Honda Spree and Elite 50 Forums

I am about of ideas on this one. The oil sight glass (plastic) on my NX50 leaks, or rather oil seeps out past the oil sight glass rubber gasket. When I research fixing this, the answers are generally to replace it with a plug, use pre-mix and throw away the tank or some other lame idea. I want to fix it so it looks original and correct and doesn't leak. I think all NX50 tanks must all leak by now. There are two tanks on eBay currently for about $130 each, but neither merchant will say that the sight glass doesn't leak. I assume that they do.

The design of the sight glass is pretty poor. The plastic dome and the plastic tank are made out of two different types of plastic. The dome is similar to clear (yellowish now) styrene, while the tank is either polyethylene or something similar. The plastic dome has a single male thread, while the tank has several female threads. The dome is supposed to go into the tank, and less than one turn ( about 3/4 of a turn is supposed to tighten enough to compress the rubber gasket. It doesn't. If you give it 4/5 of a turn, it will jump the single thread and become completely loose. None of the threads appear damaged. The single thread can apply a small amount of sealing pressure on the gasket, but not enough to seal. In the past, I have repaired it by using gasket sealer on the gasket and tightening the dome just to the point of popping, and that works for a month or two before the leak returns. Also, after 44 years, the rubber gasket has become pretty stiff. The gasket has "rings" so that there are two sealing surfaces.. an inner ring as primary, and an outer ring as backup. Unless I figure out a way to "grow" the single thread in the dome to make it taller, the dome will never screw in tight enough to put much pressure on any gasket.

Anybody have any good ideas for a solution? Any source for new rubber "ringed" gaskets. Honda OEM gaskets have been unavailable for years, but maybe there is a non-Honda application that uses a "ringed" gasket of the same size. If the gasket were new and very soft, it might work. Here is the drawing from a Honda parts page:
http://www.vintagegarage.com/honda/OilTankDrawing.jpg

Not sure why the image doesn't display, so I added in a link to it. Click on the link to see the picture.

Personally, I'd redesign a plug and 3D print in either clear or other plastic, running several full threads on the plug, then source a circle gasket in the correct diameter (or print one from TPU.) You'd need to seal the 3D printed part.

Alternately, source a plug in the correct thread diameter, and seal with new gasket. Not sure you really need a sideglass...?

img tag isn't working b/c the url's not https:

I posted a long reply. but it didn't show up. It's always tough to write up a reply the second time when the first was detailed, so I'll be briefer. I think the best fix is to 3D print a new dome out of plastic that is identical to the original, except the threaded part has a 1/16 " larger diameter. As the drawing shows, there is only one thread. There is not room for more, as the threaded hole in the tank is very shallow, and can't be deepened without destroying the function of the ball float. Unfortunately, I have no interest in taking on a new hobby, so that solution is out, but the idea is appreciated. I can see that once you get good at 3D printing, that might be your main interest..
I wonder if there is a good way to add 1/16" diameter to the existing dome thread. It makes me wonder if there is something like a Heli-coil for plastic threads?
Using the old dome with a new soft gasket may work, but not as well, and most likely not. The inside and outside diameters would have to be an exact match, as well as the thickness. Is there a gasket cement that can seal without much pressure being applied to the gasket, as pressure is pretty much impossible with the original dome?
That is a shame that photo URLs now need https certificates. That pretty much means I won't be posting photos. Was the change made to fix a non-existent or perceived problem or is the risk of posting http photos real?