Engine mount brackets?

[SilverXJ]

Anyone running upgraded engine side engine mounts? I'm talking about the Brown Dog mounts with extra points. Has anyone broken any bolts on the stock ones?

[basscat]

I bought the motor mounts and they're beefy. They'll be replacing my stock mounts along with the JKS 1" spacer. Since it is a daily driver, I chose rubber. I've done alot of metal fabrication and feel these units will easily hold up. The side mount brackets look even sturdier and I wouldn't hesitate to use them.

[SilverXJ]

I know Brown Dog makes an excellent product, no question on that. I'm with you on the rubber too.

I'm just wondering if they are necessary or is anyone broke a engine bracket/bolt as I have heard happen on some.

[5-90]

Snapping engine mount bracket screws is a known issue, with a known cause.

In some cases, the holes aren't drilled/tapped deep enough to allow the head of the screw to bottom against the surface of the bracket, as it should. This means that instead of a tensile preload being put on the screw when it gets torqued (which it should properly have,) it ends up with a /compressive/ preload and only stresses the threads in the casting.

This also results in some space between the underside of the head and the surface of the mount bracket (not much - but a few thousandths is all that is needed for this to happen...) and the screw head takes a beating. Since the screw isn't preloaded (and therefore will remain static, with relative loading being much less,) this will result in the screw head failing and breaking off from the rest of the screw.

You then have to extract the screw.

These screws are threaded (generally) 3/8"-16, so you have a couple of options:
1) Match the length under the head and get a handful of flat washers. Use enough washers that you can bottom the head of the screw against the surface of the washer, with the washer bottomed against the surface of the mount bracket. Check with gages.

2) Ideal thread engagement for strength runs 1x to 1.5x nominal screw diameter. This means you want .375"-.5625" of thread engagement for a nominal 3/8" screw. Measure the thickness of the bracket (say it's .500" thick, to be generous) and add it to the values above (.500"+.375" = .875", or 5/8". .500"+.5625" = 1.0625", or 1-1/16".) Nominal lengths in that range would be 3/4" and 1" long, so use either of those (if you're going to use a washer, use the 1" screw in the above example. Typical washer thicknesses are .060"-.090", if they're not designed and ground to a precision thickness for some reason.)

The example given in (2) is purely theoretical - you'll want to measure the thickness of the mounting bracket yourself.

Yes, I've had to solve irritating problems like this before. Often enough that the guys at the hardware store are perfectly used to seeing me come in with a caliper (in its case!) in my pocket and measuring things in detail. I've even had to take in mikes once or twice...

Whenever you lose a screw in anything, all you need to do is figure the thread size and pitch, measure the thickness of the flange that it passes through (to clamp on,) and then add 1-1.5x the nominal diameter to get in the right area to select a replacement. I'm amassing screw sizes to put into a chart in the "Tech Archives" on my site - if you know any that you don't see on there, I'd love for you to tell me so I could add them! There's a link to my site in my sig.

[SilverXJ]

Snapping engine mount bracket screws is a known issue, with a known cause.

In some cases, the holes aren't drilled/tapped deep enough to allow the head of the screw to bottom against the surface of the bracket, as it should.

That is the problem I thought I heard of and I check my bolts because of that. No issues encountered yet, and I don't want to have that issue either.. pain in the ass fix for such a mundane cause.

Yes, I've had to solve irritating problems like this before. Often enough that the guys at the hardware store are perfectly used to seeing me come in with a caliper (in its case!) in my pocket and measuring things in detail. I've even had to take in mikes once or twice...

I loved the Ace I use to frequent for that reason... they knew me and my odd projects. I also bring my calipers to hardware stores ofter. Unfortunately the Ace was closed shortly after Lowes opened... god i hate that place. I can never find anything there when I need it and their fastener selection is nothing but pathetic.

If all the bolts are tight and flush do you think I would have a problem with either the mounts or the engine bosses breaking?

[4.whoa]

I drag race and have broken many things: spider gears(who hasn't), 8.25 yolk, bent 2 driveshafts, many ujoints, snapped 8.8 flange adapter, broke trac loc on a 8.8, and twisted a ax-15 slip yolk


On launching it usually pulls the wheels 6"-10". I run the stock engine side mounts(they tightened up just fine) and use m.o.r.e. poly frame side mounts. the truck shakes like solid mts, but otherwise there have been NO problems, and I truly beat the snot out of it

I've thought about getting some of those multi point mounts,just to be safe,but if you're not that rough you shouldn't need them.

[5-90]

If all the bolts are tight and flush do you think I would have a problem with either the mounts or the engine bosses breaking?

Eh, probably not. But, if you're the cautious sort (like I am,) just get a handful of 3/8" flat washers and put them in. You can usually get away with removing one screw at a time to put the washer in (put LocTite #242 on it as well,) torquing it back in, then moving on to the next one. No special equipment required.

How do I know? Because it's one of the first things I'd done after I'd heard it was possible. I've drilled out screws, machined out screws, and even /burned/ out screws (which isn't as easy as you might think...) and it's better to /prevent/ the screw breaking than /correct/ it after it happens.