Technical Dog bone engine mount bolt snapped

[MK2lover]

So my dog bone engine mount bolt snapped as shop tried to get it out. They ended up drilling a new thread, fitted it, and the car ran nice for a few weeks until it snapped again.

Unable to get a part of the newly snapped bolt out, they welded a threaded bar onto the subframe, put the engine mount pack on. 4 days later the threaded bar ripped off the subframe.

Is there any solution that does not involve changing the subframe? I am considering welding a plate with a bolt going through it to the subframe. Are there any good/not terrible solutions?

 

[varesecrazy]

Got any pics?

Traditionally it is 1 bolt..

And probably a captive nut.

 

[portland_bill]

Whilst fixing the mounting bolt, you also need to investigatte the cause of so many snapped bolts.

I'd suggest the engine is moving too much, perhaps the other mountings are soft.

Too many harsh starts can do this too.

 

[MK2lover]

Unfortunately, I can't take a better picture atm. I have no jack...

The engine mount above the dog bone one has recently been changed. The engine mount to the passenger side seems to be fine. I compared how much I could move my engine (after the 1. repair) to how much i could move the engine on another punto we have, and it seemed to be identical.

 

[Brendan W]

I suspect that the engine mount over the gearbox is loose or broken.

 

[judderbar]

Unfortunately, I can't take a better picture atm. I have no jack...

The engine mount above the dog bone one has recently been changed. The engine mount to the passenger side seems to be fine. I compared how much I could move my engine (after the 1. repair) to how much i could move the engine on another punto we have, and it seemed to be identical.

Something must be very wrong if you are destroying so many repairs that quickly.

1. The large end of the dog bone that goes on the sub frame should have a built in oddly shaped flexible rubber connection that allows for some movement.


2. There is a fairly thick washer going between the dog bone and the subframe.

 

[portland_bill]

The mounting bolt has been pulled forward, which is the direction it will be pulled when moving away.

Options:
Moving away has been violent enough to bend the bolt or its top mounting.
The engine mountings elsewhere allow more movement than they should, putting excess stress into this mounting.
The subframe is weak, due either to age or work-related stress and has finally bent, or is weak due to corrosion. Once bent, it is weakened, so unless reinforced will never be strong again.
The centre of the mounting was not tight against its upper moounting face, so allowed to move.

Can't think of anything else at this moment, but others may add something.
Replacing the mounting and its bolt is only half the story, the cause needs to be identified and fixed.

 

[MK2lover]

New shop welded it much better and it seems to be working (for now).

The cars clutch does judder a bit. Wonder if that could be the cause.

 

[AndyRKett]

Threaded bar is often a lot softer than High tensile bolts used in these places. It might be ok for now but I suspect it will fail again.

The subframe will have been weakened by the heat of welding and now by the damage caused when the repair failed.

The subframe is only a couple of pressed steel plates welded toghether with some strengthening where things attach. Once damaged it’s not going to be as strong as new and you’re likely going to have to bite the bullet and replace it.

 

[varesecrazy]

New shop welded it much better and it seems to be working (for now).

The cars clutch does judder a bit. Wonder if that could be the cause.

The irregular load of the clutch wont help..

My mj is doing similar (new dogbone lasted almost 12 months..12k miles ) due to a low revs imbalance