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Loosing baffle screws on #4 cylinder

dbaflyer

Well Known Member
Did an oil change today and noticed one screw about 50% out and a second one missing (I found the lock washer but the screw is no where to be found).

This is the second screw that has completely fallen out in this same location. No other screws on any of the other cylinders have done the same.

Any cure for this? Maybe some blue loctite?
 

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I've had the exact same problem on the same cylinder...lowest, most aft screw went missing. Twice. Second time with blue loctite. Trying again.

Not sure why *this* screw on only this cylinder, though...
 
Safety wire

I would safety wire the screw. I think you can find a screw with a safety wire hole. I think you could even use the small safety wire, 0.025” dia.
 
Not really addressing your root cause here, but in your first picture if that's a star washer on top of a flat washer it isn't really locking much...
 
Medium Strength Loctite

I have had a couple baffle screws partially back out. Blue loctite resolved the problem.
 
I've had the exact same problem on the same cylinder...lowest, most aft screw went missing. Twice. Second time with blue loctite. Trying again.

Not sure why *this* screw on only this cylinder, though...

Exact same problem here. I've been dealing with it for 19 years. ;-) Locktite. Lock washers, etc.

I think a drilled head screw/bolt is the answer.

Fortunately (?) the cowling is off the airplane for an oil change, so it should be easy to do tomorrow or Monday.
 
I had a couple screws on the upper gear leg fairings of all places that kept coming out. Now if I remove them, I always put a dab of RTV on the threads before screwing them in. Haven't lost another or even had one of them come loose since.

Something else you can try is replace the star lock washers each time they are removed. I do this and have never had one come loose.
 
Yes, same problem here. I now use safety wire on the aft most screws for the #4 cylinder. I have also seen these same screws missing on certified aircraft that use a -360 engine.
 
Bad application for a star washer.

Oil cooler shimmy shake.

Indeed. Vibratory action and weight of the oil cooler.

I would not use a star washer for that location. Just properly a flat washer and torque that screw to Lycoming specs for the diameter, lubed, not dry. The head is hot enough that thread locker may not work anyway.

A few important places that don't use star washers for good reason.
Connecting rods
Case main bolts.
Barrel flange bolts.
 
Indeed. Vibratory action and weight of the oil cooler.

I would not use a star washer for that location. Just properly a flat washer and torque that screw to Lycoming specs for the diameter, lubed, not dry. The head is hot enough that thread locker may not work anyway.

A few important places that don't use star washers for good reason.
Connecting rods
Case main bolts.
Barrel flange bolts.

That is contrary to the FAA certified Parts Manual for my Grumman Tiger. The baffle screws call for a flat washer and an AN936 internal tooth lock washer.

Having said that, sometimes the screws "fall out" and drop of blue locktite helps. :)

And yes, the oil cooler is mounted in the same location rear of cylinder #4.
 
A counterpoint is needed I think. New star washers and torqued to spec.
Have not lost one or had one loosen in 850 hrs. Oil cooler on #4 as some have noted.
 
Ordinary 1/4-20 thread. Hex bolts, drill the heads, torque with a plain washer, wire them, done forever.

It would violate the Grumman Tiger parts manual, so I'm sure Leroy's ghost will refuse to ride in your RV ;)
 
Ordinary 1/4-20 thread. Hex bolts, drill the heads, torque with a plain washer, wire them, done forever.

It would violate the Grumman Tiger parts manual, so I'm sure Leroy's ghost will refuse to ride in your RV ;)

Actually my RV-6A uses the star washers, and also a drop of blue loctite where needed...:)

No safety wiring involved.
 
Always use new star lock washers. Get a stockpile of the different sizes. And when they come off the airplane they go in the trash and a new one is used upon re-installation.
 
I had a screw on the aft side of #3 baffle into the cylinder fall out a couple times. Yes, with new star washers each time. I put a drilled head bolt in there and wired the dang thing down.
 
Ordinary 1/4-20 thread. Hex bolts, drill the heads, torque with a plain washer, wire them, done forever.

It would violate the Grumman Tiger parts manual, so I'm sure Leroy's ghost will refuse to ride in your RV ;)

McMaster Carr has drilled head CRES Allen head screws that work great, as do the Lyc pan heads with a captive star washer.

Dan's suggestion of safety wiring works best, is easy and can't fail .
 
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