Water Outlet Drill bit size??

[Kenny Sorweide]

I am going to put a water outlet in the exhaust manifold cover on my 1975--75HP Rude. What size drill bit do I use for 1/8 pipe tap threads? My chart says use a size "R" which means nothing to me. Or maybe I should use a different kind of fitting? You guys are so knowledgeable, so knew this was the place to ask. Thanks for for your help

 

[chuckz]

Re: Water Outlet Drill bit size??

There are fractional and lettered drill bits. Size R is exactly that. A good tool store should be able to sell you a size R drill bit.

 

[Paul Moir]

Re: Water Outlet Drill bit size??

An 11/32" bit is only .005" larger than an 'R' bit (.339"). If you're tapping out a tapered pipe thread it'll make no difference. Don't tap too far or the pipe plug won't fit. Try fitting the pipe plug frequently.<br /><br />Hope this helps!

 

[R.Johnson]

Re: Water Outlet Drill bit size??

Drills come in number, Letter, and fractional. An R drill is .339. but let's make this simple. You need a 5/16 drill which is .312. This will work just fine when tapping into aluminum. A pipe tap is tapered, so only run the tap in far enough to eccept the fitting you are using. Use sealer around the thread when putting in the fitting. Any gasket sealer will be fine.

 

[Kenny Sorweide]

Re: Water Outlet Drill bit size??

Thanks guys. I have saved myself so much time and trouble since I discovered this site. Everyone is so helpful. Thanks again

 

[angus63]

Re: Water Outlet Drill bit size??

I wouldn't recommend using a smaller bit than an "R" (.339") drill in cast or forged aluminum. It is ok to go 0.005 under in wrought aluminum. An 11/32" (.344") would work well and actually what I would prefer to use in other than wrought aluminum. Tapping stresses in relatively thin cross-sections can easily cause spider cracking about the hole and because of the temp extremes, propogate over time to failure. Or it might be just fine, but why chance it.

 

[Paul Moir]

Re: Water Outlet Drill bit size??

angus63 - I agree 100% for a straight tapped hole, but in this particular case where we're talking about a tapered tap I think it's a moot point. The minor diameter is going to depend soley on how far the tap gets run in. So it really doesn't matter if the hole is undersized a bit to begin with since the tap has to cut it wider rather than 'shove' it in the case of a straight tap.<br /><br />It's a small point, but an interesting one. At least I think so anyway.

 

[R.Johnson]

Re: Water Outlet Drill bit size??

Any drill bit will cut oversize, how much depends on the quality, and grind of the bit. In a hand held, and quided drill it will be oversize. We are only going through 1/8" or slightly more.

 

[rodbolt]

Re: Water Outlet Drill bit size??

go with the 11/32<br /> a .027" undersize hole is to much for a taper thread tap in that thin casting. however I have used the 5/16th before. on the other hand as a machinist I have tapped more holes than most here. if you go with the 5/16ths then be aware not to force the tap to hard. the minor thread depth of the tap will be the size of the hole. either way go slow and keep the tap straight.

 

[rodbolt]

Re: Water Outlet Drill bit size??

kenny66<br /> with the exhaust cover in place you wont have enough room to tap before you hit the divider plate on some models. you may tap the top of the block at the water passage. if the cover is off no worries. if the cover is on its a bit harder. I did a mod like that by starting the threads with a standard tap then switching to a tap that the thread lead had been ground off.<br /> I have not done one in some years I gave up working on most the older stuff. not because they were bad they just all corroded away in my area.

 

[Kenny Sorweide]

Re: Water Outlet Drill bit size??

OK I did manage to find an "R" bit so will use that. Thanks for all your help. Rod Bolt I am going to try and drill & tap it while it is on the motor. I didn't realize it was that close. I have a gasket for it, but hate to take the power head off just because of the bottom bolts. I know where the factory covers had the outlet, but maybe as you said I am better off taking it off as I sure do not want to get into the block. How much clearance is there? Thanks again everyone for all the info.

 

[rodbolt]

Re: Water Outlet Drill bit size??

hello<br /> the clearence from the outer cover to the divider plate is maybe 3/8th of an inch in places. dont allow the drill to break through more than once. the problem you will have is tapping. the thread lead on the tap is longer than trhe depth you have to work with. thats is why I modified the second tap. but you can alo tap the topof the block near the exhaust cover. just make sure you will have room to rotate the 90* fitting down the hole. someplace out back I have some covers and divider plates. seems there is a deeper spot I just cant remember exactly where.

 

[Dhadley]

Re: Water Outlet Drill bit size??

You dont want to tap it so deep the fitting comes in contact with the inner plate. You may get a false pressure reading if the fitting is seated aginst the inner plate. The bottom starboard corner should have a small raised square place where the fitting should go. Hard to get to with the cover on. <br /><br />The top of the block is much easier to get to and work on.

 

[umblecumbuz]

Re: Water Outlet Drill bit size??

One small point that hasn't been mentioned, which applies to any hand-tapping operation - <br /><br />When you hand-tap, don't wind the tap in in one go. Turn it in, back it off, clean out. Turn it in, back it off etc. With one go you could force the tap and actually start to break off the very threads you are cutting.<br /><br />'There's a tap on the door, Henry.'<br />'That's a funny place to put a tap, Min.'<br />(Goon show fanatics understand!)

 

[Kenny Sorweide]

Re: Water Outlet Drill bit size??

Once again thanks. I did read sometime back, but am not able to find it by searching, that there was a soft plug almost the right size for a 1/8 pipe fitting. On the starboard side of my motor just below the lifting hook there is a protrusion with 2 holes. The forward hole is threaded a short ways into the hole. Both holes have what appears to be a soft plug like thingy at the end of the holes. Could this be where I had read that you can pry out the plug and put a 1/8 pipe thread into?? Also about taping the block. Do you mean in the top of the cylinder block itself? Sorry to be so naive about all this. With your Patience I will get this done yet. Thanks again.

 

[Scaaty]

Re: Water Outlet Drill bit size??

As a card carrying Journeymen Machinist, go find a 1/8 inch thick 6061 Aluminum plate (any machine shop has scrap pieces laying on the floor-or Hardware store). Drill some holes, grind/cut down a 1/8 NPT tap, and experiment with your fitting. Its a lot of fun on a winter day in Idaho waiting for the boating season, and when ya got it down pat, THEN go do the manifold. You can always screw up the plate, but seems like one shot at the manifold. Good luck!

 

[rodbolt]

Re: Water Outlet Drill bit size??

yes you can do it on the topof the block. if I think about it I willdig out one of mine and try to tell you where.<br /> robby6950 has excellent advice. practice a bit.<br /> taps and scrap is cheap, to scrap a block with a tap aint

 

[Kenny Sorweide]

Re: Water Outlet Drill bit size??

Once again I thank you guys.Robby 6950 I just happen to have some 1/inch 6061 Aluminum plate that I picked up, over in your neck of the woods, at Boeing Surplus Sales in Kent. I sure miss that place as I could always find something that was on my hafta have list. I am headed for my shop now to do as you guys suggest and practice "taping" Hope to be back out fishing on Lake Coeur d'Alene next week Thanks again.

 

[Scaaty]

Re: Water Outlet Drill bit size??

Originally posted by Kenny66:<br /> Once again I thank you guys.Robby 6950 I just happen to have some 1/inch 6061 Aluminum plate that I picked up, over in your neck of the woods, at Boeing Surplus Sales in Kent. I sure miss that place as I could always find something that was on my hafta have list.

Boeing surplus...equals ....bring money and a truck! Wish ya well........

 

[P.V.]

Re: Water Outlet Drill bit size??

As a side note to what Rodbolt has stated earlier, ask your friendly OMB/BRP dealer to show you the service bulletin specific to drilling and tapping 3 cylinder blocks and part numbers needed to do so! Will save you time and money by doing it correctly!!!