[Speargun]

Since my car came with cheby mounts on the frame I decided that I would try building some custom motor mounts.

When I had the car running before I just used a bolt through these with the engine mounts below, making it basically a solid mount.



So I gathered up these parts and put my brain in gear.



...and came up with this.



Unfortunately, I didn't account for the change in geometry when I lowered the installed height of the mount and had to start over.


Round Two:
Armed with my slide rule and high school geometry book, I went back to the chalkboard and re-designed the mount. This time I decided to just use bar stock instead of the 2x3 tube since drilling the notches in the tube was a royal pain.

I skipped some of the pre-assembly photos, but here is what it looks like welded together.



I learned another lesson from my first mount and this time I took my time with the welds and clamped another plate to the mount to help keep warpage down.

Once all the welds had cooled and I was happy with the way the mounts fit the car, it was time for the polyurethane. A little duct tape on the bottom to help seal the end and a couple of fender washers to hold everything together.



The top side got a piece of bar stock with a hole in it to help center the center tube and everything got bolted together.



I put the mounts in sand to get everything level and to contain any leaks or spills then it was time to pour and let sit overnight.



The next day the polyurethane is cured enough to handle, but wont be fully cured for a week or two.



The bottom has a nice duct tape pattern in the poly.



The top pieces had to be assisted off.



The finished product turned out pretty good.



And bolted in without those pesky geometry issues.





I think that I'll add a little brace under here so there isn't too much flexing though...



Oil pan to frame clearance was a little tighter than I had planned on, about 3/8" with a stock pan, but I think it will be alright as long as the polyurethane holds up. If it needs raised up any, a shim should be an easy fix.
This ended up being about 5/8" lower than the Chevy mounts.

[68400BIRD]

Looks good. Is the motor sitting further forward with the new mounts? Do you have a pan gasket in yet, that might give you a little less clearance. I have about a 1/4 on my car.

[Speargun]

The engine sits pretty much in the factory location. I used the transmission mount with the bolts in the middle of the slots as a guide.

There's no pan gasket on the dummy block, but the gasket on the engine I'm going to run is pretty thin. Either way, now that I have the pattern down, I can build a taller set of mounts pretty quick. I have enough material to build another set so the only additional cost would be for the polyurethane.

[punkin]

Nice! Thanks for sharing.

[mysticmissle]

wow nice job, that had to be more work than changing the frame stands.

[Speargun]

Originally Posted by mysticmissle

wow nice job, that had to be more work than changing the frame stands.

Thanks!

The hardest part was getting the geometry correct. I had to cut up & remake the mounts a second time because I got it wrong the first time.

I just put a new, milder, engine in the car this past weekend and went back to the original mounts. I discovered that the set I made were 1.5" to far forward so I also had to cut the driveshaft.

After 15,000 miles with the 455 +.060 (420hp to the rear wheels) the polyurethane showed a little wear so I think that the next set that I build will use a smaller outer tube which will use a little less polyurethane and, hopefully, prevent some of the wear.
The mount are still good to go another 15k miles, but I think that the larger outer tube, and extra poly, allows the center tube a little too much flex.

I definitely like this design over the stock mounts because, even if the poly was completely gone, the engine can't go anywhere and there is no need to chain the engine down.

[1968bird]

Nice looking motor mounts. I can tell you didn't make the ones on my firebird. Yeah they're bad 😞

[LeighP]

Thats a nice custom mount...well made.