Drill and tap aluminum casting 1

[knowlittle]

If I drill and tap an aluminum casting (gearbox) from outside, some chips will inevitably enter the gearbox. How detrimental would they be to the gears (hardened steel)? Background: An automotive gearbox has a fill plug near the top but no drain hole at the bottom. The gear oil is supposed to be good for life. But the gearbox is right next to a catalytic converter. The oil degrades from heat and premature failures occur as early as 50k-60k miles. The same model sold in Middle East has a drain plug. However carefully I may drill and tap, some chips will remain inside the box. I know aluminum casting has hard intermetallic particles dispersed in the soft matrix. Should I be concerned about the intermetallic phase? What is your advice? Thank you.

EDIT: I was mistaken. Al and Si don't form intermetallics. I just checked the phase diagram. I shouldn't be cocncerned about drilling/tapping chips remaiNing in the gear box, right?

 

[Dhurjati Sen]

Dear knowlittle,

Use a vacuum cleaner to take out the chips.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[kingnero]

I have done the same thing on the oil pan of a jag I6 engine, because previous owner ruined the drain plug.
After drilling and tapping the next size hole, and cleaning the best I could, I ran some oil through it. Most of the chips came out with it. Whatever is left, hasn't done much (if any) damage.

Depending on the gear box, it should also have a filter (could be a bronze fine mesh filter). So if anything remains there, the filter should catch it. If it goes through, it'll be gone next oil change.

 

[djhurayt]

also put a good coat of grease on the drill and tap it will help hold the chips

 

[knowlittle]

Thank you for the tips, grease on drill and tap, vacuum, flushing with oil. I think I am ready to add a drain port now.

 

[Tmoose]

I might also hook up a shop air hose etc to the fill plug so there was constant flow of < 5 psi air out the hole as I was drillin' and tappin'.

I'd turn on the air hose for 15 minutes or so after the first hole was drilled because oil etc in the face would add significantly to the unpleasantness of chips and air in the face while D-n-T-ing. .

 

[Compositepro]

Pressurizing the gearbox requires full awareness of the potential hazards. You cannot just use a valve to restrict flow into the box to get the desired pressure, which is an "obvious" technique. When the outlet restriction (the drain hole with the tap) gets plugged with chips the gear box will go to full air supply pressure, and become a grenade. Using a cheap utility-grade pressure regulator would also be dangerous, as these work poorly at 5 psi.

No one has mentioned that you should tap upwards so that chips do not fall into the gearbox. Also, a spiral tap will help to assure that chips move outward.

 

[BrianPetersen]

Presumably you are doing this on a gearbox that already has oil in it ... which will start flowing out the moment your drill bit breaks through.

On the one hand, that's going to help carry the chips out. On the other hand, the oil draining out onto your spinning drill bit and onto the drill and your hand, is going to make a big mess!

 

[romke]

I would not worry about it to much. In the past i have often drilled and tapped intake manifolds to allow the use of a vacuum gauge on a gasoline engine. Putting some grease on the drill and the tap collected the chips quite well.

If possible you could remove the gearbox from the vehicle and put the gearbox on its side when drilling and tapping. After that put it in its normal position in such a way that chips will be flushed down with the residing oil and then drain and change the oil.

When chips get trapped between teeth they will be flattened because there is very little room for them...If you are lucky they will fall down after being crushed due to gravity. If they stick to the gear surface they might lead to a crack in the tooth surface initiating some form of pitting due to cyclic loading. As long as only a few chips end up on different teeth that would not necessarily shorten gearlife.

Quite a lot of car manufacturers nowadays use filled for life gearboxes. Although quite a lot of gearboxes survive that treatment, it still is not a good idea. Over time oilthickening and oxidation may lead to poor shift quality, hardening of seals and other problems. That has lead to a lot of workshops that offer a gear oil draining and flushing procedure and they all seem to be rather busy doing so...In fact no drain gearboxes save the user the cost of a few litres of gear oil at a cost of reduced shift quality and possibly rather costly repairs.

 

[Tmoose]

If I was losing sleep leading up to the surgery I might also look at the oil suction gun options and especially how accessible the fill hole is for reverse peristalsis attempts.

Maybe even turn the processs into deliciously anti-social under car rust proofing with a device like this ?

https://www.harborfreight.com/engine-cleaning-gun-68290.html

 

[WKTaylor]

Wouldn't it be easier to insert a tube/pipe thru the oil-filler port, down to the low-point of the gear-box, and suction-out the [hot] oil?

Also, There are synthetic [polyalphaolefin] oils used in turbine engines that are also used as gear-lube oils in high stress accessory gearboxes... which operate at high stress/heat.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

Quite a lot of car manufacturers nowadays use filled for life gearboxes.

I still do some of my own basic maintenance and I take "lifetime" to mean "100,000 miles". Maximum. This applies to rad coolant, spark plugs, and tranny oil.

Tmoose,
I would love to have time available today to unpack your post (or attempt to)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Tmoose]

Hi Iron Met,

Which post needs unpacking ??

most apologetically for unnecessary, un-fun obfuscation,

Dan T