Broken motor mounts.....here's the fix

[GreenMachine]

 The bolts I used I found at Ace Hardware. I had to use metric to get the right length (I forget the size, it was a while back when I made these). I used all steel locknuts. I partially countersunk mine because it looked like Ron's were in his pic. I haven't installed mine yet because my car isn't ready and won't be for a while, but I'm confident they will fit and hold up.

Edit: They're flat head socket screws M10 x 60mm  1.5 thread pitch

[FLG]

Rons were not countersunk,

I remember him saying countersinking could permit pull through...though i dont think you will need to worry.

[1969chargerrtse]

I'm next.  Thrilled for this thread.  Thanks again Ron.   

[TylerCharger69]

I just bought a cheap pair at O'reilley's  for 4.99 a piece!!!!   Cheap enough!!!

[1969chargerrtse]

I'm not understanding how a 2 1/2" bolt will work?  This 2" bolt is even to long?


"1) a pair of 3/8 x 21/2 in grade 8 flathead bolts
(2) a pair of 3/8in "nylock" nuts and matching flat washers
(3) a good drill and 3/8in steel bit"

[dstryr]

I used 2" bolts and double nutted them with grade 8 nuts and bolts since the nylock nuts looked like the weak point while I was at the Tractor Supply picking parts.  After I put the mount together I brought that up here and was assured the nylocks would hold.  

Either way, here are pics using 2" bolts, 4th pic is the mount bolted to the block.  The 2" bolts are a little short for double nutting but plenty long for nylocks.  I could easily fit a 2-1/2" bolt in there as well.  I think Ron's bill of materials is spot on.

[1969chargerrtse]

I see why Ron said 2 1/2. The 2" just barely made the nut threads. I got my mount at a NAPA store funny thing is-----  the listing is for a 69 383 engine only, or 71 440. Bottom line it was correct. Job is done. 

[johnnycharger]

Thanks for this awesome tip. I changed my motor mount today and added the bolts. I went with hex head as I was unable to find the flat heads. It worked great and now I don't have my ugly chain on there any more!

[ugly2u]

After making this mod, my mounts will not bolt up to the k frame. The bolt heads will not let the motor sit low enough on the k frame perch. I know you shouldn't countersink the heads, but that looks like the only way it will fit...

Help?

Using flat head bolts with Allen socket.

[johnnycharger]

I used hex heads with no issues. Is you k frame setup all stock?

[ugly2u]

I guess I'm not sure about the k frame. It was a 318 car, and now has a 496 stroker.

[johnnycharger]

I'm no engineer, but I think you would be better off grinding the bolt head down than countersinking....

[Chryco Psycho]

Then there was the time I was working on a Duster checking the stall of the converter & loaded the engine in reverse Only because the mounts were original & I didn't want to buy the new mount & shroud . SO I load it up & sure enough the right engine mount fails & takes out the upper rad hose & shroud 

[Steve P.]

I drill through first and then chase the holes with a countersink bit. Then use bugle head allen bolts. The tough part is finding the right countersink bit as you want to match the angle of the bugle head. A good hardware store will have these bolts in grade 8 and should have or be able to get the bit.. There is no need to go too deep with the counter bit. also I use 3 bolts and on my 65' I got away with nylocks with plenty of room to spare. We did the same on Mike's 65' Charger that made tons of torque.

I think I have posted this before, but on Vegasmikes car we removed solid mounts that rattled our teeth out and went to this system. No more killer vibrations and because of the bolts putting some pressure on the rubber, (PRE-LOAD), they operate just as well as the solid mount.   

[ugly2u]

Thanks steve, I did read your post and that's what set me on bolted rubber mounts and not solid mounts. My mopar mechanic said "awee heck, we have been installing solid mounts for years and they have not knocked my teeth out. These cars just rumble."

I like the way your thinking, why suffer?!!

Gonna try shallow countersink, and grind the head a little. I really would like to drive the new motor next week. Been waiting for 3 months, the best 3 months of the year to dive these babies.

[ugly2u]

Oh, I did by a new rubber mount insulator from o'reily. The metal is thinner than my old mount insulator. Not gonna use the new one.

[ugly2u]

photo 1 shows how the bols are hitting the k frame mount, photo 2 shows how the bolt heads are sticking out.

Looks like counter sink is the way to go.?

[Steve P.]

Oh yeah....  MUST countersink them.....

[ugly2u]

Counter sunk about 1/2 the thickness of the head, mounts up no problem. 

No grinding on the head, and I don't think they will pull through. Wish me luck, I could be driving this baby soon.

[firefighter3931]

Counter sunk about 1/2 the thickness of the head, mounts up no problem. 

No grinding on the head, and I don't think they will pull through. Wish me luck, I could be driving this baby soon.

I don't see any forseeable problem with countersinking the bolts 1/2 way. You're good to go 



Ron

[NHCharger]

Ron, this is another thread that should have a sticky. I wish I had seen it. Just replaced the motor mount in my 71 and had to JB weld the fan shroud back together. That was a horrible noise when the fan went through the shroud.

[firefighter3931]

Ron, this is another thread that should have a sticky. I wish I had seen it. Just replaced the motor mount in my 71 and had to JB weld the fan shroud back together. That was a horrible noise when the fan went through the shroud.

Good point Brian ! I've often referred members to this thread and had to go search for it 

Sorry about your shroud 




Ron

[HeavyFuel]

I counter-sunk a bit, and the head surface of the bolt clears the K-frame by a c-hair.


But.....the other side, passenger, the mount sits directly on the K frame perch, with the perch bearing all of the weight, or so it seems.   The side with the mod has a little clearence, and it looks like the motor mount horizontal bolt is bearing the weight.  Is this all OK, and is it how you guys see it?  I know these K frames were built a little rough, and may be the tolerences are not that exact from side to side.   But I'm just wondering about the bearing on the bolt.

[TX9H6E4CUDA]

I am doing this trick to my 1971 Superbee and what is the final word on the counter sinking the bolts? I'm bringing mine to a machinest friend and should I tell him to go 1/2 countersunk or 3/4 countersunk? I want to be able to get it done in one shot and clear the k frame. Thanks for any help

[375instroke]

If you are not going to countersink the holes, why use countersunk fasteners?  Countersunk fasteners don't pull through aluminum.  The heads of countersunk steel fasteners have been known to pop off when going through an aluminum structure.  If the fasteners pull through, they are too big.  You need to use small fasteners, and more of them.  What about welding the fastener heads to the mount?