Rear engine bar, threaded vs unthreaded
 

When we put the motor in my car this weekend, it was noticed that the motor mount bar didn't have threads in it, so we mounted the motor with longer bolts and nuts. While digging through a parts bin last night, I found the engine mount with the threaded holes.

Is there any benifit to running the bar with threaded holes over non-threaded?

I don't think there's a benefit unless you don't happen to have the correct bolts laying around for the one you have and then it's a detriment.

OK, I just re-read what I wrote and *I* don't even understand it.

No benefit that I can discern.

Mike

All I can tell you is that it's much easier to get the threaded ones bolted up and torqued after an engine drop than the unthreaded ones, where you have to hold the nut under there.

Structurally, I don't know if there is a difference, but I would use a threaded one if everything else were equal.

My original crossmember bent like a candy cane when I remove the bolts. They were torqued to approximately six thousand lb/ft. I sourced a used one, then noticed that one of the bolts' threads had been damaged from the overtorque. Not wanting to take chances with this particular fastener, I got extra-long units and placed nuts under them. Best of both worlds. I inspect those nuts occasionally. My engine's not going to fall out without my permission.

I like the unthreaded beause if the bolt seized on the threaded one, you can fairly easily bend or break the bracket. On the unthreaded you can just cut the bolt out and replace it.

Ohh but there must be a weight savings on the threaded one.... Awe crap! Now I'm unsure of which I prefer....

I did exactly what Pat describes. One of my screws on a threaded bar didn't want to let go. Twisted up the end of the bar and broke the weld getting it loose. Had to get a new bar.

I will agree that using a threaded one is a bit easier during a motor install- when you can get the screws started. Otherwise, a nonthreaded one is easier because once you get the bar close, you can jam the bolt thru the motor mount and bar to get things lined up. Kinda like using a drift. With the threaded bar, you have to make sure things are somewhat nicely aligned or you risk crossthreading your screw.

How about the support that the extra threads are providing? I would think that since there is only two bolts holding this beast in, the more threads, the better, especially with the larger, heavier engines. I would stick with threaded if it came with threaded... I did bend mine when removing a couple of weeks ago and ordered a new one. Time to use some antiseize when installing...

You guys got me 50/50 on swapping. Half of me says to leave the bar in and swap out the nuts for nylon locking, the other says, swap to the threaded, use the long bolts, antiseize, and put the nylon locking nuts on anyway.

Something else to add to the list of things to do before I can drive it.

The guys in the know can clarify this, i'm pretty sure it's only the first couple threads that are doing all the work? Porsche must have had a reason for switching from nonthreaded to threaded bars.

Antiseize is definitely a good idea. That's why my bolt froze and broke the weld.

Actually the cars with the nonthreaded bars call for a lock washer beneath the nut. So a locknut is certainly a good idea. I'd use a deformed thread nut since those are typically more reuseable than a nylock. Nylocks are technically a one time use nut.

All the threads will provdie support - unless some do not touch.

The factory changed to the threaded bar, so that's agood indication of what they think.

I'd use the new one (in fact, I bought a new style bar). Drill RSR type holes in it and powder coat it silver (what I did) - doesn't save a lot of wt. but does look slick.

The engine mount bar that came with the motor I bought had been welded before. So I bought a used one in better shape for $50. New ones are like $110. I like the threaded bar, makes it easier to bolt into the car after an engine drop. But be sure to follow the tightening sequence so that the bar is not preloaded (is that the right word?). This was mentioned on another recent thread about engine mount bars. Returning to the question, the way I look at it is Porsche started with non-threaded and then updated to a threaded bar. But whatever you decide to use take a look at the welds and make sure the mount bar it is in good shape. You don't want an involuntary partial motor drop!

Thanks for the correction Randy. Here's where I got the believe that the first few threads do all of the work. My mistake. I should have said "most" instead of "all."

http://forums.pelicanparts.com/uploa...1074988551.jpg

Came from this book:

http://forums.pelicanparts.com/uploa...1074988605.jpg

Good reading for people like me who are curious about what is the difference between all the kinds of fasteners out there. The book is not excessively technical, but technical enough to be a solid source of info. about the finer points of all sorts of fasteners. Definitely should be required reading for those who think, "Ah whatever. A nut's a nut, a bolt's a bolt........... :rolleyes: "

THx for posting the book -- there is another one out at an apparently similar level. I'm gonna get the local library to IL both of them.

I find the stuff put out by the quality fastener companies to be pretty interesting -- and usually free.

A book on High Performance Hardware. That's hard core!