Missing an oil pan bolt

[brucecooner]

A few days ago I bought my 1988 Comanche. I had looked under it pretty well before buying, confirmed no major leaks in the 4.0, everything was clean, but I somehow overlooked eyeballing the oil pan where it's up under the front skid plate.

 

Today I crawl under it to look at something else and I notice the front center oil pan bolt, the one directly behind the pulley, is not there.

Yeah I literally facepalmed on that one.

 

The guy who sold it to me is a mechanic who works on lots of XJ's, and said he had replaced the rear main in this one.  Maybe he forgot to replace this bolt (which begs the question of what else he forgot).  I guess it might have vibrated out if not properly torqued or something? 

I've only driven it a couple dozen miles since I bought it though.

 

Is it dangerous to drive it in this state?

I don't see any leaking, nothing is on the upper side of the skid plate.

Everything seems dry but I hope I haven't damaged anything.

 

Anyway, is this an easily obtainable bolt for the 4.0? 

Feel free to point me at specs on it.  I'm not much of a wrencher but hopefully I can handle this.

 

EDIT: Other forums I've browsed seem to indicate the corner bolts are 5/16ths, and all others are 1/4 (except for the studs, which are foreign objects to this guy) 

So I think I'm needing a bolt that is 1/4 inch in diameter.

But I haven't found any info on depth nor threads yet except "coarse", which doesn't bring up any solid info in my non-mechanic brain.

This is like solving a puzzle, or a mystery!

 

 

Edited April 20, 2022 by brucecooner
found more info

[eaglescout526]

Well it’s possible it will leak oil from right there but you’re fine to drive it as is currently. 

[howeitsdone]

Not dangerous, but you want the most surface area contact as possible to prevent leaks. Here is a photo showing the bolts. Looks like one of the front bolts based on the pulley in your photo which is 1/4". ACE Hardware is a great place to find one if it's in your area.

 

[brucecooner]

2 minutes ago, eaglescout526 said:

Well it’s possible it will leak oil from right there but you’re fine to drive it as is currently. 

Heh, my brain had to wonder if you meant that as  "You should stop driving it once all the oil leaks out."

But I think you really mean it's okay as long as there's not like, oil gushing out of the hole. 

If oil comes gushing out of the hole, well, I don't know what I'll do but I will definitely miss that bolt much more than I do right now.

 

After more googling in my ongoing saga, it would seem that I'm on the hunt for one of...

 

1/4"-20x1/2", takes a 7/16" wrench.
5/16"-18x3/4", takes a 1/2" wrench.

 

I'm thinking I need the 1/4, although I think I'm technically looking for a bolt that goes into the timing cover and not the block.

I know just enough about motors to know not to mess with them.   I'll get this though.  I once changed a tire so I think I can figure this out.

 

Let's see, I'm guessing I need to know a torque number and what flavor of loc tite to apply.

I hope putting a bolt in out of order won't lead to the destruction of a gasket or something.

[brucecooner]

11 minutes ago, PocketsEmptied said:

Not dangerous, but you want the most surface area contact as possible to prevent leaks. Here is a photo showing the bolts. Looks like one of the front bolts based on the pulley in your photo which is 1/4". ACE Hardware is a great place to find one if it's in your area.

 

Yep, it's got to be one of the "front" ones in that picture.

And we have a nice big Ace just up the street, looks like I'll definitely be paying a visit.

 

Thanks for the help!

[howeitsdone]

No problem. As far as torque and loctite, IIRC it's 13ft/lbs and really no need for loctite, but blue if you want to go that route. My brother (a service tech) laughed at me when I told him I torqued the pan bolts. But it's added peace of mind for someone who doesn't do it for a living!

[brucecooner]

8 minutes ago, PocketsEmptied said:

No problem. As far as torque and loctite, IIRC it's 13ft/lbs and really no need for loctite, but blue if you want to go that route. My brother (a service tech) laughed at me when I told him I torqued the pan bolts. But it's added peace of mind for someone who doesn't do it for a living!

Oh I'm doing it, all the way to 13 ft/lbs, because that gives me an excuse to finally buy a torque wrench.

I want to get one of those serious sounding cordless impact wrenches because... well I own a 4x4, that seems like enough reason on its own to have a cordless impact wrench.

 

 

 

 

[howeitsdone]

25 minutes ago, brucecooner said:

Oh I'm doing it, all the way to 13 ft/lbs, because that gives me an excuse to finally buy a torque wrench.

I want to get one of those serious sounding cordless impact wrenches because... well I own a 4x4, that seems like enough reason on its own to have a cordless impact wrench.

 

 

 

 

lol they split though. So typically you'll find one in the low end that can't go high and vise-versa. I have a 15-80ft/lb wrench from Amazon and then a 25-250ft/lb ACDelco adapter with the fancy buttons and shrieking sounds. Unless you want to spend big $$$ to have best of both you'll need a couple for the range needed. I torqued mine to 15ft/lb since that's the lowest I could. Worked just fine. Good luck though! Make sure to post your build in the forums so we can follow.

[Parei_doll_ia]

You're going to want a lb*in wrench for that. 13 lb*ft = 156 lb*in. Most larger torque wrenches only go down to 20 lb*ft and their calibration is less reliable in the lower 20% of the scale.

[brucecooner]

15 hours ago, keeponjeepinon said:

You're going to want a lb*in wrench for that. 13 lb*ft = 156 lb*in. Most larger torque wrenches only go down to 20 lb*ft and their calibration is less reliable in the lower 20% of the scale.

Thanks.  The one they had at Home Depot was in lb inches.  I think for now I'll get the bolt slightly beyond hand tight and keep an eye on it, and do some research on torque wrenches. 

I read a few product reviews that mentioned the low accuracy at the bottom, which gave me pause since it seems I only need a low setting here.

Also lots of reviews bagged on the digital ones too, so I'm not sure which direction to head here.

 

Of course, it was only today that I thought to wonder if there's a bolt end broken off up in there.  Guess I'll find out.

[brucecooner]

For anyone unfortunate enough to be following this saga, today got away from me but I did get to go bolt shopping this evening.

 

The shortest length of 1/4-20 flanged head bolt sold by my local Ace Hardware is 3/4ths of an inch.  Dang.  A cutoff wheel will fix that I guess (don't craze them threads boy).

Aha, they also sell a Grade 8 (and 8 rhymes with great, so...that means good I guess) 1/4-20 bolt a half inch in length, but lacking a flanged head. 

Not being a mechanic I'm like...its a bolt, it'll probably work okay. Maybe? I could add a washer I guess.

 

Next stop Home Depot.  

Exact dimensions I need stainless bolt!

Yes!

With serrated underside of head. 

No!

Might work I'm thinking, but I can't muster any desire to rake those serrations against my new old oil pan.

Yes, I deliberated grinding the serrations off.

 

Lowe's had nothing close (that I could find anyway).

 

Fortunately for my last stop I went by Autozone and they actually had exactly the bolt I need. 

1/4-20

flanged head

half inch in length

 

In a pack of 8. 

I don't even care I'll take 'em.

 

Yes I bought all of the listed examples, and now I have eleven 1/4-20 bolts in four styles to choose from.  Surely some of those'll work!

 

I guess my next great adventure is seeing if there's an old bolt broke off up in there.

 

And figuring out which of thousands of models of torque wrench I should buy.

 

 

Edited April 21, 2022 by brucecooner

[brucecooner]

The bolt from that Autozone 8-pack box of bolts did the trick. 

The head was 3/8ths, not 7/16th, but it went right in and bottomed out without any resistance, no broke off bolt in there thank goodness.

I hand tightened then went barely the slightest smidge further.

I'm looking into a torque wrench, but I'm not going to fret about it falling out since I've got a whole box full of 'em rattling around in the glove box now.

 

You can tell in the picture it's an odd man out, a different size head from its neighbors, and it's not black. 

I assume a bolt is just a bolt here, and I don't need to worry about some destructive bi-metal situation.

But I think I'd pick up a proper one if it was easy to locate.

 

After this I cruised down to the gas station and filled it up. The sun went down on me and I had to hunt around for the headlight knob, that's how noob I am in it. 

 

Big thanks to everybody for sharing their knowledge.

 

 

 

[AZJeff]

Lots of people get all wound up about using "correct grade" of bolts for applications that are VERY benign.  

 

When I say "benign",  I means that oil pan bolts (and valve cover bolts) are examples of fasteners that are under VERY low stress, and, even more importantly, the joints they create do NOT require high clamping forces.

 

An SAE grade 5 fastener is PLENTY strong enough to do the job.  In addition, the torque requirements of oil pan bolts are such that, with practice (years of wrenching on vehicles), you can estimate the required torque without the need for fancy tools.  (I have been working on cars for 50+ years, and a 4.0 oil pan, using the modern Fel-Pro silicone gasket, gets tightened to "wrist tight" with a 1/4" drive socket/ratchet.)

 

If you are not practiced at judging torque needs on these types of fastener applications, I wouldn't say it's wrong to use a torque wrench to insure proper tightening.

 

And using Loctite is totally unnecessary, if you tighten to appropriate torque spec.

 

 

[Pete M]

if you ever have to cut a bolt to length, put a nut on it first, then cut, then round off the cut edge, then remove nut.  it'll help fix any mangling of the threads.   

[brucecooner]

On 4/22/2022 at 1:29 PM, Pete M said:

if you ever have to cut a bolt to length, put a nut on it first, then cut, then round off the cut edge, then remove nut.  it'll help fix any mangling of the threads.   

It sounds like you're using the nut as a sort of rudimentary post cut tap, to ensure the threads are cleaned in the outbound direction, instead of grabbing a burr and sending it further into the threads on first insertion.

 

Top level tip, the kind that gets in your head and doesn't leave.  Thanks!

[AZJeff]

On 4/22/2022 at 1:29 PM, Pete M said:

if you ever have to cut a bolt to length, put a nut on it first, then cut, then round off the cut edge, then remove nut.  it'll help fix any mangling of the threads.   

You are doing it all wrong.  You are supposed to KNOW to put the nut on first, but forget in your haste to cut the bolt, and then spend the next 10 minutes cleaning up the end of the cut threads with files.