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  #1  
Old April 9th, 2019, 14:19
Black1990jeep Black1990jeep is offline
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Motor Block Mount Breakage

I am going to install new motor mounts. I see that breakage of the block can occur at the mount points, and that a preventative measure is reinforcement plates such as Stinky Fab sells.

My question is how often does block breakage happen? Was it a problem with stock street driven, well maintained XJ's? i.e.... well maintained meaning mounts replaced prior to wearing out, bolts kept at torque specification, etc... what about a four wheeling rig? one that is driven cautiously and not too fast off road? or is the block breakage issue mainly for XJ's that see really hard use, racing, jumping off dunes, and such. Or mainly an issue of the bolts working loose do to improper install, thus causing breakage?

I am trying to justify my expenses. Is risk of block breakage high for my type of use? My use being slow going offroad, getting over hard stuff, but carefully, and of course highway to get to the offroading sites.

I used to modify old Porsches, some stuff was only needed for the autocross crowd, frame stiffening and such, and would be a waste to install on an otherwise stockish car for street use, Even mild hotrodded street cars would rarely get cracks. But for autocrossing it is a must to have reinforcement..

How do the motor mount reinforcements rate in utility for offroad use, slow speed, Do unreinforced well maintained offroad, slow jeeps have many failures here?

note my jeep is lifted 5.5 inches 33 inch tires, locker, Atlas 4.1.
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  #2  
Old April 10th, 2019, 08:41
Black1990jeep Black1990jeep is offline
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Re: Motor Block Mount Breakage

50 views and no replies.

Has anyone here actually had a broken engine block motor mount on the engine block? If so under what conditions, ie standard street use, slow off roading use, or racing, jumping high speed off road use?
I need to know how bad a broken motor mounting on the block problem really is, is it a frequent occurrence?

I only have so much money, 200 bucks for the reinforcement plates could be spent on rock rails or bumper stuff. But only if the chances of engine block breakage is slim for my usage.

thanks
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  #3  
Old April 10th, 2019, 09:12
RCP Phx RCP Phx is offline
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Re: Motor Block Mount Breakage

Put the money in reinforcing the Uni-body. What did you ever do about the bumpers?
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  #4  
Old April 10th, 2019, 09:31
Black1990jeep Black1990jeep is offline
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Re: Motor Block Mount Breakage

The bumpers are still not done. There were concerns the front may not be strong enough, but the rear is first priority cause it is only mounted to sheet metal, and I want to get my spare tire back on it, off of the roof. I have been busy with several overland trips, just back again from another week long trip, the one where the new tranny mount failed. So now it is back to motor and tranny mounts, and a new windshield which got shattered on the highway. the windshield of course is not simple, as I want to do some window frame rust repair while the glass is out. I also had my oil pressure gage stop working, so I need to dig into that, so for now the bumpers are on back burner.

my priorities now..

1. fix windshield and rust repair
2. tranny mount, probably a stinky fab, along with motor mounts.
3. shackle relocator.
4. rear bumper mounts, tie into frame, probably done at same time as shackle relocation, of course nothing is simple, the rear frame is a bit bent on driverside, pushed up when prior owner landed on gas tank skid plate, so bottom of frame rail is bent, need that repaired so my new nut strip square tubing can be inserted into the frame.
5. front bumper, along with steering box brace. ( reinforce round tubebumper maybe?)
6. relocate the winch relays to inside engine bay, make cables safe, cables currently disconnected at battery cause the way they was routed was extremely poor, engine fan was nicking them.
7. Nick in Time engine monitor as soon as it is available.
8. Rock sliders.

another trip planned in five weeks, so only the first few items will get done by then. number 1 and 2 are main priority now.

hence my questions on if the block reinforcement places are needed for my application. I want to get that stuff ordered asap.

thanks for the input on the reinforcement plates. I assume from your reply then that their real usefulness is for hard driven jeeps, not so much for slow crawling jeeps.

cheers!
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  #5  
Old April 10th, 2019, 09:53
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Hypoid Hypoid is offline
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Re: Motor Block Mount Breakage

I have managed to go 12 years without breaking any mounting bosses off the engine. Your intended usage pretty much matches mine: Mostly pavement, and easy with the skinny pedal when you get off the pavement.
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  #6  
Old April 10th, 2019, 10:28
bigdaddyjlove bigdaddyjlove is offline
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Re: Motor Block Mount Breakage

From what I have seen, the block usually breaks when the bolts loosen up or when some are already broken.

I haven't broken any blocks this way, but I have managed to break a few bolts where the plate mounts to the block.
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  #7  
Old April 10th, 2019, 12:32
cwyman6 cwyman6 is offline
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Re: Motor Block Mount Breakage

I sheared a bolt off when the mount came loose. I didn't install it but I have the brackets on now cause I wheel way harder than I did before. Should be fine as long as they are loctite.
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  #8  
Old April 10th, 2019, 13:17
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IslanderOffRoad IslanderOffRoad is offline
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Re: Motor Block Mount Breakage

Quote:
Originally Posted by Black1990jeep View Post
50 views and no replies.

Has anyone here actually had a broken engine block motor mount on the engine block? If so under what conditions, ie standard street use, slow off roading use, or racing, jumping high speed off road use?
I need to know how bad a broken motor mounting on the block problem really is, is it a frequent occurrence?

I only have so much money, 200 bucks for the reinforcement plates could be spent on rock rails or bumper stuff. But only if the chances of engine block breakage is slim for my usage.

thanks
I've never broken one in 10+ years of wheeling. I also have never ran bigger than 33" tires, and don't wheel near as often as I'd like to.

Jeepspeed and KOH guys have probably broken them. They're probably overkill for the average wheeler.

If your budget is limited I'd skip them for now. You can always do them later.
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  #9  
Old April 10th, 2019, 13:18
bigdaddyjlove bigdaddyjlove is offline
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Re: Motor Block Mount Breakage

Also, make sure the new bolts aren't too long. Apparently, some blocks weren't drilled deeply enough, so the bolts bottom out, don't tighten correctly (no stretch) and they break or back out (then break).
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  #10  
Old April 10th, 2019, 15:03
md21722 md21722 is offline
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Re: Motor Block Mount Breakage

The engine block mounts do not break unless the bolts are loose or bottomed out (another form of loose). The mounting plates are either an upgrade because you want to do it, or because your block boss(es) broke and now you need an alternative setup.
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  #11  
Old April 10th, 2019, 15:38
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techno1154 techno1154 is offline
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Re: Motor Block Mount Breakage

Quote:
Originally Posted by md21722 View Post
The engine block mounts do not break unless the bolts are loose or bottomed out (another form of loose). The mounting plates are either an upgrade because you want to do it, or because your block boss(es) broke and now you need an alternative setup.
And some have broken bolts remaining in the hole and cannot get the pieces out. In that case, the bracket allow you to have enough bolts to keep the engine mounts securely in place.

Yea,...I too would like to get a number of accessories for my XJ but at this moment replacing the 10+ years radiator and the transmission mount that is as old as the XJ itself takes priority. Here is where a good vibration free mount will fit the need.
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  #12  
Old April 10th, 2019, 15:55
RCP Phx RCP Phx is offline
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Re: Motor Block Mount Breakage

Quote:
Originally Posted by Black1990jeep View Post
The bumpers are still not done. There were concerns the front may not be strong enough, but the rear is first priority cause it is only mounted to sheet metal, and I want to get my spare tire back on it, off of the roof. I have been busy with several overland trips, just back again from another week long trip, the one where the new tranny mount failed. So now it is back to motor and tranny mounts, and a new windshield which got shattered on the highway. the windshield of course is not simple, as I want to do some window frame rust repair while the glass is out. I also had my oil pressure gage stop working, so I need to dig into that, so for now the bumpers are on back burner.

my priorities now..

1. fix windshield and rust repair
2. tranny mount, probably a stinky fab, along with motor mounts.
3. shackle relocator.
4. rear bumper mounts, tie into frame, probably done at same time as shackle relocation, of course nothing is simple, the rear frame is a bit bent on driverside, pushed up when prior owner landed on gas tank skid plate, so bottom of frame rail is bent, need that repaired so my new nut strip square tubing can be inserted into the frame.
5. front bumper, along with steering box brace. ( reinforce round tubebumper maybe?)
6. relocate the winch relays to inside engine bay, make cables safe, cables currently disconnected at battery cause the way they was routed was extremely poor, engine fan was nicking them.
7. Nick in Time engine monitor as soon as it is available.
8. Rock sliders.

another trip planned in five weeks, so only the first few items will get done by then. number 1 and 2 are main priority now.

hence my questions on if the block reinforcement places are needed for my application. I want to get that stuff ordered asap.

thanks for the input on the reinforcement plates. I assume from your reply then that their real usefulness is for hard driven jeeps, not so much for slow crawling jeeps.

cheers!
That's a mighty long list to be concerned over the motor mounts.
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  #13  
Old April 10th, 2019, 19:05
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cal cal is offline
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Re: Motor Block Mount Breakage

SFR sells a LOT of block plates to jeep dealers for repair on stock pavement pounders.

It happens often enough.
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  #14  
Old April 11th, 2019, 20:28
trippled trippled is offline
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Re: Motor Block Mount Breakage

It is one of those things though, would you rather wait for it to fail or be preemptive about it? Maybe consider at least replacing or retorqueing the bolts.
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  #15  
Old April 12th, 2019, 05:35
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old_man old_man is offline
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Re: Motor Block Mount Breakage

The underlying problem with breaking the block mounts is that the holes in the block are not tapped quite deep enough/the bolts are a bit too long. When the bolt is tightened, it is actually tightening up because of the bottom of the hole, not the clamping force on the bracket. In many cases, the bracket is actually able to shift constantly, causing shock loads on the block. A simple preventative step is to pull the bolts and grind about1/16" off of the tip and reinstall with Loctite or add a simple grade 8 lock washer on each bolt and torque it down correctly. This was actually covered by a TSB at one point by Jeep. I have 200k+ of offroad on my 4.7L stroker and have broken many axles, but never the block.

An ounce of prevention is worth a pound of cure.
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