Removal of stuck transmission oil fill cap on Yanmar SVE8

[billclay]

My wife and I took over ownership of her father's 1979 Hunter 27 after many years of lack of use (and lack of care!) last year. The boat was a disaster when we got it from him, and it still is, but I'm making it better every weekend.

Anyway, my most vexing problem right now is that the transmission oil fill cap (& dipstick) is hopelessly stuck in place. I have a new one, but I can't remove the old one - the 30-year-old plastic has gotten brittle and it's really stuck on there good.

The tabs along the top were broken down to nubs over the years, so they are no help. They were not tall enough anymore to get pliers on them.

I managed to get a pair of channel-lock pliers on the rim of the cap, and while I got the cap to turn for a second maybe 5 to 10 degrees, the plastic along the rim disintegrated in the jaws of the pliers, so there isn't enough structure to try that again, and of course you can't get pliers on another part of the cap due to interference, so I can't get at a "fresh" part of the rim.

Finally, getting desperate, I drilled two shallow, small-diameter holes into the top of the cap and stuck the tips of a splayed pair of needle-nose pliers into the holes and tried twisting it open that way, but it didn't budge. The pliers dredged their way through the mushy, degraded plastic. I thought I can try it again with the holes drilled further apart (and closer to the rim) for a bigger torque moment, but other than that, I am out of ideas!

Does anyone have any suggestions for how to get this blasted transmission oil fill cap off?

I will of course pump out the transmission oil afterward (and flush it a couple of times more after it gets in the water and I can run the engine) to make sure I don't have any bits of plastic left in there.

 

[timvg]

My plastic cap had broken off at the top and I was able to get a butter knife pushing down (like a screwdriver, but wider), but it appears with the holes you drilled, you have surpassed that. I now get a new cap every few years, just to make sure it doesn't happen again.

Sorry, but I don't have the answer.

 

[Ed Schenck]

Now that's a dilemma for sure. But I think you are on the right track. Using a very small bit I would drill a series of holes on the circumference. Being careful of course not to damage threads. Then two larger holes, large enough to get a good grip with the needle nose. With enough holes you should be able to pull it straight out.

Can you get a metal dipstick? My old 2QM20 with the Kanzaki tranny had one.

 

[RAD88]

Now that's a dilemma for sure. But I think you are on the right track. Using a very small bit I would drill a series of holes on the circumference. Being careful of course not to damage threads. Then two larger holes, large enough to get a good grip with the needle nose. With enough holes you should be able to pull it straight out.

Can you get a metal dipstick? My old 2QM20 with the Kanzaki tranny had one.

Maybe you can heat up the surrounding metal area with a torch - but not too much - and then it might break free.

 

[Don12364]

I would try softening it with a hot air gun used for paint stripping. On its low setting it should not generate temperatures sufficient to start a fire with the oil. You might be able to soften the plastic and pull it out in pieces with long nose pliers. At least this way you should be able to avoid it fragmenting and (any more?) pieces going down inside the gear box.

Have a fire extinguisher handy though just in case.

 

[Benny]

Drill two larger holes all the way though the cap and insert the needle nose plyers using a screwdriver for leaverage to turn the handles. The cap should screw off before it breaks. Another thing you may try is to use a flat screwdriver as a wedge between the cap rim and the transmission base by tapping it laterally with a hammer. A side blow to the plastic threads should deform the cap and release the hold. Don't be afraid to break the cap just try to do it in as few pieces as possible. Just flush the transmission afterwards.

 

[billclay]

Thanks for all the replies!!

I will try heating up the case next. I think I have a decent hold on the cap with the needle-nose pliers, so heating the case will help it form the other side of the problem, as it were. If that doesn't work, then I will try the butter-knife approach - I think it could actually work better than the needle-nose pliers, since I can probably get more torque on the cap with a wider blade than with two plier points.

I do not want to shred the cap or pick it apart because I don't think I would ever get the part of the cap that threads into the case out this way.

@ ED... My new fill cap is still plastic, but the dipstick under it is metal. Did you have a metal cap on yours?

 

[billclay]

I finally got this bugger off! After trying every tool in the box to twist the cap off with no success, and virtually destroying it in the process, I finally tacked and took a knife to it.

First, I cut out the middle of the cap to get the metal dipstick out of there, then used the knife to cut the cap flush with the top of the transmission case. I used the case as a fulcrum from a couple of different angles to force the blade into the plastic of the cap and cut it flush. I was then left with the threaded collar inside the transmission oil fill hole. I again used the blade to cut a ~30-degree wedge out of that collar, removed the wedge, then the rest came out with a screwdriver and pliers!

The reason it wouldn't budge was because the threads in case had been mauled pretty bad - perhaps by a cross-threaded metal cap? They were filthy and gritty, too. Even after cleaning the threads, the new plastic cap/dipstick would only go one about one turn (out of 5-6) before stopping. That's plenty! I can add the extra half-inch to the dipstick reading.

As I suspected, the oil in there was O-L-D!!!! I think 10 years old at least. I have never seen oil so nasty that it was totally opaque on the dipstick. Not dark, mind you - opaque, like mud.

I refilled it with some fresh 40 weight and called it a day. I will run the boat out of the harbor and back in under power this weekend, and change the oil again. The transmission will probably seize up first from surprise, though.