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Hey everyone.

After doing routine maintenance I found that my oil pan bolt appears to be stripped. I vaguely remember taking it to a shop in summer (it gets really, really hot here) and they must've air impacting the dang thing on. The bolt itself has enough tension to resist loosening by hand but after apply torque (22 ft-lbs) the bolt just turned. Attempted a few more times, and it kept turning. I didn't hear the normal, wonderful, sound of a skipped thread. But it also never "bit" which would indicate to me it's time to pull the torque wrench out. I started to get a little nervous and left it and put some oil in it so I could make it to NAPA for this job...

The oil pan itself seems fairly robust. I'm questioning if the threads on the pan are actually stripped or if the bolt is screwed up. I inspected the bolt as I usually do when I removed it and it didn't seem marred up (though I didnt look at it THAT closely). I didn't take a thread count so I have no idea if it left some of itself in the oil pan side hole though shining a light in there it also looked clean.

I called a shop to get a second opinion and they immediately suggested a new oil pan with the eye popping cost of $1,000 for replacement. The part itself is ~$130 so 9 hours of labor seems intense for a professional. I have a chilton manual but a few questions:

1. Is it possible the bolt is simply stripped and I can replace it? How common is it to strip the pan itself?
2. I've been told that oversized plugs do not work well because this pan has a "welded nut" on the other end that will get destroyed in the process. Same for timeserting.
3. Is it possible to gain enough clearance lifting the engine? The chilton manual says yes, but every youtube video I see says the intake manifold and several other parts have to come off to make room.
 

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Ok first thing…. The pan is not threaded the block is, a new pan won’t fix the hole.
 
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Ok now for the fun part, try swapping that bolt with another from a different hole, if it isn’t the same result it might be the wrong bolt……. I know it’s hard to believe but they may have lost one of your bolts, or one was missing and they stuck a “matching” bolt in the hole off who knows what.
If it’s the hole the other bolt will do the same thing when placed in said hole, in which case your going to have to either drill and re tap slightly larger or put a Helicoil in the hole. Either way if your “shop”was told exactly what you posted that it’s not threading tight, and said $1000 fir a new pan, there ripping you off and I’d look for advice elsewhere…… unless I’m reading that wrong?!
 

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Discussion Starter · #5 ·
Ok now for the fun part, try swapping that bolt with another from a different hole, if it isn’t the same result it might be the wrong bolt……. I know it’s hard to believe but they may have lost one of your bolts, or one was missing and they stuck a “matching” bolt in the hole off who knows what.
If it’s the hole the other bolt will do the same thing when placed in said hole, in which case your going to have to either drill and re tap slightly larger or put a Helicoil in the hole. Either way if your “shop”was told exactly what you posted that it’s not threading tight, and said $1000 fir a new pan, there ripping you off and I’d look for advice elsewhere…… unless I’m reading that wrong?!
I got a few more estimates and I kid you not they ranged from $894 to over $2000. One shop suggested the entire engine needed to be craned out. Indeed I told them the bolt basically twists forever and never engages.

I am curious about tapping. The stock hole in the pan for the drain bolt is 1/2-20. I can tap it up one size to 9/16-18 and just buy a bolt and crush washer from the hardware store. Is there anything I need to know about this pan before I embark on this? Obviously I will grease the tap for shavings. The pan appears to be steel so I'm not worried about any sort of structural damage.

But I am not sure what you mean by "the pan isn't threaded the block is". It appears to me the drain plug hole is at the bottom of the pan and it's the pan itself it's being screwed into. You've got me confused :unsure:.


EDIT

I UNDERSTAND THE CONFUSION LOL. I meant drain bolt NOT the mounting bolts! I'm sorry!
 

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Ok that makes sense now! You can’t helicoil that one, a new pan is likely the best bet, if you re tap it go slow and get a small magnet to poke inside the hole to get out any shavings that go up, most will fall down so unless you roll it over to work on it you should be good. As fir the cost, you gotta lift the engine at least a little to get in there to unbolt the oil pump, unless you take the block out……. Since your going to pull the oil pump might as well replace it (OEM) if you can find one, unless your block is relatively new rebuilt.
 

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I UNDERSTAND THE CONFUSION LOL. I meant drain bolt NOT the mounting bolts! I'm sorry!
That makes a difference. As you search, use the term "oil pan drain plug" instead of bolt. You'll have a fee options, depending on whether it's the plug itself or the threads in the pan that are stripped. Pull the plug out & take a look.

Best case scenario is that the plug itself is stripped. If the plug is stripped, try a new one.

If the plug looks ok, then the the threads in the pan are probably shot. I think they make self tapping slightly oversized that can cut their own threads.

Another option is an expanding rubber plug that doesn't need threads.

Another possibility, as you mentioned, is moving up a size & tapping new threads.

I think they also make a piece that you screw into the bad threads, weld in place, then it uses a smaller plug in the center of the new piece.

So, lots of ways to go. A little searching for a plug instead of a bolt should find a good piece to solve the problem.
 

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So the issue is how to do this with the pan on the truck. Any tapping or drilling is going to introduce chips to the oil pan. You will need a good flexible magnet to fish up in there and get the chips out.

My 300 has the factory oil pan with an extra quart capacity welded on. The pan can be welded fairly easily. So you could remove the old bung and weld in a new one. Lots of ways to fix this, as mentioned.

Tapping from 1/2" to 9/16 wont work because the minor diameter of 9/16-18 is smaller than the major diameter of 1/2-20. Meaning you wont get full thread form. You would need to go to 5/8.
 
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Back in the day you could buy either a rubber plug or a next size up self tapping bolt.
 

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A boat drain plug in the appropriate size should work.
 
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Discussion Starter · #11 ·
Tapping from 1/2" to 9/16 wont work because the minor diameter of 9/16-18 is smaller than the major diameter of 1/2-20. Meaning you wont get full thread form. You would need to go to 5/8.
I'm confused here as I don't know a whole lot about bolts. Glad I asked. Could you point me at some resources or give me a quick run down of minor/major diameter of a bolt so I know how to do this on other things?
 

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I'm confused here as I don't know a whole lot about bolts. Glad I asked. Could you point me at some resources or give me a quick run down of minor/major diameter of a bolt so I know how to do this on other things?
Major diameter is the biggest point at the crest of the threads. It will always be close but just smaller than the nominal size. So a half inch bolt will be .49xx".

Minor diameter is the opposite. Its the thinnest point at the bottom, or root, of the threads. It is the smallest diameter of the threaded

For inside threads, its the same, but kinda backwards because the minor diameter is now the crest and the major is the root of the threads.

Then you get into fitment class of 1A, 2A, and 3A. 2A is the normal class. 1A is a very loose fit and 3A is a very tight fit. Each have their own specifications.

Also a 1/2-20 bolt has different major and minor diameters than a 1/2-28 bolt or 1/2-13.

Threads are one of the deepest subjects in machining. The best resource is The Machinists Handbook or similar. The full handbook is bible huge and on super thin paper: its thousands of pages so an abridged version or a "knockoff" would be sufficient. And cheaper; my hardback was over $100. I learned in school so i cant really point to an online reference without searching a while.
 
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