instructions. At least following their instructions have never failed me.

[Mark89114]

Just a word of wisdom on this whole topic as this just happened to me yesterday.  Make sure you leak check them, while it might seem like a trivial gasket replacement for whatever reason they are fussy.

Over the years, we had finally gotten the gaskets to stop leaking, apparently it is a known issue with the IO-550?  This annual we had to replace a cylinder, reused the thicker silicone/neoprene gasket as it was firmly bonded to the valve cover with sealant, see previous note about long term issue of getting them to stop leaking.  The cylinder head replacement and reinstall of the covers and subsequent leak test was no issue.  Flew a couple of test flight no issue, an unrelated EGT probe and uncowling and the mechanic went back and tightened up the valve cover screws, that was just enough to squeeze the gasket out of position.  I took a quick test flight to get cheap gas and saw this oil pouring out of engine cowling.  There was a mess of oil coming out, would have been a big issue if I would have been on a longer flight.  Removed the old gaskets and installed the "rubber paper" looking ones that came with the rebuild kit.  Still took some finagling as they continued to leak.  Eventually ended up removing the spark plug wire hold down and voila not more leak.  The plug wire hold down seemed to be interfering with the hold down.  My informational session for the day.  

[N201MKTurbo]

One thing to check is the flatness of the valve cover. Especially around the screw holes. When they get overtightened it dishes in around the holes. Some smithing will get them flat again and they will seal much better.

[Yetti]

Also we used a razor blade to clean the heads.   Snap on has this really cool gasket scraper that I have not been able to find another one,  but a razor blade works in a pinch.

[DXB]

What tool do people use to set torque accurately on the screws?  Not that I would ever do this myself 

[EricJ]

1 hour ago, DXB said:

What tool do people use to set torque accurately on the screws?  Not that I would ever do this myself 

1/4" torque wrench with the appropriate range.

 

[carusoam]

Rjf...

The answers above kind of give an indication of why such a simple job is best handled with somebody that has done it before...

1) the bolts are in a tough environment getting the old ones out can be challenging...

2) The threads may need some cleaning...

3) The torque is not too tight, and not too loose... best done with a torque wrench...

4) Selecting the proper seal... my old O360 went silicone, successfully... lots of surface cleaning to get the cork remains out...

5) Whichever seal you select get the proper procedure including torque settings to use...

6) Getting it wrong... results in plenty of oil escaping out the bottom...

7) You have two challenges with escaping oil... fire, and engine ceasing.....

8) using new hardware can be a good idea too... get the right size bolts or they may bottom out before torquing tight... (no idea where this memory comes from... )

 

PP thoughts only, not a mechanic...
 

best regards,

-a-

[Rjfanjet]

Thanks for all the advice. I'm going to do this job with my IA.

[N201MKTurbo]

On 10/2/2019 at 10:26 PM, DXB said:

What tool do people use to set torque accurately on the screws?  Not that I would ever do this myself 

A screwdriver. 

Tighten it till it just starts to compress the gasket. If you can’t loosen the screw with your fingers on the shaft of the screwdriver it is tight enough. 

Edited October 4, 2019 by N201MKTurbo

[Shiny moose]

I use one like this.  its the only job it has, works very good

[RLCarter]

On 9/30/2019 at 12:16 PM, Yetti said:

Also we used a razor blade to clean the heads.   Snap on has this really cool gasket scraper that I have not been able to find another one,  but a razor blade works in a pinch.

I've used this X-Acto handle with the other blade pictured since the mid 80's and never looked back. Small enough to get in really tight spots and has very good control, I had several scraper
that I'm not even sure where they're at since using this set up, best $15.ish ($25.00 today's money) ever spent. and by the way up until a year ago it was the original blade, I just kept it sharpened on a wet-stone but I loaned it out and they had some how broke a corner off the blade.

This is the kit I purchased over 30yrs ago

[N201MKTurbo]

I use a wood chisel to scrape gasket surfaces. It is much more rigid than a razor blade and you can push harder without gouging the metal.

I rarely use any sealant on aircraft engines. If the surfaces are clean, flat and dry the gaskets don’t need any sealant. It also makes the next access to the part much easier.