Interesting Motor Mount Problem

[cjohnson]

I thought I broke my motor mount the other day and it turns out I actually sheared all three bolts holding the motor mount bracket to the block. I'm assuming I need to use something like an easy out to back out the bolts, but there's not much room in there. Has anyone dealt with this before? Better yet, has anyone ever fixed this problem without pulling the motor?

If you tell me to search, I'm going to have a coronary--if you can't help, don't respond.

Thank you!

[xjtrailrider]

Take the other side loose and jack the motor up as far as you can. Depending on which side? If it is the drivers side you may have to remove a few things; air filter box/intake/exhaust manifold. The passenger side is a little more open.

In my experiance most sheared bolts will come out pretty easy if you can get them started turning, a couple of carefull strikes with a hammer and chisel at an outer edge of the bolt will sometimes get things going but be carefull to not damage the threads in the block, that will hold the bolts in there tighter.

If that doesn't work you may try a easy out or a reverse drill bit(as the drill bit cuts in the counterclockwise rotation it may catch and spin out whats left of the bolts).

Screw and bolt extractors are another option, check at Sears.

[cjohnson]

Great, thanks!

[XJEEPER]

If you tell me to search, I'm going to have a coronary--if you can't help, don't respond.

Thank you!

I ran a search for you....based on your heart condition, and came up with this.
http://www.naxja.org/forum/showthread.php?t=40820&highlight=goatman+motor+mounts

There's a vendor that's building an HD motor mount to distribute the load but I don't recall who. The JeepSpeed folks are using them.
Keep in mind that one of the reasons than mounts/bolts get stressed to the point of breakage or torn rubber is that there is mucho flex in the unibody in the engine compartment. If you think about it, there is no crossmember support between the front of the rig to the tranny crossmember. Adding a trackbar brace that ties the unirails together under the motor is a big help, both in preventing deflection, improved steering input and reducing uniframe flex in lifted rigs, which also help your mounts live longer.

[IntrepidXJ]

MORE makes the HD motor mounts to the block

[Skullver]

MORE bombproof block mounts

http://i12.photobucket.com/albums/a230/skullver/DSCN0926.jpg
http://i12.photobucket.com/albums/a230/skullver/DSCN0923.jpg

[backpack96]

THIS EXACT SAME THING HAPPENED TO ME!! crushed my distributor in the desert...no bueno.
I had it runnin though in 2 days...i welded a nut to one of the bolts cause it stuck out a little and the other 2 i drilled out and easy-outed....wasnt a big project at all. i didnt move or take out the motor either...then i bought new grade-8's for both sides...

[cjohnson]

Yeah, I'm going to try and weld something to the nubs and see if I can back them out that way. I don't know how you got a drill in there...I'm hoping it doesn't come to that!

[jeepsrock]

Instead of starting a new thread i thought i might as well ask here.

On my way back home from a trip last night (220miles from home), i sheared all 3 passanger motor mount bolts on my XJ also. I drove it home slowly as best as i could, but the fan shroud managed to have chunks missing..

Throughout my reading, i have seen people replace these bolts with a grade 8 bolt but some suggesta grade 5 bc of its qualities, any argument for or against this ?

I havent got the bolts out yet, but just want to get the bolts and have them ready.

thanks
pete

[jeepsrock]

I went and bought some easy outs and a few brand new drill bits today, hopefully gonna try this out in a few days.

Anyone had a chance to think about that bolt question i asked above ?

pete

[5-90]

When you get replacement screws, get a handful of washers as well. If the screws bottom out in the holes - or you even think they bottom out - remove it and put a couple of washers under the head. You don't want the screw to bottom out in the hole - that's often how the heads shear off in the first place...

5-90

[jeepsrock]

What exactly do u mean by bottoming out ? Do you mean the head not having full contact with the bracket ?

Also my main question was regarding grade (5 or 8) and size ?

thanks
pete

[5-90]

Meaning that the point of the screw will hit the bottom of the hole before the underside of the head hits the surface. Screws depend upon a certain amount of "stretch" (technically known as "preload") in order to be elastic in their applications - no preload, no elasticity. Preload can be measured and quantified, which is why you "torque" a screw to a specific point - this both gives a predictable clamping force (especially good for sealing) and a predictable behaviour for the screw under stress.

I believe the size you'll want is 3/8"-16 x 1" (either hex head or socket head,) and this is an application where a SAE Grade 5 would be good - since they won't fail as dramatically as SAE Grade 8 (Grade 8 screws, being "harder," tend to fail rather more dramatically. I also use SAE Grade 5 screws and nuts for trailer hitches - they're plenty strong enough, but they'll stretch before they fail, and I check them periodically to make sure they're not working loose. Same for engine mounts.)

By the by, it's "you," not "u." Honestly, I think text messaging is going to be responsible for the death of American English as a modern language... (Sorry, but I get cranky about that.)

5-90

[jeepsrock]

No problem on the "u" thing its becoming a problem for myself.

Thanks for the size.

As far as grades go wouldnt a grade 8 bolt be better though and resist breaking in the first place better than the grade 5 ? What grade are the stock bolts ?

Pete

[5-90]

I'm not sure what OEM screws are - I haven't had to deal with them yet.

Steel is a bit of a dichotomy - the stronger it gets, the more brittle it gets. SAE Grade 8 screws are stronger than SAE Grade 5, but they're also more brittle.

When an SAE Grade 8 screw fails, it pretty much snaps immediately - it's called "rupture."

When an SAE Grade 5 screw fails, it will stretch first, then snap.

I've compared the two in one of my classes, including a test to failure of each (along with about four non-ferrous materials.) The "stretch factor" before the failure of the SAE Grade 8 was almost zero, while the SAE Grade 5 had about 5% stretch before failure - which can actually be a good thing, especially in things like this.

An SAE 5 is going to be more tolerant of cyclic stress, vibration, and suchlike - which is the sort of stresses that motor mount screws will see.

Stronger ain't always better...

5-90

[Jake_S]

5-90 is correct. The grade 8 bolts are stronger, but they do suffer from an immediate failure, that is why it is not recommended to use Grade 8's on reciever hitches, and I would think the same priciple would applie to engine mounts as well.

Jake

[jeepsrock]

Ok, i started working on trying to remove the bolts and one of them came out very easy, the second is a being a very stubborn bolt.
I tried a number 2 bolt extractor with its appropriate drill size and it didnt budge. I purchased the next screw extractor size up #3 and its drill size and i am getting no where. I can grab the extractor and twist it with the wrench until i feel its about to snap then i stop.

Any ideas ?
pete

[5-90]

Are you using left-hand twist drill bits? I've had some decent luck using those, and PB Blaster for lubricant. About 50-50 that the LH flutes will "bite" into the screw and then start backing it out for you.

If that doesn't work (and you end up drilling about halfway down through the screw or so...) try heating it with a blowtorch and touching a candle to it. The wax will melt and "wick" into the gap between the the threads which will help to loosen things up. It's an old mechanic's trick to get oil galley plugs out of engine blocks when rebuilding, and it often helps when working on stuck screws in general - especially broken ones.

A regular "Bernz-O-Matic" propane plumber's torch should serve neatly.

5-90

[bhorn]

http://www.sears.com/sr/javasr/product.do?cat=Portable+Power+Tools&pid=00910154000&vertical=TOOL&subcat=Drills&BV_UseBVCookie=Yes

http://www.sears.com/sr/javasr/product.do?cat=Power+Tool+Accessories&pid=00952156000&vertical=TOOL&subcat=Drill+Bits&BV_UseBVCookie=Yes

This combination worked really well for me. It was in a TJ, so I can't say how much room there is on an XJ.

Good luck!

[jeepsrock]

The situation has become very bad.

I have removed both front tires, removed both rubber engine mounts and have lowered the engine as much as everything will allow me. The screw extractor hasnt done a darn thing and i have started to drill larger and larger in hopes of loosening it. The problem is i dont have a clear straigh path no matter what, so everything is cockkeyed.

Any ideas on how i can get a straight path , maybe lifting it will help up ?

MAybe someone who has done this can help or make suggestions, i am really getting frustrated.

pete

[old_man]

A right angle chuck for your drill and stubby drill bits.

[jeepsrock]

Well here is an update to my mess.

I got bolt 1 and 3 out with the ez outs and the bolt thread is fine.

Bolt two on the other hand is really messed up. The ez out did nothing and almost broke. I tried progressiviely larger and larger drill bits to try to salvage the situation and honestly things may have gotten worse.

I stopped with a 5/16 drill bit and it seems that i can see the threads perfectly on one side of the hole but on the other side the drill bit killed them. So i know i basically have two options now - either use a helicoil or tap it one size larger. Whats your guys recommendation ?

Thanks
pete

[5-90]

I'd go Helicoil, but if you don't have a good centre, you're going to have to field modify the engine mount bracket anyhow (as you will if you overdrill/tap the hole to the next size up - should be 7/16"-14, I'm thinking.) And, I'm not sure if you can get screws in the next size up only one inch long - so you'd DEFINITELY have to use washers!

This illustrates why there are so many lengths of drill bits - and I keep a set of "screw machine length" drill bits around - just for cramped jobs like this. Screw machine bits and a right-angle drill will get you into some amazing places...

5-90

[jeepsrock]

Well it seems either way i have to drill a 25/64 hole in the block. After that i can either tap it with a 7/16 tap like you suggested or use the helicoil kit.

Can you explain why a helicoil would be better than just tapping it and trying another larger screw ? Why wouldnt a screw be available in an inch.

pete

[5-90]

A Heli-Coil is useful beacuse it would allow you to use the same size screw.

As far as "not being available in an inch," there is usually a minimum length in which they bother to make a certain diameter of screw. For instance, you can get 1/4"-20 screws with 1/2" underhead length, but you can't get 5/16"-18 screws easily in anything shorter than 3/4" Following that pattern, figure that 3/8"-16 screws will have a minimum underhead length of either 3/4" or 1", and 7/16"-14 screws would have a minimum length of 1" (unlikely, I think) or 1-1/4" (more likely,) but I'd have to check.

It's the same sort of standard that governs the threaded length of screws - if the shank is three "diameters" long or less, it's fully threaded. If the shank is more than three "diameters" long, they only thread three diameters' worth, unless you specially order full-thread screws. For instance, a 1/2" screw 1-1/2" long or less will be fully threaded, but 2" or longer will only be threaded for 1-1/2" of its length.

If you can get a 7/16" screw to work (probably with a stack of washers...) you'll end up needing to "clearance drill" the engine mount bracket - meaning that the hole will now need to be at least 25/64" or 15/32".

Simply stacking a batch of washers under the screw head would look a little shonky - but it's up to you. One or two can usually be hidden - six or so (which is what you'd probably need) gets ugly.

5-90

[needsrepair]

I often use an engraver for broken bolt removal. I have a chicago pneumatic that has worked for years. I also have a cheapie thats useless. If the bolt isnt bottomed or froze too bad this method works good. Get on the bolt at an angle so the tip bites in and then walk the bolt around until its out far enough to grab. With many repairs of this type finesse is needed. Sometimes penetrating oil is needed, or a little heat and wax. After the area is heated up a little the wax will suck down into the threads. Dont go wild with the heat. When removing broken bolts dont be in a hurry. If your using an engraver or using a chiesel method as mentioned above try going back and forth, dont be in a hurry and force it. It may not appear to be moving at first but work it back and forth before moving on to the next method.

[rickoregon]

Hey, some good ideas in this thread for bolt removal!

Regarding bolt length, Mcmaster.com has 7/16" - 14 bolts in 1 inch lengths, grade 5 (120,000 psi tensile strength). Even have them down to 3/4 inch length. Downside of ordering there, however, is that minimum purchase for this size bolt is a pack of 50 (cost is $8.60 for a pack). Fyi, Rick

[jeepsrock]

I am gonna try to find a helicoil kit today and try to take care of this, bc i need my car back on the road.

A few things interesting to know is that my driver side rubber mount is cracked in half, maybe thats what caused the stress to begin with.
The second thinng is that the stock engine mount bolts that sheared off are grade 8, i find it interestin that they didnt use grade 5 like you guys recomend.

Pete

[jeepsrock]

Well guys after a night of major cussing at the jeep, last night i believe i finished the job.
I ended up using the helicoil, and boy is that a little intresting device as i never used one before. Anyways i replaced the other sides bolts also as they are probably stressed from the engine hanging on them for a while. I used 3/8-16 grade5 1 inch bolts with a washer (like suggested above). I also found that the driver side rubber mount was seperated into two pieces which i replaced with a new part from pepboys.

I really hope this holds up for a while bc ,to be honest with you this was an annoying job aswell as a knuckle buster. I drove the jeep today and it did well.

thanks for the help guys
pete

[micklongley]

Hey Chip, Did you ever get this figured out? what was your solution?

Mick