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Discussion in 'Airheads' started by Tin Woodman, Feb 3, 2013.
I just read the eulogy. I'm only eight years late! The man exuded geniality.
I'm still waiting for a couple of parts as I button up the engine. Doubt continues to creep into past repairs as I contemplate reinstalling the transmission. The PO cross-threaded the drain plug but there were still a few good threads - I was never really convinced of its long term viability, however. Houseoffubar's strongly worded condemnation on Tete's thread struck a responsive chord -
This is what mine looks like -
I don't want to leave a ticking time bomb for the next owner. I agree with Houseoffubar and Plaka in that I should install a helicoil (or, I suppose, a Time Sert) with the drain hole down, flush with solvent, etc. Can you continue the explanation with more detail? Or should I simply have it done by a shop? I'm just concerned they will introduce debris into the tranny.
Heli-Coil it now (or insert your favorite thread repair instead). If you're careful you can do it without pulling the gearbox apart.
I would run a roll tap through it and see how it holds up a dozen or so times before it is installed. I might hold up just fine. First things first IMO. For a insert to really work right, you really need a different drain bolt with a wider head for a wider crush washer from there on out.
One game you can play if you have threads left is to fix it with pipe fittings.
Get the shortest 1/4 Pipe (1/4 NPT) brass nipple , a 1/4NPT brass coupler and a 1/4NPT brass plug. clean the nipple, the coupling and the hole in the tranny with brake cleaner spray. must be utterly clean. Put an LOT of red stud locker on the nipple and screw it into the hole and immediately put some red stud locker on the coupling and screw that onto the nipple. Let set up 24 hrs.
Drill a small hole through the brass plug where you put a wrench on it. This is for safety wire.
Now you can use the plug in the coupling as a drain. It's a taper thread so no gasket is needed. Safety wire it.
This will hurt the threads in the tranny slightly. Consider it a one way. It can be removed with heat but then you must do a thread repair.
You can screw a 1/4NPT nipple into good threads fully, I just did it by hand, it's a bit loose, thus the studlocker.
I can't explain doing a helicoil "hot" more than I have. I did a pair of posts on it. I'm pretty conservative thus working into fluid flow vs. drilling dry or with grease and trusting later flushing to remove the least possible chip.
Have to agree with SS on this one. Run the correct tap through it first and see what kind of threads you end up with. Might be good enough to keep the plug sealed just fine.
Plaka's idea might be useful if you had a bullet hole in the bottom of your transmission...
Actually the pitch is very close, the NPT is just a taper. I was screwing around with my oil pressure sender, same thread and a 1/4NPT will screw in the hole reasonably with some sealant/retaining compound. (I ended up making a custom fitting with the correct thread only to find I could have bought one cheap) Just don't tighten it so much you disturb the thread form in the aluminum.
This is a solid-will-last-forever kind of patch. Restore it to original when the tranny is in for other work.
An important part of my advise is using a roll tap, not a cutting tap. Good machine shop supply stores around here have them in stock.
Stole this from Snowbum:
"NOTE: Rear drive drain plugs and crush washers are available in oversizes. The oversize 16 x 20 washer is 07-11-9-963-259; and the oversize plug is 11-13-0-007-162."
Essentially doing a Heli Coil or other thread repair is two parts. First you drill the striped threads out with the correct oversize drill bit so the hole will be the needed size. Second the hole is threaded to accept the thread repair insert so the resultant threads are the original size. All this drilling and threading produces chips and debris that we don't want to be left in the transmission. The way to prevent the Aluminum debris form being left behind is to put heavy grease on the drill bit and the threading tap so the grease will catch the Aluminum bits. The bit or tap is used part way and cleaned off then more grease applied and used further.
The drain plug on a /5 four speed transmission is M14 x 1.5 Be careful when you buy the tools and parts for this because there is another thread often used that is different. It is m14 x 1.25 The one you want is M14 x 1.5
There are many brands of Heli Coil type repairs these days Some of these are a little cheaper and may come with the needed drill bit. If you buy the original Heli Coil brand the kit will not come with the drill bit. Get that extra. (this is what i usually do, I prefer the Heli Coil brand)
There are also other types of repairs. Some are called "Time Sert" or "Big Sert" These are also thread repairs and may have advantages sometimes but they are also extra work and not needed for this repair. Get the Heli Coil Kit for an M14 x 1.5 repair.
All my helicoil kits have the drill bits. They are boxed kits, from McMaster or MSC but I believe the pouched kits are the same.
A tricky aspect of the helicoil is breaking off the tank at the end. It must be done with needle noses and pulled out rather than punching it in per usual. A good method is to set the helicoil in red locktite (you do this anyway), let the locktite set up 24 hrs (at room temp, not in the cold garage) then you can twist on the tang without tearing out the coil.
The oversized plugs look like a much better repair. For one thing, you don't have to try to sell off the now unneeded helicoil kit. You do have a drill bit and tap left over tho'
I'm not a big fan of the grease method for this. You really want the hole square and the tap square. That takes a fair amount of skill to freehand. Doing multiple pecks at it just makes it harder.
I'm currently reworking an oil filter that has a similar issue, don't get any particles in side the filter when grinding away the exit hole. I'm thinking of setting up an air blast through it and grinding against the air flow.
Thanks everyone for your input.
I don't believe the existing threads are salvageable and even if they were, there would always be lingering doubt. BMW has an oversize plug for a good reason - I'm willing to bet ham fisted mechanics screw up these threads all the time. There's plenty of material on the housing to allow going to an oversize plug. The trick will be to drill and tap squarely without showering the internals with chips and debris. I watched a You Tube video tonight highlighting the grease method of catching chips - it was hilarious. All he succeeded in doing was dropping a big blob of contaminated grease into the spark plug hole he was repairing. He eventually retrieved it with a shop vac.
I like your idea, Plaka, of using positive compressed air (I believe that's what you mean) to keep debris out as I drill and tap. Could probably do it with the drain hole on its side rather than it facing up to lessen the effects of gravity.
Alternately, I could open up the gearbox again (already replaced the seals and gasket) but would prefer not to.
Overall, the larger plug has the advantage of being a more permanent solution - there's evidence to suggest inserts sometimes fail on components that are often removed and everything I've read about airhead transmissions indicates oil should be changed regularly.
No, not air. I'm grinding on an airhead strait oil filter with a high speed burr. it makes very small particles that won't go upstream against an air flow. I have an electric leaf blower, a shopvac that blows and a big gas compressor to choose from.
For larger particles you want something with more mass than air to provide the flow you work against. if you have a parts washer that's ideal. Stuff the nozzle in the fill opening. You can also use a garden hose with the sweeper nozzle. You don't need a blast, just a strong fluid flow. Using water you would finish by a flush with a water displacing solvent like WD40 ($20/gal). Then mount it, put the driveshaft on with the old bolts, take the rear wheel off and load it with cheap engine oil. Spin it with the engine for a minute, change the oil, repeat several times until the oil comes out clear. Then a flush or two with 90 wt and you're done. You can reclaim your flushing materials by heating them to 160 - 200F (use a candy thermometer or similar that registers degrees) for a few hours to drive off the moisture.
The thing is, you need the tranny oriented so you get your best shot with the drill and tap. I would bolt a square of plywood to the output end so it stands nicely wherever you're working (driveway, bathtub, etc). This is the problem with gravity and grease methods. you want to be looking strait down at the hole with the unit on the ground or a low bench so you can get over it.
You can use a drill press. Just take the press outside and then hose it with spray wd40 so it doesn't rust.
You want to use a 15mm drill bit for an m16 thread.
A high spiral flute drill would be ideal because they clear the chips upwards out of the hole more strongly than other types. But costly and I didn't spot one in a reduced shank, which means you need a 3/4" chuck. A reduced shank bit will work in a 1/2" drill. Rent one if you don't have one.
You might be able to rent taps too. Call around . Spiral flute tap would be ideal, same reason as the drill..., but very expensive. May need a semi-bottoming tap depending on how much past the hole you can go. This is critical, how much clearance do you have on the other side of the hole? If you are essentially doing a blind hole you will need two taps, a plug tap to get started and a bottoming tap to finish. This is a plug tap, pretty general purpose type.
You need a big tap wrench and unfortunately these can be the most difficult to get started strait. But you can do it if you go slow and step back and eyeball it as soon as you have enough thread for the tap to stand in the work. You can still re-align at this point.
Or you can get a helicoil kit for $45 that has everything but the tap handle. Again, beware the depth behind the hole. I can look at my kits and tell you what kind of taps they use. Installed correctly, they are a lot stronger than the original hole (stainless steel threads and much bigger) and are often used for this reason, not to make a repair.. You can make them fail, but it will take a lot more than what failed the original threads. You hear stories of them coming out---they weren't put in correctly. I put a 10mm in I-forget-what the other day where I needed to reinforce a very thin walled piece. That helicoil in red locktite was too perfect. Timeserts are even better, but costly. (If only I could remember what I was working on . Now this is really gonna bug me...)
I listen to you guys - really.
I agree the best way to drill perpendicular to the face is with a drill press - resigned myself to opening up the tranny and looking for a way to capture the swarf as I drill and tap (regardless of whether I use an oversize plug or insert). Maybe I can clean up the face of the drain hole while I'm at it.
Was instantly rewarded by finding some of the 'lost' threads -
While I'm in there, might as well change the seal on the shifter shaft -
Or am I just asking for trouble? On second thought, best to leave it alone.
Nice score on the thread fragments! Drill into a grease blob in a kitchen paper towel (never cloth, never blue shop paper towels)!). Big grease blob, like a couple tablespoons and something stiff like WBG in a tub. More paper towels behind the one with the grease blob to hold it in place. Full surgical drapes optional.
Shifter shaft seal from the outside anytime. Just did mine.
That aluminum thread shard is the softest thing in your transmission.
What's the danger, here.
Tuck one in your tranny and find out.
The first time it makes it's way between a pair of mating gear faces it'll be pulverised to aluminum dust and become a complete non-issue until your next transmission oil change.
Can't imagine it's any good for the bearings, either.
BTW, don't you guys ever sleep?
Um...no. The gears mate very closely and they are not designed to have anything between them thicker than gear oil. Know how much force it takes to forge a piece of aluminum into flake?
But maybe it ends up on the face of the gear preventing the dogs from plugging in properly. Now you grind the dog teeth off against the holes in the gear.
Perhaps it gets in the shaft splines. Then it don't shift in some gear at all.
Or how about in a bearing?. It'll jam one of those and trash it is a dozen revolutions. bearings aren't designed to be ball mills for aluminum.
Maybe just someplace trivial like blocking a lubrication hole. Hey, mechanics need the work.
Sure it's soft compared to steel. It's granite compared to gear oil.
When you beat on something with a hammer it doesn't matter how thick it is. Keep hammering until it is nice and thin. (I recently cold forged a brass shim washer. Was impressed with how long it took, even with some annealing steps.) But stuff it between gears that only have .0005" clearance and it has to go from full thickness to .0005" in one shot. Ain't happening.
I thought you were joking...or should I be looking for a snipe somewhere :eek1
BTW, guess what I did with some stainless rod I found in the scrap drawer, a long 6mm stainless bolt, a piece of 1/4-20 stainless threaded rod, a 1/4-20 threaded stainless standoff from a place I once worked, two 1/8" stainless pins, some stainless coupling nuts, a spring from the hardware store and a piece of Harris 56 silver brazing rod?