t-amos

well the other day my motor mount bolts snapped leaving me with a droopy engine. i ordered some brown dog motor and engine mounts. i have been reading on here about getting the broken bolts out, i have a pretty good idea of what to do, any last minute advice i could use?
thanks in advace

stoneattic

Been there, done that. It's real fun.

When I did mine the fist time 2 of the three came right out using a left handed bit after barely starting to drill. The third I needed to drill through and chased the thread with a tap.

The second time I had to drill each one more that the first time but they came out pretty much the same.

I used one of these:


I replaced mine with grade 8s the first time and had them shear off again a couple of years later. I replaced those with Unbrakos (http://www.unbrako.com/index.htm), with lock washers and lock-tite. 4 years later so far, so good.

t-amos

thanks stoneattic, i sure hope mine goes smoothly, can those kind of tools be rented at a auto store?

trans_am7935

u can try autozone or home depot, but i used a reguler plug in DeWalt drill. i just jacked my engine up for clearance on the busted side. mine broke last week.
i wouldn't put locktite on them cause this is a very common problem on jeeps and if they break again u will have a hell of a time getting them out. lock washers are much better.
Try tapping on them with a flat head screwdriver and atempt to turn them by yourself, two of mine came out that way.

stoneattic

I don't know about renting the drill. If I don't already have a tool I usually borrow one from my uncle (who has every tool imaginable) or if I think I MIGHT EVER use one again I buy it. The one pictured is a Milwaukee close quarter drill. I borrowed my uncles the first time and just bought it the second. It's come in handy since, like drilling out the broken front leaf spring bolt, grrrr.

stoneattic

In my experience getting these out in most cases I had to drill them. Lock-tite wouldn't have made that much (any?) worse.

I did a lot of research on these failures when mine broke the second time. One of the MANY theories out there is that the bolts had backed out a hair (possibly due to slightly over sized threads in the block) enough for the mount to shift, essentially hammering on the bolts until they failed. Hence my use of lock-tite and lock washers hoping that if that theory was correct keeping them from backing out would preventing them from failing again. Being that I've gotten gotten many more miles/years since doing that (compared to the originals and my first set of replacement) I think it may have helped.

Another theory that I thought had merit was that the holes weren't drilled perfectly perpendicular to the mating surface, therefore side loading the bolt heads. The failure mode of the bolt looked more like shearing than bending/tension to me though.

trans_am7935

same here...it looks like an odd stress point was on the bolts and that is y they broke, and i agree with the backing out part cause after i fixed my drivers side i checked my passenger side and they were already backed off

t-amos

thanks guys, im taking a break from working on it right now. im replacing both sides and the side(driver) that did not break whent in nicely. the passenger side is being more difficult. all the hardwear is getting in the way of trying to get the broken bolts out. thanks for all the advice, i guess ill have to see how mine turns out.

Timber Wolf

I just used a dremel and cut slots on the broken studs. Than just used a flathead screwdriver to back them out.

t-amos

well, the install of the passenger mount did not go as planned, getting the broken bolts out was the easiest part of the job. turns out the motor mount was not manufactured right. it did not fit around the engine mount correctly at all!. ended up calling a Brown Dog tech guy but was not really any help. ended up having to trim the mount to fit correctly around engine mount without compromising strength. not quite sure why the driver side whent in so smoothly and the passenger side took half the day. the bottom hole on the motor mount did not line up with the hole on the engine, going to have to do more drilling and trimming. hopefully i wont have any problems with this issue once im finished.

tmstow

Hey guys I just had the same thing happen to my 95 cherokee country I need it all replaced the engine mount the brackets the bolts all of it any where I can get these parts? thanks

cruiser54

THIS is why that happens with the broken bolts and what is needed to keep it from happening again.

From Jon Kelley aka 5-90 @ www.kelleyswip.com
　
　
This is a known issue.

1) Unless you're going to get silly with the skinny pedal, 2xSAE8 screws on one side won't be a huge problem. You'd be better off with three, but if you don't get silly you'll be okeh.

2) The Brown Dog engine mounts use two or three additional holes on each side, and spread the mount/clamping force over more of the block. This is invariably a good idea, and I'll probably be doing it as I refit my 88.

3) The primary reason that the screws snap is because, sometimes, the screw holes in the block aren't drilled & tapped deeply enough. This causes the screw to bottom out in the hole, so you end up torquing against the bottom of the hole instead of stretching the screw (as you're supposed to do. Not your fault - you aren't doing anything wrong.) The screw is not stretched properly, and the head is not butted up against the bracket, so there's some room to move there. Vibration then causes wear cycles on the screw, which generally leads to rupture.

The easy/cheap fix? When you replace the screws (3/8"-16x1.25", as I recall,) put two flat washers under the head before you screw it into the hole.

The check? Take a feeler gage (.003" to .005") and try to slide it under the head of the screw. You'll be able to get under the corners (look at the hex head, and you'll see that the surfaces curve toward each other slightly) if it's a standard hex head - if it's a flanged hex head, you should not be able to get under the head anywhere. If you can slip the gage under the head, you have a problem. If you can touch the shank of the screw, you have a big problem!

In no case should you reuse the screws after you take them out - they'll be stressed under the head, and you'll have a significant reduction in strength. Replace them outright, putting washers under the head as I mentioned before. The washers will make up for the slight lack of depth in the hole (two of them will be about 0.125" or so,) and allow the screw to be preloaded properly.

venomator

i have the same issue, contacted the shop ive used for years, and over the phone they gave me a quote of 140 bucks, as a minimum. that is to remove broken bolts, replace with number 8 bolts, and re-use the stock bracket

and since the engine is currently sitting on the distributor, and oil filter, ill need to tow it there, and replace the oil filter and oil im sure, which will run 60 for the tow, and 20 for filter and fluids.

cruiser54

Got a floorjack, block of wood and a drill?