Aug 11, 2011
O'day 30 313 Georgetown MD
Yep, I rounded off the bolt that is the fill plug. Why its not a plastic unit with a dip stick like on a car, is beyond me. So, I'm asking the "go to guys" on this list what to do. If I apply heat, will there be damage to the transmission? I don't know much about how they work, but if there are any rubber seals inside, my guess is that heat will damage them. So I have applied PB Blaster, I have tried one of the wrench sockets with the multiple pins that push back when you cap the nut with it. I have not done the vice grips because i think it will just break down the nut head. Drilling and using a bolt extractor wont work because the extractor will need to be small and they just snap (very experienced with them).

So guys any help?
Sep 25, 2008
Alden 50 Sarasota, Florida
Moderade heat won't cook the tranny but likely will a rubber or neoprene gasket there so heat isn't a good idea. You should be able to remove the entire fill tube. If nothing else works after which you can just replace it with the proper cap and stick.
Mar 29, 2017
Hunter 30t 9805 littlecreek
Usually a flat cut across plug and wide or custom wide flat head on an impact wrench or impact screwdriver will loosen it.
Jun 11, 2004
Oday 31 Redondo Beach
I assume this is on your O'Dy 30. I don't know what transmission you have but if it's like my Hurth I think there is a plastic washer between the transmission and the fill plug head. Hard to imagine it would be stuck that tight. I wouldn't worry about damaging the washer with heat because you'd want to replace it anyway. I just wouldn't go too crazy with the heat.
I wouldn't drill it because you might get metal in the transmission if you drilled through it or might damage the attached dip stick . The fill plug is not just a bolt but has a dip stick attached to it.
I don't think I'd want to bang on it using an impact driver. At least the ones I'm familiar with.
I'd probably go for the vice grip or maybe a small pipe wrench if you can get one on there and have it bite.
Just my 2 cents.
Good luck.


Jan 7, 2014
Beneteau 45F5 51551 Port Jefferson
I second the vice grips or use a dremel to grind the sides to fit a smaller box wrench.
Aug 17, 2010
Oday 35 Barrington
The plastic ones that are used on Yanmars FREQUENTLY break, leaving the threads in the transmission. Then you need to figure out some way to remove the threads without getting plastic bits into the transmission.

I have no idea how you are going to get your broken plug out, but I suggest that you replace it with another metal plug. Also NEVER use an adjustable wrench on this plug.
May 24, 2004
CC 30 South Florida
Apply BP Blaster and let it soak overnight, lightly but firmly tap it on top repeatedly with a hammer and then get the vice grips and turn to loosen. That bolt is stronger than it may look. Then get a replacement.
Aug 11, 2011
O'day 30 313 Georgetown MD
This plug is one SOB (and I don't mean Slide Over Baby). Pipe wrench and vise grips don't work. there is not enough flat wall space to get it to grip without it lifting off. My next step is using more PB Blaster and find a set of Bolt and Nut Extractors. The type that cuts into the head. wish me luck.


Jul 29, 2018
O'Day 35 Buzzards Bay
Careful with the PB Blaster - you don't want to get it on any seals. Apply with a Q-Tip
Jan 22, 2008
Oday 30 Stamford CT
The fill plug gasket on my 1983 O'Day 30's transmission is made of aluminum. You may also want to call a marine transmission shop and see if they have any ideas as they have probably dealt with this problem before. If you want to try on your own, I would try to put a cut in the top of the transmission plug with a hacksaw blade so that you can a tight fitting large straight slot screwdriver in it. Attach a pair of vise grips on the screwdriver for extra torque. If you have a place where you can get some dry ice I would put some dry ice on the plug to see if it will shrink it a little. If you you have a source of liquid nitrogen that you can apply to the plug, that may also work (friendly dermatologist). Dr Scholls has a Freeze Away Wart Remover kit that contains a source of liquid nitrogen that may work. You may want to try that before you drill into the plug and have the dip stick drop into the transmission or let metal filings in the transmission. Good luck
Aug 28, 2015
Oday 28 St Joseph, MI
I would soak it with the PB Blaster every day and give it a couple of raps (not necessary to beat it to death) with a ball peen hammer. I like the idea of cutting a slot. I wouldn’t use vice grips, I would file flats on opposite sides and use a tight fitting wrench.
Aug 11, 2011
O'day 30 313 Georgetown MD
These bolt and nut extractors go over the six sided head of a nut or bolt and grab into the metal. There is no drilling, but thank you for the reminder of the ramifications of drilling into the head. Maybe I need this like a hole in the head!!!!!
Aug 17, 2010
Oday 35 Barrington

Now go get the correct wrench to fit the plug and NEVER use an adjustable!
BTW - there should be a copper washer under the plug.