Trick to removing engine mount bar bolt?

[rwilner]

The mounts are 30 years old so I figured it was time to replace them. The drivers side came out with some help from a cheater, but passenger's side engine mount bolt won't budge.

Apparently I am not the first to struggle with this because the bar itself is bent, so it looks like i'll be replacing that too.

I beat on it for about 10 minutes with my impact wrench. Using the cheater just causes the cross bar to bend -- I'm sure if I put some muscle into it, it would bend even more or perhaps snap.

Any tricks to this others have tried and worked? Apply heat directly to the bolt head? There's no way I could get heat on the threads or bar easily I don't think.

Thanks
Rich

[timmy2]

1/2 or 3/4 Impact gun might do the trick.

[rwilner]

1/2" did it. I used some PB blaster and went back and forth on it for about 10 more minutes. Wow, that sucker was on there!!! So satisfying when it zipped right out.

[timmy2]

Sshh. Tdskip will be jealous...
I'm glad it worked.

[rwilner]

Well....actually it didn't work....at least not in the way I hoped it would.

think it's time to replace my engine mount cross bar, don't you?



p.s. the factory bar is a pretty cheesy piece IMO.

[peppy]

How long was the handle on the tool you used to break that off?

I think I have seen someone weld one of those back together.

[rwilner]

Originally Posted by peppy

How long was the handle on the tool you used to break that off?

I think I have seen someone weld one of those back together.

1/2" impact wrench did it. IMO -- this was pretty much unavoidable.

Oh well, rennline part on order from our host!

[KFC911]

There's an old thread somewhere in the archives where I had the same issue many years ago. In my case, my Ingersol Rand 1/2" snapped the cross member in about the same place pictured above, but the bolts didn't budge. This was after several days of spraying with Rost Off and hitting it daily with the IR (something like 650 ft/lbs of torque if I remember correctly). John Walker suggested a 3' breaker bar (section of pipe) and that's how I actually got the bolts loose. Hope this helps for others...

ps: No way would I weld and reuse...but that's just me.

[timmy2]

LOL, not quite what you wanted...
Maybe a blessing in disguise, the Rennline unit sure looks a lot more stout.
You'll be twisting the bolt heads off before breaking their welds!

[Walt Fricke]

While the threaded motor mount design is lots easier to R&R (assuming you don't have a rusted in place bolt), there was something to be said for the earlier design, which just used a nut on the end of the bolt which stuck out of the unthreaded tube. You could counterhold the nut (or the bolt), and never have the torque get to the crossbar welds.

But some of us have our engines out more often than others.

[rwilner]

This was a typical "seems like a good idea /while I'm in there" that has ballooned a little bit. The worst part is waiting for parts to be shipped from CA to MA. I should email Wayne to open up pelican parts east!

[KFC911]

I agree about the earlier design Walt. Just for clarification, the bar above doesn't appear to have snapped at the weld (nor did mine). I've got Rennline monoballs and strut brace (quality products)...alas, this was prior to the availability of the cross mount or I would have likely gone that route also.

[KFC911]

Originally Posted by rwilner

This was a typical "seems like a good idea /while I'm in there" that has ballooned a little bit...

The $lippery $lope ...BTDT!

[Targa Me]

the eng mount bars with the threads all the way through are stronger than using a bar with no threads and using just a bolt and nut. With each thread the holding strength is increased considerably.

[will hung]

stinks it happened like that, but that Rennline engine mount cries out to me daily.

[Walt Fricke]

An engineer friend, when discussing lug nut engagement (usual rap is have at least one diameter's worth of thread engagement), told me that over 90% of thread strength is achieved with the first two threads.

So I guess he would not agree that more threads equals a significant increase in strength. But I'm just taking his word for this. Though I note that there is a standard and increasing thickness for nuts used to hold bolts in tension. While thinner nuts are offered for various purposes not involving the bolt pulling through them, I don't recall extra deep nuts being offered for extra bolt tension applications. Better steel, yes. But not thicker nuts.

I don't think I have ever seen a nut used like the older system used them fail in any application at all. As long as not cross threaded or rusted closed or otherwise buggered (think of bolts holding mufflers to header secondaries for where a nut can see a hard life), the nut seems perfectly capable of dealing with the loads imposed upon it.

The weak point here seems to be the crossbar mount design. It may be a crap shoot. I have two stock mounts which I have modified with hole saws to approximate the RSR system. I did not weld on any extra flanges to the mount, but have had no issues in 15 years of track use. And this includes the one I welded the bottom nuts on so I didn't have to use a second wrench (and I am too lazy to counterhold despite what I know).

[john walker's workshop]

i've welded plenty of those back together and none failed yet. the latest was a 993 that broke by itself. on that one i welded another piece of steel over the first weld. 993 bars are even wimpier than carrera/SC bars.

[Targa Me]

Originally Posted by Walt Fricke

An engineer friend, when discussing lug nut engagement (usual rap is have at least one diameter's worth of thread engagement), told me that over 90% of thread strength is achieved with the first two threads.

Umm, think about that. According to your engineer friend, thread in the bolt 2 threads and let's say a 3rd thread for good measure and that would be sufficient to hold/support half of the engine weight. That doesn't sound very comforting to me.

[aj88cab]

It's a little late to be offering this advice, but IIRC when I changed out my mounts, I placed a short piece of 2x4 between the bar and the body or engine to keep the bar from twisting like that. It still flexed a bit, but finally the bolts broke loose with no damage.

[911pcars]

Originally Posted by Walt Fricke

..........So I guess he would not agree that more threads equals a significant increase in strength. But I'm just taking his word for this. Though I note that there is a standard and increasing thickness for nuts used to hold bolts in tension. While thinner nuts are offered for various purposes not involving the bolt pulling through them, I don't recall extra deep nuts being offered for extra bolt tension applications. Better steel, yes. But not thicker nuts.............

+1
It's not the strength of the threaded joint that's in question. It's just another "I thought it was a good idea at the time" situation by PAG. Think about it. The latest mount bar has threaded "nuts" at each end of a thin tapered section of steel whose closest anchored area is approx. 16" away. And with little to counter hold while loosening the attached bolt after 20 years of service, the failure area is predictably at the narrowest cross section of the mount.

I would drill out the remaining mount bar threads and revert to the older bolt and nut arrangement (w/antiseize for good measure).

Sherwood