Crankcase Question

[bstig60]

On the bottom of the crankcase just behind the oil filter there is a allen wrench plug. what is its purpose? I cannot find anything in the specs or the sm.

[GoldWingrGreg]

It is a screw-in core plug. All 5th gen cases have 4 of them. They come as part of a new case assembly, and they cannot be purchased individually. Therefore, there is nothing in the service manual about them.

Did you loosen one ???

[bstig60]

Yes, I removed the one I mentioned and a dribble of engine oil came out of it, a small amount. I put it back in and tightened it down.

[GoldWingrGreg]

It needs to be installed with lock-tight. That means the oil drained, the plug removed, the treads cleaned, and medium strength lock-tight used. Because I repair many 5th gen transmissions, I also do lots of 5th gen engine work, and have always torque the core plugs to 45 ft/lbs.

[Steve F]

okay, so what is a "core plug"? What does it do...why is it there? I've herd of freeze plugs, I'm going to guess it's not the same thing.

[M61A1MECH]

OK this is straight from a GOOGLE search so it has to be correct, right?


Core plug - Wikipedia
https://en.wikipedia.org/wiki/Core_plug

Core plugs are used to fill the sand casting core holes found on water-cooled internal combustion engines. They are also commonly called frost plugs, freeze plugs, or engine block expansion plugs.

[GoldWingrGreg]

Core plugs are used to fill the sand casting core holes found on water-cooled internal combustion engines. They are also commonly called frost plugs, freeze plugs, or engine block expansion plugs.

Correct ... as engine technology advanced over the decades, at some point someone decided a core plug could also pop out when coolant freezes, and such feature than becoming a new selling point. However, core plugs will not pop out and "save" an engine from cracking if its coolant freezes and wants to expand.

[bstig60]

It needs to be installed with lock-tight. That means the oil drained, the plug removed, the treads cleaned, and medium strength lock-tight used. Because I repair many 5th gen transmissions, I also do lots of 5th gen engine work, and have always torque the core plugs to 45 ft/lbs.

When I had my "Duh" moment and took out the plug, there was no coolant and just a few drops of engine oil and that was before I drained the crankcase or removed the oil filter. Why drain the engine oil to remove the plug? I understand torque specs for the plug, but why the locktite, is it going to vibrate out and what are the consequences if it does come out?

[GoldWingrGreg]

If the oil level and oil filter are full of oil, I believe if you left the plug out for a period of time, you would eventually see more drops and even a couple of quarts ... probably at least what is in the oil filter would drain. The 4 plugs are originally installed at Honda's factory with Honda med strength #2 thread locker. It is red in color. Med. strength in other brands are often blue. Since a factory only does things for a reason, my guess is they use lock tight to keep the plugs from backing out.

[bstig60]

Thanks for getting back to me. I will remove the plug again and put locktite on it and reinstall and torque to 45#s.

[Techdude2000]

On the wing engine they are there to close up the machining alley ways required to create passages internally that can’t be cast. They are locktighted due to expansion/contraction of the block during warmup and cool down cycles that would cause them to loosen up.

[bstig60]

Thanks again. The job is done...