# Accidentally drilled into oil passage



## 70 GTO (Oct 21, 2012)

Hello all, 

I had to drill into the bell housing alignment dowel pins in order to tap them to pull them out so I can install adjustable ones to index the bell housing for my new Tremec.

In doing so, I drilled too far and went clear into an oil passage behind the right dowel pin. I've drilled into the passage between the oil pump and the oil filter. I was able to remove the filter assembly and clean out the metal shavings, but now I have a 5/16" hole in the oil passage. 

I can't put a dowel pin back in and call it a day because the new pins have a screw through the center for tightening, and the oil would leak right past them. So I have to plug the hole somehow.

I would JB Weld but I'm not sure it would hold up to the oil pressure and thermal expansion.
I would tap for a pipe plug but I don't have the tools/skill to tap tapered threads.
I don't own a welder but even if I rented one, I understand that cast iron is very hard to weld correctly.

Would pressing a sleeve into the passage work? I'm open to other suggestions as well

Thanks, 
Alex


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## Duff (Jan 12, 2020)

Be careful how far you go in, but tap it and install a pipe plug.


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## Sick467 (Oct 29, 2019)

Not that I have been in your situation, but many engines have OEM oil passages that just have press-in plugs that seal them up just fine...just like a freeze plug but smaller. I agree, that drilling and tapping for a small pipe plug would be best given you have enough room to drill and tap for the smallest plug you can get. A press-in plug would work fine too so long as you can drill the hole to the precise diameter and keep the hole good and straight. I have seen 5/16" aluminum plugs for carburetors and steel 3/8" plugs can be purchased from many parts stores. If you go this route...I'd double up on the plugs (given your hole is deep enough) and give them a good coat of RTV before tapping them in.


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## kevin1727 (Aug 4, 2021)

Drilling and tapping for a tapered plug is not that difficult. You just need a tapered tap and tap handle. Drill using the correct tap drill for the plug you are using. The critical thing is tapping to the correct depth but you can do that by backing out the tap and test fitting the plug until it is correct. Maybe someone else can comment, but I'm thinking teflon tape to seal, then tighten it down. Don't put any teflon tape past the end of the plug because it will just come loose later into the oil passage.


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## armyadarkness (Dec 7, 2020)

Red Loctite is permanent and will not come free without heat. Ive used it on mass produced, press fit hydraulic pistons, at over 5000 psi. So simply clean it and press in a metal plug with red loctite. Use accelerator and let it dry.



70 GTO said:


> I can't put a dowel pin back in and call it a day because the new pins have a screw through the center for tightening, and the oil would leak right past them. So I have to plug the hole somehow


Not if you put red loctite on the screws first. However, they wont come back out without heat, either. Im not clear as why the new pins have a screw. Can you post a pic?


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## RMTZ67 (Mar 12, 2011)

Without seeing your exact issue...I agree with the others. Use drill and tap for as small of a plug as possible and something like this to seal.


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## Duff (Jan 12, 2020)

It's done all the time, but I wouldn't use teflon tape near an oil gallery.


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## kevin1727 (Aug 4, 2021)

If you press a pin, don't you have to use a reamer in the hole? It's not my experience that a drilled hole has a good enough finish or tolerance for pressing a pin.


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## kevin1727 (Aug 4, 2021)

Duff said:


> It's done all the time, but I wouldn't use teflon tape near an oil gallery.


Thanks. That was one of my concerns too. I've used teflon tape in similar applications but had to be very careful in applying the tape to the threads. I think most people get tape past the end of the fitting threads and it comes off inside.


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## Honeyharbour62 (Jul 15, 2018)

With a 5/16 hole you're nearly there for 1/8 npt. Tap drill for it is 0.339 inches or R drill in letter drills.


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## armyadarkness (Dec 7, 2020)

I'd like to see a picture of the part in question, first.

Im about to do a Tremec conversion on my 67, so Im curious... but to the OP's original dilema, he states that a screw passes through the pin and is used for tightening. If that's the case, the screw can merely be red loctited and the part will not leak. However, it also will not come back apart without heat.

And while I agree with everyone that drilling and tapping is not that difficult, and it's what I'd do, the OP is admitting that he's not comfortable with the process, so I doubt that I'd be looking to break him in on an oil galley, under his car. If the tap ever snapped, his problem would go from gecko to Godzilla. Im a 35 year seasoned metal fabricator and Ive snapped more taps in my life than I wish to recall.

Ive used epoxy on pool heaters, and while it's not the best bet, a putty type on a well cleaned surface, followed up with loctite on the screw, would likely do it.

So... Search for a pal to drill and tap it for a 1/8 pipe plug... if not then feel safe using these other methods.


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## CoveKid19 (Nov 18, 2021)

Just out of curiosity, how long are the dowel pins? I may be doing this soon and would like to know how deep the drill can safely go.


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## armyadarkness (Dec 7, 2020)

Not that it's relevant, but if I had to remove dowel pins I'd weld a bolt to them and use a steering wheel puller.


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## armyadarkness (Dec 7, 2020)




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## Jared (Apr 19, 2013)

I'm on the tap and thread using sealer team. One recommendation would be to do a couple quick oil changes after you repair this. Don't bother changing the filter until the last change, and you could probably just use really cheap oil as the flush, but I would start it up and shut it down quick. Then drain the oil, refill, and repeat. One more time if it makes you more comfortable.

This sounds like the type of mistake I am famous for. Good luck!


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## Jetzster (Jan 18, 2020)




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## 70 GTO (Oct 21, 2012)

Thanks for all of the great responses guys. I think I'm going to try to tap it for the screw-in plug. 

I did a quick google about how to tap tapered threads before I wrote the first post, and I was under the impression that a reamer was required. I've never used a reamer and I figured tapered tapping would be much harder than it's now sounding like it is. So I didn't pursue the idea further.

I know nothing about pipe threads so help me understand - since my "pipe" has an I.D. of 5/16", I need to get a 1/8 NPT tap & a type R tap drill bit, and a 1/8 NPT plug (such as Dorman 090-046)?

I would also need to get some sort of sealant or epoxy. Sounds like Teflon tape is too risky.

I've attached some pictures to hopefully better illustrate what I'm looking at. 



































































armyadarkness said:


> Red Loctite is permanent and will not come free without heat. Ive used it on mass produced, press fit hydraulic pistons, at over 5000 psi. So simply clean it and press in a metal plug with red loctite. Use accelerator and let it dry.
> 
> 
> Not if you put red loctite on the screws first. However, they wont come back out without heat, either. Im not clear as why the new pins have a screw. Can you post a pic?


It looks like you found a pic of the exact pins I have. As you can see, the split at the back of the pins would allow oil to get past so loctite on the threads wouldn't help.



CoveKid19 said:


> Just out of curiosity, how long are the dowel pins? I may be doing this soon and would like to know how deep the drill can safely go.


The pins are about 1.1 inches long, but I ended up using a helicoil tap because it's what I had and put in a helicoil, which is less than half an inch and I got them out fine. So really you would only need to drill about half way. I pulled it the same way Fast Monty's Garage on YouTube did it, except my motor is in the car.



armyadarkness said:


> Not that it's relevant, but if I had to remove dowel pins I'd weld a bolt to them and use a steering wheel puller.


If I owned a welder and had any experience welding I would definitely go that route first.



Jared said:


> I'm on the tap and thread using sealer team. One recommendation would be to do a couple quick oil changes after you repair this. Don't bother changing the filter until the last change, and you could probably just use really cheap oil as the flush, but I would start it up and shut it down quick. Then drain the oil, refill, and repeat. One more time if it makes you more comfortable.
> 
> This sounds like the type of mistake I am famous for. Good luck!


Thank you for the well wishes. Wouldn't it make more sense to quickly use a couple filters, then do a full oil change? This way I could cut open each filter to inspect for metal shavings, and I wouldn't be using up 10-15 qts of oil in the span of a day. You can see in the pictures that the oil passage the debris would be in (I cleaned it best I could) is literally a couple inches before the filter inlet.


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## kevin1727 (Aug 4, 2021)

I'm seeing something I didn't realize before. I thought you had drilled the same diameter as the dowel. You have a small hole at the bottom of a larger hole. Are you going to tap the large hole or the small hole?
The small hole looks like it may not have enough wall depth for a tapered thread. And the large hole doesn't seem to have enough depth for even a bottoming tap.


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## PontiacJim (Dec 29, 2012)

Here is a diagram for oil flow. If I am correct, the oil at the point of the hole when oil is pumping will not go through the filter, but up into the lifter galley and through all your bearings.

I might leave the filter off as in the photo and flush some thin liquid a couple times, like transmission fluid, into the hole using the single quart oil pump that screws on top of the quart. You should be able to get one locally. Let the flush drain through the oil filter hole, use a clean catch pan and look for any particles - if any.

Put a light coating of some JB Weld on the plug threads you use. The dowel pin should also act as a wall and means to keep the plug secure. Make sure the plug is flush so the pin sits flat on it.

Nothing else you can do from there and just keep fingers crossed. You should be OK.


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## BearGFR (Aug 25, 2008)

Fortunately, I have my engine out and apart right now so I could go have a look. 

The bottom hole on the oil filter adapter, the one that you drilled into, is the pressure side of the oil pump before it goes into the filter. You can see in the 5th picture you posted that shows the back side of the block, that passage makes a 90 degree turn and goes down to the oil pump. The upper passage across the back of the block is the one that comes out of the filter and goes across to the lifter gallery, "output" from the filter. So, that hole you drilled is going to "see" the maximum oil pressure that the pump puts out.

True, that's a small hole and very shallow to be able to cut a tapered thread into for a small pipe plug, but I think the good news is that I don't think it HAS to be a tapered pipe plug to work. That's because the dowel pin will be sitting on top of it, and that ought to keep whatever you put in there from backing out. If it were me, I'd consider cutting normal threads into that small hole and putting a regular hex socket plug into it, with JB weld packed into the threads to seal it. Once that dowel pin is sitting 'behind' and on top of it, you shouldn't have to worry about it backing out, and if you make sure to get both the threads on the hole and the threads on the plug nice and clean, that very thin layer of JB weld that will be left after you put the plug in ought to seal it nicely. Make sure the plug doesn't protrude into the oil passage so as not to introduce a flow restriction. If you go this route, coating your tap with heavy grease before you cut the threads will help trap the chips so they don't wind up in your oiling system. Also with the pan off and the pump removed, you can blow air into that passage from the oil pump mounting face and that will clear it out. If for some reason you don't get a good seal, it should be obvious because you'll be able to see oil leaking from around that dowel pin after it's all up and running. It wouldn't hurt to use some kind of sealant around the dowel pin, perhaps something like regular old pumber's "pipe dope" for insurance. 

My .02 - from someone who's also made more than his share of mistakes and created additional problems for himself therefrom.

Bear


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## 70 GTO (Oct 21, 2012)

kevin1727 said:


> I'm seeing something I didn't realize before. I thought you had drilled the same diameter as the dowel. You have a small hole at the bottom of a larger hole. Are you going to tap the large hole or the small hole?
> The small hole looks like it may not have enough wall depth for a tapered thread. And the large hole doesn't seem to have enough depth for even a bottoming tap.


I would be tapping the smaller hole. The larger one is the dowel pin hole so it cannot be touched because I need to put my new dowel pins in there of course. 



BearGFR said:


> Fortunately, I have my engine out and apart right now so I could go have a look.
> 
> The bottom hole on the oil filter adapter, the one that you drilled into, is the pressure side of the oil pump before it goes into the filter. You can see in the 5th picture you posted that shows the back side of the block, that passage makes a 90 degree turn and goes down to the oil pump. The upper passage across the back of the block is the one that comes out of the filter and goes across to the lifter gallery, "output" from the filter. So, that hole you drilled is going to "see" the maximum oil pressure that the pump puts out.
> 
> ...


As far as wall depth, if I understand you, I measured it at about 0.450". That's from the back of the dowel pin hole to the edge of the oil passage. To put it another way, this is the maximum length of the threads I would cut, or the maximum length of the plug. Is that enough for tapered threads?

A concern I have of cutting regular threads is, what would stop it from "backing in" to the oil passage? I know the dowel pin would stop it from backing out, but would the oil pressure (or JB Weld) -always- be sufficient to keep it from continuing into the oil passage?


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## armyadarkness (Dec 7, 2020)

There are many ways to do what you need to do.


Aside from the tap itself, theres no difference between pipe threads (tapered) and standard threads.
Pipe threads and standard threads DO NOT share terminology. So don't expect a 1/8 pipe plug to look like a 1/8 bolt.
As has been pointed out, a 5/16 hole is what you'd need for a 1/8 pipe plug.
What will stop you from screwing the plug in too far? YOU. Use loctite thread sealer, screw the plug in so that it provides the clearance needed for your alignment pin. Stop. Verify that it does not protrude into the oil galley. Regardless of whether or not it's tight, the correct loctite will seal it.
Wall thickness; if you have .45", that';s almost 1/2 inch. A 1/8 pipe plug is usually about .25 thick, so you'd have way more than enough depth... assuming that your .45 is accurate.
Above all else. Tap slow, a lot of oil, back the tap out often, and don't tap deep.
If you do all of these things and you still have a leak, it would be very slight and no more than any other leak on every 50 year old Pontiac.

On your new pins, do those slots protrude outside of the block when seated? I'd be packing the new pins with Permatex Ultra Grey, slots and threads, 24 hours before installing them. It will work like an oil seal.


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## BearGFR (Aug 25, 2008)

70 GTO said:


> As far as wall depth, if I understand you, I measured it at about 0.450". That's from the back of the dowel pin hole to the edge of the oil passage. To put it another way, this is the maximum length of the threads I would cut, or the maximum length of the plug. Is that enough for tapered threads?


So, the small hole alone is 0.450" deep? If so, that's plenty deep for what I'm about to suggest.



> A concern I have of cutting regular threads is, what would stop it from "backing in" to the oil passage? I know the dowel pin would stop it from backing out, but would the oil pressure (or JB Weld) -always- be sufficient to keep it from continuing into the oil passage?


Here's how you make sure: when you tap the straight threads, don't cut them all the way through the hole. Then use a hex socket plug that's less than 0.450" deep so that when you tighten it down into the hole, it "bottoms" out on the area where you didn't thread all the way through. In fact, if you used a regular tapered tap, you will have created some "imperfect threads" near the 'end' of the hole what will sort of act like a tapered pipe tap when you tighten the plug. As you're cutting the threads, cut them just deep enough so that you can get your plug in far enough so that the top of it is flush with the bottom of the dowel pin hole. Easy peasy.

Bear


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## Sick467 (Oct 29, 2019)

Here's a twist on Bear's tapping advise...use a tapered straight thread tap and tap into the hole, but stop well before the full taper pops out the other side. I would do this by turning the tap a turn or two at a time and then check the depth with a longish bolt and stop tapping when the depth reaches the point that the bolt stops shy of coming out the other side (about 1/8" shy)...Then, use a bottom tap, or grind the tapered portion off the first tap, and then tap the hole again to square up the threads just shy of coming out the other side (1/8" again). This would create a more firm stopping point for the treaded plug. You could cut the threaded potion off a bolt (0.45 minus the 1/8"), cut a slot in it on the pin-side to use a screwdriver to drive it in along with your choice of JB weld/thread locker sealer. I doubt this is really necessary, but it's an option. I do like the idea of leaving the tapered section to create a wedge at the end for better sealing. The bolt plug does not have to be tightened in with much force, just snug. The sealant would be doing all the work.


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## BearGFR (Aug 25, 2008)

Sick467 said:


> Here's a twist on Bear's tapping advise...use a tapered straight thread tap and tap into the hole, but stop well before the full taper pops out the other side. I would do this by turning the tap a turn or two at a time and then check the depth with a longish bolt and stop tapping when the depth reaches the point that the bolt stops shy of coming out the other side (about 1/8" shy)...Then, use a bottom tap, or grind the tapered portion off the first tap, and then tap the hole again to square up the threads just shy of coming out the other side (1/8" again). This would create a more firm stopping point for the treaded plug. You could cut the threaded potion off a bolt (0.45 minus the 1/8"), cut a slot in it on the pin-side to use a screwdriver to drive it in along with your choice of JB weld/thread locker sealer. I doubt this is really necessary, but it's an option. I do like the idea of leaving the tapered section to create a wedge at the end for better sealing. The bolt plug does not have to be tightened in with much force, just snug. The sealant would be doing all the work.


That too would work.

As an aside, because I'm running a solid roller valve train in my engine I put restrictors in all the lifter bore feed holes. Their purpose is to force good oil supply to the mains and rods while still allowing "enough" oil through the lifters, pushrods, rockers, and springs. They are made from small hex socket head plugs, about 1/8" in diameter and about 3/16" or so long, with 0.060" holes drilled through them. 

I used the the exact same process I described to cut the threads into the lifter bore feed holes. 

They tighten down nice and snug when installed, and I used blue thread-locker on them during installation just for a little added insurance. Needless to say, if one of them were to ever "come out" in either direction, bad things would happen. I've run for years with them in place. 

Bear


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## lust4speed (Jul 5, 2019)

Had a friend do exactly the same thing. we fixed his by using an Allen screw that wasn't tapered and simply coated it with red Loctite before screwing it in place. This way you can tap the existing hole without going larger trying to fit a larger tapered plug. This was over ten years ago and still running fine. Pontiac perfectly lined up the dowel hole with the oil passage.


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## robt1970 (Oct 6, 2021)

An easy test would be coat your dowel pin with blue lock itie , knock it in...coat the center small bolt with liquid teflon...tight it.Crank engine and check for a leak.


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## Machinest-guy (Jul 19, 2019)

Good evening, I think I can add some positive comments about how to fix this. I've had to do this sort of repair before and understand the groups prior suggestions and issues causing some hesitation in implementing them. 
Any repair with JB Weld or similar stuff depends on some thickness of material to work. If you smear it on then press or screw a tight fitting together there isn't any JB Weld left to do anything. I'd offer up my experience in using that product for a half century that you need about an 1/8 of thickness before you have much strength. Sections over a 1/4 inch can fail in sheer or tension at less force than you'd like to believe. JB Weld works really well when you can back it up with a patch plate or fill a cavity that has an irregular surface or embed screen into it. 

Story: I built claimer class IMCA engines for a long time. Fords with big strokes. I used Ford 300 cid rods from Industrial or UPS engines and messed with the crank diameters to get things fitting. The 300 inch rod has an oil squirt hole in it as does the bearing. I'd fill the hole with JB weld and also smear some into the bearing hole then fit the bearings etc to allow assembly. This boosted the oil pressure at the journal and gained us RPM. It also cut down windage so we gained torque. However after about 20 races the JB Weld would erode out of the hole and that advantage would be lost. 

You have the same situation here. Main line hot oil at full flow across a repair eating it a bit at a time. When I realized that I made the rod squirt hole bigger ( 3/16th ) so the JB Weld plug would be bigger. Then; when the plug eroded away it would cause a big enough leak that the journal would starve for lubrication blowing the rod up and wrecking the engine. What our team kept secret was how long the plug would hold. So if our engine was claimed any team protesting our car winning using a claim / swap rule they got a hand grenade with the pin pulled. I never had to compete against my own engines and we had great success - as long as we kept track of which engine in our inventory had run how many races. Take away - I'd recommend never using JB Weld against hot main line oil pressure unless you can inspect it regularly. Against coolant sure. Against fuel - Hummmmm - maybe. I've had modern gas disolve it in 3 weeks time. It didn't use to do that.

Any of the teflon tape / gasket sealer sorts of goo it in there repairs won't last very long against main line oil pressure despite having some "stick to it ness" unless backed up with a metal plate or gasket sandwitch. In this case that can't be done. 

You need a metal to metal repair. This leads to two options, both with drawbacks but both with certainty of success.

Typically when you break into a coolant or oil passageway the repair method is to sleeve the hole that the break in broke into. In this case you'd make a metal sleeve for the oil filter adapter boss having an ID to match the OEM oil hole size and an OD thick enough to stand pressing it in. You'd remove the engine from the car and strip the block enough to handle getting it into a machine for making an accurately sized hole to accept a sleeve. Some engines are prone to having this happen. Caterpillar, Ford, and some ISUZU engines come to mind. A company called "Lock n Stitch" in Lodi CA makes repair sleeve kits to save these blocks and heads. Give them a call and maybe you'll get lucky an existing kit will do what you need to have happen. Mostly the break through kits are for issues in head bolt bosses and injector holes. They also make repair pins which have special threads to seal against enormous pressures which I've used for decades to crack repair all sorts of castings. But in this case I don't recommend trying to pin this hole.

Story: A drill generally cuts only on the sharp end and approximately follows an existing hole. If anything is off axis the hole will egg shape and become off center. Some drills will cut on the flute edges. They generally go wilder quicker. Machine tool end mills cut on all surfaces so can't typically be successfully used in a hand drill - but don't count out trying...... 
Reamers follow the existing hole no matter if it is straight or egged, or belled or whatever. Reaming a hole to size is imperative to do if you want a good fit but depends entirely on the hole starting out on location and on size and on axis. This is nearly always screwed up laying on your back under a car with a hand drill. To be successful with a reamer and pin repair you need to stay within .003 on size which is all the reamer can handle (finish or correct).

So that gets you to an old school solution. Lead. Get a couple of old lead hunks - fishing weights, bullet noses, musket balls, drapery weights from an antique house curtain, whatever. Make a glob of lead big enough to fill the bottom of your break out hole plus the empty space behind your new adjustable dowel pin. Pound it in there tight with a punch until you can see it forming into the main line oil passageway. Cross drill the passage so it's full size. Remove the distributor and spin the oil pump to flush chips out. That will happen quick - half a quart or less of oil lost. Job done. The lead plug won't leak, won't move, and will last forever. It's held in by the new adjustable dowel pin so can't move.

Best of luck to you. Hope this helps you move forward. Ladd


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## lust4speed (Jul 5, 2019)

Better off with a pencil magnet fished into the oil gallery since the breach is only a few inches from the oil filter adapter mount and should be able to grab all the chips. Oil flow from the breach is after the oil filter and direction of oil flow is into the engine heading towards bearings and lifters.


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## lust4speed (Jul 5, 2019)

lust4speed said:


> ...Oil flow from the breach is after the oil filter and direction of oil flow is into the engine heading towards bearings and lifters.


Checked a block today and I had the wrong gallery, and need to make the correction that the dowel hole aligns with the oil pump to oil filter gallery and if chips were left behind they should be caught up in the oil filter.


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## BearGFR (Aug 25, 2008)

Machinest-guy said:


> So that gets you to an old school solution. Lead. Get a couple of old lead hunks - fishing weights, bullet noses, musket balls, drapery weights from an antique house curtain, whatever. Make a glob of lead big enough to fill the bottom of your break out hole plus the empty space behind your new adjustable dowel pin. Pound it in there tight with a punch until you can see it forming into the main line oil passageway. Cross drill the passage so it's full size. Remove the distributor and spin the oil pump to flush chips out. That will happen quick - half a quart or less of oil lost. Job done. The lead plug won't leak, won't move, and will last forever. It's held in by the new adjustable dowel pin so can't move.


Love the lead plug idea! Wish I'd thought of it.

Bear


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## Machinest-guy (Jul 19, 2019)

Thanks Bear, lol, Lets hope we never have a need to remember it....but it reminds me of a story fixing a Mini Cooper block when I moved the push rod holes over a quarter inch and found water at the deck extending 2 inches down into the block just 3 days before a national event.......that got creative.


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## 70 GTO (Oct 21, 2012)

Update:

I went with the lead method. Ordered an ingot from amazon, cut off a piece and hammered it to size. I then used a punch to hammer it into the hole. I used a long socket with an OD that was about the same ID of the oil passage hole to support the lead so that it would actually compress. Threw it all together and it seems to be working! I've only driven it for a total of maybe 30-45 minutes though, and the roads are loaded with salt around here now.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> Better off with a pencil magnet fished into the oil gallery since the breach is only a few inches from the oil filter adapter mount and should be able to grab all the chips. Oil flow from the breach is after the oil filter and direction of oil flow is into the engine heading towards bearings and lifters.


Unfortunately, my friend, lead is non-ferrous/ not magnetic!


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