drain plug size

D

ddurand

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87 Mercruiser with 5.7L engine. Need to know what size the drain plugs are for the engine. I did not find one in the engine in the spring and the one I found in the bilge seems too big. I have wire brushed the drain plug and the hole as best one can for something you cannot see.

I assume both sides are the same and its NPT.
 
the block is 1/4 inch pipe plughttp://thumbs3.ebaystatic.com/d/l225/m/mLmbzctM6TWECJ8vJbnp3SA.jpg
 
And I hope you find where the one from the bilge came from, if not the block. Ex. manifold?
 
A Battery Post Cleaner tool has a a "bottle brush" portion that might be good for a light touch-up of the threads in the block. I replaced our plugs with drain cocks and it was not easy reaching up/in there to wrench on them. They load up with grit and still require maintenance. Always hard to get the removable piece back in after cleaning them up.
 
The one I found was 3/8". I will get a 1/4" one. Hard to say where things in the bilge come from.
 
it`s not the measurement ,its what there called. a 1/4 inch pipe plug is almost a 3/8ths in diameter. The 1/8th inch pipe plug is almost a 1/4 inch in diameter
 
OK, the one I found was a 1/4", a guy at the store tried to tell me it was 3/8" and sell me a 1/4" one.

I see there is NPT and NPS for pipe threads. I assume NPT since I never heard of NPS until I look up thread chasers.

So back to square one, where the 1/4 plug does not fit into the drain plug hole.
 
I ended up buying a 1/4" NPT tap and worked it in with some oil but without the tap handle. Since I cannot really see the hole or the tap, I figured with just the tap in my fingers I probably could not cross thread it.

I'd like to get some fitting where its brass on brass that I unscrew each fall.

Maybe a petcock. But still the rust particles can be a PIA.
 
quote:
Originally posted by ddurand

I ended up buying a 1/4" NPT tap and worked it in with some oil but without the tap handle. Since I cannot really see the hole or the tap, I figured with just the tap in my fingers I probably could not cross thread it.

I'd like to get some fitting where its brass on brass that I unscrew each fall.

Maybe a petcock. But still the rust particles can be a PIA.

Click to expand...


Look up Sierra 18-4218 Drain Tap
 
That looks nice but don't rust particles get stuck in it sometimes? Then what?
 
I have aftermarket drain taps that look more like

41VtiDsHDJL._AA160_.jpg


Which is a MerC part. Ours work the same way but have a handle cast into the bronze, not a hex. The point with these is that the screw-in plug comes all the way out of the fitting in the block. So it's possible to clear clogs with a wire, clean up the threads, apply some grease, and so on. The old "radiator petcocks" don't allow that, and the handles are steel. No good for marine.
 
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