Blown Crankshaft Plug

patterson · #1 06-21-2008, 08:27 AM

I'm looking for answers as to why this happened....twice now. Luckily both times on the ground during the first few minutes of running the engine.

This may be as simple as Lycoming Service Instruction 1435.... but I'm not sure. I took the C/Speed prop off for service and fitted the plane for a fixed pitch prop. I removed the governor, placed a cover and gasket on the governor adaptor and had the local A/P + A/I install the front plug in the crank. All went well for 50 hours, then I decided to go back to the C/S and refitted the governor. the C/S prop needed service almost immediately and I decided to go back AGAIN to the F/P and repeated the process of removing the governor and placing a plug in the fornt of the Crankshaft.

This time, I started the engine and prepared to go fly. In about 3 -4 minutes the plug let go and oil spewed everywhere. I assumed the plug had been placed incorrectly and after cleaning the plane up (that's another story) and having a second plug fitted, I tried again. Same result. Big mess, but at least these events happend on the ground. The steel return line was never removed.

Now here's the question. This time, as last time, I assumed that with the governor removed, the pressure was off and did not pierce the rear plug. Did I just luck out for the 50 hours I flew with a F/P and a plug NOT pierced in the rear of the crank? Or, did I do someting this time that caused the governor adaptor to not allow relief of pressurized oil...like an improper gasket that blocks a relief port? Or was the AI/AP mechanic that put in the first plug just better than me at installing it?

I wouldn't want to bet on getting down safely with this happening in flight.

Mel · #2 06-21-2008, 08:32 AM

The rear plug MUST be pierced or removed for F/P operations! PERIOD! I have seen engines go as long as 70 hrs. but it will happen eventually.

Doug · #3 06-21-2008, 04:10 PM

As I understand it is not necessary to remove the rear cs plug provided the correct cover plate is fitted to the governor pad and the oil return lines (fitted for a C/S ) remain installed.

I have been told that he cover plate must have a couple of slots in its face to permit the oil to return to the sump. Without these slots the pressure remains in the crank and will lead to a blown cs plug.

Perhaps the cover has been installed incorrectly the second time round.

Please correct me if I am wrong.

Doug

N941WR · #4 06-21-2008, 04:52 PM

Quote:

Originally Posted by Mel

The rear plug MUST be pierced or removed for F/P operations! PERIOD! I have seen engines go as long as 70 hrs. but it will happen eventually.

What Mel said!

I used a very long Phillips screwdriver and a 3 lb sludge hammer to poke two holes in that rear plug.

Once you have punched a hole in that rear plug, re-install the front plug and you should be good to go.

157 hours later and no oil leaks.

SteinAir · #5 06-21-2008, 10:23 PM

Do what Mel said and poke a hole in the rear plug already! Quick and easy to do....it should have been done in the first place.

Cheers,
Stein

Rivethead · #6 06-21-2008, 11:44 PM

That oil has no where to go with that plug in the way. Plugged it's at engine pressure.

az_gila · #7 06-22-2008, 12:30 AM

Quote:

Originally Posted by Doug

As I understand it is not necessary to remove the rear cs plug provided the correct cover plate is fitted to the governor pad and the oil return lines (fitted for a C/S ) remain installed.

I have been told that he cover plate must have a couple of slots in its face to permit the oil to return to the sump. Without these slots the pressure remains in the crank and will lead to a blown cs plug.

Perhaps the cover has been installed incorrectly the second time round.

Please correct me if I am wrong.

Doug

I have a copy of the drawing that defines the slot mentioned above. It is a DIY modification, not a factory part.

If this type of cover is installed, then the oil pressure in the front of the crank does have somewhere to go (the accessory case) and nothing blows...

It does sound like a good solution if you want (or need) to switch frequently from FP to CS and back.

gasman · #8 06-22-2008, 03:28 AM

Quote:

Originally Posted by az_gila

I have a copy of the drawing that defines the slot mentioned above. It is a DIY modification, not a factory part.

If this type of cover is installed, then the oil pressure in the front of the crank does have somewhere to go (the accessory case) and nothing blows...

It does sound like a good solution if you want (or need) to switch frequently from FP to CS and back.

Can you post that drawing for us?....................... thanks......

AltonD · #9 06-22-2008, 05:24 AM

Here is what came on my Factory Lycoming:

http://adeweese3.home.comcast.net/~a...nor_Blank1.jpg

http://adeweese3.home.comcast.net/~a...nor_Blank2.jpg

http://adeweese3.home.comcast.net/~a...nor_Blank3.jpg

I left them full size for resolution.

No gurantees made. I have a constant speed. This is what I removed to install the governor.

Martin Sutter · #10 06-22-2008, 05:55 AM

Actually the governor drive cover with a curved slot IS a factory part. My 0360-A1A came with that cover drop shipped from Lycoming and purchased thru Van's. By the way the set up only works if a governor drive is installed and the return line from the front is in place. I used that set up for over a year before installing the cs prop.

Martin Sutter
building and flying RV's since 1988